mana dawuch small scale irrigation project … ssip...manna_dawch small scale intake irrigation...

Manna_Dawch Small Scale Intake Irrigation Project Engineering Design Final Report

ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page ii


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page iii

Amhara National Regional State

Water, Irrigation & Energy Development Bureau

(BOWIED)

Detail Design

of

Menna_Dawch Small-Scale Intake Irrigation Project

Volume IV: Engineering Design Final Report

March, 2016(Revised 2016)

Bahir Dar

Client: Bureau of Water, Irrigation & Energy Development

(BoWIED)

Address:

P. O. Box: 88

Telephone: 0528-200853/855

Fax: 251-08-20-65-68/204676/202040

Consultant: Amhara Design & Supervision Works Enterprise

(ADSWE)

Address:

P. O. Box: 1921

Telephone: +251-582-181023/ 180638/181201/181254

Fax: (058) 2180550/ (058) 2180560

E-mail: amhara [email protected]

Bahir Dar, Ethiopia

mailto:amhara%[email protected]


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page i

List of Reports

Volume I: Watershed Management

Volume II: Engineering Geology

Volume III: Irrigation Agronomy

Volume IV: Engineering Design

Volume V: Socio Economy

Volume VI: Environmental Impact Assessment

Volume VII: Economic and Financial Analysis


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page ii

Table of Contents Page Nr

List of Reports.................................................................................................................................. i

LIST OF TABLES .......................................................................................................................... v

LIST OF FIGURES ........................................................................................................................ v

SAILENT FEATURE .................................................................................................................... vi

1 INTRODUCTION ................................................................................................................... 1

1.1 Background ...................................................................................................................... 1

1.1.1 Description of the Project Area................................................................................. 1

1.2 Objectives of the Study .................................................................................................... 2

1.2.1 Major Objective ........................................................................................................ 2

1.2.2 Specific Objectives ................................................................................................... 3

1.3 Scope of the Study............................................................................................................ 4

1.4 Methodology .................................................................................................................... 4

2 HYDROLOGY ........................................................................................................................ 6

2.1 Watershed Characteristics ................................................................................................ 6

2.2 Hydro-Metrological Data Availability ............................................................................. 7

2.2.1 Climate ...................................................................................................................... 7

2.2.2 Rainfall Data ............................................................................................................. 8

2.2.3 River flow data .......................................................................................................... 8

2.2.4 Upstream & Downstream utilization ........................................................................ 8

2.3 Design Flood Analysis ..................................................................................................... 8

2.3.1 Design Rainfall computation .................................................................................... 9

2.3.2 Peak Discharge Determination ............................................................................... 11

2.3.3 Tail Water Depth Computation ............................................................................... 15

3 HEADWORK DESIGN ........................................................................................................ 19

3.1 Headwork Site Selection ................................................................................................ 19


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page iii

3.2 River Geology ................................................................................................................ 19

3.2.1 River Bed condition ................................................................................................ 20

3.2.2 River Bank Condition ............................................................................................. 21

3.3 Headwork Type Selection .............................................................................................. 22

3.4 Hydraulic Design of Headwork Structure ...................................................................... 22

3.4.1 Intake Height or Scour Depth Determination ......................................................... 22

3.4.2 Intake Dimensions .................................................................................................. 23

3.4.3 Outlet Design .......................................................................................................... 23

3.4.4 Retaining Wall Analysis ......................................................................................... 24

4 IRRIGATION AND DRAINAGE SYSTEMS DESIGN ...................................................... 25

4.1 Irrigable Area Description .............................................................................................. 25

4.1.1 Topography ............................................................................................................. 25

4.1.2 Soil characteristics .................................................................................................. 25

4.2 Irrigation Water Requirement ........................................................................................ 25

4.2.1 Crop Water Requirement (CWR) ........................................................................... 25

4.2.2 Irrigation efficiency (Ep) ........................................................................................ 26

4.2.3 Irrigation duty ......................................................................................................... 26

4.2.4 Irrigation Methods .................................................................................................. 27

4.3 Irrigation and Drainage System Layout ......................................................................... 28

4.3.1 Main Canal .............................................................................................................. 29

4.3.2 Secondary Canals .................................................................................................... 35

4.3.3 Tertiary canals ......................................................................................................... 36

4.3.4 Design of Division box ........................................................................................... 38

4.3.5 Road Crossing Structure ......................................................................................... 41

4.3.6 Drop structure ......................................................................................................... 41


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page iv

4.3.7 Design of a Typical Flume ...................................................................................... 43

4.3.8 Drainage System.................................................................................................... 44

5 SOURCES OF CONSTRUCTION MATERIALS ............................................................... 45

5.1 Rock for Masonry and Crushed Coarse Aggregate ........................................................ 45

5.2 Fine Aggregates.............................................................................................................. 45

5.3 Water .............................................................................................................................. 46

6 OPERATION AND MAINTENANCE................................................................................. 47

6.1 General ........................................................................................................................... 47

6.2 Operation of the Head Works......................................................................................... 47

6.3 Irrigation System Operation ........................................................................................... 47

6.4 Maintenance Requirement.............................................................................................. 47

