nile basin capacity building network ‘nbcbn’ river ... · watershed erosion and sediment...

Nile Basin Capacity Building Network ‘NBCBN’

River Morphology Research Cluster

GROUP III

WATERSHED EROSION AND SEDIMENT TRANSPORT

Survey of Literature and Data Inventory in Watershed Erosion and Sediments Transport

BY

Mr. Longin Ndorimana Mr. Astere Nindamutsa

Dr. Samy Abdel-Fattah Saad Dr. Bayou Chane

Dr. Ahmed Khalid Eldaw Dr. Hassan Fadul

Dr. Osman Mohammed Naggar

Coordinated By:

Dr. Kamaleldin Bashar,

Scientific Advisor: Prof. G. J. Klaassen,

UNESCO-IHE

2005

NBCBN / River morphology Research Cluster

Watershed Erosion and Sediment Transport

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EXCUTIVE SUMMARY Many parts of the Nile Basin are witnessing soil degradation and loss associated with erosion resulting from over exploitation of forests and vegetation cover. This is particularly severe in the Ethiopian highlands as well as in the Equatorial region. The arid and semi-arid regions of the basin are now experiencing serious environmental degradation and spread of desertification. Research is needed in watershed erosion and sediment transport to deal with problems such as: (1) increase of losses in soil & water; (2) increase of sediment deposition in reservoirs; (3) increase of sediment entering irrigation canals; (4) prediction in changes in river morphology; (5) evaluation of practical methods to conserve soil and water; (6) minimizing sediment transported by irrigation canals (7) appropriate sediment measuring techniques; (8) deterioration of quality of water. The overall aim of this research area is to provide Capacity Building in Watershed Erosion and Sediment Transport, in the Nile Basin Countries involved, to sustainably manage the water resources of the Basin. Considering the boundary conditions imposed by the time limit and budget constraints, the first phase proposed for this research was a survey of the literature and data inventory in water shed erosion and sediment transport.

The objectives of this research proposal are: 1/ review and synthesize available data [their sources, availability, extend and quality); 2/ identification of gaps and/or new data needed and 3/ elaborate appropriate regional database network. Four countries are involved, viz: Burundi, Egypt, Ethiopia, and Sudan. Sudan will be the regional coordinator. It has been agreed on a number of activities as shown by the following matrix (L being the Lead Country and M Being the Member Country):

Activity Matrix

Activity Burundi Egypt Ethiopia Sudan

Surveying the Literature in Sediment Yield M M L

Surveying the Literature in Soil Conservation Measures M M L M

Inventory of Sediment Transport Data M M M L

Collection of Studies in Sediment Transport M M M L

Inventory of Data on Sediment Load (including reservoir data) M M M L

Comparison of Measuring Techniques M L M M

Preparation of Report M M M L

Results Phase ( 1)

During Phase 1 the activities have concentrated on a survey of the literature and data inventory on both watershed erosion and sediment transport in the Nile basin.

• Review and synthesize available data [their sources, availability, extend and quality);



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• Identification of gaps in knowledge and data available and/or identify need for additional data collection

• Elaborate appropriate regional database network.

• Description of measuring methods and techniques for sediment transport in rivers which has resulted in the following products to be included in the Phase 1 report:

• Survey of the literature on sediment yield

• Survey of the literature in soil conservation measures

• Inventory of sediment transport data

• Collection of studies in sediment transport

• Inventory of data on sediment load (including reservoir data)

• Comparison of sediment measuring techniques

Future Research Plans

• Setting up and preparation of data base(s) on sediment yield and sediment transport in the Nile basin

• Assessment of sediment yield in selected areas using remote sensing and GIS

• Estimation of sediment from sand encroachment and gully erosion

• Proposing more improved sediment transport measurement techniques

• Cooperation with other activities like FRIEND/NILE is considered, in particular for the data base part.



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TABLE OF CONTENTS 1 INTRODUCTION .......................................................................................................................... 1

1.1 Background............................................................................................................................ 1 1.2 Why need for research in Watershed Erosion and Sediment Transport?............................... 2

1.2.1 Increase of Losses in Soil & Water ............................................................................... 2 1.2.2 Increase of Sediment Deposition in Reservoirs ............................................................ 2 1.2.3 Increasing of Sediment Entering Irrigation Canals ....................................................... 2 1.2.4 Prediction of River Morphology ................................................................................... 2 1.2.5 Evaluation of Practical Methods to Conserve Soil and Water ...................................... 3 1.2.6 Minimizing Sediment Transported by Irrigation Canals............................................... 3 1.2.7 Appropriate Sediment Measuring Techniques .............................................................. 3 1.2.8 Deterioration of Quality of Water ................................................................................. 3

1.3 Research Objectives............................................................................................................... 3 1.4 Work Group ........................................................................................................................... 4 1.5 Work Plan .............................................................................................................................. 5

1.5.1 Activities and Role of Member Countries..................................................................... 5 1.5.2 Activity Matrix.............................................................................................................. 5 1.5.3 Surveying the Literature in Sediment Yield.................................................................. 5 1.5.4 Surveying the Literature in Soil Conservation Measures.............................................. 5 1.5.5 Inventory of Sediment Transport Data.......................................................................... 6 1.5.6 Collection of Studies in Sediment Transport ................................................................ 6 1.5.7 Inventory of Data on Sediment Load (including Reservoir Data) ................................ 6 1.5.8 Comparison of Measuring Techniques.......................................................................... 6 1.5.9 Carrying Special Type of Sediment Transport.............................................................. 7 1.5.10 Preparation of the Report .............................................................................................. 8

1.6 Output .................................................................................................................................... 9 2 LITERATUR REVIEW ............................................................................................................... 10

2.1 SURVEYING THE LITERATURE IN SOIL CONSERVATION MEASURES............... 10 2.1.1 Introduction ................................................................................................................. 10 2.1.2 Soil Erosion................................................................................................................. 10 2.1.3 What is Conservation? ................................................................................................ 10 2.1.4 Causes of Soil Erosion ................................................................................................ 10 2.1.5 Soil and Water Conservation in Selected Countries in the Nile Basin: ...................... 12 2.1.6 Soil and climate types ................................................................................................. 17 2.1.7 Types of erosion.......................................................................................................... 18 2.1.8 Measuring of Soil Erosion........................................................................................... 18 2.1.9 Erosion Control Measures........................................................................................... 19 2.1.10 Run-Off Control Measures for Soil Conservation ...................................................... 20 2.1.11 River (or stream) bank erosion control........................................................................ 22 2.1.12 Maintenance ................................................................................................................ 25

2.2 SURVEYING THE LITERATURE IN SEDIMENT TRANSPORT ................................. 25 2.2.1 Introduction ................................................................................................................. 25 2.2.2 Bed Load Transport Rate ............................................................................................ 26 2.2.3 Suspended Load Transport Rates ................................................................................ 26 2.2.4 Total Load Transport Rates......................................................................................... 27 2.2.5 Bed Forms. .................................................................................................................. 28 2.2.6 Alluvial Roughness. .................................................................................................... 29 2.2.7 Fluid and Sediment Mixing Coefficient ...................................................................... 29 2.2.8 Concentration Profiles................................................................................................. 31 2.2.9 Initiation of Particle Motion. ....................................................................................... 31

3 COLLECTION OF STUDIES IN SEDIMENT TRANSPORT ................................................... 33 3.1 Introduction.......................................................................................................................... 33 3.2 Selected Papers .................................................................................................................... 33



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4 INVENTORY OF SEDIMENT TRANSPORT DATA ............................................................... 41 4.1 Introduction.......................................................................................................................... 41 4.2 Ethiopia Report .................................................................................................................... 41

4.2.1 Soil Erosion and Sediment Data at Abbay (Blue Nile) River Basin ........................... 41 4.2.2 Causes of Soil Erosion ................................................................................................ 41 4.2.3 The Current State of Knowledge................................................................................. 42 4.2.4 Other experiences........................................................................................................ 42 4.2.5 Estimates of Soil Erosion, Erodibility, and Erosion Hazard in the Abbay Basin........ 43

4.3 Sudan Report........................................................................................................................ 45 4.3.1 Introduction ................................................................................................................. 45 4.3.2 Sedimentation process................................................................................................. 45 4.3.3 Canals sedimentation................................................................................................... 45 4.3.4 Reservoirs sedimentation ............................................................................................ 45 4.3.5 Atbara and its tributaries (Baselam, Atbara and Setit) ................................................ 46 4.3.6 Blue Nile Basin and Dinder and Rahad Basins ........................................................... 46 4.3.7 Sobat-Baro-Akobo-Pibor Basin .................................................................................. 46 4.3.8 The Main Nile ............................................................................................................. 46 4.3.9 Blue Nile ..................................................................................................................... 47 4.3.10 Rahad River................................................................................................................. 50 4.3.11 Atbara River ................................................................................................................ 51

4.4 Egypt Report ........................................................................................................................ 52 4.4.1 Introduction ................................................................................................................. 52 4.4.2 Field Measurements .................................................................................................... 52 4.4.3 Measured bed load transport rate ................................................................................ 52 4.4.4 Measured total load transport rate ............................................................................... 53

4.5 Burundi Report..................................................................................................................... 54 4.5.1 Introduction: Defining the process .............................................................................. 54 4.5.2 Watershed Characteristics In Burundi Nile Basin....................................................... 54 4.5.3 Watershed Erosion and Sediment Transport in Burundi Nile Basin ........................... 56 4.5.4 Estimates of sediment yield......................................................................................... 56

5 SEDIMENT MEASURING TECHNIQUES ............................................................................... 58 5.1 Introduction.......................................................................................................................... 58 5.2 Sediment Sources................................................................................................................. 58 5.3 Sediment Yield..................................................................................................................... 59 5.4 Bed Material Sampling ........................................................................................................ 59 5.5 Bed Load Sampling.............................................................................................................. 61 5.6 Direct Measurements ........................................................................................................... 62

5.6.1 Box- and basket-type samplers ................................................................................... 62 5.6.2 Pan-type samplers ....................................................................................................... 63 5.6.3 Pit-type samplers. ........................................................................................................ 63 5.6.4 Other types of samplers............................................................................................... 64

5.7 Indirect Measurements......................................................................................................... 64 5.8 Calculation by measuring the bed material.......................................................................... 64

5.8.1 Direct Method ............................................................................................................. 64 5.8.2 Indirect Method........................................................................................................... 65

6 Conclusions and Recommendations ............................................................................................. 66 6.1 Conclusions.......................................................................................................................... 66 6.2 Recommendations................................................................................................................ 66

7 BIBLIOGRAPHY ........................................................................................................................ 67 APPENDIX A: Sample of Field Measurement of Sediments in Egypt APPENDIX B: Inventory of Data on Sediment Transport in Ethiopia APPENDIX C: Inventory of Existing Data on Sediment Transport in Burundi

APPENDIX D: Inventory of Data on Sediment Transport in Sudan



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LIST OF FIGURES

Figure 1-1 Countries Involved and Their Leading Role in the Research on Watershed Erosion and Sediments Transport ....................................................................................................................... 8

Figure 2-1 Deforestation - One of the causes of soil erosion ................................................................ 11 Figure 2-2 Forest Fire............................................................................................................................ 11 Figure 2-3 Grazing ................................................................................................................................ 11 Figure 2-4 Mine dumps ........................................................................................................................ 12 Figure 2-5 Devil’s canyon vivid............................................................................................................ 18 Figure 2-6 Steep slopes should not be denuded as it hastens the process of soil erosion due to velocity

of water run off. ............................................................................................................................ 18 Figure 2-7 Pioneers organisms .............................................................................................................. 19 Figure 2-8 Planting seedlings ................................................................................................................ 20 Figure 2-9 Spurs are effective in deflecting water current and protecting the stream bank. ................. 22 Figure 2-10 Log wood dam-cheap in cost, but not in task. ................................................................... 23 Figure 2-11Dry stone or loose rock dams - Before rain. ....................................................................... 23 Figure 2-12 Dry stone or loose rock dams – ......................................................................................... 23 Figure 2-13 Gabion to keep the small rubbles/stones intact.................................................................. 24 Figure 2-14 During rains gabion can withstand a heavy flow of water current. ................................... 24 Figure 2-15 Gabion after rain showing the amount of deposition accumulation of silts and debris.

Gabion is in intact condition......................................................................................................... 25 Figure 2-16 Definition sketch of velocity, concentration and transport. Profile of suspended load

(After Van Rijn 1993b)................................................................................................................. 27 Figure 2-17 Idealized bed forms in alluvial channels ........................................................................... 29 Figure 2-18 Fluid mixing coefficients................................................................................................... 30 Figure 2-19 Sediment mixing coefficient according to Coleman (1970). ............................................. 30 Figure 2-20 Shields diagram: dimensionless critical shear stress. ........................................................ 32 Figure 2-21 Correction of Shields diagram (After Gessler, 1971) ........................................................ 32 Figure 4-1: Severity Of Erosion In The Abbay Basin........................................................................... 44 Figure 4-2 Locations for Measuring the Sediment Transport ............................................................... 48 Figure 4-3 Blue Nile Water Discharge, eldeim (1996) ......................................................................... 49 Figure 4-4 Blue Nile Sediment and Water Discharge, eldeim (1996)................................................... 49 Figure. 4-5 Grain size distribution of the suspended sediment of the blue nile .................................... 50 Figure 4-6 Rahad River Sediment Discharge, Hawata (1993) .............................................................. 50 Figure.4-7. Rahad River Water Dischare Hawata (1993) ..................................................................... 51 Figure4-8 Rahad River Sediment and Water Discharge Hawata (1993)............................................... 51 Figure 4-10: Map of Burundi ................................................................................................................ 55 Figure5.1a Van Veen Grab Sampler Figure 5.1b Van Veen Grab Sampler ............................... 60 Figure5- 2 Bed Material Sampler (US BM-60)..................................................................................... 61 Figure 5-3 Muhlhofer Sampler (Box-type sampler).............................................................................. 62 Figure5- 4 The Arnhem Sampler (Box-type sampler) .......................................................................... 63 Figure 5-5. Delft Nile sampler (Box-type sampler) .............................................................................. 63 Figure5- 6 Delft Bottle (Depth-Integrating) .......................................................................................... 65 Figure 5- 7 The Delft Fish Used For Velocity Measurements And Suspended Sediment Sampling.... 65



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LIST OF TABLES

Table 2-1: Erosion rates estimated from the literature............................................................. 14 Table 2.2: Summary for five research stations......................................................................... 16 Table 4.1: Erosion rates estimated from the literature ............................................................. 44 Table 4.2: Hydrological Balance Mean of Water Resources per year. .................................... 55 Table 4.3 : Erosion risks and natural regions of Burundi Nile basin. ..................................... 56 Table 4.4 : Variation of L and LS in Burundi Nile Basin. ....................................................... 56



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1 INTRODUCTION

1.1 BACKGROUND The processes of erosion and transportation of fluvial sediment are complex. The detachment of particles in the erosion process occurs through the kinetic energy of raindrop impact, or by the forces generated by flowing water. Once a particle has been detached, it must be entrained before it can be transported away. Both entrainment and transport depend on the shape, size, and weight of the particle and the forces exerted on the particle by the flow. When these forces are diminished to the extent that the transport rate is reduced or transport is no longer possible, deposition occurs. Generally speaking problems, created by the sediment erosion and deposition, are many and varied. Harmful materials deposited on farmlands at the foot of slopes or on fertile flood plains may reduce the fertility of soil, impair surface drainage, and even completely bury valuable crops. Sediment deposited in stream channels reduces the flood-carrying capacity, resulting in more frequent overflows and greater floodwater damage to adjacent properties. The deposition of sediment in irrigation and drainage canals, in navigation channels and flood ways, in reservoirs and harbours, on streets and highways, and in building not only creates a nuisance but also inflicts a high public cost in maintenance removal or in reduced services. Sediment is of vital concern in the conservation, development, and utilization of our soil and water resources. Without these resources man cannot exist, and when they are of poor quality or of insufficient quantity, man’s lot is a sad one, indeed. The Nile Basin occupies the heart location in the African continent. It overlooks the Mediterranean Sea, the Red Sea, and the Indian Ocean. It is a fascinating river that eluded mankind for long time and witnessed spectacular ancient civilizations in its lower reaches in Egypt and not less important those of Merowe and Axum in its middle and outer reaches. To the old Egyptians it became a holy river bringing life and sometimes destruction to the most extensive arid and desert land in the world. In the last two decades many parts of the basin have been affected by spells of persisting drought cycles which struck the African continent from the Sahel in the west across savanna belt in the Sudan to Ethiopia in the east. Even some pockets into the interior of the basin in the equatorial region could not escape the drought hazards. Many parts of the basin are witnessing soil degradation and loss associated with erosion resulting from over exploitation of forests and vegetation cover. This is particularly severe in the Ethiopian highlands. The arid and semi arid regions of the basin are now experiencing serious environmental degradation and spread of desertification. The huge irrigation systems that have spread all along the basin since the beginning of the last century together with those of medium and small sizes that have been introduced in the upper reaches in reaction to the drought spells suffer from many constraints and problems, particularly sediment deposition in reservoirs and irrigation canals. The water quality deterioration is emerging as a threat to the basin water resources from erosion in the upper catchments of the basin creating serious sedimentation in the lower reaches. Besides the sediment deposition in reservoirs and irrigation canals as mentioned earlier, sediment creates problems in blocking the inlet channels of the pump irrigation schemes as well as causing severe problems in the operation of hydropower turbines, corrosion of pumps and drinking water supply or distribution systems. Almost all of Nile Basin countries witnessed sediment problems in a way or another.



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1.2 WHY NEED FOR RESEARCH IN WATERSHED EROSION AND SEDIMENT TRANSPORT?

1.2.1 Increase of Losses in Soil & Water In the upper of the Nile Basin opening of new lands for agricultural purposes and succession of drought years, necessarily disturbs the natural conditions. This resulted in speeding up the erosion process. Erosion, besides producing harmful sediment, may cause serious on site damage to agricultural land by reducing the fertility and productivity of soils. In more advance stages, it may modify farm fields to the extent that cultivation is no longer feasible or even physically possible. There are severe erosions in the upper catchment areas in Ethiopia and Burundi. Intense rainfall and steep gradients keep the sediment in suspension ready to deposit further down stream.

1.2.2 Increase of Sediment Deposition in Reservoirs As a stream enters a reservoir the flow depth increases and as a result, the velocity decreases. This causes a loss in the transporting capacity of the stream and the deposition of at least some of the waterborne sediments. Reservoirs located in the Nile basin suffer from sediment deposition which has resulted in tremendous reduction in their capacities, for example Roseires and Khashm El Girba reservoirs in Sudan, located respectively at the Blue Nile and River Atbara, their capacities have been reduced dramatically. Other examples may include sediment deposition on High Aswan Dam in Egypt, and dams constructed in Ethiopia. Soil erosion in the Basin has endangered reservoir projects and caused doubts about the viability of existing and future schemes. Untimely sedimentation reduces the benefit, and if it is ignored, remedial measures may become prohibitively expensive.

1.2.3 Increasing of Sediment Entering Irrigation Canals Water diverted to irrigation schemes from the Nile and its tributaries, during the flood period, carries virtually the same sediment concentrations as the Nile. Maintenance desilting has always been needed, but it is observed that (in Sudan Gezira Scheme which is irrigated from the Blue Nile) the quantities of sediment settling in canals have increased enormously in recent years. The reason for this is believed to be an increase in the concentration of sediment transported by the Blue Nile flood. Data in the ministry of irrigation and water resources of Sudan shows that between 1933 and 1938 the mean sediment concentration entering the Gezira scheme main canal in August was only 700 ppm. The average sediment concentration in August in 1989 was 3800 ppm, an increase of more than five times. This rise can be attributed mostly to an increase in rates of soil erosion on the Blue Nile catchments in Ethiopia. There has been a massive effort to clear sediments from canals, but this has not kept pace with the rates at which sediment is settling. The result has been rising canal bed and water levels, drowned control structures, difficulties in supplying parts of the irrigation schemes with water which resulted in reductions in cropped area.

1.2.4 Prediction of River Morphology The river Nile and its tributaries belong to the alluvial streams or rivers. Such types of rivers are dynamic through time in a way that change is one of the most common features associated with them. River Nile tributaries composed of non-cohesive soil and their boundaries configuration are modeled by flow. The rising and falling flood periods are as rapid so that the Nile bed deforms into wavy patterns of dunes during summer with consequent rise in depths and lower velocities. During floods, such wavy patterns or forms disappear, and the flow travels faster causing underwater bank (toe) erosion. These morphological changes have great impact on the socio-economic activities within the Nile basin countries. These problems may be classified as follow:

- Navigation problems. - Siltation and erosion problems of the pumps’ inlet channels. - Destruction of the limited cultivated areas along the river Nile where people depend

mainly on that narrow strip of the river Nile Therefore successful planning for river utilization and water resources development requires comprehensive understanding of these changes.



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1.2.5 Evaluation of Practical Methods to Conserve Soil and Water Evaluation of erosion incident to cultivation, grazing, and timber production on watershed land is a first step to correct most sediment problems. Therefore, the control of sediment by protecting watershed might present the most efficient method(s) in conserving soil and water. Watershed protection is an ancient concept. Roman and Greek engineers recognized t he cause and effect relationship between deforestation and sediment deposition in harbors. The concept was so well understood in the scientific circles and many techniques or practical methods are existing world wide. The object is to evaluate in a most effective and economical combination of vegetative and supporting mechanical practices on the surface of the land to influence the effect of precipitation where it strikes the earth.

1.2.6 Minimizing Sediment Transported by Irrigation Canals All the sediment entering the main canals settles somewhere in the irrigation schemes’ canal networks. There is little scope for reducing deposition in canals by passing a larger proportion of the sediment to the fields, as many of irrigation canals (Sudan) cannot be steepened enough to provide a useful increase in sediment transport capacity. Sediment control in the schemes is thus an exercise in managing sediment deposition so that it does not reduce canal discharges or raise water levels. There are a number of possibilities, all based on encouraging sediment deposition at selected locations by forming enlarged canal sections or settling basins.

1.2.7 Appropriate Sediment Measuring Techniques It must be reemphasized that the development of adequate measurement equipment and techniques is dependent through understanding of the erosion, transportation, and deposition phenomena. The accuracy of sediment discharge determinations is dependent not only upon the field methods and equipment utilized in the collection of data, but upon knowledge of the distribution of the sediment in the flow. Sediments in the Nile basin vary from coarser material mostly in the watershed upper reaches to suspended and wash-loaded in the downstream. Practically valuable is the understanding of the sediment distribution in a stream cross-section, together with the information on the grain size …etc. of sediment. Therefore equipment to appropriately quantify sediment properties and characteristics in the Nile Basin are of high importance.

1.2.8 Deterioration of Quality of Water Sediment is not only the major water pollutants by weight and volume but it also serves as a catalyst, carrier, and storage agent of other forms of pollution. Desirable qualities of water vary according to use and there are a few uses in which sediment in the water is desirable. Sediment alone degrades water specifically for municipal supply, recreation, industrial consumption and cooling, hydroelectric facilities, and aquatic life. In addition, chemical and wastes are assimilated onto and to sediment particles. Ion exchange occurs between solutes and sediments. Thus, sediment has become a source of increased concern as a carrier and storage agent of pesticide residue, adsorbed phosphorus, nitrogen and other organic compounds, and pathogenic bacteria and viruses. Information is needed on the chemical and biological relationships of sediment.

1.3 RESEARCH OBJECTIVES The overall aim of this research area is to provide capacity building in watershed erosion and sediment transport, in the Nile Basin Countries involved, and to sustainably manage the water resources of the Basin.

Specific objectives include:

• To look for practical watershed management techniques for reducing soil erosion and sediment yield.



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• To select suitable means and techniques for the prediction and measuring sediment transport (mountainous areas, flood plains and channels).

• To train the Nile Basin Countries involved personnel in the processes of sediment investigation, computation and watershed management techniques.

• To provide database in sediment flows and characteristics; this can be disseminated among researchers and stakeholders in the region.

• To raise level of awareness of stakeholders and public at large on soil erosion and

• Sediment transport related problems.

A suitable means for realizing the above mentioned objectives is through specific applied joint research of interest to the countries involved. The countries involved in this research area (still there is a space for other interested riparian countries) included: Sudan as a Coordinator, Burundi, Egypt, and Ethiopia Considering the boundary conditions imposed by the time limit and budget constraints, the

Survey of Literature and Data Inventory in Watershed Erosion and Sediments Transport has been proposed as a research project.

1.4 WORK GROUP The group of researchers includes the following:

Name Country

Dr. Siddig Eissa Ahmed- Ex Group Coordinator

Dr. Osman Mohammed Naggar Group Coordinator

Mr. Longin Ndorimana

Mr. Astere Nindamutsa

Dr. Samy Abdel-Fattah Saad

Dr. Bayou Chane

Dr. Ahmed Khalid Eldaw

Dr. Hassan Fadul

Dr. Kamal Eldin Bashar

Sudan

Sudan

Burundi

Burundi

Egypt

Ethiopia

Sudan

Sudan

Sudan

Prof. G.J. Klaassen, Scientific Advisor UNESCO-IHE



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1.5 WORK PLAN

1.5.1 Activities and Role of Member Countries The activities of the research proposal on: Survey of Literature and Data Inventory on Watershed Erosion and Sediments Transport will be:

• Surveying the Literature in Sediment Yield

• Surveying the Literature in Soil Conservation Measures

• Inventory of Sediment Transport Data

• Collection of Studies in Sediment Transport • Inventory of Data on Sediment Load (including reservoir data) • Comparison of Measuring Techniques • Preparation of the Report & Submission for Approval

The following table shows the member interest for the various activities as well as who will play the leading role for each activity.

1.5.2 Activity Matrix Activities Burundi Egypt Ethiopi

a Sudan

Surveying the Literature in Sediment Yield M M L M

Surveying the Literature in Soil Conservation Measures M M L M

Inventory of Sediment Transport Data M M M L

Collection of Studies in Sediment Transport M M M L

Inventory of Data on Sediment Load (including reservoir data) M M M L

Comparison of Measuring Techniques M L M M

Preparation of Report M M M L

1.5.3 Surveying the Literature in Sediment Yield Earthy or rocks particles are removed from one location and deposited at another, and there is a need to quantify these erosion and deposition rates. Because water is the prime entraining agent and mover of eroded materials, it is virtually impossible to plan, design, construct, or maintain river basin projects rationally without postulating the distribution of these materials to downslope and downstream. Information or data required may include the following: Soil loss, sediment delivery ratio, sediment yield and rate of erosion …etc. This activity also may include the identification of the various institutes involved in each country.

1.5.4 Surveying the Literature in Soil Conservation Measures Soil and water are basic principal natural resources of a country. Heavy population pressure, over exploitation of the land, torrential rain, have created natural imbalance. When natural harmony is disturbed, these resources become vulnerable to erosion. The loss of soil through erosion reduces the productivity of land not only to present day but the generations to come. Since the economy of any country depends primarily on the soil and its products, soil erosion can seriously affect the



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development and the progress of any nation. It is obvious that all production, whether of food, housing, clothing or other goods, depends directly and indirectly on soil and water. It is important to note that formation of fertile top soil which is essential for agricultural crop is a very slow process. Similarly the available water resource for use is very limited percentage of the total water. Therefore such scanty but essential natural resource should be judiciously used and zealously guarded. Conservation of these items is essential for existence and development of civilization. Conservation means the utilization of these resources to sustain a high level of production. Soil and water conservation consists of prevention and control of soil erosion caused due to wind and water; it also includes conservation of rain water. Soil erosion severely affects hilly areas because of the steep slope, and in these areas soil conservation measures ought to be adopted.

1.5.5 Inventory of Sediment Transport Data Some of the Nile Basin Countries started measuring sediment characteristics and discharges. Normal measurements made on some streams include suspended load samples as well as discharge measurements. The latter measurements consist of depth and mean velocity determinations at a number of selected verticals from which one can get the total discharge, Q, and the cross sectioned area, A. The suspended load samples give the mean measured sediment discharge concentration, C at each of the verticals in which the mean velocity is measured. The activity is meant to include the following data pertinent to sediment transport:

- Hydraulic variables - Sediment concentrations - Sediment grain size - Morphological characteristic (bed levels, slope, …etc.)

1.5.6 Collection of Studies in Sediment Transport The intention here is to collect studies on erosion and sediment transport carried on the Nile Basin region, whether internationally, regionally or on country basis. These studies may include:

- Consultation works carried by overseas consultants or regional ones - Research results from international institutes or institutes in the region - Academic works.

1.5.7 Inventory of Data on Sediment Load (including Reservoir Data) Many of the Countries in the Nile Basin Countries have undertaken specific sediment load measurements or monitoring programs. The activity is meant:

- To collect data on sediment load in each of the country involved (measured data) - To make inventory on the computed sediment load formulae (Computed Data) - Data on reservoirs sedimentation.

1.5.8 Comparison of Measuring Techniques Regarding the measuring procedures of sediments load it is essential to distinguish between bed load and suspended load.each of these modes of transport requires its own procedure. On the other hand , for morphological phenomenon, the distinction between bed materials transport and wash load is more relevant.

The bed load transport can be obtained by adding bed load and that part of the suspended load, which does not belong to wash load.to determine the latter part, analytical methods are applied using particle size distribution of the bed material.

There are a wide range of instruments has been developed, from simple mechanical samplers to sophisticated optical and acoustical samplers.the selection of instrument is largely dependent on the variables to measured, the available facilities and the required accuracy.

a. Bed Materials Sampling: to enable the determination of size distribution of the bed material, samples are taken from the river bed. It is obvious that the selection of sampler as well as sampling method has to be based on the actual circumstances. For instance, instruments which



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have to be forced by hand into the stream bed can only be used in shallow water. In deep water, either the free-fall principle can be applied or an instrument can be selected, the operation of is based on its weight and shape. Two main categories of samplers can be distinguished; i.e. samplers which are filled by dragging them along the bed, and samplers which collect bed material by grabbing or digging.

b. Bed load Sampling: bed load can be measure by trapping the sediments moving along the bed in an instrument which is placed on the river bed for a fixed period of time. Either the volume or the mass of the material collected is measured. Bed load transport should be measured in a number of verticals in a cross-section. When dune lengths are large in comparison with the depth of water, it is not possible to place the sampler with sufficient accuracy in a particular location on a sand dune. Therfore, sampling has to be made at different locations along the bed form dune length.

c. Suspended load Samplings: the determination of suspended load in a cross section of a stream (per unit width) is based on measurements on a number of verticals and with this information; integration over the cross section is possible. The data for the verticals can be obtained in two ways: (i) depth integration over the vertical, and (ii) point integration in a number of points in each vertical and integration over the vertical.

Sample for suspended sediment transport were developed according to two different principles: the direct and the indirect measuring of the transport. The direct method is based on the direct measurement of the time-averaged sediment transport in a certain point (point integrating) or over certain depth range (depth-integrating).

The indirect method is based on the simultaneous but separate measurement of the time-averaged fluid velocity and the time-averaged sediment concentration, which are multiplied to obtain the time-averaged sediment transport.

To measure the suspended load transport, a wide range of instruments is available. Most samplers are used as point-integrating samplers, which mean the measurement of the relevant parameters in a specific point above the bed as a function of time. Some instruments are used as depth-integrating samplers, which mean continuous sampling over the water depth by lowering and raising the instrument at a constant transit rate.

1.5.9 Carrying Special Type of Sediment Transport Since sediment transport affects much the planning, design and management procedures of all water structures, it is a very important issue to get to perfectly control the erosion and sediment transport phenomena in the watershed. As far as the Nile Basin is concerned, especially in the very upstream part of the it, we have been able to carry out a number of suspended and liquid discharge measurements. In Burundi for which 50 % of the area falls in the Nile Basin and drained by the so called Ruvubu river, tributary of the Nile, between 1988 et 1998, we have been able to carry out 117 couples of data ( liquid discharge/suspended load) at different locations of which 4 are on the main stream of the Nile river tributary. The method used for suspended load samplings is that of measuring or a number of verticals with integration over the cross section of the river.Water discharge is measured at the same time. We therefore believe that this available data can serve as the starting ground for our research work to come. As of literature survey, some extensive work on (doctoral thesis) on erosion evaluation under banana culture in the area located in the central Burundi within the Nile Basin has been made. This work can be documented in the local libraries. More information is expected to be collected from others research institutions in the country even though some concern exclusively the other half of the country lying within the Congo Basin. Concerning other type of sediment load measurements including reservoir data and bank erosion phenomena, no data is readily available. However some investigation on the subject can be foreseen under the research activities of the future.



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Lastly we must regret that in our region and for this year he rainy season set on late (November instead of October) and we were unable to start field measurements due to a number of difficulties including lack of material and financial capabilities in our services.

Figure 1-1 Countries Involved and Their Leading Role in the Research on Watershed Erosion and Sediments Transport

1.5.10 Preparation of the Report This final report was prepared by the group coordinator with the input from country members. The contents of the report are:

• Executive Summary • Chapter 1 : Introduction • Chapter 2 : Literature Review • Chapter 3 : Collection of studies on Sediment Transport • Chapter 4 : Inventory of Sediment Transport Data • Chapter 5 : Sediment Measuring Techniques • Chapter 6 : Conclusion and Recommendations • References • Appendices

SUDAN REGIONAL

COORDINATOR

EGYPT BURUNDI

• Sediment Measuring Techniques

• Sediment Transport Data • Studies in Sediment

Transport • Data on Sediment Load • Preparation of Report

• Sediment Yield • Soil Conservation

ETHIOPIA

Special Types of Sediment Transport

Measures



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1.6 OUTPUT The expected output of these researches will be:

1. Compilation of studies and data pertinent to watershed erosion, and sediments transport. 2. Review of the available data (their sources, availability, extend and quality); 3. Identification of gaps and/or new data needed; and 4. Establishment of a regional data base and networking.



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2 LITERATUR REVIEW

2.1 SURVEYING THE LITERATURE IN SOIL CONSERVATION MEASURES

2.1.1 Introduction Soil and water are basic principal natural resources of a country. Heavy population pressure, over exploitation of the land, torrential rain, have created natural imbalance. When natural harmony is disturbed, these resources become vulnerable to erosion. The loss of soil through erosion reduces the productivity of land not only to present day but the generations to come. Since the economy of any country depends primarily on the soil and its products, soil erosion can seriously affect the development and the progress of any nation. It is obvious that all production, whether of food, housing, clothing or other goods, depends directly and indirectly on soil and water. It is important to note that formation of fertile top soil which is essential for agricultural crop is a very slow process. Similarly the available water resource for use is very limited percentage of the total water. Therefore such scanty but essential natural resource should be judiciously used and zealously guarded. Conservation of these items is essential for existence and development of civilization.

2.1.2 Soil Erosion Soil erosion and sedimentation are natural phenomena, responsible for the formation of the landscape. In the last decades, soil erosion has been accelerated by human intervention, through deforestation, overgrazing and poor farming practices. Soil erosion is a widespread problem causing soil and organic matter losses and hence loss of fertility and reduction in crop yields. In addition to these on-site problems, it also produces important off-site effects, like downstream sediment deposition in fields, floodplains and water bodies, water pollution, eutrophication and reservoir siltation. It is, therefore, important to assemble quantitative data on the extent, magnitude and actual rates of erosion/sedimentation as well as on their economic and environmental consequences. As erosion and sedimentation are related problems, there are advantages in studying them simultaneously. Land degradation can be defined as the temporary or permanent lowering of the productive capacity of land. This is brought about through soil erosion (by water and wind); chemical and physical deterioration, primarily compaction with loss of structure and pore space; and, linked with many of these adverse changes, loss of soil organic matter and the beneficial activities of soil biota. Soil and water conservation measures are the heart of afforestation work in arid and semi-arid areas. These will vary from site to site and therefore each site should include in its treatment plan carefully designed soil and water conservation measures. Decisions regarding the specifications of work items and their quantities must be made carefully.

2.1.3 What is Conservation? Conservation means the utilization of these resources to sustain a high level of production. Soil and water conservation consists of prevention and control of soil erosion caused due to wind and water; it also includes conservation of rain water. Soil erosion severely affects hilly areas because of the steep slope, and in these areas soil conservation measures ought to be adopted.

2.1.4 Causes of Soil Erosion The main causes of soil erosion are:

i- Cutting of Forest(Deforestation) ii- Fire iii- Over Grazing iv- Torrential Rain v- Mine Dumping vi- Faulty Agricultural Land Use



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Figure 2-1 Deforestation - One of the causes of soil erosion

Figure 2-2 Forest Fire

Forest Fire: “A good servant but bad master” Fire induces certain synergistic effects. It raises the temperature of the soil, the best consumes organic matter and breaks down soil aggregates increasing bulk density of soil and decreasing its permeability. This change reduces infiltration of water into soil, increases surface runoff and promotes erosion and soil slippage on sleep slopes. It eliminates interception of rainwater by the thick foliage of large trees thus helping to increase the moisture content of the soil. Fire arrests the course of succession and modifies the edaphic environment very much. Fire causes sublimination of chlorine, sulphur and to some extent phosphorus. Thus some elements are permanently lost from the soil. Calcium, potassium, phosphorus left in the ash are changed to soluble forms and exposed to leaching and run-off.

Figure 2-3Grazing

Grazing: grazing has certain other ecological effects, reduction of the mulch cover of the soil occur, microclimate becomes more dry and severe and is readily invaded by xerophytic plants. Due to absence of humus cover mineral soil surface is heavily trampled when wet and produces puddling of the surface layers. This in turn reduces the infiltration of water into the soil and accelerates its runoff producing drought. The grazing and browsing adversely affect the aeration of soil and make it



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compact and hard and finally render the soil unfit for the growth of trees and shrubs. Forests open to grazing are changed first into shrubby vegetation and finally into grassland. Due to grazing shoot or root growth retards and expose land surface to erosion. Once soil is saturated excess water begin to rundown the slope and the clay and humus are splashed up and settle on the top.

Figure 2-4 Mine dumps

Mine dumps reduces the infiltration of water and accelerates its run off due to absence of pervious cover and the filmy dust cover, and soil slippage on steep slopes.

2.1.5 Soil and Water Conservation in Selected Countries in the Nile Basin: ETHIOPIA: There is a wealth of largely qualitative information available concerning soil erosion in Ethiopia. However, the difficulties of assessing this information are enormous. The Ethiopian highlands reclamation study (EHRS) reviewed most of the available data; therefore the following data is referred from it.

Ethiopian Highlands Reclamation Study (1986) The EHRS used soil depth as an important single indicator of soil erosion status; soil depth affects both soil water holding capacity and plant rooting depth providing a direct link between ‘erosion status’ and productivity. They found correlation between soil depth and zone, the deeper soils being associated with the higher potential zones; and correlation with altitude shallower soils occurring especially at higher altitudes. Soil depth information, augmented by field estimates of erosion severity, provided a basis for estimating severity of existing (mid 1980s) accelerated erosion. Over the high lands as a whole, half the area was found to be significantly eroded and one quarter seriously eroded. The other half of the highlands, assessed as without significant accelerated erosion, was nevertheless considered as at future risk because of the inherent erodible nature of the soils and likely extension of cropping. Almost 60% of the severest erosion (of the highlands as a whole) was found to be in the LPC zone, which occurs in the northeast of the Abbay basin (Wello, Northern Shewa). Shit and rill erosion were considered as most important Soil Conservation Research Project (SCRP) The soil conservation research project (SCRP) has been in operation for a number of years with seven research locations throughout the country. Two of these fall in the Abbay basin –at Andit Tid in north Shewa and Anjeni in west Gojam (36º45’E and 10º15’N, 65km NNW of Debre Markos). Another occurs in Illubabor near Metu, just south west of the basin, and a fourth at Maybar, in Wello, south east of Dessie and just outside the Abbay basin. The others occur in situations with environmental conditions often similar to those found in the basin, and results may be extrapolated to the basin. The SCRP have published various research reports. A selection of their reports is discussed.



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Other experiences Soil erosion and conservation on large scale mechanized farms in Ethiopia (Alemayehu Tafesse, 1992). This paper reports that some 25%of the state farms are (were) seriously affected by erosion. The study is of particular interest as the focus is on six state farms largely located within the Abbay(Blue Nile) basin (uke, Anger, Didessa, Bello, Bereda and Loko). At Didessa, an annual soil loss of 27-94 t/ha/yr had been estimated (up to 1cm annually). On steeper land, at the time of the survey, the topsoil had already disappeared and exposed the sub soil, after 10 years of operation. Conservation measures consisted of graded terracing, with priority to slopes >8%, although agronomic measures were also being introduced. Based on calculations using the USLE, terracing with 40m spacing was estimated to reduce erosion to 9.9 t/ha/yr, and with 14.5m spacing to 14.4 t/ha/yr. However, costs were estimated at US$35-40 (ETB 70-80) per hectar, with a 6.1% loss of cropland. The above forms the known quantitative database for soil erosion in the country. Conversely, there is wide experience of soil conservation. The world food program (WFP) has been extensively involved with soil conservation throughout the highlands, with a concentration on bunding programmes. Many NGOs have also been involved at a local, participatory level. A number of other publications are reviewed in subsequent sections of this report, relating to other aspects of soil erosion and conservation Estimates of Soil Erosion, Erodibility, and Erosion Hazard in the Abbay Basin (Summary of Existing Information): From the review above, of both the theoretical basis for soil erosion as applied to the basin, and the review of the existing studies, a number of conclusions may be drawn relevant to an assessment of the current state of erosion in the basin: - A broad range of measurements and opinions exist which render impossible any attempt to arrive

at a quantitative estimate of erosion which would meet general agreement. However, there is consistency in the estimates to the degree that all agree that the situation is serious. Unfortunately these differences have allowed their interpretation as substantive differences and a corresponding avoidance of addressing the problems

- The existing quantitative data is summarized in Table 4.1. They consistently show that in most situations, of continuous cultivation, soil losses exceed the rate of destruction of the soil, resulting in near term economic losses (yield losses, increased fertilizer requirement) and long term actual loss of productive land. Based on the literature reviewed, large areas of land could be lost to production over the next century. This land loss is occurring in face of increasing population and increased demand for land and food.

- The experimental data demonstrate that soil erosion varies greatly with local circumstance, most especially with slope gradient, land cover, and length of cultivation. This has several implications. Firstly, soil conservation needs to be addressed on a site-specific basis. Any overview assessment, such as the current text, is necessarily general and limited. Secondly, land cover and length of cultivation are most amenable to management; managing slope gradient is difficult and expensive. Thirdly, the importance of land cover is well demonstrated; conservation farming must aim to maximize both the quantity and period of cover. The issue of length of cultivation is strongly related to the diversion from the land of crop residues and dung; thus soil conservation cannot be separated from the total farming system, and grazing management and fuel provision are two important aspects of soil conservation in basin.

- Erosion is also seen to vary greatly with the timing and erosivity of particular rainfall events, especially in relation to the prevailing land cover at that time. Therefore, averages hide an enormous variation both spatially and temporally, and are essentially meaningless. A single rainfall event, occurring at an inopportune time, can do more damage than has occurred in several previous years. As such, constant vigilance, in terms of constant application of conservation farming methods, is required.



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- The issue of soil degradation is demonstrated as a critical aspect of soil conservation picture of the basin. In the near term on most sites, and absolutely on sites of low erosion, losses from soil degradation may be very high and may exceed those directly attributable to erosion.

- Soil erosion: Losses are often seen as directly related to reducing depth. Indeed, the EHRS used soil depth as a proxy for estimating the severity of soil erosion. However, in some soils the majority of the fertility is found in the upper layers of the soil; loss of these upper layers may thus have an overall productivity impact far in excess of the percentage soil loss. That is, these soils may remain relatively deep but show huge losses of productivity. These soils must be considered to be especially susceptible to erosion (high erosion hazard); the Alisola, Nitisols and Acrisols in the basin fall within this category

Soil and water conservation experiences in or relevant to the Abbay River Basin National Experience The scale of conservation activities in Ethiopia as a whole has increased dramatically since the 1973-1974 drought. Population increase and resulting increased land pressure has meant that conservation has been accorded relatively high priority within the country. Table 2-1: Erosion rates estimated from the literature

EROSION RATE T/HA/YR

Source

Calculation

LAND USE

Low High Average

NET LOSS (%)

EHRS Estimated Cultivated 130 10 SCRP

Grass Near zero

- Grunder 1986*

Measured

Tef - 282

72

Solomon Abate 1994

Measured Cultivated 139

Hurni 1983b USLE Estimate

Cultivated 120 17

Hurni 1988 USLE Estimate

Crop 42

Bare soil 293 - - Belay Tegene 1992

Dom cult - - 75

2

Gebre Michael 1989

Measured Cultivated 78 218 152.5

Bojo & Cassells 1994

Estimated 20

Tolcha 1991 Mean annual net loss 8.3 t/ha/yr.

* Quoted in Tolcha 1991; Hurni 1985 The 1975 rural land reform act and the subsequent formation of peasant associations provided the means of mobilizing labor for conservation program and other development activities .the world food program (WFP) of food for work provided a major boost in construction activities by providing labor with some incentives .With in the government the community forest and soil conservation department(CFSCD) was set up with in the ministry of agriculture(MoA) to plan the oversee conservation projects.



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This department’s brief was to plan soil conservation and community forestry by water shed country wide. Up to 1991 work was undertaken on soil conservation measures such as soil and stone bunds, terracing, cut off drains, gully control and road drainage as well as community forestry work. These were largely by forced or campaign labor, paid for by food for work, and had a mixed success rate. In some areas the stone bunds constructed one year were destroyed by the villagers to provide work the next. Unfortunately few records exist as to the amount of work undertaken in this way. Certainly no records exist on a water shed basis. Those that do exist are on a regional basis and detail the supposed work carried out 1979-1991. There are also no records of the actual number or area or present state of these conservation works. The government with international assistance and especially in association with the WFP has undertaken a major effort to implement soil conservation measures. The national government and WFP accepted to take a wide spread and extremely serious situation through a blanket approach. However soil and water conservation needs to be sites specific, responding to both local physical and socio-economic conditions. It has also been widely reported that measures have been implemented without sufficient consultation with the local farmers, whose resistance has been subsequently expressed through poor maintenance of structural and even active destruction. Similarly, the association of the programs with food has identified conservation as both as a government program and paid labor, rather than as in the farmer’s interest; again, this has contributed to poor maintenance and destruction. Until recently the main emphasis of the conservation program has been on reforestation with terracing on denuded hillsides. These measures have not been as successful as hoped for a variety of reasons, given below. • Soil erosion was seen as a physical process to be controlled by physical means, with erosion

prevention seen as an end in itself. • The effects on agricultural production were largely ignored with farmers and pastoralists regarded

as part of the problem to be solved. • The farmers were not generally consulted and were forced to work on projects which were highly

labor intensive. • The real causes of land misuse, such as land tenure, lack of economic incentive or labor shortage,

were never addressed. • Following a major review of the conservation program by the Ethiopian highlands reclamation

study (EHRS) IN 1983-1985, more attention is now being given, and should be given in the future, to the protection of currently productive land rather than the rehabilitation of degraded land.

Despite the overall negative situation, the situation in the Abbay river basin is relatively positive. Whatever the past resistance of the farming community, it appears from casual field observation that many farmers now have embraced the concepts of soil conservation. Another positive element in the basin is the continued maintenance of community forests and other reforestation measures. Soil Conservation Research Project (SCRP) As part of their research activities, the SCRP have evaluated the effectiveness of different soil conservation methods. Indeed from both research and practical perspectives, the SCRP is the main source of information on soil conservation in Ethiopia, including the guidelines for development agents on soil conservation in Ethiopia (1986). However, it should be appreciated that their reset must be applied carefully, in response to local circumstances; “responses of soils to different conservation practices vary from one station to another and from one soil to another, depending on the agro-ecological characteristics, soil type and slope gradient .No single land use or mechanical conservation method is the most appropriate one needed everywhere” (SCRP 1996a). To this might be added the variable response of the farmers, based on local socio-economic circumstance.



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Kefeni Kejela (1991), reporting on the Gojam research station, notes that soil loss relative to a control plot was reduced 32% with graded bunds, 54% with graded fanya-juus, and 66% with grass strips, i.e., grass strips, graded fanya-juu>graded bund. Thomas Tolcha (1991 –western Hererge) evaluated the efficiency of different mechanical conservation measures. In the 1st year of measurement (excluding bulge rains), in terms of runoff and soil loss, level fanya-juu, grass strips, level bund, graded fanya-juu, graded bund. However, in the 2nd year of measurement (all year), soil losses were in the order of level fanya-juu, level bund, graded bund, graded Fanya-juu, grass strip. Solomon Abate (1994-Illubabor region, similar to south western Abbay river basin) discusses agronomic and soil management practices. Of physical structures, experimental results show that, compared to a control plot (100%), soil loss was in the order of grass strips (129%), graded bund (87%), graded Fanya-juu (82%), level bund (66%), Fanya-juu (59%). Grunder summarizes results from the SCRP trials, which show that, measured against soil erosion from a control plot (100%), the effectiveness of tested soil conservation measures is graded bunds (68%), graded Fanya-juus (46%), grass strips (34%), level bunds (20%), level Fanya-juus (11%). Thus Fanya-juus provide greatest conservation. However the labor requirement for construction and maintenance of Fanya-juus is much higher than for grass strips. Grass strips are therefore recommended on lower slopes, although physical structures are still considered necessary on steep slopes SCRP (1996a) discusses selection of “best” management practices for any location. Practices considered should include local traditional technologies. The selected practices should include several criteria: • . Promote productivity (quantity and quality) • . Conservation soil and reduce losses of nutrients, sediment, and polluting chemicals. • . Be economically and socially feasible • . Simplicity in implementation and administrative requirements A decision process for selecting the optimum soil conservation methods is then provided. Summary tables based on the five research stations are provided; these are extracted below. Table 2.2: Summary for five research stations Impact on soil loss(% increase or decrease) Impact on runoff (% increase or decrease) Station Graded

fanya-juu

Graded bund

Grass strip

Level fanya-juu

Level bund

Graded fanya-juu

Graded bund

Grass strip

Level fanya-juu

Level bund

Dizi -91 -87 -71 -85 -96 -59 -40 -57 -29 -66 Maybar -4 +73 -55 -72 -37 +8 +46 -33 -48 -25 Andit Tid

-63 -41 -73 -88 -86 -2 -5 -33 -45 -62

Anjeni 28%

-68 -66 -72 N/A N/A -33 -32 -41 N/A N/A

Anjeni 12%

-81 -63 -57 N/A N/A -50 -40 -19 N/A N/A

Gununo -93 -88 -84 -98 -97 -71 -53 -55 -93 -85 BURUNDI: Many parts of Burundi Nile basin are witnessing soil degradation and loss associated with erosion resulting from over exploitation of forests and vegetation cover. Some soil conservation measures are needed in order to solve many constraints and problems particularly sediment deposition in reservoirs, rivers and irrigation canals. If we do that, we limit the problems such as: the blocking of inlet channels of pump irrigation schemes as well as the problems of the operation of hydropower turbines, corrosion of pumps and drinking water supply or distribution systems. We also need to low sediment yield in order to limit sediment deposition through watershed management which is the best method.



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This includes the method of erosion control techniques and sediment control. It includes also all those methods which are adopted to reduce erosion of soil and to make it more and more stable. This method is the most effective method for controlling siltation, because when the soil erosion is reduced, automatically the sedimentation problem is reduced. But the methods of treating the catchment in order to minimise erosion are very costly. SUDAN: Sudan is a large country with an area of 2.5 million Km2. More than half the area of the country is arid and semi-arid. However, the country's economy, as the case in many African countries of the same conditions, is mainly based on agriculture. Under such conditions, soil and water are basic and important natural resources that deserve every care. Nevertheless, soil misuse has led to degradation resulting in desert advance into better fertile areas. Practices like shifting cultivation, uncontrolled grazing, irrational use of machines on light soil, and fires are amongst the most serious factors causing soil erosion (Musnad & el-Rasheed). Agricultural expansion, both public and private, has proceeded without any conservation measures. The consequences have manifested themselves in the form of deforestation, soil desiccation, and lowering of soil fertility and the water-table. These evils gained momentum until they resulted in a drought problem, especially in the west, gully erosion in the Northern Province (Haddam) and the Kerreb lands of Kassala and the Blue Nile, and dune invasion in the western and eastern parts of the country (Musnad & el-Rasheed). Musnad (1975) stated that erosion by water remained unchecked in wetter areas and in areas of vulnerable soil moreover he mentioned that it had spoiled more than 50,000 ha in the el-Suki area alone and the jagged outline of the map of the Rahad Scheme is an attempt to avoid eroded areas. He concluded that the extent of such damage in other areas in the country remains unknown. The literature cited showed that large sectors of the officials dealing with land were well aware of the consequences resulting from misuse of soils. Despite this, unfortunately, conservation measures were neglected in the majority of land-use activities. The same methods that degraded soils in Agabey and Grabeen, for example, are now being used at Um Sbnat and Habeela (Musnad & el-Rasheed). These are new areas deforested for mechanized grain production. Measures such as leaving natural tree belts between farms and round natural drains were not carried out. In these areas gully erosion is now well advanced. The Khashm el-Girba Scheme emerged without adequate shelter belts and wind breaks for its crops and canals. The canals frequently silted up, resulting in severe droughts at stages which adversely affected yield. The Jabel Marra is being exploited by machines with no thought for the light volcanic type of soil or the vulnerable slopes(Musnad & el-Rasheed).

2.1.6 Soil and climate types The extent of soil erosion is largely dependent on climate, soil types and land use. Undoubtedly, soil and climate are important factors affecting soil erosion. The climatic factors affecting soil erosion include the amount, intensity and duration of rainfall. The effects of soil and climate on soil erosion are compounded by the type of land use practices. These practices include slopping cultivation, uncontrolled burning, overgrazing, improper road design and construction etc. Various soil types have varying susceptibility to soil erosion. Generally, fine textured soils (clay, silt) are more resistant to soil erosion than coarse textured ones such as sand. This trend is largely due to the high water holding capacity of fine textured soils. The texture of the soil is a general indication of the water holding capacity and erodability of the soil.



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Figure 2-5 Devil’s canyon vivid

formation due to Geological erosion: Soil formation is started by disintegration or weathering of parent rocks by falling of rain drops or hail, the wave action of water on the banks, cutting action of running water.

2.1.7 Types of erosion There are two types of erosion, geologic and accelerated. Geologic erosion is a normal process, representing erosion of land in its natural environment without the influence of man. Geologic erosion has been going on since the time continents emerged from the sea. It is caused mainly by the action of water, wind temperature variations, gravity and glaciers. Geologic erosion includes soil forming as well as eroding processes. The rate of this erosion, combined with the complex processes of soil formation largely determines the kind of soil that has developed and its distribution on the earth surface.

Figure 2-6 Steep slopes should not be denuded as it hastens the process of soil erosion due to

velocity of water run off. Accelerated erosion: Accelerated erosion results from man’s activities when preparing land for the production of food, fibre and as a place to build homes, industrial plants, road and transport facilities. Unless measures are taken to guard against destructive erosion it becomes the most potent single factor contributing to deterioration of productive soil. The action of water and wind are the primary causes of accelerated erosion.

2.1.8 Measuring of Soil Erosion Soil erosion has been measured for many years with conventional methods, like erosion plots and other techniques. The main problems associated to these methods are the need of long-term observation periods to produce statistically acceptable results and the results are point-specific, applicable only to the conditions of the experiment. In addition, it is very difficult to upscale the results to bigger areas, like catchments, to calculate soil losses and sediment export factors.



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For many years a new method, capable of providing such soil erosion data has been necessary. It should also have the capability to provide unbiased data on soil erosion and show spatial patterns of erosion and deposition within fields. Fallout radionuclide, and in particular 137Cs, have the potential to assess soil erosion and sedimentation in a larger scale and with time-integrated results. 137Cs is introduced in the atmosphere/stratosphere by nuclear weapon explosions. It is transferred to the soil through wet and dry deposition. This radionuclide is strongly adsorbed by the soil particles. As it has limited chemical and biological mobility, this radionuclide accompanies the soil particles in any subsequent movement. Changes in 137Cs soil inventories relate quantitatively to the gain or loss of soil particles in a given point. 137Cs a real distribution can be related to soil redistribution, providing the basis for quantitative assessment of soil erosion (lower budgets) and sedimentation (higher budgets), when compared to a reference value, obtained in a nearby undisturbed area (reference site). The 137Cs technique is now an established nuclear technique that could be used conservation studies.

2.1.9 Erosion Control Measures Vegetative (bionomic) Measures: The Vegetative or bionomic measure refers to the use of vegetation to provide the soil with protective cover to minimise or prevent acceleration of erosion. The objective of the procedure is to reduce the kinetic energy of the raindrops splash and the velocity of the overland flow which contribute to decrease the soil erosion. The vegetative measures are used for protection against soil erosion by using species like grasses, herbs, trees etc.

Figure 2-7 Pioneers organisms

The first organisms to become established in an ecosystem undergoing succession are known as pioneers. It is the primary succession in the process of species colonization and replacement in which the environment is initially virtually free of life. The sere involved in primary succession is called preserve. Barren areas, such as rock outcrops, sand dunes, mine dumps or disturbed areas, abandoned cultivated fields or road banks are natural biological vacuum eventually to be filled by living organisms. Plants that colonize such sites comprise the pioneer species. Pioneers help to reduce soil erosion in due course.



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Figure 2-8 Planting seedlings

As undergrowth in erosion prone areas is an ideal measure to arrest soil erosion. It favors the under growth and increase the area of interception of rain water by the thick foliage thus helping to reduce soil erosion and also increasing the soil moisture. Mechanical measures: Mechanical measures are ground works, which include terracing, contour furrowing, or contour bounding and structural measures such as the construction of check dams, riprap gabions or masonry dams. Mechanical structures are generally used in places where vegetation cannot be immediately established and gullies, channels or rivers and road banks that have to be stabilized and protected. Structural measures are elected for the following purpose:

• To control and/or divert it where it can be safely disposed. • To reduce velocity of runoff and prevent scouring of the land.

To provide an effective barrier or sieve for moving soil and promote reclamation of eroded area for vegetation to grow.

2.1.10 Run-Off Control Measures for Soil Conservation The run-off resulting from storm rainfall is a principal cause of erosion. Soil erosion results in the loss of productivity of agricultural lands, causes sedimentation in downstream areas and has a negative effect on water quality. There are three important principles to consider in the control of erosion:

• Land should be used in accordance with its capability. • The surface of the soil needs to be protected by surface cover involving stubble

management practices in cropping land and careful stocking strategies in grazing land. • Run-off needs to be controlled before it develops into an erosive force.

Adequate levels of surface cover play an important role in erosion control by avoiding the effects of raindrops failing on bare soils. Surface cover also encourages run-off to spread rather than to concentrate. However there is a natural tendency for run-off to concentrate as it moves down-slope. Property improvements such as fences, dams and roads can also lead to run-off concentration. This literature review describes a range of run-off control measures. They are most effective when used as part of an overall soil conservation strategy that includes a range of soil conservation measures. Cropping lands Measures used to control run-off in cropping lands include diversion banks, contour banks, constructed waterways and strip cropping. To work effectively, these measures involve careful planning, design and implementation.



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Gully Control Gullies are formed by excessive surface runoff with high velocity and force that is sufficient to detach and carry away soil particles. Diversion banks Diversion banks are earthen banks surveyed with a low gradient (e.g. 0.5 percent) that divert run-off away from cultivation or buildings and into, stable waterways, natural depressions or water storages. Diversion banks are usually constructed to a height of at least 1 metre with a 2 metre wide, flat, grass-covered channel. Contour banks Contour banks are earthen banks constructed at intervals down a slope in cultivation paddocks. They intercept run off and safely channel it into stable grassed waterways or natural depressions. Contour banks are not strictly on the contour. They are surveyed with a low gradient (e.g. 0.1% - 0.3%). Spacing between contour banks depends mainly on slope and is influenced by soil type. They are usually designed to carry run-off water from a storm with a probability of occurring once in 10 years. However the ability of a contour bank to carry run-off is very dependent on the condition of the channel at the time the rainfall is received. Contour banks may be built with either a narrow base or a broad base. Hillside Terracing Many farmers construct terraces or earthen ridges across hill slope to control erosion by slowing the flow of rainwater runoff. The terraces break long slopes into shorter ones. They usually follow the contour of a hill. As water makes its way down a hill, terraces serve as small dams to intercept water and guide it to an outlet Farming on the Contours By planting rows of crops along a slope’s natural curve, a practice known as contour farming, farmers can reduce soil erosion by as much as 50% over farming up and down the slope. Crop rows planted on the contour create hundreds of small dams that slow water flow and increase infiltration into the ground. This, in turn, reduces erosion. Conservation Tillage Bare soil is highly susceptible to rainwater runoff. Today’s farmers protect the soil from erosion by practicing conservation tillage. Stalks and leaves of harvested crops are left on crop fields to create natural mulch. This protective ground cover shields soil particles from rain and wind until new seedlings can produce a protective canopy. Constructed waterways Constructed waterways carry run-off from contour banks and other structures into natural watercourses or farm dams. They are built when a suitable, natural drainage area is not available. They are wide, flat-bottomed structures and usually have retaining banks on both sides. Each waterway is designed separately and takes into account the size of the catchment’s area, soil type, land use, and expected grass cover in the channel Grassed Waterways Farmers redirect rainwater runoff away from unstable or eroding areas such as gullies and hills and onto shaped drainage areas that have been stabilized with grass. Runoff water flowing down the grassed waterways moves across the grass to a stabilized outlet rather than tearing away soil and forming a large gully. Strip cropping Strip cropping is used on very low sloping land such as the flood plains where slopes are less than 1%. Alternate strips of protective vegetation are arranged on the contour. Their purpose is to reduce the velocity of flood flows causing them to spread out. Sediment is deposited in the strips as the velocities are reduced. Grazing lands Run-off control measures are used less frequently in grazing lands than they are in cropping lands. If grazing lands are well managed with adequate levels of surface cover, run-off control measures should not be required.



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Shallow water ponding In more and areas, shallow water ponding is used to assist in reclaiming scalded land. Banks for shallow water ponding are normally maintained at a height of 30 cm. Water spreading Water spreading is used mostly in semi-arid areas. Large volumes of run-off may flow from hard ridges or other high run-off areas after relatively small amounts of rain. Water spreading schemes intercept this run-off with a diversion bank and divert it to a flatter more productive area of pastures. The run-off is usually spread over the pasture area by a level bank, which allows water to spread through a series of gaps in the bank. Grass strips Grass strips are used when cultivating for establishment of improved pastures. Leaving alternate uncultivated strips on the contour helps to spread run-off, increases water intake into the soil and prevents erosion. The width of the uncultivated strip should be one machine width while the width of the cultivated strip can be one or two machine widths.

2.1.11 River (or stream) bank erosion control Stream bank erosion is frequently associated with gully erosion because it is essentially a process of lateral cutting. Gullies often begin in at the banks of natural water course and by waterfall erosion and move back into adjacent lands. In controlling bank cutting in small streams it is seldom necessary to use heavy timber, concrete or masonry structures which are ordinarily required for control on large streams. Before vegetation can be established temporary jetties, wing dams, fences, tree and cables revetments or other types of deflectors are usually necessary along the eroded bank to slow down the water and start silting deposition.

Figure 2-9 Spurs are effective in deflecting water current and protecting the stream bank.

Temporary groins This method is used for wide and shallow river-beds and streams. With the help of groins the direction and velocity of the current, and partly the deposition of sediments, can be influenced. Temporary groins are installed by driving posts of about 15 cm diameter into the riverbed. Trees or branches of trees are placed horizontally on the upstream side of the posts and anchored firmly. To resist flood the posts must be reinforced by supports of braces. Revetment Revetment is a structure which may be built in contact with the bank, near the bank, or at various moderate distances from it, but running roughly parallel to the bank, throughout the length of the damaged channel. Revetments are built to protect the bank from erosion but not to change the direction of flow or region of the stream except in the immediate vicinity of the structures. Stabilization of gullies After treating and improving the watershed and stabilizing the gully heads, the gully beds have to be treated to prevent further deepening and widening. This is primarily achieved by: i) Check dams, and ii) Gabions



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Check dams Brushwood dams: These are temporary and are constructed in areas where stones are not available. They are best suited for gullies with small drainage areas and with soil conditions that permit the driving of posts. Log or pole dams:-These are constructed of poles or logs. Two rows of vertical poles are driven into the bed of the gully extended to the sides above flood level and are spread at 60 cm to keep the horizontal poles in place. The second method is a simple structure of a single row of posts driven side by side to form a wall of logs secured by horizontal poles.

Figure 2-10 Log wood dam-cheap in cost, but not in task.

Stone or loose rock dams:-These are commonly used in gully control as dry-rock wall. The construction of a loose - rock dam starts with the smoothening of the gully banks of the dam site to about 45% or 1:1 slope.

Figure 2-11Dry stone or loose rock dams - Before rain.