7 CONCLUSION AND RECOMMENDATION .................................................................... 49

8 REFERENCE ........................................................................................................................ 50


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page v

LIST OF TABLES

TABLE 2-1: THE SLOPE CLASSES AND PROPORTION OF THE WATER SHED ..................................................................... 6

TABLE 2-2: OUTLIER TEST ANALYSIS ............................................................................................................................ 9

TABLE 2-3: TEST FOR GOODNESS TO FIT USING D-INDEX ............................................................................................ 10

TABLE 2-4: RUNOFF ANALYSIS ..................................................................................................................................... 13

TABLE 2-5: HYDROGRAPH COORDINATES .................................................................................................................... 14

TABLE 2-6: STAGE DISCHARGE ANALYSIS ................................................................................................................... 15

TABLE 2-7: RIVER DISCHARGE COMPUTATION AT DIFFERENT STAGES OF FLOW ........................................................ 18

TABLE 3-1: TYPICAL DESIGN OF MASONRY RETAINING WALL ...................................................................................... 24

TABLE 4-1: HYDRAULIC PARAMETERS OF MAIN CANAL .............................................................................................. 34

TABLE 4-2: HYDRAULIC PARAMETERS OF SECONDARY CANALS .................................................................................. 35

TABLE 4-3: HYDRAULIC PARAMETERS OF TERTIARY CANALS ..................................................................................... 36

TABLE 4-4: HYDRAULIC PARAMETERS OF DIVISION BOXES ......................................................................................... 40

TABLE 4-5: DROP HYDRAULIC DESIGN ........................................................................................................................ 43

TABLE 4-6: HYDRAULIC PARAMETERS OF FLUME ........................................................................................................ 44

LIST OF FIGURES

FIGURE 1-1: LOCATION MAP OF THE PROJECT AREA...................................................................................................... 2

FIGURE 2-1: DRAINAGE MAP OF MENNA_DAWCH WATERSHED .................................................................................... 7

FIGURE 2-2: COMPLEX HYDROGRAPH .......................................................................................................................... 14

FIGURE 2-3: HEADWORK SITE RIVER SECTION............................................................................................................. 15

FIGURE 2-4: RATING CURVE ........................................................................................................................................ 16

FIGURE 2-6: RIVER SLOPE PROFILE .............................................................................................................................. 17

FIGURE 3-1: RIVER BED AT THE PROPOSED INTAKE SITE ............................................................................................. 21

FIGURE 4-1: TYPICAL CROSS SECTION OF TERTIARY CANALS ...................................................................................... 36

FIGURE 4-2: TYPICAL DIVISION BOX PLAN ................................................................................................................... 38


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page vi

SAILENT FEATURE

1. Project name: Menna_Dawch Small Scale Intake Irrigation Project

2. Name of the stream: Menna river

3. Location of the intake site using

Easting: 0383459

Northing:1354398

Zone: (North Gondar)

Wereda: (Mirab Belesa)

Average Altitude: 1992 masl

4. Hydrology

Design rainfall: 82.5 mm`

Catchment area: 62.36 Km2

Longest flow path length: 8.9 Km

Design flood: 157.09 m3/sec

Design base flow: 270 lit/se.

5. Intake

Intake type: Reinforced Concrete.

Height: 2 and 2.7 m

Gross crest length: 80 m

Intake crest level: 1993 m.a.s.l

HFL: 1995 m.a.s.l

6. Outlet

Sill level: 1992.4 m.a.s.l

Opening dimension: 0.6*0.6 m2

Discharge capacity: 220 lit/sec.

Irrigation and drainage systems Infrastructure

Command area size: 180 ha

Type of soil of the command area is dominantly clay &silt soil


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page vii

Design discharge of the main canal = 216 l/sec

Irrigation system layout consists of one earthen & lined main canal, 4 secondary canals and 19 tertiary

canals

Main irrigation structures designed are;

Gully crossing structures

Flume

Road Crossing

Supper Passage

Project Costs ummary

Components Costs ETB

General items 2,792,000

Headwork 2,263,354.00

Infrastructure 6,385,729

Total 11,441,083

VAT 15% 1,716,162

Total 13,157,245

cost per ha(180ha) 73,095.81


ADSWE, Irrigation & Drainage P.O. Box: 1921 Tel: 058--218--06--38/10 23 Fax : 058--218-0550/0560 Page 1

1 INTRODUCTION

1.1 Background

In Ethiopia, under the prevalent rain-fed agricultural production system, the progressive degradation of the

natural resource base, especially in highly vulnerable areas of the highlands coupled with climate variability

have aggravated the incidence of poverty and food insecurity. The major source of growth for Ethiopia is still

conceived to be the agriculture sector. Hence, this sector has to be insulated from drought shocks through

enhanced utilization of the water resource potential of the country, (through development of small-scale

irrigation, water harvesting, and on-farm diversification) coupled with strengthened linkages between

agriculture and industry (agro-industry), thereby creating a demand for agricultural output. In line with the

above, efforts have been made by the government to improve the situation in the country in areas of domestic

water supply provision, irrigation, watershed Management, etc. The Amhara Water Resources Development

Bureau is playing its role in the development of small scale irrigation projects in the region. Accordingly, as

part of the water sector development program, the office has initiated the study and design of a small scale

irrigation scheme on Menna River at Dawch Kebele and signed an agreement with Amhara Design &

Supervision Works Enterprise (ADSWE) for the study and design of the project.

1.1.1 Description of the Project Area

1.1.1.1 Location

Menna_Dawch irrigation project is located mainly at Dawch Keble, Mirab Belesa Wereda of North Gondar

Zone in the Amhara Region. The proposed irrigation project is to be undertaken on Menna River and the

headwork structures are specifically located at an altitude of about 1992 masl and geographical coordinates

of 1354398 N and 0383459 E (UTM, ADINDAN).



Figure 1-1: Location Map of the Project Area

1.1.1.2 Accessibility

The project site is 40km from Arbaya, capital city of Mirab Belesa woreda, in east direction. 18km is gravel

road which is all weathered road. 15km dry weathered and 7km is accessible on foot.

1.1.1.3 Previous Irrigation Practices

In the study area traditional irrigation practices are under taken by individual farmers that use the river flow

to the right side is with laborious temporary diversions. So, the farmers in the project area are very much

interested in the idea of upgrading the traditional scheme to modern scheme. Menna_Dawch Intake irrigation

project is proposed to upgrade existing traditional scheme to modern scheme.

1.2 Objectives of the Study

1.2.1 Major Objective

The major objective of this study is upgrading the existing irrigation practice and expanding the command

area by saving water loss due to improper water conveyance system.



Hence the objective of this project is to contribute a substantial share in the effort to reduce the risk of

production decrease due to rainfall variability, reducing water loss and increase the productivity of the

resource in the project specific area. Specifically, the project is targeted for the following.

To make sustainable the rain-fed crop production and make extra production in the dry season

possible for 180 ha of land through irrigation.

There is a general consensus that irrigation investments will achieve broader food security and

poverty reduction impacts and if efforts are also geared towards up-grading existing traditional

farming practices with support to enhance access to input supply, output marketing and extension to

facilitate access to information and innovations.

This objective is to be realized by constructing intake structures across the Menna River and

diverting the river flow.

1.2.2 Specific Objectives

Other benefits that can be expected to appear with the launching of the project are:

Efficiency of water use improvement;

Improved local nutrition/food security gains;

Improved Management of scarce natural resources (land and water);

Resilience against drought risk;

Rationale for erosion control and watershed Management;

Rationale for the intensification and modernization of small-holder agriculture and rural lifestyles.

The engineering study and design enables the realization of the project by the provision of

engineering structures that will allow the appropriate abstraction of the river water for delivery in to

the identified irrigation fields of the study area. Hence, this engineering design is specifically

targeted to:

Analyze hydrologic requirements of the project and engineering structures;

The formulation of sound and stable structure, with necessary provisions that allow safe, easy and

low-maintenance operation in the service life of the project;

Design canals, flumes, super passages, division boxes and foot path roads

Develop working drawings;

Estimation of construction costs.



1.3 Scope of the Study

The irrigation design shall ensure reliability, equity and flexibility of water delivery to farmers. It will

aim at reducing conflicts among water users and will lead to lower operation and maintenance costs.

Updating the existing computation of the actual evapo-transpiration, crop water requirement, irrigation

demand/duty using the existing and recent agronomic, climatologic and soil data using more appropriate

methodologies.

Design proper irrigation system compatible with local conditions and Management capabilities,

Planning and layout of the irrigation system, which include irrigation canals, drainage channels,

inspection roads and alignments, canal spacing, canal length, location of structures, and water profiles

along canal and drains at specified reaches, which is most economical easily Manageable and aligned

with topographic feature and geological investigation.

Determination and estimation of water application conveyance and other losses and irrigation

efficiencies and consideration of those parameters in design steps.

Check and test hydraulic and structural designs of main canal considering total demand and the required

capacity and the base flow availability,

Prepare general plans and drawings for all irrigation infrastructure and irrigation systems designs,

1.4 Methodology

In the study and design procedure, Designers used the following steps.

Specific Site identification:

o DEM, Google earth

o Local farmers interview and discussion

o Wereda and Zone Agriculture section expertise

o On foot travel along the river channel and farm areas.

Topographic survey:

o Surveying the headwork site and the Command area with sufficient radius, using Total station

Flow estimation

o Physical observation on flood mark indications and local information about high flood and

critical flow condition of the river

o Base flow estimated during the reconnaissance field visit by floating method.

Irrigable area identification:

o Using local information



o Detail Topographic Surveying data map.

Study and design of the irrigation method to be adopted,

Study and design of the irrigation system layout and associated structures,

Design of the different conveyance canals,

Planning and design of the different irrigation and drainage structures,

Preparation of the longitudinal profiles of the different irrigation and drainage canals.



2 HYDROLOGY

2.1 Watershed Characteristics

The watershed consists of all land forms in slope classes. Slopes within the watershed range from flat to very

steep, in excess of above 30%, mountain land forms. The land escape of the watershed is characterized by

hill and mountain, which constitute 72.49 % of the watershed area.