Figure 2-12 Dry stone or loose rock dams after rains

The impact of the check dams is quite obvious. This helps to control erosion and impounded water acts as a water hole for the wild animals. It favors evergreen vegetation to come up all along the waterway. Permanent check dams: As much as possible gully control should be achieved by vegetation and by the use of simple structures. However, there are cases where only permanent dams or structures can solve the problems. Permanent dams may be recommended for the following gully conditions:

i. The volume of runoff cannot be controlled by vegetation.



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ii. In adverse conditions when soil is very unstable. iii. The area is remote and regular maintenance is difficult. iv. Temporary dams are either inadequate or impractical

Silt trap dam: When an excessive sediment load threatens water supply down the stream a silt trap dam is necessary. A fast and positive reduction of sediment movement can be achieved by constructing permanent silt trap dams. Gully- head check dam: To check the advance of the gully headcut a permanent check dam will be necessary to stop the active head from eating its way steadily up -stream and before it threatens a road or bridge. Masonry check dam: These dams are used in gullies or small stream channels with high rates of runoff or where vegetation cannot be established. This dam is recommended only when rocks or stones are available. Concrete hollow blocks, tiles, or stone or any hard and durable material may also be used. Concrete check dam: Concrete dams are recommended when there are inadequate materials for masonry check dams. The disadvantage of masonry and concrete structures in erosion control is that they are very inflexible. Once damaged, they are not easy to repair. Gabions: Using Gabions is an erosion control technique that originated in Italy. They are large rectangular wire crates filled with stones. They are flexible, permeable and economical in places where stones are abundant. Gabions may be constructed from locally available mesh wire with a diameter not less than 2.5 mm.

Figure 2-13 Gabion to keep the small rubbles/stones intact

Figure 2-14 During rains gabion can withstand a heavy flow of water current.



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Figure 2-15 Gabion after rain showing the amount of deposition accumulation of silts and

debris. Gabion is in intact condition.

2.1.12 Maintenance Run-off control measures require regular maintenance if they are to carry out their role effectively. A maintenance program should include:

• Removal of silt from the channel of banks and waterways. • Maintaining the recommended bank height. • The repair of any breaks or low spots in banks as soon as possible. • Maintaining grass cover in waterways and around gully control structures.

Siltation in the banks of channels and waterways increases maintenance costs. It can be greatly reduced by controlling erosion through maintaining high levels of vegetative cover on the soil surface. Therefore, it can be concluded that soil conservation measures can increase productivity and decrease costs of production. Choosing the appropriate control measures needs careful consideration. Some structures such are not always necessary the best solution to an erosion problem, and should be used in conjunction with appropriate land use and sound land management practices.

2.2 SURVEYING THE LITERATURE IN SEDIMENT TRANSPORT

2.2.1 Introduction Sediment transport involves a complex interaction between numerous interrelated variables. However, theoretical approaches in the study of sediment transport are based upon simplified and idealized assumptions. It has been common practice to assume that the rate of sediment transport can be determined by certain dominant variables such as water discharge, velocity, the energy gradient, shear stress, stream power, relative roughness, the froude number, etc. When different equations are applied to a specific river, the results may vary drastically from one to another. Such differences raise questions regarding the accuracy and validity of the various equations, Simons and Senturk (1992). Transport can be defined most generally as a quantity of sediment which is moving (with a velocity). More especially sediment transport in water is defined as the product of a sediment concentration and a velocity. The transport of bed material particles by a flow of water can be of the form of bed load and suspended load. The type of the transport depends on the size of bed material particles and the flow conditions. The suspended load may also contain some wash load. The wash load is mainly determined by land surface erosion and not by channel bed erosion. Although in natural conditions there is no sharp division between the bed load transport and the suspended load transport, it is necessary to define a layer with bed load transport for mathematical representation. The sediment transport in a steady uniform current is assumed to be equal to the transport capacity defined as the quantity of sediment that can be carried by the flow without net erosion or deposition, Van Rijn (1993b).

The particle motion can be classified into three modes as: (a) rolling, sliding; (b) siltation (jumping), and (c) suspended particle motion.



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The type of movement depends on the bed shear velocity. When the value of the bed shear velocity just exceeds the critical value for initiation of motion, the particle will be rolling, sliding or both, in continuous contact with the bed. For increasing value of bed shear velocity, the particles will be moving along the bed by more or less regular jumps, which are called saltation. When the value of bed shear velocity exceeds the fall velocity of particles, the sediment particles can be lifted to a level at which the upward turbulent forces will be comparable with or of higher order than the submerged weight of the particles and as a result the particles go in suspension, Van Rijn (1992). Various types of formulae are available to predict the bed load, suspended load and total load transport rates. Each of them are based upon varying theoretical considerations, statistical interpretations of basic data and limited verification of the relations with field data. The majority of these relationships have been developed to apply to sand-bed channels. The transport of sediment from watersheds and in natural river systems depends on numerous interrelated variables. It is concluded that there is no universal equation that is applicable to all conditions.

2.2.2 Bed Load Transport Rate Einstein (1950) defines bed load transport as the transport of sediment particles in a thin layer of two particle diameters thick just above the bed by sliding, rolling and sometimes by making jumps with a longitudinal distance of a few particle diameters. The bed layer is considered as the layer in which the mixing due to turbulence is so small that it can not influence the sediment particles and therefore suspension of particles is impossible in the bed load layer. Bagnold (1966) defines the bed load transport as that in which the successive contacts of the particles with the bed are strictly limited by the effect of gravity. Van Rijn (1993b) defines the bed load transport as the transport of particles by rolling, sliding and siltating. There are many formulae to predict the bed load transport rate. The earliest formula is that of Du Boys (1879) who assumed that the sediment particles are moving along bottom in layers of progressively decreasing velocities in vertical downwards. After Du Boys (1879), numerous bed load equations relating the bed load discharge, flow condition and composition of the bed material have been proposed(MacDougall (1934), Shields (1936), Mayer - Peter and Muller (1948), Einstien (1950), Einstien - Brown (1950),Bagnold (1966), Van Rijn (1984a) Many of these equations are similar. They all derived assuming steady flow and thus they were strictly applicable for this condition. Presently, steady flow equations are adapted and utilized to analyze unsteady, non-uniform flow conditions. A review for the bed load formulae has been presented as follows:

2.2.3 Suspended Load Transport Rates In general the variation in concentration of bed material with height above bed can be described as:

O = dZ

(Z) dC (Z) + C(Z) W sε

This equation assumes that the current and concentration distribution are stable (no change in time and place). The upward sediment transport is equal to the downward sediment transport.



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Figure 2-16Definition sketch of velocity, concentration and transport. Profile of suspended load

(After Van Rijn 1993b). The general solution of the above equation is as follows:

C(Z) = ](Z)

dZ [-W . Cs

haaε

∫exp

in which: Z = height above bed (m) W = fall velocity of sediment particle (m/s) Ca = reference concentration [fixes the actual position of concentration profile shape],

(kg/m3). εs(Z) = diffusion coefficient for sediment [which defines the shape of concentration]. The type of diffusion distribution can be one of the following two distributions: 1- Coleman type 2- Rouse/Einstien type

Bagnold (1966) developed an equation It is based on an energy balance concept relating the suspended load transport to the work done by the fluid. Bijker (1971) used his own bed load transport formula with the concept of Einstien for suspended load distribution to determine the reference concentration Ca. A simplified method was given by Van Rijn (1984b) based on computer computations in combination with a roughness predictor. Using regression analysis, the computational results for a depth range of 1 to 20 m, a velocity range of 0.5 to 2.5 m/s and a particle range of 100 to 2000 µm were represented by a simple power function.

2.2.4 Total Load Transport Rates. The total load is the sum of the bed load and suspended load. At low transport rates, where most of the sediment moves in contact with the bed or in shallow flow, the bed load may approximate the total load. Conversely, in a deep river the bed load may only 10 to 20 percent of the total load. In research work, one normally deals separately with bed load and suspended load in a uniform flow. The total load results from summing up the bed load and the suspended load. As there is no sharp line dividing bed load and suspended load, at least two points assure this division: - The differences in forms of transport require two physically different models. - The two loads are measured by different methods; the bed load is measured by using a

sand trap placed on the bed and the suspended load is measured by sampling the water sediment mixture.



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Besides the indirect determination of total load transport rate by summing up the bed load and suspended load transport rates, the total load transport rate can be estimated by other methods such as the methods of Engulend and Hansen (1967), Ackers-White (1973) and Yang (1973) which do not make a distinction between bed load and suspended load transport, but directly give the total load transport rate. Einstien (1950) Bagnold(1966), Bijker (1971), and Van Rijn (1984b) used prediction formulae which are the summation of their own formula for bed load and suspended load transport rates: qt = qb + qs Bagnold formula was found to be applicable to fully turbulent flows and its results are the best for large transport rates. Engelund-Hansen (1967) method is based on energy balance concept as follow:

]C d g )1-[(s)(u 0.05 = q

350

0.52

5

t

in which : qt = volumetric current-related total load transport (m2/s)

The Engelund-Hansen formula is based on measurements with d50 < 1 mm and gave good results in comparison with sediment transport measurements in rivers. Finally, an equation can be applied to a river, only if the flow and sediment conditions are similar to that from where the equation was derived.

2.2.5 Bed Forms. For flow in channels composed of erodible granular material, a strong physical interrelationship exists between the friction factor, the sediment transport rate and the geometric configuration assumed by the bed surface. The changes in bed forms result from the interaction of the flow, fluid and bed material. Thus the resistance to flow and sediment transport are functions of the slope and depth of the stream, the viscosity of the fluid and the size distribution of the bed material. The bed forms are of interest in practice for several reasons such as: - Bed forms determine the roughness of a stream. A change in bed form can give

changes in friction factor of 4 and more. - Navigation is limited by the maximum bed level and depends therefore on the height

of the bed deformation. - Bed forms and sediment transport have a mutual influence. A generally accepted classification depending on the flow regime, according to Breusers (1988), is the following.

Lower flow regime. Froude number Fr =[ u/(gh)0.5 ] < 0.7 ± 0.2; (no sharp transition) Flat bed: at values of the bed shear stress just above the critical, sediment transport without deformation of the bed is possible. Grains are transported by rolling and bouncing. Ripples: for sediment sizes <0.6 mm and increasing bed shear stress, small regular waves appear with wave lengths in the order of 5-10 cm and heights in the order of 1 cm. Dunes: for all sediment sizes and increasing shear stress, dunes are developed. Dunes are more two dimensional than ripples and have much greater wave lengths and heights. Upper flow regime Froude number Fr =[ u/(gh)0.5 ] >0.7±0.2; (no sharp transition) Plane bed: as the velocity is further increased, the dunes are flattened, gradually disappear and the bed becomes flat. Sediment transport are high. Antidunes: a further increased in velocity to Froude number around 1.0 causes the water surface to become instable. Interaction of surface waves and the bed gives a bed form called antidunes.



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Chute and pools: at still higher velocities chute and pools are formed. For illustration, the bed forms are shown in the figure below(Simons and Richardson 1966).

Figure 2-17 Idealized bed forms in alluvial channels

2.2.6 Alluvial Roughness. Each type of the bed forms has its specific roughness. For a flat bed without transport it can be assumed that the roughness is in the order of the grain size (for example d65 or d90). For flows over ripples and dunes the total resistance consists of two parts: 1- The roughness of the grains 2- The form drag of the bed forms. The roughness of a dune bed is much greater than that of a flat bed and the corresponding friction factor is also much larger. Dunes generally give the maximum roughness of a flow. Where the friction factor for rough flow: (fc) = ( 8g / c2 ) = 0.24 [ log(12h/ks) ]-2 A flat bed with sediment transport can have a friction factor slightly different from that of a flat bed without transport. The presence of antidunes does not appreciably change the magnitude of the effective roughness of the bed if compared with a flat bed. It cannot be expected in general that the friction factor of an alluvial channel is constant. Experiments have shown that the friction factor can vary by a factor 5 or more.

2.2.7 Fluid and Sediment Mixing Coefficient Various distributions of the fluid mixing coefficient (εf) can be found in the literature such as: constant : εf = 1/α1 ( k u* h ) linear : εf = 1/α2 ( k u* h ) (z/h) parabolic : εf = ( k u* h ) (z/h) (1 - z/h ) parabolic-constant : εf = ( k u* h ) (z/h) (1 - z/h ) for z/h < 0.5

εf = 0.25 ( k u* h ) for z/h > 0.5 in which



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z = vertical coordinate α1, α2 = coefficients

Figure 2-18 Fluid mixing coefficients.

Figure 2-19 Sediment mixing coefficient according to Coleman (1970).

The parabolic distribution is most satisfactory in a physical sense because it is based on a linear shear distribution and a logarithmic velocity profile. A disadvantage of the parabolic distribution is that it yields a zero-concentration at the water surface. Mixing coefficients based on the analysis of the measured concentration profiles of Colman (1970) indicate a parabolic -constant distribution rather than a parabolic one. The mixing or diffusion of the sediment particles (εs) is related to the fluid mixing coefficient for a clear fluid The β-factor describes the difference in the diffusion of a fluid particle and a discrete sediment particle. Carstens (1952) concluded that β < 1 because the sediment particles cannot fully respond to the turbulent velocity fluctuations. Singamsetti (1966) found β >1 because of the presence of centrifugal forces acting on the particles (higher density) causing the particles to be thrown to the



31

outside the eddies with a consequent increase of the effective mixing length. Van Rijn (1984) used the results of Coleman (1970) to determine the β-factor, defined as ( β = εs / εf ) and he deduced a relation to represent the β-factor. Equation) specifies a value larger than unity indicating a dominant influence of the centrifugal forces acting on the particles causing the particles to be thrown to the outside of the eddies with a consequent increase of the effective mixing length. The φ-factor expresses the influnce of the sediment particles on the turbulence structure of the fluid.

2.2.8 Concentration Profiles The most acceptable concentration profile is the parabolic form: C/Ca = {[(h-z1)/z1][a/(h-a)]}Z in which C = concentration at height z1 above the mean bed level (kg/m3) C a = reference concentration at height (z1 = a) above bed level (kg/m3) Z = suspension number or (Z-parameter) = Ws/(βku*) (-) W s = fall velocity which can be found from the bulk suspended samples (m/s) β = ratio of sediment and fluid mixing coefficient (-) u* = bed shear velocity which can be obtained from data fitting of the measured velocity profiles (m/s) The above expression is called Rouse profile. Chien (1954) applied Equ. (68) to determine the Z-parameter from the measured concentration profiles. The results show smaller measured Z-values which can be interpreted as a β-factor larger than 1 (β > 1).

2.2.9 Initiation of Particle Motion. Initiation of particle motion is of great importance for design of stable channels in which practically no sediments are moving and for sediment transport equations. When the shear stress over the bed exceeds its critical value, the particle motion begins. Many researchers such as Shields (1936), White (1940), Simons and Richardson (1966), Vanoni (1964) and Gessler (1971), ... etc., have attempted to solve the problem of the definition of initiation of motion, exactly. Shields (1936) did, experimentally, a series of systematic tests and deduce a graphical presentation which is widely accepted. He determined his relationship by measuring the bed load transport for various values of [ τ/(γs - γ)ds ] at least twice as large as the critical value and then extrapolated to the point of vanishing bed load. This procedure was used to avoid the implications of the random orientation of grains and variations in local flow conditions that may result in grain movement even when [ τ/(γs - γ)ds ] is considerably below the critical value. Where τ is the bed shear stress, ds is the characteristic diameter of the particle, γs is the specific weight of the particle and γ is the specific weight of water. He used uniform grain size material and found that in the region of rough boundary, the Shields parameter [ τc / (γs - γ)ds ] is independent of the grain Reynolds number [ R*e= u* ds / v ] and equal to 0.06. Where u * is the bed shear velocity and v is the kinematic viscosity of water. Gessler (1971) modified Shields diagram by regrouping the dimensionless variables and developed a dimensionless graphical relation. The modification is based on Shields diagram that includes the dependent variable in only one of the two dimensionless parameters and used grain size mixtures. Gessler showed that Shields work has pitfalls such as the bed load measurements were made when ripples and small dunes prevailed. Shields used the overall bed shear stress without differentiation between form drag and surface drag. This resulted in critical values of shear up to 10 % higher than for incipient motion on a flat bed, Gessler used Shields parameter equal to 0.047 when R*e > 200.



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Figure 2-20 Shields diagram: dimensionless critical shear stress.

Figure 2-21 Correction of Shields diagram (After Gessler, 1971)



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3 COLLECTION OF STUDIES IN SEDIMENT TRANSPORT

3.1 INTRODUCTION This Chapter contains selected studies, technical reports, and papers carried in the field of sediment transport. Part of these studies is theoretical which describes the phenomenon of sediment erosion, transport and deposition in general. The other part is applied studies carried in the Nile Basin, particularly in Burundi,, Egypt, Ethiopia, and Sudan

3.2 SELECTED PAPERS

Author Title Remarks Abdelaziz F. Zaki, Gamal Kotb, Nadia A. El-Bahnsawy, M. Samir M. Farid.

Erosion Classification of Natural Streams in East Sinai

HRI

Abdel-Fattah, S. (1997a)

"Field measurements of sediment load transport in the Nile river at Quena",

Technical Report, HRI, Delta Barrage, Egypt.

Abdel-Fattah, S. (1997b).

"Field measurements of sediment load transport in the Nile river at Sohag",


Abdel-Fattah, S. (1997c).

"Field measurements of sediment load transport in the Nile river at El-Korimat (Beni-Sweif),

Report 2, Technical Report, HRI, Delta Barrage, Egypt.

Abdel-Fattah, S. (1997d).

"Field measurements of sediment load transport in the Nile river at Aswan",


Adel Makary, Dr. Magdy Samuel, and Medhat Aziz

“River Nile Bank Erosion”

Gaweesh, M. T. K. "Calibration of the Delft Nile sampler at HRI flume."

Rep., HRI, Delta Barrage, Egypt. (1993).

Gaweesh, M. T. K., and Van Rijn, L. C. (1992). Proc.,

"Laboratory and field investigation of a new bed load sampler for rivers."

2nd Int. Conf. on Hydr. and Envir. of Coast., Estuarine and River Waters, Vol. 2, Bradford, England.

Gaweesh, M.T.K., Ramadan, K.A. and El-Balasy, A

"Field measurements of sediment load transport in the Nile river at El-Korimat (Beni-Sweif)"

Technical Report, HSRI, Delta Barrage, Egypt. .(1994).

Khaled A. Kheireldin, Deputy Director of Strategic

“Stream Power Analysis for the Progress of Scour Around Bridge Abutments”

Research Unit, National Water Research Center, El-Qanatir, Administrative Building, 13621/5

Khaled A. Kheireldin.

‘Stream Power Analysis for the Progress of Scour around Bridge Abutments.’

M. Manohar

"Characteristics of river flow in alluvium and hydrology of River Nile at Merowe, Sudan"

June 1980

M. N. Manohar "Stability analysis of flow boundary at Nuri-Karima stretch of the River Nile"

November 1982



34

M.A.Saad EL-Shazaly and M.M. Gasser Hydraulic

Bed forms of Nile river

M.Moattasem & M.R Abdel Bary.

Changes in the fluvial characteristics of the Nile River after the Aswan High Dam

Proceeding of the International Conference on Efficient Utilization and management of Water Resources in Africa. 1 – 4 Feb.1994.

M.T.K Gaweesh and M.M Gasser

Sediment Transport Measurements in the Nile river at bani Mazar:

Hydraulic Engineering-Proceedings of the 1991 National conference: July 29 - August 2, 1991 ISBN 0-87262-816-7

Magdy Hosny, Fathy El-Gamal and Yasser Raslan

“Impact of Dry-Wet Cycle on Local Scour of Montmorilonite Cohesive Soil”

Mohamed A. Sonbol “Surface Erosion and Sediment Transport throughout the Watershed”

Mohamed El-Moattassem

“Protection and Development of the River Nile an overview”

8th International Symposium on River Sedimentation, Cairo Egypt, 3 – 5 Nov.2001

Mohammed M. Gasser Calibration of Bani-Mazar Movable Bed model

Hydraulic Engineering-Proceedings of the 1991 National conference: July 29 - August 2, 1991 ISBN 0-87262-816

S. Abdel-fattah and M.B.A Saad

“Protection of the City Front of Kafr El-Zayat Using 2-D Mathematical model”

Salaheldien Y. I. & S. Berlamont

On the Quantitative of Erosion Rates of Cohesive Sediments

Proceeding of the International Conference on Efficient Utilization and Management of Water Resources in Africa. 1 – 4 Feb 1994.

Samir Ibrahim, Eng. Mohamed Elsayed

“Effect of Control Structure on River Regime”

Sohier M. M. Kamel, Mary Samy Labib, Mostafa T.K. Gaweesh, Mohamed M. Nour El-Din, and Mostafa M. Soliman

“Effect of Water Level variation on the Stability of Slopes.”

A. P. Van Der Boom Report on the measurement Programme in Kassala Area, Gash River

November 1976

Abbas Abd Alla Ibrahim Sediment Pattern of GASH River, Kassal, Sudan”

Abdalla Abdelsalam Ahmed

"Sedimentation in Sudan Multi-Purpose Reservoirs

" [Paper prepared for the presentation in Karlsruhe ICID, Germany in 1992



35

Abdel Azim S. Eisa and Siddig E. Ahmed

“ Impact of River Morphology on Irrigated agriculture”

1998

Abu Obieda B. Ahmed and Mohamed Sharef Eldin and Omer Mustafa

“The State of the Gezira & Managil Main Canals: Reach Offtake I Km 57 Volume II. Results

February 1998

Abu Obieda Babiker Ahmed.

“The Effect of Canal Sedimentation on the Adequacy of Releases through their head regulators – Case Study

9th international Conference on rainwater Catchments system 8th ICRCS, 21 – 25 April 1997. Tehran, I.R. Iran,

Abu Obieda Babiker and Mohamed Sharaf Eldin Mohamed

"The State of the Gezira and Managil Main Canals: Reach Offtake K. 57

October 1997.

Ahmed A. Ibrahim

“Impact of Desertification on the Nile’s River Environment”,

Presented at the Khartoum Conference “save the Nile”

Ahmed A. Ibrahim and Younis A. Gismallla

"Morphology of the River Nile at Dabak and Design of Khartoum Refinery Pumping Station" Prepared for the Ministry of Energy and Mining. Study of River Morphology Section No. 1

Ministry of Irr. & WR , Sudan

Ahmed Adam Ibrailm and A. A. Basher

"Contribution of Creeping Sands to the Instability of the Nile River in the Northern Region" (in Arabic).

Paper presented at the Conf. on Environmental Impacts of Desertification in the Northern Region of .the Sudan, 1981

Ahmed A.F and M.M Gasser

Movable-Bed Model to evaluate Nile river Dredging

Proceedings of the 1991 National conference: July 29 - August 2, 1991 ISBN 0-87262-816-7-7

Ahmed S.S Hussein, Abdalla A. Ahmed and Siddig E. Ahmed.

Sedimentation Problems in the Gazira Scheme

Proceedings of the international conference on water resources Needs and Planning in Drought Prone Areas, Khartoum 6-12 December 1986

Ahmed M. Adam & Eng. Seif Eldin H. Abdalla.

'"Tutti Island Time and Defiance" (Erosion Problem at Tutti Island).1990

June 1990., Ministry of Irr. & WR , Sudan

Ahmed M. Adam and Ahmed K. Eldaw

"Investigation of scour hole in front of the regulator of New Managil branch-Km 57.00"

April_1988. ., Ministry of Irr. & WR , Sudan

Ahmed M. Adam and Dafalla M. Yousif

"Hydrographic survey of inlet channel to main pump station Of Kenana Sugar Project".

April 1988 ., Ministry of Irr. & WR , Sudan

Ahmed M. Adam and Hassan O.B.

Northern region irrigation rehabilitation project, hydrographic survey of Kelli, Saiyal, Kabushiya and Fadlab n pumping stations (season 87/88)" LJ

January 1989., Ministry of Irr. & WR , Sudan

Ahmed M. Adam and Seif Eldin H. Abdalla

"Breaching of Rahad Main Canal in reach (Km 62.00 -65.00)" 0".

April 1988., Ministry of Irr. & WR , Sudan



36

Ahmed M. Adam and Seif Eldin H. Abdalla

"Implications of river widening in view of bank erosion in the northern provi.nce"

May 1989 ., Ministry of Irr. & WR , Sudan

Ahmed M. Adam and Siddig E. Ahmed

"Investigation of a suitable site for the route of Shendi- OI U Matuma ferry"

July 1988

Ahmed M. Adam, Bedawi F. El Monshid and Siddig E. Ahmed

Bank Erosion of the River Nile in North Sudan

proceeding of Khartoum Nile 2002 Conference: Comprehensive Water Resources Development of the Nile Basin: The Vision Ahead 29th January – 1st February 1994.

Ahmed M. Adam, Prof. B.E.F. El Monshid)1 and Dr. Siddig E. Ahmed

"Impact of Water Control Structures on the River Nile Regime'"

(Cairo Conference in February 1992)

Ahmed M. Adam, Seif Eldin H. Abdalla and Hassan B. Hardlow "

"Northern region irrigation rehabilitation project n hydraulic graphic. survey of Kelli, Saiyal, Kabushiya and Fadlab [pumping stations (season 1989)"

1989., Ministry of Irr. & WR , Sudan

Ahmed M. Adam, Siddig E. Ahmed and Seif H. Abdalla

"Northern, region irrigation. rehabilitation project hydrographic survey of Kelly, Siyal, Kabushiya and Fadlab Pump’ stations"

May 1987., Ministry of Irr. & WR , Sudan

Ahmed S. A. Hussein "Sediment control in the Gezira Scheme"

May 1988 '"

Ahmed S. A. Hussein & Dafalla M. Yousif "~

"Prediction of Settling Basins Performance for Very fine Sediment:

Paper presented at the IAHR Conference, Khartoum, 1-4 : February 1994

Ahmed S. A. Hussein and Abdalla A. Ahmed

"The effect of the proposed brick factory at EI Baggier on the Blue Nile regime" ,

February 1986., Ministry of Irr. & WR , Sudan

Ahmed S. Ahmed and Ahmed A. Ibrahim

"Study of erosion in the northern province"


Ahmed S.A. Hussein .1991

"Sediment Problems and Management in the Gezira Scheme

" ODU Bulletin No. 21, HRL, Walling ford, OK

Ahmed S.A. Hussein and Ahmed A. Ibrahim 1985

Studies of Bank Erosion along the Nile in the Northern Region". (In Arabic)

Paper presented at the Conference on the Comprehensive Development of the Northern, province, Dongola

Ahmed S.A. Hussein, Abdalla A. Ahmed and Siddig E.Ahmed

"Sedimentation Problems in the Gezira Scheme

Proc. Internal Conf. on Water Resources Needs and Planning in Drought Prone Areas, Khartoum Dec. 1986

Ahmed S.A. Hussien & Dafalla M. Yousif

Prediction of Settling performance for Very fine Sedimentation

Proceeding of the International Conference on Efficient Utilization and Management of Water Resources in Africa. 1 – 4 feb.1994



37

Ahmed S~A. Hussein and K.V.H. Smith

"Flow and Bed Deviation Angle in Curved Open Channels".

J. Of Hydraulic Research, Vol. 24, No.2, pp 93-108,1986., Ministry of Irr. & WR , Sudan

Ahmed Salih A. Hussein.

“Estimation of Removal Ratio in Settling Basins”.

1997. ., Ministry of Irr. & WR , Sudan

Ahmed Salih A. Hussein

"Upstream Soil Erosion Impact on Downstream; A case studded" Sudan Gezira Scheme"

Paper presented at the workshop on , environmentally sound management of the Upper Nile watershed, Khartoum.,1993

Ahmed Salih A. Hussain

“Minimizing the effects of the sedimentation on Hydropower generation at Roseires dam”

a study in Arabic submitted to the National Electricity Corporation. September 1997

Alemayehu Tafesse

Erosion, conservation and small scale farming,

Edited by Hans Hurni and kebede Tato,1992

B.E.F.EI Monshid, M.A. Mukhtar, S.E. Ahmed, et al.

Bathymetric surveys of Roseires dam reservoir

May 1982

Chadhokar, P. A. Erosion, conservation and small scale farming

Edited by Hans Hurni and kebede Tato,1992

Dafalla M. Yousif

Fail Velocity of Very Fine Sediment in Turbulent Flow:

(Sudan) proceeding of Khartoum Nile 2002 Conference: Comprehensive Water Resources Development of the Nile Basin: The Vision Ahead 29th January – 1st February 1994.

Dafalla M. Yousif

"Hydrographic Survey of Blue Nile From Nureldeen to Elhurga Pump Stations"

Submitted to: Japan International Cooperation Agency (JICA) January 1991

Dafalla M. Yousif

"Fall Velocity of Very Fine Sediment in Turbulent Flow

Paper presented at the Khartoum Nile 2002 Conference, 29th January – 1st February 1994.

Dafalla M. Yousif and Asaad Y. Shamseldin

Investigation of Main Canals One and two of Kenana Sugar Project" Submitted to Kenana Sugar Company


Dafalla M. Yousif and Eng. Asaad Y. Shamseldin

Survey of Main Canals Three and Four of Kenana Sugar Project "


Dafalla Mohamed Yousif

"Determination of Settling Velocities of Cohesive Mud in Turbulent Flow"

April 1993 ., Ministry of Irr. & WR , Sudan

Dixey, F., and G. Aubert "Arid Zone Research in the Sudan Arid Zone, No. 16 (June 1962), pp. 5-16. Unesco,Paris,1962

E. M. Lates, Ahmed S. Ahmed and Abdalla A. Ahmed

"Analysis of main river bed morphology at Abu Halima pump1 station and recommendations for improving the operation of the pumping station"




38

E. M. Lates, B.E.F. EI Monshid, et al.

"Hydraulic analysis and experimental results for prototype design,” Hydraulic analysis of a compact flow/water volume measurement-structure to be used at farmers ditch (Abu XX) .U : Interim Report.

July 1985

El Zein El Siddig Abdalla

"Siltation Problems Encountered in Front of the Pump Station of Guneid”.

1995

El Zien El Siddig Abdalla

“ On the Scaling of Mobile Bed River Models”

Paper presented at the IAHR conference, Khartoum, Feb 1994

Ibrahim Salih Adam

"Blasting as Solution of Water Recession Problem At Mograt Island Northern State"

Jan Bojo and David Cassells

Land degradation and rehabilitation in Ethiopia: a re-assessment

Draft paper. World Bank, Washington, and D.C,1994

Matalo, F. Reservoir Sedimentation mechanism: case study from Mtera Reservoir –Tanzania

Proceedings of the International Conference on Efficient Utilization and Management of Water Resources in Africa 1 – 4 Feb.1994

Mohammed M. Gasser; Siddig E. Ahmed and Mohamed B. Sad

Effect of Maning’s Roughness coefficient in Simulating flow parameters in natural Channels

Hydraulic engineering Proceedings of the 1991 National conference,July 29 - August 2,

Musnad,H.A.

Forests as a Means of Utilising Marginal Lands in the Sudan

Paper read at the First Conference of Arab Agriculturalists,1970

Musnad,H.A.,and el-

Rasheed, M.A.

Soil conservation and land reclamation in the Sudan,

1978

Osman Bashir Hashim

Construction and Performance of a Vortex Tube Sediment Ejector".


P. Lawrence & Ahmed S.A. Hussein

"Sediment monitoring study in the Gezira scheme -draft final- report"

1990 ., Ministry of Irr. & WR , Sudan

P. Lawrence and Ahmed S.A. Hussein

"Sediment management in the Gezira Scheme -draft final report"

., Ministry of Irr. & WR , Sudan

P. Lawrence, Ahmed Salih Hussein and J. Russell

“Deposition of Fine Sediments in Irrigation Canals” Transaction of ICDI 15th

Congress, The Hague, the Netherlands, 1993

Salih -H. Hamid and Siddig E. Ahmed '.1

Sediment Monitoring Program: "Rahad Phase I Scheme Main Canal"


Salih Hamad Hamid "El Rahad Main Canal Siltation' Survey Carried Out in January 1992"

Salih Hamad Hamid

"El Rahad Main Canal Siltation Problems Results of Survey carried out in January 1992"

January1992 ., Ministry of Irr. & WR , Sudan



39

Salih Hamad Hamid & Hussein Gadain Mohammed

"El Rahad Supply Canal Siltation Problems" Results of Survey carried out in March 1992.

June 1992., Ministry of Irr. & WR , Sudan

Sallh Hamad Hamid "The Rahad River Earth Dams. What is the Alternative?"

December 1994., Ministry of Irr. & WR , Sudan

Seif Eldin Hamad Abdalla & Mustafa Abdel Galil Mukhtar.