Table 2-1: The Slope Classes and Proportion of the Water Shed

No

Slope

Slope Class (%)

Area Coverage

Description Class (%) Hectare (ha) Proportion (%)

1 Flat Plain 0-3 92.8948 1.489731

2 Rolling Plain 3-8 666.1101 10.68224

3 Undulating Plain 8-15 956.5312 15.33965

4 Hill 15-30 1692.194 27.13729

5 Mountain

30-50 1637.947 26.26735

>50 1190 19.08374

Total 6235.6771 100

Certain physical properties of watersheds significantly affect the characteristics of the runoff and sediment

yield and are of great interest in hydrologic analyses. The rate and volume of runoff, and sediment yield from

the watershed have much to do with shape, size, slope and other parameters of the landscape. These suggest

that there should be some important relations between basin form and hydrologic performance. If the basin

and hydrologic characteristics are to be related, the basin form must also be represented by quantitative

descriptors. These parameters can be measured from maps.

The watershed characteristics are analyzed and presented in of the Watershed Feasibility Study Report of the

same project. In summary:

Catchment Area = 62.36km2

Stream Length = 8.9Km

CN(II) = 84.85

Time of Concentration = 2.92



At the selected reference point, the area of Menna_Dawch catchment is 62.36km2

and consists of a network

of tributaries as shown in Figure 2-1 below.

Menna River at the headwork site is characterized by well-defined channel system and considerable flows. It

looks that the gradient of the river is getting low and hence there exists significant deposition of sediment

mainly cobbles and boulders.

Figure 2-1: Drainage Map of Menna_Dawch Watershed

2.2 Hydro-Metrological Data Availability

2.2.1 Climate

Small scale irrigation project designers and planners are faced with lack of good data on the hydrology of the

stream/river system that will be their water source and on local weather and climate conditions. Stream

gauging stations are virtually non-existent in remote rural areas of Ethiopia; meteorological stations are



almost rare. Likewise, at Dawch Kebele (Project area location) and in the catchment area of this project,

there is no meteorological station of any level. Moreover, there are no flow data for the river near the project.

Therefore, data for the hydro-meteorological analysis is taken from the nearby station and similar areas.

Rainfall & temperature data are considered from Addis Zemen Meteorological station. In fact, this station is

very close to the project area about 10km.

As per the data of the station, March – April are identified as high temperature periods whereas December–

January are low temperature periods. The mean annual rainfall amount is more than 44.42mm (1998 - 2008

data) and most of it occurs from June to August.

2.2.2 Rainfall Data

In order to compute the design flood for the Intake structure, the daily maximum rainfall is collected from

Addis Zemen Metrological stations with a record of 12 years.

2.2.3 River flow data

The base flow which is measured on April 2007 E.C is 270 l/s. Since this base flow is measured during the

dry months of the year, this figure is adopted for design.

2.2.4 Upstream & Downstream utilization

Downstream of the proposed site, appreciable need for water is anticipated for locals and cattle provisions.

Therefore, at least 54 l/s (21%)of the minimum flow has to be released for downstream requirements and the

river has ground water at downstream so that there is no any conflict between u/s and d/s of the projects.

For the sake of planning and design, however, the outlet for the intake is designed for a discharge of 220l/s

for this project and the project is to be developed for 180 ha of land, which is most of the time achievable as

the flow for most of the time is significant to support this size of command area.

2.3 Design Flood Analysis

For the design and analysis of structures to be constructed on the river, estimation of flood magnitude is an

important task. This can be done using different techniques depending on the data available. For this

particular case, there are no river flow data and hence the flood estimation is done using the rainfall data and

applying SCS Curve Method.



2.3.1 Design Rainfall computation

2.3.1.1 Outlier Test

Higher Limit, , Kn = 1.87 for 12 Years of data.

Lower Limit, , Kn = 1.39 for 12 Years of data.

Table 2-2: Outlier Test Analysis

Year Daily heaviest Rainfall (mm) Descending order (X) Logarithm value (Y)

1998 32.4 69 1.8388

1999 42 57 1.7559

2000 46.5 53.2 1.7259

2001 27 48.4 1.6848

2002 53.2 46.5 1.6675

2003 38 42.5 1.6284

2004 48.4 42 1.6232

2005 57 42 1.6232

2006 69 38 1.5798

2007 35 35 1.5441

2008 100 32.4 1.5105

2009 42 27 1.4314

SUM 533.00 19.6136

MEAN 44.42 1.6345

STANDARED DEVIATION 11.49 0.1114

SKEWNESS COEFFICIENT 0.679 0.0055

NUMBER OF DATA: 12 19.6136

Higher Limit, YH = 1.87

Lower Limit, YL = 1.39

Therefore,



Upper limit of rainfall = 10^1.87 = 74.51mm

Lower Limit of rainfall = 10^1.39 = 24.93mm

Conclusion: The rainfall values are within the limits.

2.3.1.2 Check for variance

After checking the outliers, the data should be checked for variability. For variability the formula used is

Where, δn-1 = Standard deviation =11.49

N = Nr of recorded data =12

Mean = 44.42

= Standard error

Acceptable

Therefore the data shows no variability.