"Sediment Deposition Problem in Northern Province Co-operative Schemes"

August 1990 ., Ministry of Irr. & WR , Sudan

Siddig E. Ahmed Computation of bed changes in alluvial channels

Ahmed proceeding of the International Conference of Efficient Utilization and Management of Water Resources in Africa. 1 – 4 Feb 1994.

Siddig E. Ahmed Alluvial Canals Adequacy Journal of Irrigation and Drainage engineering, Vol. 118 No.4 Jul /Aug 1992. ASCE

Siddig E. Ahmed “Computation of Bed Changes in Alluvial Channels"

Paper presented at the IAHR Conference, Khartoum, 1-4 February 1994 J February 1994.

Siddig E. Ahmed and Dr. M.N. Manohar

"Bathymetric survey of Roseires dam reservoir period 12-21 February 1983"

May 1983., Ministry of Irr. & WR , Sudan

Siddig E. Ahmed and Mohammed B. Saad

Prediction of Natural Channel Hydraulic Roughness"

ASCE, Journal of Irrigation and Drainage Engineering, Vol. 118, No.4, pp 632-639. . 1992

Siddig E. Ahmed and Omer M.A. Elawad

Environmental Impact of the Alluvial Nature of the Nile on Irrigated Agriculture in Sudan”

Presented in Addis Ababa Nile 2002 Conference, May 2002

Siddig Eissa Ahmed “Prediction of Hydraulic and Sediments variables in Alluvial Channels”

Journal of Irrigation and Drainage ASCE,1998

Siddig Eissa Ahmed, Dr. Abdalla A. Ahmed and Dr. Ahmed M. Adam

"Prediction of Flow and Transport Parameters in Alluvial. Channels" (Cairo Conference in February 1992)

October 1991. ., Ministry of Irr. & WR , Sudan

Tag El Sir Ahmed and Osman Eltom Hamad

"Sediment Transport in Relation to Reservoirs

Proc. Internal Conf. on Water Resources Needs and Planning in Drought Prone Areas, Khartoum 1986

Tawfig E. Musa. Anew Method for Desedimentation of Reservoirs

Proceedingsof the international conference on water resources Needs and Planning in Drought Prone Areas, Khartoum 6-12 December 1986

Younis A. Gismalla “The Blue Nile sediments Monitoring” December 1998., Ministry of Irr. & WR , Sudan

Younis A. Gismalla Bathymetric Survey of Roseires Reservoir, Volume 1"

October 1993., Ministry of Irr. & WR , Sudan



40

Younis A. Gismalla

“Reservoir Sedimentation: Roseires Case” Proceedings 6th Nile 2002 Conference, Kigali, Rwanda.

199., Ministry of Irr. & WR , Sudan 8



41

4 INVENTORY OF SEDIMENT TRANSPORT DATA

4.1 INTRODUCTION This chapter contains the contribution of the group members from the participating countries. The chapter is divided into four reports from Ethiopia, Sudan, Egypt and Burundi

4.2 ETHIOPIA REPORT

4.2.1 Soil Erosion and Sediment Data at Abbay (Blue Nile) River Basin Application to the Abbay river basin of the different types of erosion and other considerations provides a first indication of probable erosion. The basin provides a combination of the following parameters: • High intensity rainfall: Rain fall is characterized by short and intense storms, with intensity

enhanced by strong winds. Data from the SCRP indicate that between 50% and 80% of annual soil losses occur during the five most intense storms in a year (EHRS, 1986).

• Erodible soils of the basin tend to be poorly structured with extremely low and declining organic matter. EHRS found soils derived from siliceous parent material to be more erodible than those from basaltic, calcareous or volcanic rock; luvisols and cambisols were found to be most erodible and nitosols, vertisols and some phaezems and acrisols less erodible.

• Presence of steep and long slopes (especially in the highland areas) is among the major factors for the intensive erosion.

• Poor and intermittent vegetation cover over much of the basin, including much of the steeper areas. The conversion of highland vegetation to cultivation and grazing suggests a very high potential for erosion.

• Land management practices which are poorly adapted for soil and water conservation, including row cropping/ cultivation up-and-down slopes, intensive tillage(especially Teff), bare soil (teff fields) for much of the rainy season, diversion of dung and stover to other uses, etc. However, most critical is a general lack of vegetation cover due to deforestation, over grazing, low density crops, and large amounts of land for teff kept bare during much of the rainy season. Cropping is also undertaken on slopes due to water logging and tillage difficulties on the heavier soils of the flatter lands. SCRP data (quoted in the EHRS) indicate erosion losses as highest from cropped land, highest (80% of annual losses) on crop land during ploughing months and the first month after planting and highest from teff crop fields.

Under these conditions, high erosion should be expected. Indeed, given these circumstances the degree of visible erosion is surprisingly low. Either the soils are more resilient than theoretical considerations suggest, or visible indicators are insufficient to defining the severity of the situation. If the latter is the case, then the danger exists of major and possibly sudden collapse of the agricultural production system. (This also attests to the aforementioned difficulty of mapping soil erosion). These theoretical considerations also provide an initial framework for evaluation of development proposals.

4.2.2 Causes of Soil Erosion The above review has concentrated on the physical mechanics of soil erosion. However, the causes of soil erosion have to be viewed within a broader context. People dependent on the land also destroy the land indirectly. That they managed the land in a destructive way is a function of a host of socio-economic, institutional and political parameters which constrain the choices of the land manager. Key parameters contributing to land management causing erosion in the Abbay river basin include

- Poverty: The general poverty of the majority of the population requires satisfaction of immediate food needs, minimization of risk (including the risk of new techniques), allows no capital for land improvements, and doesn’t provide an environment for long term thinking and management.



42

- The general social condition of the majority rural population, especially the lack of education and deep rooted cultural traditions, again works against long term thinking and against adaptation and change.

- Farmers may simply not recognize the problem. Much soil erosion is essentially invisible. Small annual yield losses from erosion may be obscured by larger inter annual yield fluctuations due to other factors.

- The history of insecure land tenure has militated against long term investment in land management .Things such as land re-distribution in Amhara region, whatever its justification from a social justice perspective; serve to maintain the perception of insecure tenure and reluctance to invest.

- Underlying all of these parameters is population increase. Population pressure puts more demands on the land resource base, and therefore impacts erosion, both directly and indirectly through such factors as land fragmentation.

4.2.3 The Current State of Knowledge There is a wealth of largely qualitative information available concerning soil erosion in Ethiopia. However, the difficulties of assessing this information are enormous. The Ethiopian highlands reclamation study (EHRS) reviewed most of the available data; therefore the following data is referred from it.

- Ethiopian Highlands Reclamation Study (1986): The EHRS used soil depth as an important single indicator of soil erosion status; soil depth affects both soil water holding capacity and plant rooting depth providing a direct link between ‘erosion status’ and productivity. They found correlation between soil depth and zone, the deeper soils being associated with the higher potential zones; and correlation with altitude shallower soils occurring especially at higher altitudes. Soil depth information, augmented by field estimates of erosion severity, provided a basis for estimating severity of existing (mid 1980s) accelerated erosion. Over the high lands as a whole, half the area was found to be significantly eroded and one quarter seriously eroded. The other half of the highlands, assessed as without significant accelerated erosion, was nevertheless considered as at future risk because of the inherent erodible nature of the soils and likely extension of cropping.

The erosion map, as applied to the Abbay river basin, is presented in figure 4.2 Almost 60% of the severest erosion (of the highlands as a whole) was found to be in the LPC zone, which occurs in the northeast of the Abbay basin (Wello, Northern Shewa). Shit and rill erosion were considered as most important.

- Soil conservation research project (SCRP) The soil conservation research project (SCRP) has

been in operation for a number of years with seven research locations throughout the country. Two of these fall in the Abbay basin –at Andit Tid in north Shewa and Anjeni in west Gojam (36º45’E and 10º15’N, 65km NNW of Debre Markos). Another occurs in Illubabor near Metu, just south west of the basin, and a fourth at Maybar, in Wello, south east of Dessie and just outside the Abbay basin. The others occur in situations with environmental conditions often similar to those found in the basin, and results may be extrapolated to the basin. The SCRP have published various research reports. A selection of their reports is discussed.

4.2.4 Other experiences - Soil erosion and conservation on large scale mechanized farms in Ethiopia (Alemayehu Tafesse,

1992.) This paper reports that some 25%of the state farms are (were) seriously affected by erosion. The study is of particular interest as the focus is on six state farms largely located within the Abbay basin (uke, Anger, Didessa, Bello, Bereda and Loko). At Didessa, an annual soil loss of 27-94 t/ha/yr had been estimated (up to 1cm annually). On steeper land, at the time of the survey, the topsoil had already disappeared and exposed the sub soil, after 10 years of operation.



43

Conservation measures consisted of graded terracing, with priority to slopes >8%, although agronomic measures were also being introduced. Based on calculations using the USLE, terracing with 40m spacing was estimated to reduce erosion to 9.9 t/ha/yr, and with 14.5m spacing to 14.4 t/ha/yr. However, costs were estimated at US$35-40 (ETB 70-80) per hectar, with a 6.1% loss of cropland.

- Area closure for soil conservation in Ethiopia - potential and dangers (P. A. Chadhokar, 1992) - Land degradation and rehabilitation in Ethiopia: a re-assessment (Jan Bojo and David Cassells, 1994. Draft paper. World Bank, Washington, and D.C The above forms the known quantitative database for soil erosion in the country. Conversely, there is wide experience of soil conservation. The world food program (WFP) has been extensively involved with soil conservation throughout the highlands, with a concentration on bunding programmes. Many NGOs have also been involved at a local, participatory level. A number of other publications are reviewed in subsequent sections of this report, relating to other aspects of soil erosion and conservation

4.2.5 Estimates of Soil Erosion, Erodibility, and Erosion Hazard in the Abbay Basin From the review above, of both the theoretical basis for soil erosion as applied to the basin, and the review of the existing studies, a number of conclusions may be drawn relevant to an assessment of the current state of erosion in the basin:

- A broad range of measurements and opinions exist which render impossible any attempt to arrive at a quantitative estimate of erosion which would meet general agreement. However, there is consistency in the estimates to the degree that all agree that the situation is serious. Unfortunately these differences have allowed their interpretation as substantive differences and a corresponding avoidance of addressing the problems

- The existing quantitative data is summarized in Table 4.1. They consistently show that in most situations, of continuous cultivation, soil losses exceed the rate of destruction of the soil, resulting in near term economic losses (yield losses, increased fertilizer requirement) and long term actual loss of productive land. Based on the literature reviewed, large areas of land could be lost to production over the next century. This land loss is occurring in face of increasing population and increased demand for land and food.

- The experimental data demonstrate that soil erosion varies greatly with local circumstance, most especially with slope gradient, land cover, and length of cultivation. This has several implications. Firstly, soil conservation needs to be addressed on a site-specific basis. Any overview assessment, such as the current text, is necessarily general and limited. Secondly, land cover and length of cultivation are most amenable to management; managing slope gradient is difficult and expensive. Thirdly, the importance of land cover is well demonstrated; conservation farming must aim to maximize both the quantity and period of cover. The issue of length of cultivation is strongly related to the diversion from the land of crop residues and dung; thus soil conservation cannot be separated from the total farming system, and grazing management and fuel provision are two important aspects of soil conservation in basin.

- Erosion is also seen to vary greatly with the timing and erosivity of particular rainfall events, especially in relation to the prevailing land cover at that time. Therefore, averages hide an enormous variation both spatially and temporally, and are essentially meaningless. A single rainfall event, occurring at an inopportune time, can do more damage than has occurred in several previous years. As such, constant vigilance, in terms of constant application of conservation farming methods, is required.

- The issue of soil degradation is demonstrated as a critical aspect of soil conservation picture of the basin. In the near term on most sites, and absolutely on sites of low erosion, losses from soil degradation may be very high and may exceed those directly attributable to erosion.



44

- Soil erosion losses are often seen as directly related to reducing depth. Indeed, the EHRS used soil depth as a proxy for estimating the severity of soil erosion. However, in some soils the majority of the fertility is found in the upper layers of the soil; loss of these upper layers may thus have an overall productivity impact far in excess of the percentage soil loss. That is, these soils may remain relatively deep but show huge losses of productivity. These soils must be considered to be especially susceptible to erosion (high erosion hazard); the Alisola, Nitisols and Acrisols in the basin fall within this category

Figure 4-1: Severity of Erosion in the Abbay Basin Table 4.1: Erosion rates estimated from the literature Source

Calculation

Land Use

Erosion Rate t/ha/yr

Net Loss (%)

Low High Average

EHRS Estimated Cultivated 130 10

SCRP

Grunder 1986* Measured Grass Near zero

- 72

Tef - 282

Solomon Abate 1994 Measured Cultivated 139

Hurni 1983b USLE Estimate

Cultivated 120 17

Hurni 1988 USLE Estimate

Crop 42

Belay Tegene 1992 Bare soil 293 - - 2

Dom cult - - 75



45

Gebre Michael 1989 Measured Cultivated 78 218 152.5

Bojo & Cassells 1994 Estimated 20

Tolcha 1991 Mean annual net loss 8.3 t/ha/yr.

* Quoted in Tolcha 1991; Hurni 1985

4.3 SUDAN REPORT

4.3.1 Introduction One of the most known problems associated with the operation and maintenance of irrigation systems and the reservoirs is the problem of sedimentation, which affects directly their individual components, thus jeopardizing its ability to fulfill its function and to perform satisfactory. The main source of sedimentation is those Nile tributaries originating from the Ethiopian Plateau (Blue Nile, Atbara, Dinder, Rahad). The sediment load of the Blue Nile amounts to 140 million tons per year, (Eltahir, 2002). The Blue Nile serves almost 70% of the irrigated area in the country, and represent the main source of hydropower. During its flood period, the river transports very high sediment concentration reaching 2.6%, by weight recorded at Roseires reservoir during the historic flood in 1988, (Hamid, 2002). The sediment concentration vary from year to year, but the average peak is about 1% by weight at the end of July and it reaches to few hundreds ppm by the end of October. The transported sediment consists of significant quantities of silt and clay. Records of the quantities of sediment removed from the Gezira scheme (880,000 ha) show an enormous increase since its inception in 1925. Intensification, diversification and watershed degradation complicated the problem even more. Watershed management, operation of water facilities and monitoring programs are very essential. Bank erosion and sand dunes encroachment have increased the sediment load of the Main Nile and its tributaries. They have led to two phenomena: 1) morphological changes in the course of the rivers and their flood plains resulting in abandoning fertile alluvial soils, and 2) frequent flooding caused by downstream sedimentation.

4.3.2 Sedimentation process Watershed degradation is the main cause of the sedimentation process. Watershed degradation mainly resulted from the clearance of vast areas of forested lands for cultivation, fuel wood, brick making, and over grazing. Silt deposition in the Blue Nile and Atbara rivers has interfered with their flow regimes. Bank erosion along the rivers has contributed to increased sedimentation elsewhere. Excessive siltation in the irrigation canals reduced water flows and thus decreased water availability and favored aquatic weed growth which in turn reduces the velocity of water flow and increased sedimentation creating a vicious circle. The recurrent costs involved in cleaning silt deposits from the reservoirs and irrigation canals are enormous, unfortunately there are very few empirical or quantitative studies that assess their magnitude.

4.3.3 Canals sedimentation The problem of sedimentation is clearly felt in the irrigation canals. In dry years when there is scarcity of rain, more silt - laden water is diverted to the canals. siltation takes place especially in the minor canals where the water is supposed to be stored during the night. Another reason for extra quantities of sediment - laden water is the intensification and diversification of crops in the major irrigated schemes. Growth of aquatic weeds provides traps for silt when the velocity of flow is low. Sedimentation in canals is a headache for water managers as it causes reduction in conveyance capacity, higher water levels in poorly maintained canals and hydraulic structures, and elevation of crop fields.

4.3.4 Reservoirs sedimentation Silt and debris carried down the Blue Nile and Atbara River have affected the water supply system especially the limited reservoir storage facilities. Operational measures are taken to minimize the rate



46

of sedimentation during the flood season. Nevertheless, Roseires, Sennar and Girba reservoirs have lost 30%, 40% and 60% of their original capacities respectively. Inlet channels for the pumps on those rivers are frequently blocked by the deposition of silt carried during the flood season. It become more acute when the rainy season is good as the water needed for supplementary irrigation is minimum and the pumps would be idle most of the time. Inlet channels are usually dredged each year after the recession of the flood. The annual silt deposits behind the Roseires Dam on the Blue Nile have increased from 40 million tons in 1965 to 140 million tons in 1979 indicating a close correlation between clearing for agriculture and increased silt load on the Blue Nile. While comparative silt load and land clearing data for the Atbara and Main Nile are not available, silt load is increasing at a similar rate.

4.3.5 Atbara and its tributaries (Baselam, Atbara and Setit) the valley of the Atbara River and its tributaries , Setit and Basalam is confined between latitudes of approximately 130 00" to 160 30" N and longitudes 340 00 to " 360 00" E. The Atbara River flows through four climatic zones: dry sub-humid, semi-arid, arid, and hyper-arid zones. South of Khashem Elgirba dam, the Atbara River has steep gradients and is deeply incised in its sub-stratum. The clearance of natural vegetation for traditional rainfed agriculture has accelerated water erosion, leading to loss in arable land and the development of bad land (Kerib Land). Kerib is the name, referring to typical bad land terrain that has developed and is characterized by extensive gullying along the rivers draining from the Ethiopian Highlands. Kerib is defined as sloping land, severely dissected and eroded between the clay plain and the alluvial flood plain bordering streams and water courses. The landscape of Atbara River consists of the riverbed, its flood plains and the adjoining ‘kerib’ land along its upper reaches. In the kerib land, both topsoil and subsoil have been removed and have exposed a surface of abundant calcium carbonate concentrations with light color and irregular topography. The clay plain is composed of mostly expansive clays (cracking clays, vertisols). These clays are characterized by expansion when wet and shrinking when dry. The clay plain occupies a higher position than the flood plain with steep slopes. The extent of kerib land, measured from a map produced from TM satellite image in 1987 was about 2070 km2 along Atbara River, 761 km2 along Setit tributary and 73 km2 along Basalam and Atbara tributaries. Gully erosion has serious adverse consequences, such as loss of arable land and silting of the Khashm el Girba dam.

4.3.6 Blue Nile Basin and Dinder and Rahad Basins The soils of the Blue Nile basin are mainly alluvial deposits of more than 60% smectic clays. The area west of the Blue Nile is separated by a divide line between the White and Blue Nile. From the divide line towards the Blue Nile, the landscape is gently to undulating landscape, characterized by numerous channels, which are active during the rainy season draining the whole area. The banks of the Blue Nile are very steep and liable for bank failure and gully erosion. The high run-off is eroding the soils and increasing sediments load. The Dinder and Rahad rivers are characterized by their meandering nature in a flat clay plain. They occur in a semi-arid zone with rainfall ranging from 300 to 700 mm. They are seasonally flowing rivers, forming low lakes and cut of meanders. They are characterized by erosion and sedimentation along their banks and bed.

4.3.7 Sobat-Baro-Akobo-Pibor Basin The soil, are mainly dark gray clays. The landscape is flat with some depressions. The main hazards are severe floods and inundation.

4.3.8 The Main Nile This is the part of the Nile between Khartoum to Aswan High Dam. The main features are sedimentation, bank erosion and sand dune encroachment. Sand bars and submerged islands block the



47

pump intakes. Bank erosion, especially during the flood season, eats away valuable fertile land and mature fruit trees. Sand blown by the north wind covers valuable agricultural and residential land. It sometimes reaches the river forming sand bars and deviations. Bank erosion, morphological changes in the riverbed and sand movement to the fertile land and the river pose serious threats to the Nile and its people along this reach.

4.3.9 Blue Nile The Blue Nile can transport very high sediment concentrations, for example the 2.6% by weight recorded at Roseires during the historic 1988 flood. Concentrations vary from year to year, but typically peak at about 1% by weight at the end of July, Figure 1, reducing to about a few hundred parts per million in October.

High concentrations are usually maintained for only a few weeks, on the rising limb of the flood hydrograph. Fig. 3 shows that there is a clear relationship between sediment discharge and the river flow discharge, with a linear correlation of 0.82. The linear correlation ( R ) between the river discharge ( iY ) and the sediment discharge ( iX ), is computed by:

∑ ∑

∑

−−

−−=

N N

ii

N

ii

XXYY

XXYYR

1 1

22

1

)()(

))((

Where the linear correlation coefficient

The sediment discharge measurements were carried out at three stations on the Nile River, namely, Eldeim, Wad Elais and Sennar. The measurements were carried out at for the years 1995, 1996, 1997, 1998, and 1999. The 10 days mean sediment in Table (1).



48

Figure 4-2 Locations for Measuring the Sediment Transport



49

Figure 4-3 Blue Nile Water Discharge, eldeim (1996)

Figure 4-4 Blue Nile Sediment and Water Discharge, eldeim (1996)



50

Figure. 4-5 Grain size distribution of the suspended sediment of the Blue Nile

4.3.10 Rahad River Rahad River originates from the Ethiopian plateau. The annual water discharge The Dinder and Rahad rivers are characterized by their meandering nature in flat clay plain. They occur in a semi-arid zone with rainfall ranging from 300 to 700 mm. They are seasonally flowing rivers, forming low lakes and cut of meanders. They are characterized by erosion and sedimentation along their banks and bed. Figure 5 and 6 show the sediment and water discharge at Hawata hydrological station. Figure 7 shows that the relationship between the water discharges and the sediment discharge measured by the linear correlation amounts to 0.54, which lower than the Blue Nile. Table 3 shows the 10 days average sediment concentration at Hawata hydrological station, in the main canal, and at Abu Rakham Barrage.

Figure 4-6 Rahad River Sediment Discharge, Hawata (1993)

0102030405060708090

100

0.00 0.05 0.10 0.15 0.20 0.25 0.30Grain size (mm)

Per

cent

age

pass

ing

Gezia main canalManagil main canalD/S RoseiresW ad ElmahiLog. (Gezia main canal)Log. (D/S Roseires)Log. (W ad Elmahi)Log. (Managil main canal)



51

Figure.4-7. Rahad River Water Dischare Hawata (1993)

Figure4-8 Rahad River Sediment and Water Discharge Hawata (1993)

4.3.11 Atbara River The landscape of Atbara River consists of the riverbed, its flood plains and the adjoining ‘karab’ land along its upper reaches. ‘Karab’ refers to typical undulated terrain that is characterized by extensive gullying along the rivers draining from the Ethiopian highlands. In the karab land, both topsoil and subsoil have been removed and have exposed the surface of abundant calcium carbonate concentrations with light color and irregular topography. The clay plain is composed of mostly expansive clays (cracking clays, vertisols). These clays are characterized by expansion when wet and shrinking when dry. The clay plain occupies a higher position than the flood plain with steep slopes.

Fig. 4.6:

y = 436.89x + 1770.2R2 = 0.2948

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

0 5 10 15Water Discharge (Mm3/day)

Sed

imen

t Dis

char

ge (m

3/da

y)



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4.4 EGYPT REPORT

4.4.1 Introduction The entire length of the Nile River in Egypt consists of four reaches. The first reach locates between High Aswan Dam and Essna barrage. The second reach locates between Essna and Naga Hammadi barrages. The third reach locates between Naga Hammadi and Assuit barrages. The fourth reach locates between Assuit and Delta Barrages. Field measurements in the Nile have included bed load transport, suspended load transport, local water surface slope, and flow velocity.It was performed to get the required information about the current flow and sediment conditions in the Nile River

4.4.2 Field Measurements The Delft-Nile Sampler (Van Rijn and Gaweesh, 1992; Van Rijn, 1993a, Gaweesh and Van Rijn, 1994), which was operated from an anchored boat, was used in the measurements. This mechanical sampler was designed to measure, in contact to the bed, the bed load and the suspended load up to 0.5 m above the bed (the sampler height). Three small propeller meters were attached to the sampler to measure the current velocities at 0.18, 0.37 and 0.50 m above the bed. The bed load transport is defined as the transport between the bed surface and the top of the intake opening of the bed load sampler (about 0.055 m). This application of this practical definition may result in some oversampling, as part of the suspended sediment is trapped. However, a special patch of 0.5 mm mesh size was used at the upper side of the bed load bag to allow the suspended sediment to leave the bag. The oversampling error was estimated to be of the order of 10% to 20% (see Gaweesh and Van Rijn (1994) and Kleinhans and Ten Brinke (2001)). The suspended sand transport is defined as the transport between the top of the intake opening of the bed load sampler and the water surface. A separate device (Delft fish) equipped with a small nozzle connected to a suction pump, a propeller meter and an echo sounder for depth determination is used to measure suspended load at different water depths above the bed and near the water surface. The locations of the measurement cross sections should be selected in a stable reach to avoid non-steady bed conditions during the measurements. Echo sounding for the three cross-section profiles should also be performed. The cross section profile should be subdivided into a number of measurement stations, based on statistical error analysis (Abdel-Fattah, 1998). A longitudinal echo sounding profile over 100 m length is to be conducted at the location of each station to determine the local bed form dimensions. The positioning of the boat is determined using a laser range finder with respect to fixed stations on the bank of the river.

The local water surface slope is determined by measuring the water level at two points with a distance of about 1000 m. The flow discharge is derived from the velocity measurements at various stations across the river. During the measurement period the local water surface slope, water level and flow discharge at the measurement site should be almost constant.

The measurements of bed, suspended load and velocity profiles should also be conducted at the measurement stations. At each station, measurements are performed at locations distributed over the length of the longitudinal section, which is about equal to the mean bed form length.

All bed load samples, taken at each location in the measurement station, are separately dried and weighed and then put together to obtain a bulk sample, which represents the bed load material at the measurement station. The bed material samples for the three locations, at each measuring station, were also put together to obtain a bulk sample, which represents the bed material at each station. The samples of each station were analyzed.

4.4.3 Measured bed load transport rate To determine the measured time-averaged bed load transport rate, the 10% biggest samples and the 10% smallest samples were excluded. The measured time-averaged bed sediment load transport rates in each cross section were obtained by integrating the bed load transport over the cross section



53

4.4.4 Measured total load transport rate The total load transport rate at each cross section was obtained by summation of the suspended and bed load transport rates together.

Figure. 4-9 . Location of the Measurement Site along the Nile River



54

4.5 BURUNDI REPORT

4.5.1 Introduction: Defining the process Soil is continually being removed from land surfaces of the earth and transported downstream in rivers until it is deposited in lakes, seas, and the oceans. Since water is the primary agent of erosion and transport, the process is of interest to the hydrologist. Erosion may be viewed as stating with the detachment of soil particles by the impact of raindrops. The kinetic energy of the drops can splash soil particles will be entrained in the flowing water and moved downslope before settling to the soil surface. The splash and overland flow processes are responsible for sheet erosion, the uniformly degradation of the soil surface. So, the climatic factor is the causes of the phenomena. In another words, the soil type, vegetal cover, rainfall regime and land slope are the factors controlling erosion. The action of man plays also an important role on the degradation of soil by the erosion.

4.5.2 Watershed Characteristics In Burundi Nile Basin Location: The Burundi Nile basin watershed lies between 2o15'S and 3o55'S of latitude and 29o30 E and 30o35E of longitude. It is located in the central plateaus and depressions of north of Burundi of which altitude ranges between 1000m up to 2300m. Relief: The borders of the watershed are: • to the North, North West, and North-East: peneplains of Rwanda and Tanzania natural region;

altitude 1250m up to 1600m, • to the West: foothills of eastern parts of the Congo-Nile crest; altitude 1600 up to 2300m. These

foothills lead to the massifs and ranges of mountains making up the crest; altitude 2000 up to 2500m,

• to the South: foothills ( altitude 1800m-2000m ) of the Burundi-Rutovu massif; altitude 2000m-2200m,

• to the South-East and East: narrow old peneplains; altitude 1250-1500m resulting in the valleys of eastern ( altitude 1200m-1600m ).

Hydrography: Burundi has 2 major watersheds: one of Congo Basin and another for Nile Basin. Many tributaries flow into the Nile river through Ruvubu and Kanyaru- Kagera River inside Burundi and Kagera River outside the country which in return flows into Lake Victoria, feeding from there to the Nile River.



55

Figure 4-10: Map of Burundi

Table 4.2: Hydrological Balance Mean of Water Resources per year.

This table shows that the mean discharge of the Nile basin in the part of Burundi territory is around 137 m3/s which the equivalent is 355.1 hm3 of mean per month. Also, we have 112 m3/s (290.3 h m3 of the mean per year) which pass through the exit point of the basin of Ruvubu per month. Climate: The Nile basin in Burundi have a tropical climate but moderate by altitude. The following characteristics are:

- The mean annual temperature is a function of topography and ranges between 18oc and 20o c, - The annual rainfall amounts reach 1000m up to 1200m. The rainfall regime is characterized

by two rainy seasons, the small and long rainy season. These two rainy seasons lasts from mid-September to December immediately followed by January which is generally a small dry season.

Watershed Mean discharge National territory (m3/s)

Imported discharge from Rwanda(m3/s)

Imported discharge from Tanzania (m3/s)

Exported discharge to Rwanda (m3/s)

Exported discharge to Tanzania (m3/s)

Ruvubu 108 4 -112

Kanyaru 21 25 -46

Kagera 8 134 -142



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The long rainy season starts in February to May followed by a long season from June to around mid-September. Soil and vegetation: The soils are rocky, lateritic, lithogenic, clay or sandy. The schisto-quartz rocks are characteristic of the basin. The Nile basin occupies first of all the northern part of Burundi, southern and western part of Kirimiro central natural region and characterized by the presence of wood savanes. Thus, most of these soils are favourable to agriculture. The main crops matching with these soils are, among others, maize, beans, bananas, manihoc , collocate and coffee. Population distribution: The average population in the Nile basin area is 115 habitants per square km; the high population density is found in areas with fertile soils. During the dry season, the population practices farming activities in the marshlands to get subsistence food and other needs. Bananas local brew and coffee are the essential sources of population income.

4.5.3 Watershed Erosion and Sediment Transport in Burundi Nile Basin Many parts of Burundi Nile basin are witnessing soil degradation and loss associated with erosion resulting from over exploitation of forests and vegetation cover. Some soil conservation measures are needed in order to solve many constraints and problems particularly sediment deposition in reservoirs, rivers and irrigation canals. If we do that, we limit the problems such as: the blocking of inlet channels of pump irrigation schemes as well as the problems of the operation of hydropower turbines, corrosion of pumps and drinking water supply or distribution systems. We also need to low sediment yield in order to limit sediment deposition through watershed management which is the best method. This includes the method of erosion control techniques and sediment control. It includes also all those methods which are adopted to reduce erosion of soil and to make it more and more stable. This method is the most effective method for controlling siltation, because when the soil erosion is reduced, automatically the sedimentation problem is reduced. But the methods of treating the catchment in order to minimise erosion are very costly. Table 4.3 : Erosion risks and natural regions of Burundi Nile basin. Parameters R K LS C/natural

vegetation cover A natural vegetation (t/ha)

A cultural (t/ha)

Central Plateau(1)

475 0.07-0.14 1.1-8.3 0.001 or 0.0-0.7

0.04-0.6 3.7-386.4

Central Plateau(2)

475 0.07-0.14 1.1-8.3 0.01 0.4-5.5 3.7-386.4

Depressions of North

375 0.07-0.14 0.6-2.5 0.01 0.15-1.98 1.5-85.8

Table 4.4 : Variation of L and LS in Burundi Nile Basin. Regions Slope (S) Length of slope (L) Topographic factor

in value (LS ) Central Plateau (KIRIMIRO)

10%-25%

20m 40m 60m

1.10-4.80 1.58-6.80 1.92-8.25

4.5.4 Estimates of sediment yield The total sediment outflow from a river watershed measured in a specified period is known as the sediment yield. This is expressed in terms of the average sediment yield of the watershed to determine at what rate the canal or reservoir will fill with sediment. Information or data on sediment delivery



57

ratio is important where the percentage of on-site eroded sediment per unit of watershed area that is transported to a downstream location is called the sediment delivery ratio.

It depends on the size and texture of eroded sediment, and on the areas of sediment storage available within the watershed.

Also, for estimation of sediment yield of watershed in area lacking adequate data on sediment regime, the sediment delivery ratio method is used. The ratio between the observed sediment yield at a cross section of a stream and the total quantity of soil eroded in the catchment above that section is the sediment delivery ratio .

DR= Qs/T

Where:

DR= Sediment delivery ratio. Qs= Observed sediment yield at the centeral section at the mouth of the river basin. T= Total quantity of soil eroded from the watershed above the centeral section at the mouth.