2.3.1.3 D-Index test

After checking the consistency of the data for higher and lower outlier, the 12 years data is obtained as

representative for the analysis using D-index. The D-Index test is believed to be the better goodness to fitness

in many literatures. Hence in this study it was used to determine the best statistical distribution to estimate

the peak rainfall. The D-index for the comparison of the fit of various distributions is summarized as follows.

Where Xi and Xi’ are the ith highest observed and computed values for the distribution respectively.

Table 2-3: Test for Goodness to Fit Using D-Index

Normal

Log Pearson

Type III Log Normal

Pearson

Type III

Gumbel

EVI Gumbel

XI - XI -'XI' XI -'XI' XI -'XI' XI -'XI' XI -'XI'



'XI'

Sum/Mean 0.348 0.247 0.255 0.33 0.289 5.050

All the candidate distributions give almost identical correlation coefficients. However, the standard errors are

significantly lower for the log Pearson type III Method which is 0.247. But accordingly our country criteria,

the design rain fall for this distribution has been selected the highest result. In this study the Gumbel method

has been selected.

The design rainfall using Gumbel Method is given as

KRR nmeanf *. 1

Where Rf = Design rainfall

Rmean = average of all values of annual heaviest fall = 44.42 mm

σn-1 = standard deviation of the series = 11.49 mm

)1

ln(ln

T

TYt , T= Return period = 50 years

9.3)150

50ln(ln

tY

Yn, Sn = constant found from Gumble’s extreme value distribution table for N= 12 Years

Yn = 0.501and Sn = 1.02

32.3)02.1

501.09.3(

K

mmR f 5.8231.3*49.1141.44

Point Design Rainfall = 82.5 mm

The design rainfall at points for 50 years return period is 82.5 mm and the areal design rainfall is calculated

in the following section.

2.3.2 Peak Discharge Determination

2.3.2.1 General

The River is not gauged river. The design flood is calculated by method using SCS unit hydrograph method.

Thus, it is preferred to base the flood analysis on rainfall data, which are better both in quantity and quality



of data. In the hydrologic analysis for drainage structures, it must be recognized that there are many variable

factors that affect floods Peak flood analysis by SCS unit hydrograph method.

Design flood is calculated method of SCS (The United States Soil Conservation Service). This method is

widely adopted and more reliable method for flood estimation. The approach considers, watershed

parameters, like Area, Curve number, and time of concentration.

2.3.2.2 Time of concentration (Tc)

Time of concentration has been calculated by taking the stream profile of the longest streamline and dividing

it in to different elevation. Kirpich formula is adopted for computation.

The formula is,

Tc = 2.92 Since Tc < 3hr., duration of excess rainfall difference, D = 0.5hr.

Time to peak,

= 2hr

Base time,

= 5.34hr

Recession time,

= 3.34hr.

2.3.2.3 Area Rainfall

As the area of the catchment gets larger, coincidence of all hydrological incidences becomes less and less.

This can be optimized by changing the calculated point rainfall to aerial rainfall. The conversion factor is

taken from standard table that relate directly with the size of watershed area and type of the gauging station.

(IDD manual)

For the case of Menna_Dawch irrigation project,

Total watershed area =62.36 Km2

Type of gauging station = Daily rainfall (24 hr.)

Aerial Rainfall = (Point Rainfall) x (Conversion factor)



2.3.2.4 Run off Analysis

Input data:

Design Point Rainfall = 82.5mm

Curve number at antecedent moisture condition III = 93.34

Catchment Area, A = 62.36 Km2

Tc = 2.92hr, D = 0.5hr., Tp = 2 hr; Tb = 5.34 hr; Tr = 3.34hr.

Direct run-off,

Where, I = Rearranged cumulative run-off depth (mm

S = Maximum run off potential difference,

Peak run-off for incremental;

Where, A = Catchment area = 62.36 Km2

Tp = Time to peak (hr)

Q = Incremental run-off (mm)

Table 2-4: Runoff analysis

Duration

(hrs)

Cumulative run off

(mm)

Incremental

run off

(mm)

Peak run off

incremental

(m3/sec)

Time of

begin

Time to

peak

(hrs)

Time to

end

0.0-0.5 3.31 3.31 0.00 0.00 0.00 0.00

0.5-1 7.88 4.57 0.79 0.79 5.19 0.50

1-1.5 14.46 6.58 4.01 3.22 21.07 1.00

1.5-2 31.49 17.04 16.80 12.79 83.75 1.50

2.5-3 40.07 8.58 24.24 7.44 48.74 2.00



Table 2-5: Hydrograph coordinates

Time Coordinate of Hydrograph (m3/Sec)

(hr) 1 2 3 4 5 6 Total

0.00 0.00 0.00

0.50 0.00 0.00 0.00

1.00 0.00 1.30 0.00 1.30

1.50 0.00 2.59 5.27 0.00 7.86

2.00 0.00 3.89 10.53 20.92 0.0 35.33

2.50 0.00 5.19 15.80 41.87 12.18 0.0 75.02

3.00 0.00 4.41 21.07 62.81 24.36 6.51 119.16

3.50 0.00 3.63 17.91 83.75 36.55 13.02 154.87

4.00 0.00 2.86 14.76 71.21 48.74 19.53 157.09

4.50 0.00 2.08 11.60 58.67 41.44 26.04 139.84

5.34 0.00 0.78 6.31 37.62 29.19 19.50 93.39

5.84 0.00 3.15 25.08 21.89 15.60 65.73

6.34 0.00 12.54 14.60 11.70 38.83

6.84 0.00 7.30 7.80 15.10

7.34 0.00 3.90 3.90

7.84 0.00 0.00

Figure 2-2: Complex Hydrograph

From the analysis, the 50 year return period design run off is 157.09 m 3/s



2.3.3 Tail Water Depth Computation

Tail water depth of the river is equal to the flood depth and amount at the proposed intake site before

construction of the intake. It is used to crosscheck peak flood estimated by the SCS unit hydrograph method

with tail water computation.

1992

1993

1994

1995

1996

1997

1998

0.00 20.00 40.00 60.00 80.00 100.00 120.00 140.00

River crose section

Figure 2-3: Headwork Site River Section

Table 2-6: Stage Discharge Analysis

ELEVATION H P A R V Q

1993.00 0.00 0.00 0.00 0.00 0.00 0.00

1993.30 0.30 1.17 6.82 0.17 1.03 1.21

1993.60 0.60 3.17 12.08 0.26 1.37 4.34

1993.90 0.90 7.17 17.34 0.41 1.85 13.29

1994.20 1.20 13.17 23.37 0.56 2.28 30.00

1994.50 1.50 24.13 49.80 0.48 2.06 49.71

1994.80 1.80 40.77 61.33 0.66 2.54 103.70

1995.00 2.00 53.29 65.20 0.82 2.92 157.09

1995.10 2.10 60.03 67.29 0.89 3.10 185.80

1995.40 2.40 81.03 73.24 1.11 3.57 289.50



0

0.5

1

1.5

2

2.5

0 20 40 60 80 100 120 140 160

Tail

Dep

th (

m)

Discharge (m3/s)

Figure 2-4: Rating Curve

From the above stage discharge table and curve the maximum flood level corresponding to the computed

design peak discharge is 157.09m3/s (2.0 m from the river bed) and it is considered as the high flood level i.e.

expected at the intake axis before construction of the intake.

HFL = 1995 masl.

a) Average river bed slope

Average river bed slope of River is estimated by two different techniques. One is by end area method and the

other is by using best fit line method. Designers have adopted the end area method output for further

analysis.

The water level of the river is taken at different points along the river channel around the head work site.

Surveying work done for 190m length. And then, average water surface slope is considered as the river bed

slope. For comparison of the two procedures, refer the attached Excel file.



Figure 2-5: River Slope Profile

b) Manning’s Roughness coefficient

The Manning’s roughness coefficient is taken from standard table based on the river nature. The river at the

headwork site has got braded feature and curving nature. The river banks are defined and relatively smooth.

Manning’s roughness coefficient (n = 0.04) is adopted.

c) Discharge of the river

Input data:

Manning's roughness coefficient, n = 0.04

Average river bed slope, S = 0.018

SRn

V 3/21,

Where, R = Hydraulic radius = (Area/Perimeter)



Table 2-7: River Discharge Computation at Different Stages of Flow

Sr. Nr Elevation H P A R V Q

1 1993.00 0 0 0 0.00 0 0

2 1993.30 0.3 1.17 6.818 0.17 1.03 1.21

3 1993.60 0.6 3.17 12.0775 0.26 1.37 4.34

4 1993.90 0.9 7.17 17.335 0.41 1.85 13.29

5 1994.20 1.2 13.17 23.3725 0.56 2.28 30.00

6 1994.50 1.5 24.13 49.7958 0.48 2.06 49.71

7 1994.80 1.8 40.77 61.33 0.66 2.54 103.70

8 1995.00 2.00 53.29 65.20 0.82 2.92 157.09



3 HEADWORK DESIGN

3.1 Headwork Site Selection

Head work site selection for right side of the Menna_Dawch River is more appropriate for irrigation

development and at 4 places on the river, there are traditional diversions in the form of the intakes to irrigate

the right side of the river. All canals that emerge from the head work site creep along the right bank of the

river. These canals are exposed to the floods. The constructed traditional canal is usually taken away by flood

during rain seasons. Reconstruction has to be executed to use the water for irrigation development. This is

basic problem to the site, which has to be solved by this project.

The headwork site has been selected at the upstream of three traditional diversions to combine them for the

irrigation development.

Taking into consideration, the geological formation of the headwork site, proximity of the command area to

headwork, river topography, water head required, construction material availability, crossing structure along

the route of the main canal and expected flood intensity, intake is proposed as headwork structure.

3.2 River Geology

It is a common fact that the river development tends to accommodate itself to the local geology that develops

along the structurally weak zones like faults, joints, folds, etc. The drainage system of the study area is

strongly influenced by geological structures and formations, the nature of the vegetation cover and climate.

The nature of geological formations and structures has also strong influence on the development of the

channel.

The present morphology of the Menna River channel is a function of a number of processes and

environmental conditions, including the composition of the bed and the banks stable clay soil formation.