At present, in using the delivery ratio defined by the above equation, there are two different methods of estimating T. The first is by using the ''universal Soil Loss Equation'' which is discussed before (2). The second method is by adopting the sum of the products of sheet, gully, and channel erosion (UP,GU,and CH respectively) as the total quantity of soil eroded in the watershed.

T=UP+GU+CH.

These two methods of estimating the total quantity of soil eroded in the watershed can both be used when erosion rates for the slopes and gullies are approximately the same. In case of a wide difference between the two, and for regions or cathments in which the total area of the gullies compromises a considerable percentage of the total area of the watershed, the two methods give different results. So, rill erosion is a larger contributor, to the total sediment yield. High sediment yield is usually associated with a high rill density. Sediment production decreases as percent of grass cover increases.

One of the most appreciable difficulties in estimating the sediment yield of a watershed using the sediment delivery ratio lies in the lack of practical formula for calculating the total quantity of soil eroded from the catchment. The delivery ratio for medium and small watersheds is almost near unity. This could be explained by the hyper-concentration of sediment during floods. So, the average sediment yield of the Nile Basin part of Burundi is estimated to be 424.8*10-3 million tons per year.



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5 SEDIMENT MEASURING TECHNIQUES

5.1 INTRODUCTION The study of sediment transport is highly important where morphological problems exist. As far as sediment-measuring procedures are concerned it is essential to distinguish between bed-load and suspended-load. Each of these modes of transport requires its own procedure. On the other hand, for morphological phenomena, the distinction between bed material transport and wash load is more relevant. Knowledge of the bed material transport is needed for description and prediction of erosion and sedimentation; in places where the flow velocity decreases to such an extent that the fine particles are able to settle, for instance upstream of dams, in estuaries and in river ports, knowledge of the wash load is important.

The bed material transport can be obtained by adding bed-load and that part of the suspended load, which does not belong to the wash load. To determine the latter part, analytical methods are applied using the particle-size distribution of the bed material, for which purpose sampling and analysis are necessary.

It is of essential importance to have detailed knowledge of the local morphological variables such as the bed material size, the settling velocities of the suspended solids and the transport rates. To obtain this information, an extensive field survey should be carried out.

Various instruments have been developed to measure the sediment discharge. Such measurements are necessary to determine directly the amount of sediment load/or to establish or check analytical or empirical relations, which permit direct calculation of the sediment load. Very few of the developed instruments are universally accepted. It thus becomes necessary to use the instruments with extreme care, and within the range of hydraulic and sediment parameters as specified by manufacturers.

Before the actual field survey, it is important to select the most appropriate instruments, which usually is a rather difficult problem because a wide range of instruments has been developed from simple mechanical samplers to sophisticated optical and acoustical samplers. The selection of instruments is largely dependent on the variables to be measured, the available facilities (boat, winch, ..etc.) and the required accuracy. Especially, the required accuracy should be considered carefully. For example, a basic research study requires the use of much more sophisticated instruments than an observation study.

5.2 SEDIMENT SOURCES The analysis of sediment sources aims at estimating the total amount of sediment eroded on the watershed on an annual basis, called annual gross erosion. The annual gross erosion AT depends on the source of sediments in terms of upland erosion AU, gully erosion AG, and local bank erosion AB: Thus AT = AU + AG + AB Upstream erosion generally constitutes the primary source of sediment; other sources of gross erosion. The impact of raindrops on a soil surface can exert a surface shear that exceeds the bonding forces between soil particles. The detached particles are transported through the sheet flow into rills and small channels. The Unit upland sediment discharge from the sheet erosion can be written as: Qt = a * Sb * Qc

The values of b range between 1.2 and 1.9 and that for c range between 1.4 and 2.4. The equation of Kilinc (1972) for sheet erosion is recommended for bare sandy soils for Q (feet square per second, and Q in meter square per second): Qs (lb/ft*s) = 1.24 * 105 * S1.66 * Q2.035



59

Qs (tons/m*s) = 2.55 * 104 * S1.66 * Q2.035

Considering the various soil types and vegetation, the annual rainfall erosion losses can be calculated from the Universal Soil-loss Equation (USLE): AU (total loss per unit area) = RKLSCP Normally in tons per acre Where: R is the rainfall erosivity factor K is the soil erodibility factor (usually in tons per acre) L is the field length factor S is the field slope factor C is the cropping-management P is the conservation practice factor The rainfall erosivity factor R can be calculated from: R = f( rainfall intensity) In more general case of erosion from sheet flow, modification of the USLE equation, to reflect the influence of soil type, vegetation, and practice factors using factors K, C, and P:

Qs (tons/m*s) = 1.7 * 105 * S1.66 * Q2.035 * KCP

5.3 SEDIMENT YIELD The rate at which sediment is carried by natural streams is much lower than the gross erosion on its upstream watershed. Sediment is deposited between the source and the stream cross section whenever the transport capacity of runoff water is insufficient to sustain transport. The sediment delivery ratio SDR denotes the ratio of the sediment yield Y at a given cross section to the gross erosion AT from the watershed upstream from the measuring point. The sediment yield can be therefore written as: Y = AT * SDR

5.4 BED MATERIAL SAMPLING The particle size distribution of the bed material is a necessary component in the computation of bed material load by analytical methods. It should be noted that analytical methods could only be applied to riverbeds of non-cohesive material. To enable the determination of the size distribution of the bed material, samples are taken from the riverbed. Strictly, the composition should be determined for various circumstances since, for example, at high stages; layers may be uncovered which are not exposed to flow at low stages. As it is difficult to predict which layers will constitute the active bed at various stages, the average composition of samples taken at various stages is usually considered. The particle size of the bed material may vary considerably in a lateral direction, therefore, a sample be taken in each vertical in which sediment transport is measured. It is obvious that the selection of sampler as well as sampling method has to be based on the actual circumstances. For instance, instruments, which have to be forced by hand into the streambed, can only be used in shallow water. In deep water, the free-fall principle can be applied or an instrument can be selected, the operation of which is based on its weight and shape. If the bed material contains rather coarse particles certain instruments should not be used if complete closure could be prevented by coarse particles caught between jaws. This would enable the fine particles of the sample to be washed out.



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The flow velocity should preferably not exceed 1.5 m/s when the sampling takes place. Where there is a higher flow velocity the weight of the sampler may have to be increased. Certainly, when digging samplers are used in a compact bed, heavy samplers should be selected irrespective of flow velocity. Two main categories of samplers can be distinguished, i.e. samplers which are filled by dragging them along the bed and samplers which collect bed material by grabbing or digging. To illustrate the grabbing type instruments, the grab bucket sampler is showed in Fig.5.1, as an example. This sampler consists of cupped jaws, which close to trap a sample of bed material. Closure of the jaws is obtained either by a pull on an auxiliary line or by an automatic spring arrangement.

Figure5.1a Van Veen Grab Sampler Figure 5.1b Van Veen Grab Sampler (before catching the sample) (after catching the sample)

When the bed material has D50 exceeding 300 µm, the instrument should preferably not be used because the original composition of the sample may be disturbed due to loss of fine particles. Most measuring devices used for sampling the bed under flowing water have one disadvantage in common, namely, that fine particles are often lost while the equipment is recovered. Bed material samplers could be either grabbing devices or boring pipes. Two rather simple but common grabbing devices are the scoop and the dredge.

Figure 5.2 shows another type of bed material sampler (US BM-60), which was invented by the Interagency Committee on Water Resources (1963) in the United States. The weight of the instrument is about 50 kg. It is designed to be suspended from a cable and take a sample of bed material (the sample is about 8 cm wide and 5.5 cm maximum depth). When the sampler with the bucket completely retracted contacts the streambed, the tension in the suspension cable is released and a heavy coil spring quickly rotates the bucket through 180 degree, scooping up the sample. At the close of sampling operation, the cutting edge rests against a rubber stop, which prevents any sediment from being lost. For this instrument reference is made to Vanoni (1977). Examples of other types and instruments of bed material sampling can be found in Van Rijn (1986).



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Figure5- 2 Bed Material Sampler (US BM-60) Various methods can be used for particle-size analysis; sedimentation methods for particles in the clay and silt range; sieving in the case of sand and gravel; weighing when cobbles and boulders are present. The analysis may result in particle-size distribution curves. From these curves the information needed for computation of bed material load can be read. When the percentage of organic and carbonate (Shell) material is relatively small (≤ 50%) and the sample mainly consists of silt or sand particles (≥ 90%), the analysis method can be simplified considerably. Usually, it is sufficient to determine only the size or fall velocity distribution of the dominant fraction. Organic material present in a silty sample should always be removed because it may bind together the silt particles resulting in flocculation.

5.5 BED LOAD SAMPLING Bed load can be measured by trapping the sediment moving along the bed in an instrument, which is placed, on the riverbed for a fixed period of time. Either the volume or the mass of the material collected is measured. The transport can then be determined using a calibration curve. However, it is known from experience that the amount of sediment trapped in the sampler varies considerably. This is due to the stochastic nature of the transport phenomenon as well as to accidental circumstances related to the position of the sampler on the riverbed. Many efforts have been made to improve instruments and methods in order to arrive at a more accurate estimation of the true bed load. The usual aim of measuring bed load is to select the most relevant bed load formula for the particular river. After selection, application of the formula enables estimation of the bed load for other hydraulic conditions in present or future situations. This is reflected in the following two main requirements for the selection of the measurement site (Jansen, 1979): (i) a stable river reach has to be selected in order to avoid non-steady bed conditions during the

measurements, (ii) Reliable measurements of the hydraulic conditions (depth, flow velocity, grain size and

energy slope) have to be possible. Bed load transport (qb) should be measured in a number of verticals in a cross-section. In each of these verticals a good estimate of (qb) is necessary. It should be recalled that (qb) has a fluctuating magnitude; the (periods) present in these fluctuations are governed by the wave period of the bed form (ripples and dunes). Except in rare cases, where dune lengths are large in comparison with the depth of water, it is not possible to place the sampler with sufficient accuracy in a particular location on a sand dune. Therefore, sampling has to be made at different locations along the bed form dune length λd. Obviously; it is essential to know λd under the given circumstances. Therefore, sounding along lines perpendicular to the cross-section is necessary before bed load measurements are taken with samplers.



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Since, the presence of the measuring device is frequently disturbing the flow pattern sufficiently so that behaviour and intensity of the bed load are altered. Furthermore, it is often difficult to give the equipment correct vertical and horizontal alignment with the bed load flow. In addition, it is very difficult to have a device, which collects all the size fractions of the bed load, from the coarsest to the finest grains. If a correct measurement of the bed load is desired, the following should be kept in mind: 1. Bed load measuring devices should be calibrated and their efficiency, the ratio of sampled to actual

bed load, should be determined. It is not only very difficult to determine the efficiency of a given device but also the efficiencies are variable and, thus, uncertain. Efficiencies of bed load samplers have been determined in laboratory flumes with fixed and movable beds by way of testing scale models.

2. At any cross section in a stream, the bed load is subject to fluctuations with respect to space and

time. The first is explained by the shear stress distribution over the cross section, the latter is due to the fact that the bed load transport represents an unsteady phenomenon. It is thus desirable to obtain long-term measurements at various points throughout a cross section.

3. Wrong measurements may be obtained by improper operation of the entire measuring equipment.

Under such circumstances, the sampler may scoop up the bed material and/or may collect suspended load material. Proper care must be taken in the selection of a reliable timing device.

4. Bedforms apparently influence the sampling procedure. The relations of the geometry and size

of bedforms and the measuring equipment have a strong influence on the efficiency of the equipment.

There are two methods to measure the bed load: direct and indirect measurements.

5.6 DIRECT MEASUREMENTS For trapping bed load there are three basic types of samplers; the basket or box-type; the tray or pan-type, and the Pit-type (Jansen, 1979).

5.6.1 Box- and basket-type samplers Bed load samplers of this type consist of a pervious container where bed load accumulates, of a supporting frame and cables to make the sampler portable, and of a vane(s) to give the sampler the appropriate direction. The sampling operation consists of lowering the sampler to the bed and, on contact with the bed, the front gate of the sampler opens and a timer is released. The water and the bed load enter the box or basket, experience a velocity reduction which is often aided by a screen, and thus the bed load is deposited in the trap. At the end of the measurement, the gate is closed, the measuring time is recorded, and the sampler now, containing the bed load, is lifted. The bed load can be removed and carefully measured. Figures 5.3 and 5.4 shows two examples of the Box-type samplers.

Figure 5-3 Muhlhofer Sampler (Box-type sampler)



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Figure5- 4 The Arnhem Sampler (Box-type sampler) Another example of the basket type sampler is the Delft Nile sampler, (Van Rijn and Gaweesh, 1992) shown in Fig. 5.5.

Figure 5-5. Delft Nile sampler (Box-type sampler)

5.6.2 Pan-type samplers Bed load samplers of the pan-type consist of pan with a bottom and two sidewalls. Within this pan there may or may not be a baffle system to retard the water-sediment mixture and, thus, trap the sediment. However, it was recommended that this kind of sampler be limited to streams with low velocities and small bed load rates.

5.6.3 Pit-type samplers. Depressions (pits) in the channel bottom may be installed to catch and accumulate the bed load. If a mechanical device is installed which removes continuously the accumulated sediment, a continuous record of the bed load rate at the measuring section is obtained. The efficiency of such a sampler is reported as rather high.



64

5.6.4 Other types of samplers. A device consisting of a nozzle and a pump was suggested by Hiranandani (1943) and reviewed by Hubbell (1964). The nozzle is located within the bed load layer, and is used to withdraw a point-integrated sample.

5.7 INDIRECT MEASUREMENTS

5.7.1 Calculation by measuring the bed material. Since most of the available methods to measure bed load are rather involved, frequently not too accurate but always costly, analytical methods may be used to obtain the bed load. Analytical methods require knowledge of the bed composition. Thus the bed composition has to be determined experimentally. Einstein (1950) remarked that, in fact, the bed material composition at each stage should be known. However, such information is seldom available, and the bed sampling at a representative river stage is usually performed.

5.7.2 Sound Sampler The bed load scraping along the bottom creates audible sound waves. Acoustic instruments are designed to pick up these waves. The equipment is simple, consisting of an underwater microphone located at a certain distance from the bottom, an amplifier, and a recorder. Most of these instruments have underwater microphones of various designs.

5.7.3 Tracking of bedforms. The determination of bed load in the lower flow regime is possible by knowing the velocity of the bedform, the bedform height, and the porosity of the bed. These parameters can be observed and measured in clear and/or shallow water. In deep and less clear water, continuous depth measurements have to be performed. Maps of bottom (depth) contours for different times may be evaluated such that bedform velocity and height are available and the bed load rate may be calculated.

5.8 SUSPENDED LOAD SAMPLING The determination of suspended load (qs), in a cross-section of a stream (per unit width) is based on measurements in a number of verticals and with this information integration over the cross-section is possible. The data for the verticals can be obtained in two ways:

(i) depth integration over the vertical, and (ii) Point integration in a number of points in each vertical and integration over the vertical.

The determination of the transport in suspension, in principle, concerns bed material load in suspension as well as wash load. If a distinction between the two is required, then grain size analysis of the suspended particles is necessary. Some rivers show a marked difference in grain-size for the two modes of transport. In general, however, a sharp distinction between the two modes cannot yet be made. Samplers for suspended sediment transport were developed in the past according to two different principles: the direct and the indirect measuring of the sediment transport.

5.8.1 Direct Method It is based on the direct measurement of the time-averaged sediment transport in a certain point (point integrating) or over a certain depth range (depth-integrating). This latter procedure implies vertical movement at a uniform speed of the sampler over a certain depth-range. Using a mechanical sampler based on the collection of a water-sediment sample, this procedure is only applicable in shallow streams. Example of samplers based on the direct measuring principle is the Delft Bottle, Figure 6.



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Figure5- 6 Delft Bottle (Depth-Integrating)

5.8.2 Indirect Method The indirect method is based on the simultaneous but separate measurement of the time-averaged fluid velocity and the time-averaged sediment concentration, which are multiplied to obtain the time-averaged sediment transport. The time-averaged concentration can be measured in a single point (point-integrating) or over a certain depth range (depth-integrating). Examples of samplers based on the indirect measuring principle are the simple bottle and trap samplers, the pump samplers, the optical samplers, and the delft fish as shown in figure 7.

Figure 5- 7 The Delft Fish Used For Velocity Measurements And Suspended Sediment Sampling



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6 CONCLUSIONS AND RECOMMENDATIONS

6.1 CONCLUSIONS The aim of this research area was to provide capacity building in watershed erosion and sediment transport, in the Nile Basin Countries involved, and to sustainably manage the water resources of the Basin. Specifically, the research was carried out in line to provide information pertaining to:

• The practical watershed management techniques for reducing soil erosion and sediment yield. • Provide suitable means and techniques for the predicting and measuring sediment transport in

mountainous areas, flood plains and channels. • The capacity of the Nile Basin Countries and improve the capacity of the involved personnel

in the processes of sediment investigation, computation and watershed management techniques.

• The database of sediment flows and characteristics. • The level of awareness of stakeholders and public at large on soil erosion and provide means

for raising it. • Sediment transport related problems.

A suitable means for realizing the above mentioned objectives is through specific applied joint research of interest to the countries involved. The countries involved in this research area include Sudan as a Coordinating country, Burundi, Egypt, and Ethiopia. During Phase 1 of this research the activities have concentrated on a survey of the literature and data inventory on both watershed erosion and sediment transport in the Nile basin.

· Available data is reviewed and synthesized and their sources, availability, extend and qualities were assessed;

· Gaps in knowledge and data available were identified as well as the need for additional data collection

· Appropriate regional database network is created.

· Measuring methods and techniques for sediment transport in rivers were described which has resulted in the following products to:

• Survey of the literature on sediment yield • Survey of the literature in soil conservation measures • Inventory of sediment transport data • Collection of studies in sediment transport • Inventory of data on sediment load (including reservoir data) • Comparison of sediment measuring techniques

6.2 RECOMMENDATIONS The following recommendations were drawn

• Setting up and preparation of data base(s) on sediment yield and sediment transport in the Nile basin

• Assessment of sediment yield in selected areas using remote sensing and GIS • Estimation of sediment from sand encroachment and gully erosion • Proposing more improved sediment transport measurement techniques • Cooperation with other activities like FRIEND/NILE is considered, in particular for the data base

part.



67

7 BIBLIOGRAPHY

Abdel-Fattah, S. (1997a)."Field Measurements of Sediment Load Transport in the Nile River at Quena", Technical Report, HRI, Delta Barrage, Egypt.

Abdel-Fattah, S. (1997b)."Field Measurements of Sediment Load Transport in the Nile River at Sohag", Technical Report, HRI, Delta Barrage, Egypt.

Abdel-Fattah, S. (1998)."Prediction of sediment rate in the Nile River ", Ph. D. Thesis, Faculty of Engineering, Ain Shams University, Egypt.

Ackers, P. and White, W.R., (1973). "Sediment Transport: New Approach and Analysis", Journal of the Hydraulic Division, ASCE., No. HY 11, USA.

Ackers, P. and White, W.R., (1973). "Sediment Transport: New Approach and Analysis", Journal of the Hydraulic Division, ASCE, No. HY 11, USA.

Adam A. M., El Monshid B. F. and Ahmed S. E. (1994), " Bank Erosion of the River Nile in North Sudan" Proceeding of Khartoum Nile 2002 Conference, Comprehensive Water Resources Development of the Nile Basin: The Vision Ahead 29th January – 1st February 1994.

Ahmed S. E. and Elawad. O. M.A. (2002) “Environmental Impact of the Alluvial Nature of the Nile on Irrigated Agriculture in Sudan” Presented in Addis Ababa Nile 2002 Conference

Ahmed, S. E. and Saad M. B. (1992) "Prediction of Natural Channel Hydraulic Roughness" Journal of Irrigation and Drainage Engineering, ASCE, Vol. 118, No.4,

Ahmed, S. E., (1996), Sediment Monitoring Programme (Blue Nile System), Ministry of Irrigation and Water Resources, Sudan

Ahmed, S. E.,(1994) "Computation of bed changes in alluvial channels" Proceeding of the International Conference of Efficient Utilization and Management of Water Resources in Africa.

B.E. El Monshid , El Awad O. M.A. and Ahmed S. E. (1997), “Environmental impact of the Blue Nile Sedimentation on Reservoirs and Irrigation canals” Proceeding 5th Nile 2002 Conference, Addis Ababa, Ethiopia.

Bagnold, R.A. (1966). "An Approach to the Sediment Transport Problem from General Physics", Geological Survey Prof. Paper 422-1, Washington.

Bagnold, R.A. (1966). "An Approach to the Sediment Transport Problem from General Physics", Geological Survey Prof. Paper 422-1, Washington.

Bekele, T. and Egziabher, T. B. G., (1998), Environmental consideration in water Resources development of the Blue Nile basin," Proceedings of 5th Nile 2002 Conference, February 24-28, 1997, Addis Ababa, Ethiopia, Ministry of Water Resources

Conway, D. and Hulme, M., (1992), "Recent Fluctuation in precipitation and runoff over the Nile basin and implications for assessing future climate change," Climatic Research Unit, School of Environmental Sciences, University of East Anglia, Norwich, UK.

Delft Hydraulics (1986). "Sand Concentration Profiles for Currents and/or Waves", Data Base, M1695-04-1, The Netherlands, pp. 8-13.

Delft Hydraulics (1986). "Sand Concentration Profiles for Currents and/or Waves", Data Base, M1695-04-1, The Netherlands, pp. 8-13.

Einstein, H. A., (1950). “The Bed Load Function for Sediment Transportation in Open Channel Flows, U.S. Dept. Agric., Soil Conserv., T.B. no. 1026.

Engelund, F. and Hansen, E., (1967). A Monograph on Sediment Transport in Alluvial Streams. Teknisk Forlag, Copenhagen, Denmark.



68

Engelund, F. and Hansen, E., (1967). A Monograph on Sediment Transport in Alluvial Streams. Teknisk Forlag, Copenhagen, Denmark.

Fitzjohn, C., J.L. Ternan & A.G. Williams, (1998). “Soil moisture variability in a semi-arid gully catchment: implications for runoff and erosion control”, Catena 32, 1998, pp. 55-70.

Frijlink, H.C., (1952). " Discussion of Bed Load Movement Formulas", Report No. X2344/LV, Delft, The Netherlands.

Gaweesh, M.T.K., (1992). "Measurements of Sediment Transport in the Nile River at Bani-Mazar with the Delft Nile Sampler", Technical Report, HRI, Delta Barrage, Egypt.

Gaweesh, M.T.K., (1992). "Measurements of Sediment Transport in the Nile River at Bani-Mazar with the Delft Nile Sampler", Technical Report, HSRI, Delta Barrage, Egypt.

Gaweesh, M.T.K., Ramadan, K.A. and El-Balasy, A. (1994). "Field Measurements of Sediment Load Transport in the Nile River at Beni-Sweif", Technical Report, HSRI, Delta Barrage, Egypt.

Gismalla Y.A. (1998) “Reservoir Sedimentation: Roseires Case” Proceedings 6th Nile 2002 Conference, Kigali, Rwanda.

Gismalla, Y. A., (1998), Sediment Monitoring Programme (Blue Nile System), Ministry of Irrigation and Water Resources, Sudan



Hubbell, D. W., (1964). “Apparatus and Techniques for Measuring Bed Load”, U. S. Geol. Survey, Water Supply Paper 1748.

Hussein, A. S. (1993) "Upstream Soil Erosion Impact on Downstream; A case study Sudan Gezira Scheme presented at the workshop on , Environmentally sound management of the Upper Nile watershed.

Hussein, A. S., Ahmed, A. A. and Ahmed S. E.(1986) "Sedimentation Problems in the Gezira Scheme" Proc. Internal Conf. on Water Resources Needs and Planning in Drought Prone Areas, Khartoum

Hussien A.S. & Yousif, D.M.(1994), "Prediction of Settling performance for Very fine Sedimentation" Proceeding of the International Conference on Efficient Utilization and Management of Water Resources in Africa.

Jansen, P. PH., (1979). “Principle of River Engineering, The Non-Tidal Alluvial River”, Delfts Uitgevers Maataschappij, Delft, The Netherlands.

Julian, P. Y. (1995)."Erosion and Sedimentation" Cambridge University Press, USA.

Kishk, M. A., (1986), Land degradation, Egyptian in the Nile Valley. Ambio, Vol. 15(4): 236-230

Klaassen, G. J., Ogink, H., and L.C., Van Rijn, (1986). "Delft Hydraulics Laboratory Research on Bed Forms, Resistance to Flow, and Sediment Transport”, Proc. 3rd Intern. Symp. on River Sedimentation, Jackson (USA), 25 pp.

Kleinhans, M.G. and Ten Brinke, W.B.M., (2001). “Accuracy of cross-channel sampled sediment transport in large sand-gravel-bed rivers”, J. Hydr. Eng., ASCE, Vol. (127), No. (4), 258-269.

Kleinhans, M.G. and Ten Brinke, W.B.M., (2001). “Accuracy of cross-channel sampled sediment transport in large sand-gravel-bed rivers”, J. Hydr. Eng., ASCE, Vol. (127), No. (4), 258-269.

Kort, J., C. Collins & D. Ditsch, (1998). “A review of soil erosion potential associated with biomass crops”, Biomass and Bioenergy, 14-4, 1998, pp. 351-359.



69

Lates E. M. and El Monshid, B.F(1986) " The influence of the Hydraulic Operation of pump station energy Dissipaters on the Pattern and Size of Downstream Scouring in the main Irrigation Cannel" Proceedings of the international conference on water resources Needs and Planning in Drought Prone Areas

Matalo, F. (1994) Reservoir Sedimentation mechanism: case study from Mtera Reservoir," Proceedings of the International Conference on Efficient Utilization and Management of Water Resources in Africa.

McCornick, P., Kamara, A.B. and Girma Tadesse (eds), (2003), "Integrated water and land management research and capacity building priorities for Ethiopia," Proceedings of

Meyer-Peter, E. and Muller, R, (1948). "Formulas for Bed-Load Transport ", Sec.Int. IAHR congress, Stockholm, Sweden.

Moattasem, M. & Abdel Bary, M.R "Changes in the fluvial characteristics of the Nile River after the Aswan High Dam," Proceeding of the International Conference on Efficient Utilization and management of Water Resources in Africa.

Natural Resource Sciences, (2001), “Run-off control measures for soil conservation”, The State of Queensland, Department of Natural Resources and Mines, Australia.

Salaheldin, Y.A. & Berlamont, J.,(1994),"On the Quantative measurement of erosion rates of cohesive sediment", Proceeding of the International Conference on Efficient Utilization and Management of Water Resources in Africa.

Soil and Water Conservation Measures, Goa Forest Department, Soil Conservation Division, Dhavali, Ponda, Goa, Indai.

Upreti, G., (1994), "Environmental conservation and sustainable development require a new development approach," Environmental Conservation 21(1): 18-29.

Van Rijn, L.C., (1984a). "Sediment Transport, Part I: Bed Load Transport", Journal of Hydraulic Engineering, ASCE, Vol. 110, No.10.

Van Rijn, L.C., (1984a). "Sediment Transport, Part I: Bed Load Transport", Journal of Hydraulic Engineering, ASCE, Vol. 110, No.10.

Van Rijn, L.C., (1984b). "Sediment Transport, Part II: Suspended Load Transport", Journal of Hydraulic Engineering, ASCE, Vol.110, No.11

Van Rijn, L.C., (1984b). "Sediment Transport, Part II: Suspended Load Transport", Journal of Hydraulic Engineering, ASCE, Vol.110, No.11

Yang, C. T. (1996)."Sediment transport: Theory and practice" McGraw Hill series in water resources and environmental engineering, The McGraw Hill Companies, USA..

Yousif, D. M.,(1994), "Fail Velocity of Very Fine Sediment in Turbulent Flow," Proceeding of Khartoum Nile 2002 Conference: Comprehensive Water Resources Development of the Nile Basin: The Vision Ahead

APPENDIX (A)

Sample of Field Measurement of Sediments in Egypt

A 1

This Appendix is part of Egypt Report which covers a sample of field measurement of sediments in Egypt 1. Introduction Field measurements in the Nile River were carried out through the research work of group-3 in the field of watershed erosion and sediment transport. These measurements included bed load transport, suspended load transport, local water surface slope, and flow velocity. It were performed to get the required information about the current flow and sediment conditions in front of a power plant located at Bani-Sweif south of Egypt. This data will be used to solve the sedimentation problem at the intake of the Power Plant. The entire length of the Nile River in Egypt consists of four reaches. The first reach locates between High Aswan Dam and Essna barrage. The second reach locates between Essna and Naga Hammadi barrages. The third reach locates between Naga Hammadi and Assuit barrages. The fourth reach locates between Assuit and Delta Barrages. The sediment load transport measurements were carried out at three cross sections in front of Kurimat village, located at km 831 (measured downstream High Aswan Dam). Figure 1 shows the location of Kurimat with respect to the existing main barrages across the Nile River in Egypt. The location of the three measuring cross sections at Kurimat is shown in Fig. 2. The first cross section was located in the eastern branch of the Nile River upstream the intake of Kurimat power plant by a distance of 1300 m. The second cross section was located in the western branch of the Nile River upstream the intake by a distance of 1700 m. The third cross section was located upstream the intake, between a small artificial island and the left bank of the river, by a distance of 600 m. 2. Measurement Techniques The Delft-Nile Sampler (Van Rijn and Gaweesh, 1992; Van Rijn, 1993a, Gaweesh and Van Rijn, 1994), which was operated from an anchored boat, was used in the measurements. This mechanical sampler was designed to measure, in contact to the bed, the bed load and the suspended load up to 0.5 m above the bed (the sampler height). Three small propeller meters were attached to the sampler to measure the current velocities at 0.18, 0.37 and 0.50 m above the bed. The bed load transport is defined as the transport between the bed surface and the top of the intake opening of the bed load sampler (about 0.055 m). This application of this practical definition may result in some oversampling, as part of the suspended sediment is trapped. However, a special patch of 0.5 mm mesh size was used at the upper side of the bed load bag to allow the suspended sediment to leave the bag. The oversampling error was estimated to be of the order of 10% to 20% (see Gaweesh and Van Rijn (1994) and Kleinhans and Ten Brinke (2001)). The suspended sand transport is defined as the transport between the top of the intake opening of the bed load sampler and the water surface. A separate device (Delft fish) equipped with a small nozzle connected to a suction pump, a propeller meter and an echo sounder for depth determination was used to measure suspended load at different water depths above the bed and near the water surface, Fig (3).

The locations of the measurement cross sections were selected in a stable reach to avoid non-steady bed conditions during the measurements. Echo sounding for the three cross-section profiles were performed. The cross section profile was subdivided into three measurement stations, based on statistical error analysis (Abdel-Fattah, 1998). A longitudinal echo sounding profile over 100 m length was conducted at the location of each station to determine the local bed form dimensions. The positioning of the boat was determined using a laser range finder with respect to fixed stations on the bank of the river.

The local water surface slope was determined by measuring the water level at two points with a distance of about 1000 m. The flow discharge was derived from the velocity measurements at various stations across the river. During the measurement period the local water surface slope, water level and flow discharge at the measurement site were almost constant.

A 2

The measurements of bed, suspended load and velocity profiles were conducted at the three measurement stations (St1 to St3, Fig. 4). At each station (St1 to St3), measurements were performed at three locations (L1, L2, and L3) distributed over the length of the longitudinal section, which is about equal to the mean bed form length. Figure (4) shows the layout of the measurement stations and locations at one cross section. In all, measurements were performed at 9 locations per cross section.

At each station the following measurements were performed for the three locations:

• ten instantaneous samplings using the Delft Nile Sampler with a bag of mesh size 250 µm; the sampler was lowered to the bed and immediately was raised up after the nozzle had touched the bed (‘zero’-samplings; these values are subtracted from the bed load samplings of 3 minutes to correct for the initial disturbance effect);

• Eight bed load samplings of 3 minutes each using the Delft Nile Sampler with the same bag size;

• Suspended load samplings along the water depth using the Delft Nile and the Delft Fish Samplers. The suction of the samples was driven by a set of pulsation pumps. The samples were collected (volume = 5 litters) in plastic buckets;

• Velocity profiles along the water depth using propeller current-meters installed on the Delft Nile and the Delft Fish Samplers. The flow velocity measurements were carried out as follows:

• at 0.18, 0.37 and 0.50 m above the bed level by using three propeller-type current-meters attached to the Delft Nile Sampler;

• from 0.50 m above the bed level to the water surface by using propeller-type current-meter attached to the Delft Fish;

• one bed material sample at the end of each measurement using a grab sampler; • water temperatures were measured;

All bed load samples, taken at each location in the measurement station, were separately dried and weighed and then put together to obtain a bulk sample, which represents the bed load material at the measurement station. The bed material samples for the three locations, at each measuring station, were also put together to obtain a bulk sample, which represents the bed material at each station. The samples of each station were analyzed. 3. Results and Analysis of Measurements Bathymetry data Echo sounding of the three cross-section profiles were carried out, Figures 5, 6, and 7. The local water surface slope was determined by measuring the water level at two points with a distance of about 1000 m. During the measurement period the local water surface slope, water level and flow discharge at the measuring site were almost constant. The measured local water surface slope was found to be 7.0 cm/km and the measured flow discharge was found to be 1014 m3/s. Velocity profile data The data of the measured velocity profiles at cross section (1) are given in the Tables from 1 through 3. And at cross section (2) are given in the Tables from 4 through 6. And at cross section (3) are given in the Tables from 7 through 9. It was assumed that bed load transport takes place by migrating mini ripples with a height in the order of 0.03 m. Therefore, the velocity profiles were extrapolated down to a height of 0.03 m above bed, and the local depth-averaged velocities were computed.