The size and composition of the sediment moving through the channel; the rate of sediment transport through

the channel and deposition on the banks and beds; and the regional degradation due to erosion processes.

Both left bank and the bed are composed of loose silt clay soil and coarser alluvial sediment as the result the

stream shows highly meandering nature both up and downstream from the proposed site but at the particular

intake site it shows not straight river channel. The river has wider section in upstream & downstream.



3.2.1 River Bed condition

The stream bed at proposed headwork site is characterized by straight, undefined and uniform surface

situations and formed with uniform geological materials, as seen from surface and subsurface observations.

Due to undefined flow direction and bank shape of the river, the stream bed has a very wide range from left

bank to right bank. This stream bed has 80m length during in the time of study and the whole surface of the

bed is covered by thick alluvial deposits, across the stream bed from right to left bank. The alluvial deposits

that cover all stream bed in both upstream and downstream direction including the intake axis. The deposit is

characterized by boulder, cobble, gravel, sand and silt formations. The test pit is taken from this stream bed

near the right bank with 3m height and from the observation of this subsurface investigation; the bed rock is

not exist at near distance. The test pit material is characterized by silty sand and gravel soil until the end of

pit depth with higher moisture content. The laboratory test has been done for this pit to characterize the

gradation of the deposit and according to laboratory testing (especially for gradation test); the deposit is

characterized by the following results:

Gravel (>4.75mm) =37.15%

Coarse sand (4.75-0.425mm) =40.25%

Fine sand (0.425-0.075mm) =16.67%

Silt and clay (<0.075mm) =5.93%



Figure 3-1: River Bed at the Proposed Intake Site

3.2.2 River Bank Condition

3.2.2.1 Right Bank

The right bank of the project headwork site composed from SILTY CLAY and CLAY with brown color

soils. The bank has 2m height from the river bed to upper area along the proposed axis. The main canal out

let is part of this bank and traditional canal exists in this side and the canal is during in the time of study is

functional for irrigation purpose by local people. The bank nature is undefined in both upstream and

downstream direction including the proposed axis due to less erosion resistance materials. In general the

bank has no defined shape and the river flow direction changes from season to season. There is no any type

of rock out crop in general in the banks, so that always bank erosion and sliding condition is increasing due

to year to year. From observation of bank geology and stream flow condition, the area is unstable,

unworkable and not durable, so that the area required different erosion and sliding protection structures such

that masonry or retaining wall during in the time of project construction. Along in this section of the bank the

masonry or retaining wall should be constructed within 75m and 30m in both the upstream and downstream

direction respectively, if not the river strictly changed current flow direction and the hydraulic structure that

constructed in the area is out of function.



3.2.2.2 Left Bank

The left bank of the project headwork site geological formation is SILTY SAND and SILTY CLAY soils in

both the upstream and downstream direction including the axis. The bank nature is gentle area and less

erosion activity resistance, so that due to this less erosion resistance material the bank shape becomes gentle

and move towards the farmland area year to year. In the last time the river could be diverted by weir structure

but from this weak nature of bank material the flow of river changed out of the weir and still the weir

structure is not functional, so that to avoid this problem the river should be diverted by intake structure and

different retaining structures are also required to protect river flow direction. The river flows has no

permanent flow direction and in summer season the flood which comes from the surrounding mountain from

the upstream direction highly affected this bank. From less erosion resistance bank material nature, this bank

required flood resistance structure such that masonry structure or retaining wall in both the upstream and

downstream direction from the axis. In both upstream and downstream direction the masonry or retaining

structures are required within 80m and 30m length respectively.

3.3 Headwork Type Selection

Considering the river geology features and expected flood amount, Intake is chosen.

Simple for construction.

Intake section is expected of the peak flood while the remaining flood will pass over the overflow

section of the river course.

There is no significant bed load (boulder effect) in the river.

3.4 Hydraulic Design of Headwork Structure

3.4.1 Intake Height or Scour Depth Determination

The following major factors have been seen in determining the Intake crest level:

Maximum command area elevation

Deriving head of the intake structure

Loss

Lowest Point of river center



3.4.2 Intake Dimensions

3.4.2.1 Flow over the Intake crest

a. Crest Length

Actual river section width of the over flow section of the river is = 80m

b. Discharge over the intake section

Design discharge, Q = 157.09 m3/s. (Result is obtained from hydrology report of same

document).

3.4.3 Outlet Design

3.4.3.1 Canal outlet level

The head regulator is provided on the right-side .The sill level of this head regulator is fixed from different

angle observations. The main conveyance system is more than 2.6km which passes more gullies and

undulating alignment. Hence this level is fixed based on the optimum route alignment and the maximum

irrigated command level including minor and major losses criteria. Based on this condition, the sill level is

fixed to be1992.40m.

• Outlet capacity

The minimum command area is determined by the minimum flow of the river but the canal capacity should

be determined for maximum command area and the corresponding discharge. In this case the outlet capacity

is fixed considering maximum duty and command area are considered to account the variation of duty.

Outlet capacity = Duty x command area

Where, maximum duty for 20hr irrigation 1.22 L/s/ha

Command area = 180ha.