3.1 Suspended sediment concentration profile data The basic data of the suspended sediment measurements for the three cross sections are given in the Tables from 10 through 18. The concentration profiles were also extrapolated down to 0.03 m above bed according to the assumption explained above. The depth-integrated suspended sediment transport was computed.

3.2 Grain size characteristics The results of the sieve analysis for the three cross sections are presented in Tables 19.through 21, respectively. Comparison of D10, D50 and D90 values of bed material and the bed load samples shows

A 3

that the overall average values of bed load samples are slightly smaller than those of the bed material samples.

3.3 Measured suspended load transport rate The measured time-averaged suspended sediment load transport rates in each cross section were obtained by integrating the suspended load transport over the cross section. The results are given in Tables 22, 25, and 28 for the three cross sections, respectively.

3.4 Measured bed load transport rate To determine the measured time-averaged bed load transport rate, the 10% biggest samples and the 10% smallest samples were excluded. The measured time-averaged bed sediment load transport rates in each cross section were obtained by integrating the bed load transport over the cross section. The results are given in Tables 23, 26, and 29 for the three cross sections, respectively

3.5 Measured total load transport rate The total load transport rate at each cross section was obtained by summation of the suspended and bed load transport rates together. The measured total load transport rates are given in Tables 24, 27, and 30 for the three cross sections, respectively. 4. Sediment Transport Rate in Front of the Intake The sediment transport rate in front of the intake in the cross section located between the right bank and the small artificial island was obtained from the measured data as follows: Suspended load transport over the cross section = suspended load transport over the cross sections (1+2-3) = 2.7492 (kg/s) Bed load transport over the cross section = bed load transport over the cross sections (1+2-3) = 0.4011 (kg/s) Total load transport over the cross section = total load transport over the cross sections (1+2-3) = 3.1507 (kg/s) TABLE (1) Velocity Profile Data Measured at Different Locations At Cross Section 1 - Station 1

Location Water Depth (m)

Height above Bed (m)

Current Velocity (m/s)

Mean Velocity (m/s)

1

3.4

0.18 0.37 0.50 1.40 2.40 3.40

0.41 0.46 0.50 0.55 0.56 0.60

0.52

2

3.25

0.18 0.37 0.50 1.25 2.25 3.25

0.38 0.43 0.49 0.52 0.62 0.62

0.52

3

3.0

0.18 0.37 0.50 1.00 2.00 3.00

0.47 0.49 0.56 0.57 0.61 0.64

0.55

A 4

TABLE (2) Velocity Profile Data Measured at Different Locations at Cross Section 1 - Station 2 Location Water Depth

(m) Height above

Bed (m)


Mean Velocity (m/s)

1

3.7

0.18 0.37 0.50 1.00 1.70 2.70 3.70

0.50 0.56 0.63 0.67 0.68 0.76 0.78

0.67

2

3.60

0.18 0.37 0.50 1.00 1.60 2.60 3.60

0.56 0.63 0.71 0.72 0.75 0.82 0.83

0.72

3

4.0

0.18 0.37 0.50 1.00 2.00 3.00 4.00

0.41 0.47 0.51 0.64 0.74 0.75 0.75

0.65

TABLE (3) Velocity Profile Data Measured at Different Locations at Cross Section 1 - Station 3




Mean Velocity (m/s)

1

4.40

0.18 0.37 0.50 1.40 2.40 3.40 4.40

0.57 0.67 0.71 0.80 0.84 0.88 0.89

0.78

2

5.00

0.18 0.37 0.50 1.00 2.00 3.00 4.00 5.00

0.29 0.34 0.38 0.53 0.66 0.77 0.91 0.91

0.68

3

4.40

0.18 0.37 0.50 1.40 2.40 3.40 4.40

0.52 0.60 0.62 0.71 0.78 0.80 0.81

0.71

A 5


(m) Height above

Bed (m)


Mean Velocity (m/s)

1

3.25

0.18 0.37 0.50 1.25 2.25 3.25

0.59 0.65 0.67 0.82 0.89 0.94

0.78

2

3.30

0.18 0.37 0.50 1.30 2.30 3.30

0.49 0.62 0.66 0.84 0.92 0.93

0.79

3

2.90

0.18 0.37 0.50 1.00 1.90 2.90

0.61 0.74 0.76 0.85 0.87 0.90

0.79





Mean Velocity (m/s)

1

3.30

0.18 0.37 0.50 1.30 2.30 3.30

0.51 0.65 0.68 0.84 0.89 0.95

0.78

2

3.10

0.18 0.37 0.50 1.10 2.10 3.10

0.55 0.65 0.67 0.81 0.91 0.92

0.78

3

3.30

0. 18 0.37 0.50 1.30 2.30 3.30

0.53 0.62 0.64 0.76 0.81 0.83

0.72

A 6


(m)



Mean Velocity

(m/s)

1

3.10

0.18 0.37 0.50 1.10 2.10 3.10

0.62 0.71 0.72 0.76 0.81 0.83

0.75

2

3.10

0.18 0.37 0.50 1.10 2.10 3.10

0.39 0.50 0.56 0.72 0.81 0.82

0.69

3

2.80

0.18 0.37 0.50 1.00 1.80 2.80

0.53 0.64 0.66 0.74 0.78 0.80

0.71


Location Water Depth

(m)



Mean Velocity

(m/s)

1

2.35

0.18 0.37 0.50 1.00 1.50 2.35

0.50 0.62 0.67 0.72 0.78 0.78

0.69

2

2.40

0.18 0.37 0.50 1.00 1.70 2.40

0.44 0.56 0.61 0.69 0.73 0.74

0.64

3

2.50

0.18 0.37 0.50 1.00 1.70 2.50

0.47 0.56 0.57 0.69 0.70 0.78

0.64

A 7


(m)



Mean Velocity

(m/s)

1

2.40

0.18 0.37 0.50 1.00 1.70 2.40

0.52 0.62 0.64 0.67 0.70 0.75

0.65

2

2.25

0.18 0.37 0.50 1.00 1.60 2.25

0.55 0.62 0.65 0.67 0.68 0.74

0.64

3

2.20

0.18 0.37 0.50 1.00 1.60 2.20

0.57 0.67 0.70 0.71 0.74 0.75

0.68


Location Water Depth

(m)



Mean Velocity

(m/s)

1

5.00

0.18 0.37 0.50 1.00 2.00 3.00 4.00 5.00

0.47 0.55 0.60 0.66 0.67 0.75 0.77 0.80

0.69

2

5.00

0.18 0.37 0.50 1.00 2.00 3.00 4.00 5.00

0.52 0.58 0.65 0.67 0.72 0.77 0.79 0.80

0.72

3

4.40

0.18 0.37 0.50 1.00 1.70 2.40 3.40 4.40

0.51 0.61 0.65 0.74 0.82 0.83 0.84 0.86

0.77

A 8

TABLE (10) Measured Concentration Profile Data Measured at Different Locations at Cross Section 1 - Station 1

Location 1 Location 2 Location 3 Z (m) C (Mg/l) Z (m) C (Mg/l) Z (m) C (Mg/l) 0.10 44 0.10 36 0.10 38 0.18 38 0.18 32 0.18 26 0.37 34 0.37 26 0.37 22 0.50 20 0.50 22 0.50 18 1.40 18 1.25 18 1.00 14 2.40 14 2.25 14 2.00 10 3.40 10 10 3.00 6


Location 1 Location 2 Location 3 Z (m) C (Mg/l) Z (m) C (Mg/l) Z (m) C (Mg/l) 0.10 36 0.10 52 0.10 40 0.18 30 0.18 44 0.18 32 0.37 26 0.37 28 0.37 26 0.50 22 0.50 22 0.50 22 1.00 20 1.00 18 1.00 18 1.70 18 1.60 14 2.00 14 2.70 12 2.60 12 3.00 8 3.70 8 3.60 10 4.00 6


Location 1 Location 2 Location 3 Z (m) C (Mg/l) Z (m) C (Mg/l) Z (m) C (Mg/l) 0.10 62 0.10 36 0.10 30 0.18 44 0.18 30 0.18 28 0.37 30 0.37 27 0.37 25 0.50 26 0.50 23 0.50 21 1.40 22 1.00 20 1.40 18 2.40 18 2.00 18 2.40 14 3.40 14 3.00 12 3.40 10 4.40 10 4.00 9 4.40 8

5.00 6


Location 1 Location 2 Location 3 Z (m) C (Mg/l) Z (m) C (Mg/l) Z (m) C (Mg/l) 0.10 33 0.10 40 0.10 56 0.18 30 0.18 33 0.18 34 0.37 27 0.37 26 0.37 28 0.50 22 0.50 22 0.50 24 1.25 19 1.30 20 1.00 18 2.25 15 2.30 16 1.90 13 3.25 10 3.30 9 2.90 8

A 9


Location 1 Location 2 Location 3 Z (m) C (Mg/l) Z (m) C (Mg/l) Z (m) C (Mg/l) 0.10 58 0.10 70 0.10 140 0.18 46 0.18 46 0. 18 100 0.37 34 0.37 33 0.37 64 0.50 30 0.50 29 0.50 54 1.30 25 1.10 26 1.30 36 2.30 19 2.10 14 2.30 22 3.30 14 3.10 8 3.30 16







A 10


Location 1 Location 2 Location 3 Z (m) C (Mg/l) Z (m) C (Mg/l) Z (m) C (Mg/l) 0.10 38 0.10 38 0.10 46 0.18 32 0.18 29 0.18 34 0.37 28 0.37 26 0.37 30 0.50 24 0.50 22 0.50 26 1.00 20 1.00 19 1.00 22 2.00 17 2.00 15 1.70 19 3.00 14 3.00 12 2.40 16 4.00 11 4.00 10 3.40 12 5.00 8 5.00 7 4.40 7

TABLE (19) Grain Size Analysis of Bed Material Samples and Bed Load Samples o The Nile River at cross section 1

Station

Grain Size (µm)

Bed Material Samples Collected by The

Grab Sampler

Bed Load Samples Collected by The

Delft Nile Sampler

D10

D50

D90

óg

D10

D50

D90

óg

1

178

308

492

1.484

131

284

439 1.566

2

213

379

720

1.578

208

380

716

1.534

3

273

467

853

1.541

289

460

831

1.439

TABLE (20) Grain Size Analysis of Bed Material Samples and Bed Load Samples of The Nile River at cross section 2

Station

Grain Size (µm)

Bed Material Samples Collected by The

Grab Sampler


Delft Nile Sampler

D10

D50

D90

óg D10

D50

D90

óg

1

304

466

712

1.383

231

437

683

1.515

2

188

274

432

1.366

186

272

358

1.312

3

188

249

348

1.298

182

241

335

1.296

TABLE (21) Grain Size Analysis of Bed Material Samples and Bed Load Samples of The Nile River at cross section 3

Station

Grain Size (µm)

Bed Material Samples Collected by The Grab Sampler


Delft Nile Sampler

D10 D50

D90

óg

D10

D50

D90

óg

1

214

355

686

1.659

210

315

534

1.396

2

296

474

860

1.436

283

460

848

1.477

3

219

362

665

1.647

216

350

844

1.619

A 11

TABLE (22) Measured Suspended Load Transport Rates in Cross Section 1

Station Number

Suspended Load Transport Rates

( kg / m.s )

Station Width

( m )

Transport Rates

( kg / s )

1 2 3

0.02766 0.04126 0.05333

86 57

100

2.3787 2.3518 5.3330

Total Suspended Load Transport Rate Integrated Over The Cross Section

( kg / s )

10.0635

Station 1 is at 62 m from the left bank; Station 2 is at 111 m from the left bank; Station 3 is at 157 m from the left bank. TABLE (23) Measured Bed Load Transport Rate in Cross Section 1

Station Number

Bed Load Transport

Rate ( kg / m.s )

Station Width

( m )

Transport Rate

( kg / s )

1 2 3

0.000413 0.003547 0.012630

86 57

100

0.0355 0.2022 1.2630

Total Bed Load Transport Rate Integrated Over The Cross Section

( kg / s )

1.5007

Station 1 is at 62 m from the left bank; Station 2 is at 111 m from the left bank; Station 3 is at 157 m from the left bank.

TABLE (24) Measured Total Load Transport Rate in Cross Section 1


( kg / s )

Bed Load Transport

Rate ( kg / s )

Total Load Transport

Rate ( kg / s )

10.0635 1.5007 11.5642


Station Number


( kg / m.s )

Station Width

( m )

Transport Rates

( kg / s )

1 2 3

0.04376 0.06323 0.08016

82 56 82

3.5883 3.5408 6.5731

Total Suspended Load Transport Rate Integrated Over The Cross Section

( kg / s )

13.7022


A 12

TABLE (26) Measured Bed Load Transport Rate in Cross Section 2

Station Number

Bed Load Transport Rate

( kg / m.s )

Station Width

( m )

Transport Rate

( kg / s )

1 2 3

0.010101 0.007500 0.009307

82 56 82

0.8283 0.4203 0.7632

Total Bed Load Transport Rate Integrated Over The Cross Section

( kg / s )

2.0118 Station 1 is at 55 m from the left bank; Station 2 is at 110 m from the left bank; Station 3 is at 165 m from the left bank.



( kg / s )

Bed Load Transport

Rate ( kg / s )


Rate ( kg / s )

13.7022

2.0118

15.7140


Station Number


( kg / m.s )

Station Width

( m )

Transport Rates

( kg / s )

1 2 3

0.04966 0.03213 0.05400

172 116 162

8.5415 3.7270 8.7480

Total Suspended Load Transport Rate Integrated over The Cross Section

( kg / s )

21.0165


TABLE (29) Measured Bed Load Transport Rate in Cross Section 3

Station Number

Bed Load Transport

Rate ( kg / m.s )

Station Width

( m )

Transport Rate

( kg / s )

1 2 3

0.006904 0.011346 0.003750

172 116 162

1.1874 1.3161 0.6075

Total Bed Load Transport Rate Integrated over the Cross Section

( kg / s )

3.1110 Station 1 is at 55 m from the left bank; Station 2 is at 110 m from the left bank; Station 3 is at 165 m from the left bank.



( kg / s )

Bed Load Transport

Rate ( kg / s )


Rate ( kg / s )

21.0165

3.1110

24.1275

A 13

Computation of Depth-Integrated Suspended Sediment Transport and Depth-Averaged Velocity from the Measured Velocity and Concentration Profiles at Kurimat (April 2003)

(Cross section 1 Station 1 located at 62 m from left bank)

Location (1) Location(2) Location(3) Z V C Z V C Z V C

(m) (m/s) (kg/m3) (m) (m/s) (kg/m3) (m) (m/s) (kg/m3) 3.4 0.6 0.01 3.25 0.62 0.01 3 0.64 0.006 2.4 0.56 0.014 2.25 0.62 0.014 2 0.61 0.01 1.4 0.55 0.018 1.25 0.52 0.018 1 0.57 0.014 0.5 0.5 0.02 0.5 0.49 0.022 0.5 0.56 0.018 0.37 0.46 0.034 0.37 0.43 0.026 0.37 0.49 0.022 0.18 0.41 0.038 0.18 0.38 0.032 0.18 0.47 0.026 0.15 0.392 0.043 0.15 0.363 0.033 0.15 0.449 0.027 0.12 0.37 0.046 0.12 0.343 0.034 0.12 0.425 0.028 0.09 0.345 0.048 0.09 0.32 0.036 0.09 0.395 0.029 0,06 0.312 0.051 0.06 0.289 0.037 0.06 0.357 0.03

0.03 0.262 0.054 0.03 0.432 0.038 0.03 0.3 0.031 Vmean = 0.531 m/s Vmean = 0.54 m/s Vmean = 0.572 m/s Ss = 0.0318 kg/ m.s Ss = 0.0294 kg/m.s Ss = 0.0218 kg/ m.s Computation of Depth-Integrated Suspended Sediment Transport and Depth-Averaged Velocity from the Measured Velocity and Concentration Profiles at Kurimat (April 2003)

(Cross section 1 Station 2 located at 111 m from left bank ) Location (1) Location(2) Location(3)

Z V C Z V C Z V C (m) (m/s) (kg/m3) (m) (m/s) (kg/m3) (m) (m/s) (kg/m3)

3.7 0.78 0.008 3.6 0.83 0.01 4 0.75 0.006 2.7 0.76 0.012 2.6 0.82 0.012 3 0.75 0.008 1.7 0.68 0.02 1.6 0.75 0.014 2 0.74 0.014 1 0.67 0.022 1 0.72 0.018 1 0.64 0.018 0.5 0.63 0.026 0.5 0.71 0.022 0.5 0.51 0.022 0.37 0.56 0.03 0.37 0.63 0.028 0.37 0.47 0.026 0.18 0.5 0.036 0.18 0.56 0.044 0.18 0.41 0.032 0.15 0.478 0.037 0.15 0.535 0.046 0.15 0.392 0.033 0.12 0.452 0.038 0.12 0.506 0.05 0.12 0.37 0.034 0.09 0.42 0.04 0.09 0.471 0.053 0.09 0.345 0.036

0.06 0.38 0.041 0.06 0.426 0.057 0.06 0.312 0.037 0.03 0.319 0.042 0.03 0.358 0.06 0.03 0.262 0.038 Vmean = 0.684 m/s Vmean = 0.825 m/s Vmean = 0.668 m/s Ss = 0.0447 kg/ m.s Ss = 0.0433 kg/ m.s Ss = 0.0358 kg/ m.s

A 14


(Cross section 1 Station 3 located at 175 m from left bank) Location (1) Location(2) Location(3)


4.4 0.89 0.01 5 0.91 0.006 4.4 0.81 0.008 3.4 0.88 0.014 4 0.82 0.009 3.4 0.8 0.01 2.4 0.84 0.018 3 0.77 0.012 2.4 0.78 0.014 1.4 0.8 0.022 2 0.66 0.018 1.4 0.71 0.018 0.5 0.71 0.026 1 0.53 0.02 0.5 0.62 0.021 0.37 0.67 0.03 0.5 0.38 0.023 0.37 0.6 0.025 0.18 0.57 0.004 0.37 0.34 0.027 0.18 0.52 0.028 0.12 0.4545 0.045 0.12 0.29 0.03 0.12 0.497 0.029 0.12 0.515 0.048 0.15 0.277 0.031 0.12 0.47 0.03 0.09 0.479 0.05 0.09 0.262 0.032 0.09 0.437 0.031

0.06 0.433 0.053 0.06 0.244 0.033 0.06 0.395 0.032 0.03 0.364 0.055 0.03 0.22 0.034 0.03 0.0332 0.032 0.185 0.034 Vmean = 0.801 m/s Vmean = 0.49 m/s Vmean = 0.725 m/s Ss = 0.00673 kg/ m.s Ss = 0.0413 kg/ m.s Ss = 0.0468 kg/ m.s




3.25 0.94 0.01 3.3 0.93 0.009 2.9 0.9 0.008 2.25 0.89 0.015 2.3 0.92 0.016 1.9 0.87 0.13 1.25 0.82 0.019 1.3 0.84 0.02 1 0.85 0.018 0.5 0.67 0.022 0.5 0.66 0.022 0.5 0.76 0.024 0.37 0.65 0.027 0.37 0.62 0.026 0.37 0.74 0.028 0.18 0.59 0.03 0.18 0.49 0.033 0.18 0.61 0.034 0.15 0.564 0.032 0.15 0.468 0.034 0.15 0.583 0.035 0.12 0.533 0.032 0.12 0.443 0.036 0.12 0.551 0.036 0.09 0.496 0.033 0.09 0.412 0.037 0.09 0.513 0.038 0.06 0.448 0.034 0.06 0.0372 0.038 0.06 0.463 0.039

0.03 0.377 0.035 0.03 0.313 0.04 0.03 0.39 0.04 Vmean = 0.802 m/s Vmean = 0.805 m/s Vmean = 0.816 m/s Ss = 0.0451 kg/ m.s Ss = 0.0472 kg/m.s Ss = 0.039 kg/ m.s

A 15


(Cross section 2Station 2 located at 110 m from left bank) Location (1) Location(2) Location(3)


3.3 0.95 0.014 3.1 0.92 0.008 3.3 0.6 0.016 2.3 0.89 0.019 2.1 0.91 0.014 2.3 0.57 0.036 1.3 0.84 0.025 1.1 0.81 0.026 0.5 0.56 0.054 0.5 0.68 0.030 0.5 0.67 0.029 0.37 0.49 0.064 0.37 0.65 0.034 0.37 0.65 0.033 0.18 0.47 0.100 0.18 0.51 0.046 0.18 0.55 0.046 0.15 0.449 0.104 0.15 0.487 0.047 0.15 0.525 0.047 0.12 0.425 0110 0.12 0.461 0.049 0.12 0.497 0.049 0.09 0.395 0.117 0.09 0.429 0.051 0.09 0.462 0.052 0.06 0.357 0.124 0.06 0.388 0.053 0.06 0.418 0.054 0.03 0.3 0.131 0.03 0.326 0.056 0.03 0.351 0.056 Vmean = 0.805m/s Vmean = 0.803 m/s Vmean = 0.552 m/s Ss = 0. 061 kg/ m.s Ss = 0.0497 kg/m.s Ss = 0.079 kg/ m.s Computation of Depth-Integrated Suspended Sediment Transport and Depth-Averaged Velocity from the Measured Velocity and Concentration Profiles at Kurimat (April 2003)

(Cross section 2Station 3 located at 165 m from left bank) Location (1) Location(2) Location(3)


3.3 0.83 0.02 3.1 0.82 0.014 2.8 0.8 0.012 2.1 0.81 0.028 2.1 0.81 0.018 1.8 0.78 0.018 1.1 0.76 0.044 1.1 0.72 0.034 1 0.74 0.036 0.5 0.72 0.06 0.5 0.56 0.06 0.5 0.66 0.064 0.37 0.71 0.068 0.37 0.5 0.076 0.37 0.64 0.08 0.18 0.62 0.096 0.18 0.39 0.093 0.18 0.53 0.14 0.15 0.592 0.099 0.15 0.373 0.098 0.15 0.506 0.147 0.12 0.65 0.103 0.12 0.352 0.102 0.12 0.479 0.158 0.09 0.521 0.108 0.09 0.328 0.107 0.09 0.446 0.171 0.06 0.471 0.113 0.06 0.296 0.111 0.06 0.403 0.184

0.03 0.396 0.118 0.03 0.249 0.116 0.03 0.339 0.198 Vmean = 0.761 m/s Vmean = 0.699 m/s Vmean = 0.718 m/s Ss = 0.0992 kg/ m.s Ss = 0.0669 kg/m.s Ss = 0.0744 kg/ m.s

A 16




2.35 0.78 0.01 2.4 0.74 0.012 2.5 0.78 0.01 1.5 0.78 0.014 1.7 0.73 0.018 1.7 0.7 0.013 1 0.72 0.023 1 0.69 0.023 1 0.69 0.022 0.5 0.67 0.04 0.5 0.61 0.032 0.5 0.57 0.04 0.37 0.62 0.05 0.37 0.56 0.052 0.37 0.56 0.108 0.18 0.5 0.106 0.18 0.44 0.066 0.18 0.47 0.198 0.15 0.478 0.111 0.15 0.42 0.074 0.15 0.449 0.251 0.12 0.452 0.122 0.12 0.398 0.079 0.12 0.425 0.291 0.09 0.42 0.134 0.09 0.37 0.085 0.09 0.395 0.336 0.06 0.38 0.147 0.06 0.334 0.09 0.06 0.357 0.389

0.03 0.319 0.161 0.03 0.281 0.096 0.03 0.3 0.45 Vmean = 0.655 m/s Vmean = 0.649 m/s Vmean = 0.673 m/s Ss = 0.0307 kg/ m.s Ss = 0.0343 kg/m.s Ss = 0.0314 kg/ m.s Computation of Depth-Integrated Suspended Sediment Transport and Depth-Averaged Velocity from the Measured Velocity and Concentration Profiles at Kurimat (April 2003)

(Cross section 3 Station 2 located at 235 m from left bank) Location (1) Location (2) Location (3)


2.4 0.75 0.01 2.25 0.74 0.013 2.2 0.75 0.01 1.7 0.7 0.01 1.6 0.68 0.016 1.6 0.74 0.015 1 0.67 0.018 1 0.67 0.024 1 0.71 0.02 0.05 0.64 0.024 0.5 0.65 0.029 0.5 0.7 0.026 0.37 0.62 0.04 0.37 0.62 0.036 0.37 0.67 0.032 0.18 0.52 0.054 0.18 0.55 0.046 0.18 0.57 0.041 0.15 0.497 0.061 0.15 0.525 0.048 0.15 0.545 0.043 0.12 0.47 0.066 0.12 0.497 0.051 0.12 0.515 0.045 0.09 0.437 0.071 0.09 0.462 0.053 0.09 0.479 0.047 0.06 0.395 0.076 0.06 0.418 0.055 0.06 0.433 0.049

0.03 0.332 0.082 0.03 0.351 0.057 0.03 0.364 0.051 Vmean = 0.655 m/s Vmean = 0.649 m/s Vmean = 0.673 m/s Ss = 0.0307 kg/ m.s Ss = 0.0343kg/m.s Ss = 0.0314 kg/ m.s

A 17


(Cross section 3 Station 3 Located at 340 m from Left Bank)

Location (1) Location(2) Location(3) Z V C Z V C Z V C

(m) (m/s) (kg/m3) (m) (m/s) (kg/m3)

(m) (m/s) (kg/m3)

5 0.8 0.008 5 0.8 0.007 4.4 0.86 0.007 4 0.77 0.011 4 0.79 0.01 3.4 0.84 0.012 3 0.75 0.014 3 0.77 0.012 2.4 0.83 0.016 2 0.67 0.017 2 0.72 0.015 1.7 0.82 0.019 1 0.66 0.02 1 0.67 0.019 1 0.74 0.022 0.5 0.6 0.024 0.5 0.65 0.022 0.5 0.65 0.026 0.37 0.55 0.028 0.37 0.58 0.026 0.37 0.61 0.03 0.18 0.47 0.032 0.18 0.52 0.029 0.18 0.51 0.034 0.15 0.449 0.033 0.15 0.497 0.03 0.15 0.487 0.035 0.12 0.425 0.034 0.12 0.47 0.031 0.12 0.461 0.036 0.09 0.395 0.035 0.09 0.437 0.032 0.09 0.429 0.037 0.06 0.357 0.036 0.06 0.395 0.033 0.06 0.388 0.038 0.03 0.3 0.037 0.03 0.033 0.332 0.03 0.326 0.039

Vmean 0.693m/s Vmean 0.719m/s, Vmean 0.775m/s, Ss 0.054kg/m.s Ss 0.0507kg/m.s Ss 0.0573kg/m.s

A 18

Figure 1. Location of the Measurement Site along the Nile River

A 19

Figure 2. Sketch of the Measuring Technique

Figure 3. Layout of the Measurement Stations and Locations

APPENDIX (B)

Inventory of Data on Sediment Transport in Ethiopia

B 1

Inventory of Data on Sediment Transport in Ethiopia

This Appendix covers the available sediment transport data of Ethiopia Report. The appendix represents only a summary of the original document which has been received. The original document consists of many tables and graphs covering a broader perspective. Water sediment data were available from 47 recording stations. These were translated into water sediment per hectare for the catchement of the recording station. The number of stations was too few to provide a basin-wide picture of relative erosion. More over, data from nearby stations was not always consistent. However, the data are interesting from two perspectives:

• The range of data was from 0.23 t/hr/yr to 21.29 t/hr/yr. Applying the EHRS 10% estimated delivery rate to the rivers, this give a range of soil erosion of from 2.3 t/hr/yr to 212.9 t/hr/yr. this is in line with the experimental data and other estimates discussed in section 1.3. For the basin as a whole, there is a recording station on the Abbay River just east of the Sudanese border; this shows sediment load of 19.46 t/hr/yr that translates into 195 t/hr/yr of erosion for the basin as a whole. Given that most of this must come from cultivated areas, this suggests an overall erosion rate on cultivated land in the basin of at list 300 t/hr/yr. This is consistent with estimates of sediment at Rosaries dam in Sudan of 130M tons of sediment per year (see environment report). Applied to the Abbay basin area of 17 200 000 ha (excluding the North West drainage which joins the Nile bellow the Rosier dam) this translates into 7.5 t/hr/yr, of the sediment yield to the river. Applying the EHRS delivery rate of 10 % this implies an average erosions rate for the basins of 75 t/hr/yr. As o\most of this will come from cultivated land, which constitutes perhaps a third of basins, an erosion rate of as least 200 t/hr/yr. (2 cm per year) on cultivated land, on average, is indicated. Some areas will obviously be higher and slower. While these figures appear as impossibly high, they point to the severity of erosion in the basin, especially in the cultivated areas, and offer support for the erosion rates suggested in the literature.

• The data are too sparse to give a good impression of regional variations but some patterns are apparent. As expected, the few stations in the lowlands and the south and southwest of the basin have relatively low sediment rates—generally below 2t/ha/yr. in the south-west (<20t/ha/yr. erosion) rising somewhat in the highlands of the south. There are few stations in the ‘eroded’ areas of the northeast and east; however. Those that exist suggest relatively low erosion—0.5-2.5t/ha/yr. in the water, translating to 5 to 25t/ha/yr. land erosion. However, there are stations in and around Gojjam Agew Awe area. This is one of the main cereal producing areas of the country and is generally considered to be only slightly to the range of 16-21 t/ha especially around Mount choke; these translate to 160 to 210t/ha/yr. erosion from the land around 2cm soil loss per year. At this rate, 10cm of soil is lost every 5 years; assuming an average current depth of 150cm (optimist; many soils in the area are mapped as only moderately deep), the average soil depth with be too shallow (<40cm) for cultivation within about 55 years. Moving away from Mount Choke, erosion rates decline but are still typically above 70t/ha/yr. (<7t/ha/yr. in water)

Orally, the river sediment data provides strong support to the expressed here as to the severity of the basin. Based on these sediment data, the erosion rates suggested in the literature appear entirely reasonable, and erosion rates of as much as 100t/ha/yr. on cultivated land in the better areas of the basin appear to be entirely probable. Conversely, the sediment data for areas such as Gojjam and Agew Awe contrasts with the field estimated erosion level. This is simply explained and points to the hazards of trying to estimate erosion over large areas. Most of the erosion in these areas is sheet and rill erosion; are of minor importance. However, these are cultivated areas and evidence of sheet/rill erosion is removed with each cultivation. The author passed through these areas late in the season, when there was little active cultivation, and saw significant evidence of erosion in the form of erosion scars on convex slopes. Thus the assessment of sheet/rill erosion in any area may vary widely depending on when the area is viewed, relative to cultivation activities. It is also noted that many soils in this area, especially those

B 2

closer to Mount Choke, were the field to be only moderately deep. As these are often soils, which would normally be deep, such as luvisols, then the possibility exists that their current limited is the product of a product of erosion. Further onto the plateau, erosion has not yet reduced depth sufficiently to be identified in the mapping, but active erosion may be on going. The results for the Gojjam Agew Awe area, and continuing into South and North Gonder, should not be too surprising. Although these areas of low slope, they are also the areas of the heaviest rainfall, highest cropping intensity, and greatest production of Teff. The literature shows clearly the relationship between erosion and rainfall and land use, with cropping and especially Teff clearly related to high erosion. We tried to get some data regarding water sediment data in the basin. Estimated Erosion with in the Abbay River Basin The various data described above may be merged to provide a generalized picture of relative erosion the Abbay River basin. As noted, the USLE analysis has been largely discounted. Data, primarily topographic data, proved insufficient to allow a viable USLE estimate. From the other data source, a generalized picture of the basin emerges:

• The northeast and east of the basin is an area generally acknowledged as severely eroded. Soil depths are now at or below the minimum required for cultivation. With the step slopes and inadequate soil conservation measures, continuing erosion renders this area unsuited for sustained cultivation. Moreover, soils are so shallow and slopes so steep that often-physical soil conservations measures are not viable. Conversely, erosion is already so far advanced that current erosion rates are relatively low. While this provide a general picture, it is recognized that there are both significant pockets of deeper soils and everywhere there may be local variations including local areas of deeper soils; these should be protected and may then be used for agriculture.

• The low-slope areas of the main highland area -- Gojjam, Agew Awe, and North and west Shewa – appear to have high current erosion rates, probably the highest in the basin. However, soils are deep and erosion is primarily sheet/rill erosion; the evidence of erosion is removed with very cultivation, and the depth effects of erosion have not yet been manifested in these areas. These are both the current and the future high potential areas, with significance at both basins, regional and national levels. Protecting these areas become of critical importance, and are relatively easy to do given the low slopes and relatively good condition of the soils.

• The south west of highlands has many low slopes and is in the process of development for cultivation. The later tends to lead to i) an under estimate of the land cover factor, as ongoing conversion is not considered, and ii) an under estimate to the k-value as the soils tend to have higher organic matter and better structure than may be expected once cultivation is fully developed. Slopes will also be under estimated due to the factors previously discussed. Therefore the USLE may be expected to under estimate both current and potential erosion in this area. In fact it is expected that, while current erosion is low the move to continuous cultivation will result in serious erosion in the future. This will be exacerbated by the concentration of fertility in the upper soil layers. Conversely, development of coffee and other perennials could make a major contribution to conserving these soils.

• The low land parts of the basin are currently relatively uneroded, simply by virtue of the absence of vegetation clearance and their use for cultivation. However, cultivation extension into these areas could result in serious erosion. Again many of the soils are classed those in which fertility is concentrated in the upper soil layer, implying a requirement for careful soil management under cultivation.

B 3

Sample of Sediment Data from Abbay River Basin

Location: Wani Gedel catchment(Blue Nile Basin) The Wani gedel catchment (North Shewa research unit) which belongs to the Blue Nile basin, encloses an area of 481 ha and is considered typical for all highly degraded highland parts above 3000 m.a.s.l. of the central highlands, such as the Simen mountains in Gonder region, choke mountains in Gojam region, or Amba Ferit in Wello region (Hurni, 1982). The research unit is typical of areas with bimodal rainfall, in the low potential ox-plough, cereal dega and wurch belt of the eastern higher lands 180 km east and north east of Addis Ababa. The research project has been functioning since 1981. The study area is located in an area typical of the agro-climatic zone, which is well defined catchment area together with the field research station. Many parts of the catchment are very steep and dissected. This tends to make the land more vulnerable to degradation. About 75% of the study area has steep slopes i.e. greater than 25% gradient and about 10% of the total area has very steep slopes, with gradients greater than 55% (Yohannes, 1989: 25). The rainfall of the research unit is mainly influenced, both by the Inter Tropical Convergence Zone (ITCZ) and the sub-tropical pressure cells as a result of which the annual rainfall of the area is highly variable. The main rainy season (Kremet) normally lasts from June to October, with the rainfall peaking in August, then declining markedly in September and October. Generally, the Kremet season, accounts for about 72% of the total annual rainfall. The long rainy season is normally preceded by a shorter rainy season (Belg), which usually occurs from wurch to March to May, with peak rains in May. It accounts for about 28% of the annual rainfall. The causes of soil erosion in the Andit Tid area are classified as human and physical factors. The major human induced causes are intensive cultivation, population pressure increases, shortening of fallow periods, luck of maintenance of already constructed terraces and unimproved traditional soil conservation techniques, while the major physical factors causing soil erosion in the research unit area high erosive power of rainfall which in concentrated in the months of June, July and August, a period of the year when crop cover is limited. The rugged topography of the research site cause runoff and ultimate soil degradation. Soil Loss and Runoff Data under Different Conditions This sections gives an overviews of soil erosion in the SCRP research catchment in Andit Tid, based on analysis on monthly and annual data. When computing annual values, incomplete years were not considered. Nevertheless, all possible monthly values were included to determine monthly means. Usually the first year of measurement and the period of war and insecurity (in 1991 and part of 1992) were not included in the analysis of annual totals. The term “runoff” is synonymous with over land flow measured on test plots. At catchment level, the term “river discharge” is used for the volume of water passing the gauging station at the outlet of the catchment. The term “soil loss” refers to the amount of the sediment moving from the plots into the collection tanks, and the term “sediment yield” refers to the suspended sediment passing the gauging station at the outlet of the catchment. Surface flow (field runoff, river discharge) and eroded material (soil loss, suspended sediment yield) are two of the main indicators continuously monitored in all SCRP research stations. They are measured at different levels: Micro-plots (MP, 1X3), Test plots (TP, 2X15), Experimental plots (EP, 6X30). Research catchment level (river gauging station) before and after conservation treatment

B 4

1. TEST PLOT RESULTS Annual data results show considerable variation as shown in the table

Table B(i) Mean annual runoff and soil loss result (1983 - 1992)

TP1, 23% Slope TP2, 39% Slope TP3, 48% Slope TP4, 48% Slope Year Precipita

tion Erosivity Crop Runoff Soil Loss Crop Runoff Soil Loss Crop Runoff Soil Loss Crop Runoff Soil

Loss [mm] [J/mh] Type [mm] [t/ha] Type [mm] [t/ha] Type [mm] [t/ha] Type [mm] [t/ha] 1983 1546.80 647.25 fl 672.20 242.08 lt 768.70 286.67 fl 503.00 204.52 bl 281.00 182.51 1984 979.50 281.78 fl 303.40 124.11 wt 270.70 149.69 li 135.70 64.72 bl/fp 128.90 40.92 1985 1446.60 572.22 lt 409.40 144.92 lt 617.70 221.89 lt 385.60 151.81 fp 250.70 29.77 1986 1663.00 388.79 wt 480.40 163.40 wt 659.30 183.10 wt 442.20 123.20 bl 237.40 58.30 1987 1032.90 216.24 lt 273.00 121.30 lt 324.60 160.00 fl 222.80 68.80 lt 117.00 41.90 1988 1388.00 605.33 wt 586.10 211.30 bl 705.80 199.20 fl 585.90 141.60 bl 389.70 154.50 1989 1287.10 394.77 lt 437.10 168.30 lt 510.90 223.90 wt 370.80 171.20 fl 153.70 11.80 1990 1072.40 476.71 fl 466.40 144.10 wt 596.30 293.90 fl 394.70 76.70 bl 248.20 155.50 1991 1690.20 887.62 lt 750.10 239.70 lt 668.80 268.50 fl 533.30 73.40 fl 459.80 93.10 1992 1472.00 403.48 li 614.50 127.80 li 691.60 137.60 lt 413.30 130.70 bl 252.90 96.70 Mean 1379.44 505.95 499.26 168.70 581.44 212.45 398.73 120.67 251.93 86.50 SD 242.63 187.30 147.17 43.99 156.65 53.70 129.31 45.92 103.08 56.93 CV 0.18 0.37 0.29 0.26 0.27 0.25 0.32 0.38 0.41 0.66 Mean Dev

208.34 158.90 125.17 37.40 127.62 46.53 96.81 39.81 75.14 49.96

Rel Dev 0.15 0.31 0.25 0.22 0.22 0.22 0.24 0.33 0.30 0.58 Median 1446.60 476.71 473.40 154.16 638.50 210.55 404.00 126.95 249.45 75.70

B 5

Some examples may therefore help to further interpret the results. 1987: This is the year with the lowest erosivity followed by lowest precipitation. Correspondingly, soil losses on all TP are low as well, although not the lowest measured. Still, the order of magnitude ranging from 41 to 160 t/ha is very high. Erosion could be observed throughout Kremt, but unlike other years, in October 1987 soil losses were unusually high, amounting upto one fifth of the annual values. 1991: This year showed the highest erosivity and precipitation, which caused as well one of the highest soil losses on TPs 1 and 2 (both lentil). TPs 3 and 4 were left fallow and thus a little less eroded. 1986: TPs 1, 2 and 3, wheat: according to the slope steepness, TP 1 (23%) showed a lower soil loss compared to the steeper TP 2 (39%). The steepest plot, TP 3 (48%) however, has the lowest value measured. In this case, slope steepness seems to be dominated by the soil characteristics on TP 3 leading to high infiltration. Although TP 1 and TP 3 are both located on eutric Regosol, TP 3 has the higher infiltration capacity. 1992: all TPs, fallow: There was no significant difference in soil loss of TP 1 to 3. Only TP 4 showed the usual lower erosion rates. TP 3 performance is unusual in a sense that despite considerably lower annual runoff, the soil loss is not different from TPs 1 and 2. High mean annual soil losses: The soil losses can occur more or less evenly distributed over many months, or it can be, and this is more frequently the case for high values, a matter of a short period only. On TP 1, 1991 (lentil), 239.7 t/ha were accumulated through the entire Kremt with high mean monthly values for all months. On TP 2, 1990 (wheat), out of the annual 293.9 t/ha, 49% alone were collected in July and 28% in August. In the same year, on TP 4 (barley) out of the annual 155.5 t/ha, 47% were registered in July and 35% in August. Monthly variation of test plots In Andit Tid erosion happens mainly in Kremt season. Soil losses on cultivated land are the highest in July, at the beginning of the big rainy season. Although rainfall, erosivity and runoff increase again in August, soil losses slightly diminish because of a more protective vegetation cover. However, the absolute soil losses are extremely high and can easily exceed 20 t/ha on average even in May and September. Although rains and erosivity are much lower than in Kremt, soil losses measured on test plots can still amount to more than 30 or 40 t/ha from March to May. In Andit Tid, there is no grass plot as such. TP3 as continuous fallow is subject to intensive grazing and therefore also to severe erosion, despite the fact that soil losses are lower than on the less steep TPs 1 and 2 which are cultivated. TP2 is an exceptional plot indicating the erosion hazard under influence of interflow. Runoff values often exceed rainfall values, because of interflow frequently reaching the soil surface at this location. It is astonishing that the steepest cultivated plot, TP4 on 48 % slope shows the lowest mean soil loss. The relatively low runoff on both steep plots TPs 3 and 4 (48%) suggests a better infiltration (on eutric Regosol and ochric Andosol, respectively). Table B (ii): Mean monthly runoff and soil loss result (1982 - 1992) TP1, 23% Slope,

cultivated TP2, 39% Slope, cultivated

TP3, 48% Slope, hacked Fl

TP4, 48% Slope, cultivated

Month

Runoff Soil Loss Runoff Soil Loss Runoff Soil Loss

Runoff Soil Loss

[mm] [t/ha] [mm] [t/ha] [mm] [t/ha] [mm] [t/ha] Jan 0.57 0.05 0.13 0.00 0.29 0.03 0.23 0.00 Feb 0.72 0.17 0.13 0.00 0.37 0.02 0.20 0.02 Mar 12.14 5.89 7.35 4.96 6.45 6.63 2.70 1.34 Apr 14.95 8.45 16.48 8.29 10.75 6.70 5.14 2.31 May 32.92 19.38 41.63 24.13 20.79 13.19 14.78 15.31 Jun 12.06 8.50 12.87 8.89 6.52 5.44 7.01 3.73 Jul 114.61 50.63 133.32 66.29 87.50 38.00 61.95 24.09 Aug 188.83 49.62 231.52 63.09 168.22 34.27 106.67 28.34

B 6

Sep 94.30 20.53 113.08 29.91 81.64 13.38 41.17 8.38 Oct 20.34 4.02 20.76 6.08 13.34 2.24 8.65 1.70 Nov 0.60 0.03 0.40 0.01 0.09 0.00 0.08 0.00 Dec 7.22 1.42 3.77 0.80 2.77 0.76 3.35 1.29 Remarks: hacked Fl: hacked fallow. Data source: Runoff and soil loss: atplrssr.dbf, secondary database. 1982 Measurements start in July. 2. Micro Plot Results Table (III) and (iv) shows that the behavior of annual and monthly variations of the micro-plot results are similar to the respective annual and monthly variation of Test Plot results. Annual Data In Andit Tid ,TP4,MP5, and MP6 are located at the same spot as shown in table iii. The comparable time of measurement is 1983 to 1991. MP 6 shows the expectedly high soil loss and runoff values due to the permanent hacking. The difference to MP5 should express the combined influence of vegetation and soil management on the erosion process. Comparing the remaining TP 4 and MP 5, the longer slope produces more soil loss, which means that entrainment by runoff increases with slope length at least up to 15m. This is expected particularly in high rainfall areas with moderate or low vegetation cover.

B 7

Table B (iii) : Mean annual runoff and soil loss MP5, 48% Slope MP6, 48% Slope Year Precipitation Erosivity Crop Runoff Soil Loss Crop Runoff Soil Loss [mm] [J/mh] Type [mm] [t/ha] Type [mm] [t/ha] 1983 1546.80 647.25 bl 459.90 113.84 hacked fl 449.20 224.03 1984 979.50 281.78 bl/fp 217.70 30.90 hacked fl 245.00 313.16 1985 1446.60 572.22 fp 376.50 16.29 hacked fl 498.00 286.68 1986 1663.00 388.79 bl 360.70 7.60 hacked fl 351.30 22.90 1987 1032.90 216.24 lt 229.60 21.70 hacked fl 261.80 182.30 1988 1388.00 605.33 bl 591.60 83.70 hacked fl 547.00 303.20 1989 1287.10 394.77 fl 264.10 6.90 hacked fl 480.10 226.40 1990 1072.40 476.71 bl 388.80 67.20 hacked fl 413.30 273.30 1991 1690.20 887.62 fl 689.90 91.40 hacked fl 671.60 541.00 Mean 1345.17 496.75 397.64 48.84 405.71 229.00 SD 254.26 194.44 151.75 38.25 128.37 128.71 CV 0.19 0.39 0.38 0.78 0.32 0.56 Mean Dev 224.17 161.21 121.88 35.73 104.36 88.67 Rel Dev 0.17 0.32 0.31 0.73 0.26 0.39 Median 1388.00 476.71 376.50 30.90 449.20 273.30

B 8

Monthly Variation of Micro-Plot Results The variations are given in table iv below. Table B (iv): Mean monthly runoff and soil loss result MP5, 48% Slope MP6, 48% Slope Month Runoff Soil Loss Runoff Soil Loss [mm] [t/ha] [mm] [t/ha] Jan 1.14 0.00 1.22 0.20 Feb 1.22 0.04 1.83 2.22 Mar 11.07 0.85 11.14 1.57 Apr 14.29 1.37 16.47 4.66 May 26.79 7.89 25.43 23.34 Jun 9.82 0.61 9.72 3.21 Jul 104.19 14.45 119.13 85.34 Aug 146.42 17.90 164.47 96.83 Sep 58.98 3.35 66.86 38.62 Oct 16.13 1.01 13.29 6.38 Nov 0.33 0.00 0.38 0.00 Dec 7.26 1.34 5.31 1.28 3. Experimental Plot Data Results The size of the experimental plots is 6x30. Slope and soil type on all experimental plots are constant: the slope is 24%, the soil type is Regosol. Each plot has a specific conservation a structure. In Andit Tid six experimental plots (one set) were established in 1987 and featured the following techniques:

• one control plot with no conservation structures, • one plot with graded Fanya Juu, • one plot with graded bunds, • one plot with level Fanya Juu, • one plot with level bunds, • one plot with grass strips.

Interpretation of data from experimental plots must be submitted to the following restriction: it is problematic to compare graded structures and level structures on a one-to-one basis. Indeed, under on-farm condition, graded terraces have a water way every 50 to 100m in order to drain excess water. In contrast, the EPs have a width of 6m only, which means that the corresponding water way is only a small drainage ditch. The relation of the drainage ditch to its catchment is thus distorted. Furthermore, EPs with level structures cannot exactly simulate normal on-farm conditions such as overflow because of their relatively small plot size. Therefore EP values only hint at the degree of erosion on terraces.

B 9

Annual Runoff and Soil Loss on Experimental Plots In Andit Tid on average the Fanya Juu on EPs retained less water than the comparable soil bunds. Due to the water logging hazard in high rainfall areas like Andit Tid level structures can therefore not be recommended, even if they showed the best values for soil loss reduction. On graded structures a considerable amount of water was drained, particularly under fallow conditions. This helped to prevent water logging, but it does not reduce soil loss as much as needed. Absolute values were still above 10-20t/ha. Grass strips and graded structures reduced soil loss by 40-73%. To further decrease soil loss, runoff velocity should be reduced.

Table B (v): Mean annual runoff and soil loss Runoff [mm] Soil Loss [t/ha Year Crop Control Grass Graded Graded Level Level Control Grass Graded Graded Level Level Plot Strip Fanya Juu Bund Fanya Juu Bund Plot Strip Fanya Juu Bund Fanya Juu Bund 1987 bl/le 183.20 58.50 112.60 78.30 78.00 17.10 42.00 3.50 15.00 14.30 3.30 0.50 1988 fp/ho 687.90 607.10 651.70 708.30 509.40 503.00 139.90 50.50 53.50 85.00 22.70 30.20 1989 bl 386.40 223.70 271.10 346.80 122.60 91.60 54.70 8.40 16.70 33.20 2.60 3.10 1990 fl 255.10 153.40 303.60 280.90 115.00 31.00 3.20 1.40 2.10 6.10 0.80 0.60 1991 fl 258.40 138.30 401.50 261.50 144.30 22.00 2.10 1.20 1.70 5.10 0.40 0.00 Mean 354.20 236.20 348.10 335.16 193.86 132.94 48.38 13.00 17.80 28.74 5.96 6.88 SD 179.24 192.74 177.99 206.74 159.21 186.96 50.28 18.93 18.92 29.88 8.44 11.71 CV 0.51 0.82 0.51 0.62 0.82 1.41 1.04 1.46 1.06 1.04 1.42 1.70 Mean Dev 146.36 148.36 142.80 153.91 126.22 148.02 39.14 15.00 14.28 24.29 6.70 9.33 RelDev 0.41 0.63 0.41 0.46 0.65 1.11 0.81 1.15 0.80 0.85 1.12 1.36 Median 258.40 153.40 303.60 280.90 122.60 31.00 42.00 3.50 15.00 14.30 2.60 0.60

B 10

Conclusive Remarks on Experimental Plot Results Comparisons should be made either between graded structures and control plot and grass strip, or between level structures and control plot and grass strip. On average graded structures show higher soil loss and runoff values than level structures because of the drainage ditch. Thus, however, by no means indicated that level structures are generally more recommendable. The decision whether level or graded structures should be implemented must take in to account the rainfall regime. For example, areas with high rainfall need graded version s to drain excess water, whereas low rainfall areas require level structures to retain moisture. Differences in soil loss and runoff between graded and level EPs are not adequate criteria for such a decision. The experiment focuses on the performance of (mainly) mechanical SWC. EP results have shown that it is possible to reduce erosion by mechanical measures, but not sufficiently. Soil loss was still generally high. Drainage remain the critical factor, since in order to reduce soil loss it would have been necessary to further reduce runoff, but as a consequence water logging would have affected production. Moreover, waterways easily develop into gullies. Soil loss and runoff were reduced but production remained mostly below the values in the untreated plot, at least during the first years after construction. But productions needs to be at least maintained at the current level, or increased in order to cover the costs of SWC and to convince farmers of the efficiency of conservation measures. The results imply that the benefits of mechanical conservations are limited. Mechanical measures alone will not lead to immediate benefits in terms of increased production: they must be supported by agronomic and biological SWC. However, high altitude and low temperature limit the variety of species and vegetation growth, particularly at the beginning of Belg. For Kremt, the potential for biological conservation requires further investigation. Results of Hydrometric Measurements on the Catchment The total size of the Hydrological catchment is 477.3ha. According to monthly rainfall distributions, Andit Tid is bimodal, having Belg (small rain between March and June) and Kremt (main rain period between July and September). The rainfall distribution during the Belg is between 59.8 and 130.0 mm with a peak rainfall and erosivity of 39.4 J/mh in May. The rainfall distribution during the Kremt season is varying between 200.0 and 362.4 mm with a peak rainfall in August and with a peak erosivity value of 153.0 J/mh in September. In accordance with season wise rainfall contribution, 62 % of the rain is during Kremt and about 27 % during Belg season. Table B(vi)lists the monthly and annual discharge of the Hydrometric station for the period from 1982 to1993. Annual discharge varied between 298mm (1987) and 1359mm (1985). Table B(vii) shows the monthly and annual suspended sediment yield. The annual suspended sediment yield leaving the catchment varied between 3.2t/ha (1987) and 14.7t/ha (1988). And the annual sediment concentration is between 0.8g/l (1992) and 2.8g/l (1984).

B 11

Table B (vi): Monthly and annual discharge JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR (1) [mm] Monthly and annual depth of discharge for the different years:

Data collection has started since July 1982. The annual total for 1982 is given in brackets indicating the incomplete data base. This value has not been used for the compilation of the statistic of the annual time base given in section (2).

1982 --.-- --.-- --.-- --.-- --.-- --.-- 10.4 41.8 26.9 43.6 7.2 1.6 (131.6) 1983 0.0 0.2 6.6 8.2 137.2 30.3 41.0 170.4 41.9 17.7 4.7 2.4 460.8 1984 9.4 8.8 9.4 11.2 60.2 33.0 67.3 40.3 58.6 7.4 4.2 5.1 315.0 1985 5.1 4.0 3.5 11.4 16.7 5.3 140.3 669.4 440.4 28.1 18.8 15.6 1358.6 1986 13.7 9.7 29.9 43.7 43.8 69.4 272.9 311.9 257.6 70.0 7.7 5.1 1135.5 1987 5.1 5.5 8.7 24.3 63.3 7.7 2.8 78.7 20.1 76.0 3.1 2.4 297.8 1988 7.7 4.5 4.6 5.4 3.9 3.0 80.4 395.0 233.9 111.5 9.4 5.7 865.0 1989 5.1 6.8 15.4 59.4 8.5 7.5 107.4 186.4 147.4 49.3 6.5 41.0 640.5 1990 10.0 11.5 26.7 31.1 4.7 2.0 118.0 221.3 244.9 82.2 10.8 3.2 766.4 1991 3.5 4.7 13.4 21.1 22.8 9.3 118.7 440.1 257.3 90.8 3.1 82.5 1067.3 1992 5.5 5.2 2.8 4.8 5.7 2.1 27.7 289.6 239.7 41.3 8.4 5.5 638.4 1993 9.2 19.4 4.7 45.3 102.3 8.4 162.6 205.7 88.6 89.5 14.0 3.7 753.3 (2) [mm] Statistical Measures based on section (1) characterising the period 1982-1993:

The monthly means for January to June are only based on data from 1985 to 1993. However, the other monthly means are based on data from 1982 to 1993 as data collection started in July 1982. The annual total for 1982 has also not been used for the compilation of the statistic of the annual time base.

MEAN 6.8 7.3 11.4 24.2 42.6 16.2 95.8 254.2 171.4 58.9 8.2 14.5 754.4 STD 3.7 5.1 9.3 18.6 44.5 20.7 76.0 182.9 128.6 32.5 4.7 24.1 336.9 Cv [%] 55.1 69.3 80.9 76.7 104.3 127.7 79.4 72.0 75.0 55.1 57.0 166.0 44.7 MAX 13.7 19.4 29.9 59.4 137.2 69.4 272.9 669.4 440.4 111.5 18.8 82.5 1358.6 MIN 0.0 0.2 2.8 4.8 3.9 2.0 2.8 40.3 20.1 7.4 3.1 1.6 297.8 (3) Mean monthly discharge (Q, l/sec), mean monthly discharge volume (Qv, m³) mean monthly discharge yield (l/s·km²) for he period

1985-1993: Q 12.06 14.41 20.38 44.54 75.98 29.80 170.71 453.02 315.70 105.04 15.05 25.82 114.18 Qv 32300 34859 54599 115436 203515 77244 457236 1213359 818291 281337 39000 69152 3600875 q 2.53 3.02 4.27 9.33 15.92 6.24 35.77 94.91 66.14 22.01 3.15 5.41 23.92 Notation: --.--: Data not available or calculation not possible.

B 12

Table B(vii): Monthly and annual suspended sediment yield

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC YEAR(1) [t/ha] Monthly and annual suspended sediment yield for the different years

Data collection has started since July 1982. The annual total for 1982 is given in brackets indicating the incomplete data base. This value has not been used for the compilation of the statistic of the annual time base given in section (2).

1982 --.-- --.-- --.-- --.-- --.-- --.-- 0.659 0.802 0.259 0.162 0.006 0.000 (1.888) 1983 0.000 0.000 1.116 0.551 5.948 0.154 0.819 0.821 0.022 0.010 0.000 0.000 9.440 1984 0.000 0.000 0.000 1.410 4.354 0.190 2.077 0.197 0.425 0.000 0.000 0.000 8.653 1985 0.000 0.000 0.000 1.247 0.480 0.024 4.627 6.364 1.486 0.010 0.000 0.000 14.238 1986 0.000 0.000 0.768 0.286 1.326 1.931 2.330 1.917 0.950 0.109 0.000 0.000 9.618 1987 0.000 0.011 0.117 0.460 0.670 0.000 0.000 1.118 0.267 0.596 0.000 0.000 3.239 1988 0.054 0.014 0.000 0.034 0.057 0.000 5.259 7.139 1.631 0.516 0.000 0.000 14.707 1989 0.000 0.001 0.438 0.565 0.056 0.364 3.601 1.911 2.943 0.108 0.000 0.036 10.024 1990 0.003 0.011 0.221 0.191 0.000 0.000 3.985 4.321 1.441 0.014 0.000 0.000 10.187 1991 0.000 0.000 0.748 0.682 0.020 0.000 3.020 3.352 0.998 0.126 0.000 1.053 9.999 1992 0.006 0.000 0.000 0.027 0.511 0.035 0.511 2.345 1.366 0.043 0.012 0.000 4.856 1993 0.000 0.344 0.001 0.763 1.662 0.000 2.096 1.196 0.651 0.119 0.000 0.000 6.833 (2) [t/ha] Statistical Measures based on section (1) characterising the period 1982-1993:

The monthly means for January to June are only based on data from 1985 to 1993. However, the other monthly means are based on data from 1982 to 1993 as data collection started in July 1982. The annual total for 1982 has also not been used for the compilation of the statistic of the annual time base.

MEAN

0.006 0.035 0.310 0.565 1.371 0.245 2.415 2.624 1.037 0.151 0.001 0.091 9.254

STD 0.016 0.103 0.399 0.451 1.978 0.571 1.720 2.249 0.810 0.198 0.004 0.303 3.442 Cv

[%] 280.2 296.5 128.7 79.8 144.2 232.8 71.2 85.7 78.1 130.8 248.1 334.0 37.2

MAX 0.054 0.344 1.116 1.410 5.948 1.931 5.259 7.139 2.943 0.596 0.012 1.053 14.707 MIN 0.000 0.000 0.000 0.027 0.000 0.000 0.000 0.197 0.022 0.000 0.000 0.000 3.239 (3) Mean monthly suspended sediment rate (Qs, t), mean monthly mean suspended sediment

concentration (Cs,, g/l) for the period 1982-1993: Qs 2.77 16.56 147.96 269.69 654.56 117.09 1152.8

4 1252.27

494.79 72.09 0.71 43.33 4416.91

Cs 0.09 0.48 2.71 2.34 3.22 1.52 2.52 1.03 0.60 0.26 0.02 0.63 1.36 Notation: --.--: Data not available or calculation not possible.

The peak of river discharge is in August. Sediment yield was highest in July/ August (Kremt) and may, while sediment concentration was generally high during the Belg. Even though the mean annual sediment yield (9.3t/ha) was fairly high. The annual rates of river discharge and sediment yield do not indicate a major impact of mechanical soil conservation measures at catchment level.

APPENDIX (C)

Inventory of Existing Data on Sediment Transport in Burundi

C1

Inventory of Existing Data on Sediment Transport in Burundi

Measuring methods Field measurements are essential to determine the local morphological variables such as: bed materials size, fall velocity, bed load and suspended load. The selection of the most appropriate instruments depends on: - The wide range from simple mechanical samplers to sophisticated samplers; - The variables to be measured; - The available facilities(boat,ect); - The required accuracy(observation study or basic research study) In our case, we are able to do the measurement on suspended load sampling. The method used is the direct method, where direct measurements of the time-averaged sediment transport in a certain point or over a certain depth range. The sampler has a vertical movement at a uniform speed over the depth. After, the analysis of suspended sediment samples is done.

Existing data on Sediment Transport in Burundi

Rivers Stations Dates Suspended

load (mg/l)

Disch. (m3/s)

Area (Km2)

Ann. Mean Disch. m3/s

Water Quality

Ann. mean

PH T( 0C)

Sed. Trans.MT/y

Kaniga Dispensaire 19/10/1988 26/11/1988 12/4/1990

37 266 150

1.88 5.876

- 216 11 5.88 20 0.0016

Kayongozi Nyankanda

21/12/1988 3/7/1989

15/1/1990 23/4/1991 1/9/1991

28/4/1993 29/9/1993 12/1/1998

24 102 17 14 21 16 35

324

4.624 6.000 4.894 7.662 3.055

13.978 2.338

20.137

835 202 5.44 20.1 .0139

Mubarazi Murongwe

19/10/1988 25/11/1988 11/4/1990 2/8/1990

19/3/1991 12/9/1991 1/9/1992

29/03/1993 5/10/1993 7/1/1998

176 1624 566 94

355 52 60

334 183 719

9.862 24.714 17.750 8.326

11.336 7.709

- 15.402 4.001

17.404

932 579 5.83 20.5 0.237

C2


load (mg/l)

Disch. (m3/s)

Area (Km2)


Water Quality

Ann. mean

PH T( 0C)

Sed. Trans.MT/y

Ndurumu Shombo

28/04/1989 22/7/1989 1/4/1990 1/8/1990

23/3/1991 8/8/1992 1/8/1992 2/4/1993

6/10/1993 15/1/1998

59 38 67 30 10 65 40 20

187 303

15.062 8.566

12.098 7.453 6.812 6.200 4.936

10.715 4.432

12.273

542 305 5.92 21.1 .0250

Nyabaha Mubuga

24/11/1988 15/10/1990 9/9/1991 1/4/1993

5/10/1993 6/10/1993

162 63 34

513 146 29

8.382 5.106 5.832

10.288 -

2.655

977 284 6.27 21.1 0.0518

Nyakijanda Buhoro

20/10/1988 20/12/1988 3/7/1989

15/1/1990 12/4/1990 22/4/1991

2/9/191 27/4/1993 28/9/1993 13/1/1998

80 51 93 74

160 68 54 60 53

113

1.817 1.780 4.243 3.540 6.437 3.407 1.671 3.575 1.252

14.852

Nyakijanda Buhinda

20/10/1988 20/12/1988 3/7/1989

15/1/1990 12/4/1990 16/10/1990 22/4/1991 2/9/1991

27/4/1993 28/9/1993 13/1/1998

120 50 82

102 110 142 77 50

100 122 313

1.157 1.332 3.301 2.681 3.910 1.398 2.110 1.080 2.476 0.778 7.626

211 74 5.97 20.4 0.006

Nyamuswaga Gisha

25/4/1989 20/7/1989 29/3/1990 21/3/1991 12/8/1991 28/7/1992 16/3/1993 14/9/1993 28/1/1998

64 117 88 12

119 11 19 17

640

5.815 3.913 8.479 3.651 3.468 2.759 3.443 2.297 6.967

C3


load (mg/l)

Disch. (m3/s)

Area (Km2)


Water Quality

Ann. mean

PH T( 0C)

Sed. Trans.MT/y

Ruvubu Kanabusoro

24/4/1989 19/7/1989 3/8/1990 6/8/1991

27/7/1992 15/3/1993 13/9/1993 27/1/1998

875 163 211 234 119 397 69

479

8.978 4.540

- 4.213 3.431 3.852 2.057 6.452

443 189 6.21 18.7 0.060

Ruvubu Burasira

17/10/1988 25/11/1988 11/4/1990 20/3/1991 12/9/1991 1/9/1992

30/3/1993 5/10/1993 7/1/1998

160 218 323 320 114 81

1716 720 355

- - -

8.370 7.313

- -

3.951 11.573

1059 387 5.80 21.0 0.172

Ruvubu Gitongo 19/10/1988 25/11/1988 11/4/1990 7/1/1998

90 105 233 444

- - - -

2493 802 5.9 21.6 0.175

Ruvubu Muyinga

28/4/1989 8/8/1991

31/7/1992 19/3/1993 8/9/1993

31/1/1998

33 97 86

230 100 339

- -

54.510 86.547 41.424 179.049

Ruvyironza Nyabiraba

21/10/1988 28/11/1988 26/7/1990 26/3/1991 13/9/1991 2/9/1992

7/10/1993 26/12/1997

70 153 44

143 90 71 48

412

4.124 7.699 5.747 7.623 5.062

- 2.865

20.551

Ruvyironza Kibaya

17/10/1988 26/11/1988 11/4/1990 2/8/1990

19/3/1991 12/9/1991 1/9/1992

30/3/1993 7/10/1993 8/1/1998

158 335 508 136 74

128 76

278 49

724

19.235 29.565 38.064

- 18.313 15.497

- 25.897 7.340

37.166

1994 844 6.23 20.7 0.202

C4


load (mg/l)

Disch. (m3/s)

Area (Km2)


Water Quality

Ann. mean

PH T( 0C)

Sed. Trans.MT/y

Ruvyironza Muyange

22/10/1988 28/11/1988 25/7/1990 26/3/1991 13/9/1991 9/10/1991 17/10/1991 2/9/1992

8/10/1993 26/12/1997

475 258 49 90 76 69

220 38 50

495

18.109 18.848

- - - - - -

6.770 43.559

1452 817 6.09 19.0 0.153

Waga Nkondo

22/10/1988 28/11/1988 26/7/1990 26/3/1991 13/9/1991 9/10/1991 17/10/1991 2/9/1992

8/10/1993 26/12/1997

157 653 36 36 96 53

169 22 23

615

8.087 9.323

- 8.306 7.161 5.687 8.522

- 3.008

16.095

1452 394 6.06 19.3 0.073

Kayave Mparamirundi

25/4/1989 20/7/1989 29/3/1990 4/8/1990

20/3/1991 7/8/1991

27/7/1992 16/3/1993 13/9/1993 28/1/1998

1076 152 623 35

193 165 65

106 20

340

2.431 1.823 2.200 1.721 1.638 1.819 1.522 1.399 0.963 2.346

Buyongwe Kiremba

26/4/1989 20/7/1989 30/3/1990 4/8/1990

21/3/1991 12/8/1991 28/7/1992 17/3/1992 12/9/1993 29/1/1998

41 183 100 70 59

106 108 29

109 340

1.853 1.759 3.101 1.784 1.322 1.405 0.955 1.333 0.897 2.535

C5


load (mg/l)

Disch. (m3/s)

Area (Km2)


Water Quality

Ann. mean

PH T( 0C)

Sed. Trans.MT/y

Ndurumu Marangara

26/4/1989 20/7/1989 30/3/1990 4/8/1990

21/3/1991 12/8/1991 28/7/1992 17/3/1993 12/9/1993 28/1/1998

90 145 206 103 18

100 166 33 29

349

1.535 1.132 1.822 1.009 1.067 1.187 0.722 1.057 0.503 1.825

Runombe Kabanga

27/4/1989 21/7/1989 31/3/1990 9/8/1991

30/7/1992 18/3/1993 9/9/1993

30/1/1998

60 70 85 80 25 55 21

300

2.166 1.218 1.970 1.176

- 1.270 0.795 2.616

D 1

APPENDIX (D)

Inventory of Data on Sediment Transport in Sudan

D 1

This Appendix covers part of the inventory of sediment transport data of Sudan Report. The appendix represents only a summary of the original document which has been received. The original document consists of many tables and graphs covering a broader perspective. .

Location of the Measurement Sites along the Nile River in Sudan

D 2

Table 1: Sediment Data of the Blue Nile @ El Deim DATE Sand

Cone SEDIMENT

CON. (PPM)

WATER DISCHARGE

(Mm3/day)

SEDIMENT DISCHARG

E (1000g/day)

Sediment DISCHARGE

(m3/day)

Gauge Reading

26-Jun-93 75 1727 87 156020 66962 8.34 30-Jun-93 42 1726 124 218601 93820 8.84 4-Jul-93 354 3146 189 660095 283303 9.54 8-Jul-93 380 3511 163 632835 271603 9028 12-Jul-93 148 2919 172 528641 226885 9.38 16-Jul-93 295 4120 253 1118543 480061 10.11 20-Jul-93 952 3065 275 1103878 473767 10.28 24-Jul-93 588 3025 404 1458759 626077 11.17 28-Jul-93 816 3268 442 1804098 774291 11.4 10-Aug-93 316 2741 526 1606575 689517 11.87 15-Aug-93 696 3025 452 1681826 721814 11.46 19-Aug-93 264 2862 454 1418270 608699 11.47 24-Aug-93 821 2213 466 1413351 606588 11.54 28-Aug-93 279 3187 480 1663447 713926 11.62 1-Sep-93 427 3897 469 2029421 870996 11.56 5-Sep-93 406 2924 597 1989427 853831 12.24 9-Sep-93 154 2692 630 1793420 769708 12.4 13-Sep-93 154 2461 415 1085512 465885 11.24 17-Sep-93 404 1719 409 867454 372298 11.2 2 1 -Sep-93 256 1858 324 683997 293561 10.64 25-Sep-93 174 1534 335 572201 245580 10.72 29-SqY-93 185 1858 305 623981 267803' 10.51 4-Oct-93 106 1215 366 483721 207606 10.93 8-Oct-93 50 972 335 342363 146945 10.72 12-Oct-93 23 591 247 151800 65150 10.06 16-Oct-93 172 521 201 139519 59880 9.66 20-Oct-93 74 140 164 35010 15026 9.29 26-Oct-93 100 209 170 52652 22597 9.36 30-Oct-93 35 383 205 85516 36702 9.69

D 3

Table 2: The Blue Nile Sediment Data @ Wad Alais DATE Sand

Cone SEDIMENT CON. (PPM)

WATER DISCHARGE

(Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

Gauge Reading

26-Jun-93 89 680 166.9 128346 55803 10.31 30-Jun-93 86 1320 150.29 211308 91873 10.15 4-Jul-93 76 1019 124.54 13637 159292 10.33 8-Jul-93 62 2344 184.08 442896 192564 10.04 12-Jul-93 66 3241 157.21 519893 226041 10.04 16-Jul-93 161 2984 217.16 682968 296943 11.5 20-Jul-93 713 2515 229.47 737501 320653 11.36 24-Jul-93 92 3539 307.22 1115516 485007 12.69 27-Jul-93 82 3070 374.19 1179447 512603 13.16 1-Aug-93 583 3539 499.48 2058857 895155 14.09 5-Aug-93 291 3241 566.92 2002361 870592 14.58 9-Aug-93 800 2600 520.96 1771264 770115 14.1 15-Aug-93 490 2515 477.77 1435699 624217 13.78 19-Aug-93 385 2174 534.44 1367632 594623 14.33 25-Aug-93 39 2046 467.5 974738 423799 14.16 29-Aug-93 121 2644 530.11 1465754 637284 14.5 2-Sep-93 114 2515 533.02 1401310 609265 14.35 18-Sep-93 134 1892 429.07 869296 377955 14.07 22-Sep-93 54 1760 341.8 620025 269576 13.22 26-Sep-93 246 1468 262.4 449754 195545 12.51 4-Oct-93 108 1468 320.04 504383 219297 13 8-Oct-93 150 1493 423 694989 302169 19.27 12-Oct-93 18 1517 231.54 355414 154526 12.96

D 4

Table 3: The Blue Nile Sediment Data @ Wad Alais DATE SEDIMENT

CON. (PPM)

WATER DISCHARG

E (Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARG

E (m3/day)

5-Jul-95 2964 95.64 283477 123251 11-jul-95 2503 79.39 198713 86397 17-Jul-95 1436 94.45 135630 58970 21-Jul-95 3254 168,96 549796 239042 25-Jul-95 2582 220.86 570261 247939 29-Jul-95 2819 364.93 1028738 447277 2-Aug-95 2240 348.8 781312 339701 6-Aug-95 2490 517.38 1288276 560120 10-Aug-95 2635 465.84 1227488 533691 14-Aug-95 3491 496.37 1732828 753403 19-Aug-95 32-54 504.6 1641968 713899 23-Aug-95 2569 486.28 1249253 543154 27-Aug-95 3122 504.86 1576235 685320 31-Aug-95 2622 353.89 927900 403435 6-Sep-95 2925 378.95 1108429 481926 12-Sep-95 1324 250.23 331305 144045 16-Sep-95 790 159.8 126242 54888 20-8cp-95 1660 149.67 248452 108023 24-Sep-95 356 159.17 56665 24637 1-Oct-95 237 141.62 33564 14593 5-Oct-95 263 132.98 34974 15206 9-oct-95 356 150.44 53557 23285

Table 4: The Blue Nile Sediment Data @ Wad Alais

DATE SEDIMENT CON. (PPM)

WATER DISCHARG

E (Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

14-Jul-96 3209 293.86 942997 409999 18-Jul-96 5638 413.2 232%22 1012879 22-Jul-96 2984 453.4 1352946 588231 26-Jul-96 2842 469.16 1333353 579719 30-Jul-96 3735 480.05 1792987 779559 3-Aug-96 3325 433.91 1442751 627283 7-Aug-96 1478 464.36 686324 298402 11 -Aug-96 2411 489.13 1179292 512736 15-Aug-96 3346 693.63 2320886 1009081 19-Aug-96 2055 446.1 916736 398581 23-Aug-96 1871 649.33 1214896 528216 27-Aug-96 1726 657.13 1134206 493133

D 5

Table 5: The Blue Nile Sediment Data @ Sennar DATE Sand

Cone SEDIMENTCON. (PPM)

WATER DISCHARG

E (Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

11-Jul-93 104 3737 15 437874 190380 20-Jul-93 258 5613 168 986328 428838 29-Aug-93 342 2026 476 1127168 490073 2-Sep-93 51 2221 404 917888 399082 7-Sep-93 649 1857 577 1445962 628679 23-Sep-93 112 1450 186 290532 126318 28-Sep-93 32 932 108 104112 45266 5-Oct-93 22 802 274 225776 98163

Table 6: The Blue Nile Sediment Data @ Sennar DATE SEDIMENT

CON. (PPM)

WATER DISCHARG

E (Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

16-Jul-95 1693 339.97 643-563 279810 23-Jul-95 3706 487.66 1807264 785767

17-Aug-95 3043 83.54 254206 110524 10-Sep-95 2055 336.19 690877 300381 21-Sep-95 97 114.35 11092 4823 5-Oct-95 101 107.48 10855 4720

12-Oct-95 1321 50.29 6638 28006

Table 7: The Blue Nile Sediment Data @ Sennar DATE SEDIMENT

CON. (PPM)

WATER DISCHARG

E (Mm3/day)

SEDIMENTDISCHARG

E (1000g/day)

Sediment DISCHARGE

(m3/day)

31-Jul-96 3517 470.34 1654186 719211 5-Aug-96 2543 444.41 1130145 491367 10-Aug-96 3043 494.21 1503893 653867 14-Aug-96 0.224 588.68 1318650 573326 21-Aug-96 2121 550.02 1166582 507209 26-Aug-96 1818 698.33 1269569 551987 31-Aug-96 1923 551.69 1060906 461263 4-Sep-96 1435 505.6 725540 315452

D 6

Table 8: 10-days Mean Sediment Concentration of the Blue Nile @ Different locations

Mean Sediment Concentration (PPM) Month Period El Deim Wad Alais Sennar II June III 1956 1172 - I 3361 2454 3200 II 3895 2724 4072 July III 4335 3274 3612 I 5660 2772 2790 II 3095 2859 2415 August III 2948 2654 2154 I 3589 2588 1887 II 2305 1669 1500 Sept. III 1755 1028 1442 I 1294 990 900 II 591 946 Oct. III 317 -

Table 9: Rahad Sediment Data @ Hawata DATE Sand

Cone SEDIMENT

CON. (PPM)

WATER DISCHARGE

(Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

Gauge Reading

23-Jul-93 47 2365 4.15 10009 4352 4.23 26-Jul-93 17 1829 2.03 3753 1632 3.36 30-Jul-93 46 1793 8.17 15033 6536 5.52 2-Aug-93 63 2544 6.76 17620 7661 5.1 5-Aug-93 6 1436 9.28 13381 5818 5.83 9-Aug-93 2 1507 9.98 15063 6549 6.02 12-Aug-93 179 2293 8.99 22223 9662 5.75 16-Aug-93 50 1007 10-28 10869 4726 6.1 19-Aug-93 21 1614 12.97 21203 9219 6.78 23-Aug-93 102 685 12.89 10142 4409 6.76 26-Aug-93 79 1293 1147 18474 8032 6.9 30-Aug-93 54 1078 13.76 15574 6771 6.97 2-Sep-93 301 292 13.8 8184 3558 6.98 6-Sep-93 56 920 14.05 13716 5963 7.04 12-Sep-93 90 1179 12.4 15732 6840 6.64 21-Sep-93 162 1178 11.28 15120 6574 6.36 25-Sep-93 100 1068 8.45 9875 4294 5.6 27-Sep-93 198 1178 9.46 13021 5661 5.88 30-Sep-93 178 994 7.93 9296 4042 5.45 7-Oet-93 278 1326 9.17 14710 6395 5.8 13-Oct-93 284 883 10.63 12400 5391 6.19 17-Oct-93 136 920 6.25 6595 2867 4.94 20-Oct-93 137 772 4.1 3723 1619 4.21

D 7

Table 10: Sediment Data of the Rahad River @ E1 Hawata DATE Gauge

Reading SEDIMENT CON. (PPM)

WATER DISCHARGE

(Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

5-Jul-96 3.55 727 2.45 1780 774 8-Jul-96 2.98 1149 1.29 1481 644 3-Aug-96 644 1736 11.6 20134 8754 9-Aug-% 5.84 1939 9.32 18064 7854 13-Aug-96 5.6 1315 8.45 11118 4834 16-Aug-96 6.6 1505 12.24 18415 8007 19-Aug-96 6.7 923 12.64 11668 5073 22-Aug-96 6-8 512 13.05 6682 2905 25-Aug-96 6.7 575 12.64 7269 3160 28-Aug-96 6.7 1285 12.64 16244 7062 2-Sep-96 6.98 838 13.8 11565 5028 5-Sep-96 6.58 891 12.16 10831 4709 8-Sep-96 6.36 101 11.28 1140 495 1 1-Sep-96 6.9 814 13.47 10961 4766 15-Sep-96 7.06 47 14.14 664 289 18-Sep-96 7.11 1294 14-35 18570 8074 22-Sep-96 6.9 413 13.47 5561 2418 25-Sep-96 6.09 656 10.25 6721 2922 29-Sep-96 6.88 403 13.38 5393 2345 2-Oct-96 6.42 553 11.52 6370 2770

Table 11: Dinder Sediment Data @ Gawisi93 DATE Sand


WATER DISCHARGE

(Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

GaugeReading

5-Aug-93 36 790 7.02 5801 2522 8.47 16-Aug-93 160 1116 2.47 3157 1372 7-87 26-Aug-93 74 21 25.67 22979 9991 10.4 7-Sep-93 210 600 23.76 19243 8367 10.22 18-Sep-93 148 438 12.21 7156 3111 9.06 3-Oct-93 252 535 11.66 9176 3989 9 19-Oct-93 128 148 3-38 932 405 8 Table 12: Dinder Sediment Data @ Gawisi DATE Sand


WATER DISCHARGE

(Mm3/day)

SEDIMENT DISCHARGE

(1000g/day)

Sediment DISCHARGE

(m3/day)

Gauge Reading

10-Sep-96 500.6 39.3 19673 8554 11.76 14-Sep-96 777.24 34.53 26839 11669 11.2 19-Sep-96 843.11 26.19 22078 9599 10.6 24-Sep-% 289.82 21.25 6158 2678 9.98 28-Sep-96 395.21 21.46 8479 3687 10

D 8

Table 1: Sediment Grain Size for the Different Stations Station Sediment Grain Size

Range (mm) (minron) Hawata 0.005-0.054 5-54 Supply Canal 0.005-0.052 5-52 U/S AIRB 0.004-0.048 4-48 Head (Main Canal) 0.004-0.048 4-48 U/S K. 22.6 0.004-0.048 4-48 D/S K. 22.6 0.004-0-046 4-46 U/S K. 36.4 0.005-0.055 5-55 D/S K. 36.4 0.005-0.051 5-51

Table 2: Daily Measured Sediment Concentrations U/S Abu

Rakham Barrage Date Sediment Concentration (ppm) Standard Supply U/S Abu Rakham Deviation Hawata Canal MC CC Ratio 6-Jul-96 460 663' 464 580 1.5 0.42 9-Jul-96 452 1678 2667 1419 0.53 -0.3 12-Jul-96 2144 1579 571 1715 3 2.17 15-Jul-96 468 15-50 1204 1175 98 0.14 18-Jul-96 573 1853 1460 1426 0.98 0.15 21-Jul-96 1534 1792 1228 1604 1.31 0.47 24-Jul-96 2094 626 19171 1954 0.99 0.16 27-Jul-96 1733 729 1280 1733 1.35 0-52 30-Jul-96 1571 479 2383 1552 0.65 -0.18 2-Aug-96 1522 1141 1548 1518 0.98 0.15 5-Aug-96 1381 809 4925 1368 .0-28 -0.55 8-Aug-96 1532 4014 6474 1578 0.24 -0.59 11 -Aug-96 21-54 1896 8668 2149 0.25 -0.58 14-Aug-96 1339 1284 4966 1338 0. 27 -0.56 17-Aug-96 1360 1323 3011 1360 0.45 -0.38 20-Aug-96 1380 573 1668 1380 0.83 0 25-Aug-96 575 369 1415 575 0.41 -0.42 28-Aug-96 1285 1005 4263 1285 0.3 -0.53 31-Aug-96 979 2816 7750 979 0.13 -0.7 3-Sep-96 845 1361 4345 845 0.19 -5.64 6-Sep-96 883 825 2777 882 0.32 -0.51 9-Sep-96 255 391 976 259 0.27 -0.57 12-Sep-96 415 637 1217 415 0.34 -0.49 15-Sep-96 47 771 811 47 0.06 -0.77 18-Sep-96 1294 435 445 1294 2.91 2.08 24-Sep-96 224 384 984 224 0.23 -0.6

D 9

Table 3: Daily Measured Sediment Concentrations Along The Rahad Main Canal

Sediment Concentration (ppm)

K 22 K 36 Date D/S A/RB U/S D/S U/S D/S

11 Jul-96 1404 2550 2521 1130 1157

14-Jul-96 15229 3106 4664 816 1848

17-Jul-96 1628 1188 1643 1226 1281

20-Jul-96 2008 1918 2269 1805 225

23-Jul-96 1915 2392 2049 2357 1.545

26-Jul-96 18-50 3097 5387 2281 3607

29-Jul-96 1985 2524 2139 2038 3706

04-Aug-96 1318 1716 1760 1086 1182

07-Aug-96 4710 1708 3965 2404 669

10-Aug-96 2459 1230 1067 837 903

13-Aug-96 7544 5143 598 1627 1076

16-Aug-96 561 217 173 515 449

19-Aug-96 577 199 248 427 101

22-Aug-96 592 205 738 292 212

25-Aug-96 3567 703 624 542 411

30-Aug-96 5614 1298 1.659 605 514

05-Sep-96 559 166 222 116 306

08-Sep-96 1116 166 404 91 283

11-Sep-96 537 265 248 148 161

14-Sep-96 1460 403 364 331 332

17-Sep-96 472 783 445 347 333

D 10

Table 4: 10-Days Mean Sediment Concentrations of the Monitoring Stations Upstream Abu Rikham Barrage

Sediment Concentration (ppm)

Period Hawata Supply Canal U/S Abu R&Afflam Barrage

JULY I 737 1148 1149 JULY II 1090 1642 1460 JULY III 1727 760 1858 AUG I 14-53 1397 3303 AUG II 1395 1618 5082 AUGIII 848 1001 3235 SEP I 674 1115 3457 SEP II 463 580 857 SEP III 867 352 624 OCT I 1022 168 243 OCT II 514 473 OCT III 185 431

Table 5: 10-Days Mean Sediment Concentrations along the Rahad Main Canal

Sediment Concentration (ppm) K. 22.6 K 36.4 Period Head U/S D/S U/S D/S

JULY I 911 974 887 II 3381 2354 3149 2133 2865 III 3100 2635 2883 2154 2889

AUG I 3016 1575 2617 1338 1073 II 3454 2231 1924 721 527 III 3602 904 1231 690 511

SEP I 2249 321 548 221 330 II 779 549 477 313 287 III 454 843 527 407 449

OCT I 184 455 577 501 611 II 188 507 542 572 529 III 228 426 306 355 281

D 11

Table 6: Water Balance for the Discharge Input to the Rahad Scheme

Dishrag in Million M3/day Period Supply

Canal Hawata Main

Canal D/S Rahad

1-Jul-1996 3.08 2.58 3.396 0 4-Jul-1996 3.36 2.75 3.921 0.4 7-Jul-1996 0.36 2.45 3.94 0 10-Jul-1996 3.85 1.29 3.473 0 13-Jul-1996 3.36 0.75 3.165 0.86 16-Jul-1996 3.36 2.29 2.828 0.86 19-JUI-19% 3.36 5.44 3.227 2.6 25-Jul-1996 0.864 11.88 3.448 3.2 28-Jul-1996 0.108 1172 4.3 2.6 31-Jul- 1996 0.144 10.43 3.014 1.9 3-Aug-1996 0.245 9.17 3.112 4.2 6-Aug-1996 0.28 11.92 2.99 8.6 9-Aug-1996 0.08 11.21 2.99 7.8 14-Aug-1996 0.213 8-53 0.763 12.8 17-Aug-1996 0 12-08 0.707 9.5 23-Aug-1996 0 12.97 1.388 9 26-Aug-1996 0 12.72 1.685 11.7 29-Aug-1996 0 12.8 1.976 10 1-Sep-1996 0 13.59 1.059 14.4 4-Sep-1996 0 13.72 0.412 10.3 7-Sep-1996 0 12.24 0.309 10.5 10-Sep-1996 0 11.68 0.81 10.3 13-Sep-19% 0 13.8 0.913 10.5 16-Sep-19% 0.105 14.14 1.019 10.4 19-Sep-1996 0 14.35 3.25 10.2 22-Sep-1996 0 14.48 4.5 9.5 25-Sep-1996 0.21 12.56 5 4.75 28-Sep-1996 0 10.97 5.5 4.8 1-Oct-1996 0 12.97 6 3.2 4-Oct-1996 0 10.51 6 3.4 7-Oct-1996 0 8.85 6 1.7 10-Oct-1996 0.144 6.06 6 0 15-Oct-1996 0.84 7.35 5 0.47 18-Oct-1996 0 4.77 4 0 21-Oct-1996 1.68 3.06 4 0 24-Oct-1996 1.68 2.23 3.5 0 27-Oct-1996 2.52 2.03 3.5 0 30-Oct-1996 2.82 1.45 3.5 0

D 12

Table 7: Water Balance for the Discharge Output to the Rahad Scheme Discharge in Million m3 /day

Date Main Cana1 Major 1 Reg. K.

22

Difference in balance Reach 1

Reg. K 36 Major 2 Sub

Main Difference in

Balance Reach 2

1-Jul-1996 3.396 0.117 3.118 0.162 2.78 0.162 0.486 -0.311 6-Jul-1996 3.921 0.239 4.033 -0.351 3.275 0.288 0.686 -0.216

10-Jul-1996 3.473 0-256 3.588 -0.371 3.085 0-286 0.557 -0.34 13-Jul-1996 2.165 0.347 3.189 -0.371 2.847 0.11 0.143 0.09 16-Jul-1996 2-828 0-335 178 -0187 2.285 0-342 0.094 0.059 19-JUI-1996 3.227 0.319 3.446 -0.538 2.737 0.47 0.181 0.058 22-Jul-1996 4.402 0.329 4.021 0.053 3.192 0.492 0.57 -0.233 25-Jul-1996 3.448 0.141 3.634 -0.327 3.227 o.437 0.403 -0.433 30-Jul-1996 3.426 0.147 3.718 -0.439 3.16 0.404 0.445 -0.291 2-Aug-1996 2.91 0.152 2.767 -0.009 2.267 0,283 0.23 -0.013 5-Aug-1996 2.99 0.153 3.134 -0.297 2.571 0.12 0.22 0.223 8-Aug-1996 2.99 0.113 2.738 0.139 2.419 0.057 0.063 0.199

11 -Aug- 1996 1.995 0.113 1.889 -0.007 1.72 0.058 0.046 0.064 14-Aug-1996 0.763 0.043 0.783 -0.063 0.45 0.059 0.045 0.229 17-Aug-1996 0.707 0.043 0.757 -0.093 0.541 0.057 0.018 0.14 20-Aug-1996 0.921 0.043 0.964 -0,086 0.612 0.059 0,013 0.279 23-Aug-1996 0.388 0.045 1.412 -0.069 0.999 0.057 0.019 0.337 26-Aug-1996 1.685 0.043 1,939 -0.298 1.689 0.087 0.017 0.146 29-Aug-1996 1.976 0.044 2.142 -0.21 1.728 0.092 0 0.322 1 -Sep- 1996 1.059 0.044 1.174 -0.159 0.927 0.088 0 0.159 4-Sep-1996 0.412 0.044 0.391 -0.023 0.18 0 0 0.212 7-Sep-1996 0.309 0.046 0.349 -0.085 0.009 0 0 0.34

10-Sep-1996 0.81 0.044 0.819 -0.053 0.577 0.102 0.049 0.09 13-Sep-1996 0.913 0.047 1.128 -0.262 0.746 0.04 0.047 0.295 16-Sep-1996 1.019 0.047 1.084 -0.112 0-915 0-035 0.043 0.09 19-Sep-1996 2.201 0.047 1.792 0.362 1.532 0.035 0.09 0.135 22-Sep-1996 3.402 0.138 2.759 0.506 2.222 0.033 0.025 0.478 25-Sep-1996 4.568 0.409 4.126 0.033 4.08 0.048 0.059 -0.061 29-Sep-1996 4.492 0.498 4.277 0.217 3.947 0.049 0.304 -0.024 1 -Oct-1 996 5.081 0.495 4.336 0-25 3.954 0-232 0.52 -0-371 2-Oct-1996 5.129 0.522 4.592 0.014 3.981 0.223 0.523 -0.135 5-Oct-1996 5.304 0.498 4.382 0.424 3.941 0,559 0.482 -0.6 9-Oct-1996 5.304 0.57 4.833 -0.099 4.139 0.546 0.486 -0.337

12-Oct-1996 5.304 0.574 4.983 -0.253 3.951 0.564 0.541 -0.073 15-Oct-1996 4.965 0.573 2.898 1.494 3.499 0.608 0.878 -2.088 18-Oct-1996 4.782 0.386 3.893 0.503 3.022 0.517 0.769 -0.414 21-Oct-1996 3.973 0.458 2-709 0.806 1-869 0-37 0.636 -0-166 24-Oct-1996 3.263 0.326 2.832 0.105 1.778 0.329 0.991 -0.265 27-Oct-1996 3.263 0.262 2.901 0.1 1.912 0.262 0.757 -0.03 30-Oct-1996 3.662 0.385 3.175 0.101 2.16 0.285 0.465 0.265

D 13

Table 8: Sediment Discharge of the Monitoring Stations Upstream Abu Rakhma Barrage Hawata Supply canal Period Conc.

(ppm) Water Disch.

(Mm3/day)

SedimentDisch. (Tons)

Conc. (ppm)

Water Disch.

(Mm3/day)

Sediment Disch. (Tons)

Conc. (ppm)

Water Disch.

(Mm3/day)JULY I 737 1.752 1291 1148 3.433 3941 1149 5.18

II 1090 3.655 3989 1642 3.26 5353 1460 6.91 III 1727 11.147 19251 760 0.827 629 1858 11.97

AUG I 1453 10.442 15172 1387 0.155 215 3303 10.6 II 1395 11.466 15995 1618 0.142 230 5082 11.61 III 848 12.943 10976 1001 0 0 3235 12.94

SEP I 674 12.635 8516 1115 0.056 62 3457 12.69 II 463 14.211 6580 580 0.011 6 857 14.22 III 867 12.451 10795 352 0.021 7 624 12.47

OCT 1 1022 8.558 8746 168 0.014 2 243 8-57 II 5.254 - 514 0.365 181 473 5.62 III 1.746 185 2.194 406 431 3.94

Table 9: Sediment Distribution Entering the Rahad Main Canal

Head (K.00) K.22.6

Period Period Conc. (ppm)

Water Disch.

(Mm3/day)

SedimentDisch. (Tons)

Conc. (ppm)

Water Disch.

(Mm3/day)

Sediment Disch. (Tons) Conc. (ppm)

JULY I 911 3.62 3298 887 3.35 2971 -3.1 II 3381 3.24 10954 3149 2.93 9226 2865 2.69 III 3200 3.69 11808 3000 3.5 10500 2889 3.1

AUG I 3016 2.96 8927 2617 2.83 7406 1073 2.59 II 3454 0.95 3281 1924 0.89 1712 527 0.64 III 3602 1.53 5511 1231 1.47 1810 511 1.39

SEP I 2249 0.56 1259 548 0.51 279 330 0.36 II 779 1.6 1246 477 1-3 620 287 1.07 III 454 4.82 2188 527 3.8 2003 449 3.39

OCT 1 184 5.8 1067 577 4.48 2585 611 2.53 II 188 5.1 959 532 4.2 2234 529 3.1 III 228 4 912 306 2.87 878 281 1.9

D 14

Table 10: Sediment Deposited Pattern along the Main Canal Reach 1 (Head- 22.6)

Reach 1

(Head-K. 22.6-36.4)

Period Cone. Head

(11139m)

Conc. K.

22.6 (ppm)

Water Disch. (Tons)

Sediment Deposi (Tons)

Cone. d/s K. 22 (ppm)

Conc. U/sK.

36 (ppm)

Water Disch.

(Mm3/day)

Sediment Deposi (Tons)

JULY I 911 974 3.62 - 887 - 3.35 - II 3381 2354 3.24 3328 3149 2133 2.93 2977 III 3200 2635 3.69 2095 3000 2154 3.5 2961

AUG I 3016 1575 2.96 4265 2617 1338 2.83 3620 II 3454 2231 0.95 1162 410 721 0.89 III 3602 904 1.53 4128 1231 690 1.47 795

SEP I 2249 321 0.56 1080 548 221 0.51 167 II 779 549 1.6 368 477 313 1.3 213 III 454 843 4.82 - 1166 1970 3.8 -

OCT I 184 455 5.8 - 577 501 4.48 340 II 188 507 5.1 - 532 572 4.2 - III 228 426 4 - 306 355 2.87 -

GROUP MEMBERS NAME Country Organization Address Fax Telephone E-mail

Dr. Kamal Eldin Bashar

Sudan UNESCO Chair in Water Resources (UCWR)

Khartoum- P.O. Box 1244,

Sudan

249 183 779599

249 183 779599 [email protected] [email protected] [email protected]

Dr. Osman Mohammed

Naggar Sudan

UNESCO Chair in Water Resources

P. O. Box: 1244, Khartoum 11111

00-249-11-779604

00-249-11-779599

[email protected] [email protected]

Dr. Ahmed Khalid Eldaw

Sudan Ministry of Irrigation and Water Resources

P. O. Box: 878 Khartoum

00-249-11-779604

00-249-11-761378


Prof. Hassan M. Fadul

Sudan Agriculture Research Corporations (ARC)

P. O. Box: 126 Wad Medani 00-249-511-43213

00-249-511-43055

[email protected]

Mr. Ndorimana

Longin Burundi Geographic Institute of

Burundi (IGEBU) P. O. Box: 34 GITEGA, Bujumbura

00-257-40-2625

00-257-40-3744 [email protected] [email protected]

Mr. Nindamutsa

Burundi Geographic Institute of Burundi (IGEBU)

P. O. Box: 34 GITEGA, Bujumbura

00-257-40-2625

00-257-40-3744 [email protected] - [email protected] [email protected]

Dr. Samy Abdel-Fattah

Saad Egypt

Hydraulics Research Institute, Egypt

Delta Barrage, 13621, Egypt 00-202-2189539

00-202-2188268 [email protected] [email protected]

Dr. Bayou Chane Ethiopia

Addis Ababa University, Technology Faculty

Addis Ababa University, Technology Faculty , P.O. Box 385

00-251-552601 00-251-1-232439 [email protected] [email protected]

Prof. Gerrit J. Klaassen

The Netherlands

UNESCO- IHE Institute for Water Education

P. O. Box: 3015, 2601 DA Delft,

00-31-15-2151739 00-31-527-241605

00-31-15-2122921


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