Outlet capacity = 1.22 L/s/ha x 180ha = 220 L/sec

• Outlet size

From the intake discharge formula the outlet size is determined as follows

Q = CLHe3/2

Where; C = coeff. of discharge = 1.7

L = Length of water w

mxCHe

QL 2.0

1.07.1

22.02/32/3



⇒ Waterway length = 0.6m from hydraulic computation canal parameters.

Hence, provide an outlet size of 0.6mx 0.9m (length x height) by adding free board 0.30m .The gate of the

off take canal is to be vertical sheet metal of 0.7m x 0.90m for the closure of the opening space. The grooves

are to be provided on the walls using angle iron frames at the two sides of the gate openings.

3.4.3.2 Trash rack and Operation Slab

A vertical raised gate is designed for the canal outlet regulator. These gates slides over the operation slab on

the outlet of canal during opening and closing.

For easy operation of these gates, operation slab is provided. The size of the operation slab is fixed from the

point of construction and free movement. The size of the operation slab is shown in the drawing for canal

outlet thickness 0.2m.

The actual arrangement of angle irons, spindles, shafts and operation slab including other components is

shown on the design drawing. For each arrangement and further information, refer to the design drawing.

Trash rack is provided to protect the opening off take from the incoming boulders and debris. Size of trash

rack is 0.8m width and 0.9m height. Trash racks of diameter 12mm with c/c spacing of 20cm has to be

provided u/s of the gate to prevent entry of debris to the canal.

3.4.4 Retaining Wall Analysis

At the right side of the intake, walls have been provided to safeguard the river bank and the structure from

scour at the ends and also as a facility to the canal outlet operation and maintenance at the canal outlet

portion.

Table 3-1: Typical design of masonry retaining wall

Over turning = (M+ve/M-ve) >1.5 Fo 3.962444 >1.5 OK

Sliding = (µxFv/Fh),---µ=0.75 >1.5 Fs 1.801367 >1.50 OK

Tension: X= (Net Moment/Sum Fv), e=x-B/2, e<B/6X 1.562326

B/6= 0.583333 e 0.187674 <B/6 OK



4 IRRIGATION AND DRAINAGE SYSTEMS DESIGN

4.1 Irrigable Area Description

4.1.1 Topography

Topography is an important factor for the planning of any irrigation project as it influences method of

irrigation, drainage, erosion, mechanization, and cost of land development, labor requirement and choice of

crops.

The topographic feature of the project command area is mainly mild sloping type. Its elevation range is from

1991 to1936 meters above sea level. Nevertheless, it requires soil and water conservation measures or

structures (i.e. constructing bunds, bio-physicals, check dams, artificial water ways, etc).

The project command area is situated at the right side of Menna River (to the west side of the river). The

natural topographic feature of the command area has inclined from the North- to the North-West direction.

4.1.2 Soil characteristics

Soil properties (physical, chemical, etc.) greatly influence the growth and thereby yield of crops which is

grown. The command area has predominantly silt and clay and silt sand soil textured. Soils of the command

area are suitable for most of the selected crops to be grown (for further detail see the Agronomy Study of the

same project.

4.2 Irrigation Water Requirement

4.2.1 Crop Water Requirement (CWR)

The calculation of crop water requirement is a very important aspect for planning of any irrigation project.

Several methods and procedures are available for this. The Food and Agriculture Organization (FAO) of the

United Nations has also made available several publications on this subject and other issues related with this.

The computer program available in FAO Irrigation and Drainage Paper No. 56 “CROPWAT” has been used

for the calculation of Crop Water requirement. This program is based on Penman-Monteith approach and

procedures for calculation of crop water requirements and irrigation requirements are mainly based on

methodologies presented in FAO Irrigation and Drainage Paper No. 24 “Crop Water Requirements” and No.

33 “Yield Response to Water”.



The corresponding values of the crop water requirements of the proposed crops of the project are presented

in the Agronomy Study of the same project.

4.2.2 Irrigation efficiency (Ep)

To complete the evaluation of the demand, the efficiency of the water distribution system and of application

must be known.

The gross requirement of water for irrigation system is very much dependent on the overall efficiency of the

irrigation system, which in turn is dependent on several factors: Method of irrigation, type of canal (Lined

and/or Unlined), method of operations (simultaneously and continuous or Rotational water supply), and

availability of structures (for controlling and distribution and measuring and monitoring).

On the basis of these factors, the project has planned to impose surface irrigation method (using furrows).

The canal system is unlined other than canal near the head work. Hence, the conveyance efficiency has been

estimated to be 90%, distribution efficiency 85%, and field application efficiency 60%. As a result of these

the overall irrigation efficiency has been estimated to be 46%. According to soil Lab result, soils of the

command area are predominantly characterized as silt sand soils.

4.2.3 Irrigation duty

Irrigation duty is the volume of water required per hectare for the full flange of the crops. Moreover, it helps

in designing an efficient irrigation canal system.

The area, which will be irrigated, can be calculated by knowing the total available water at the source and

the overall duty for all crops required to be irrigated in different seasons of the years.

The proposed cropping pattern of Menna_Dawch intake irrigation project has showed a maximum net

irrigation water requirement (NIWR) in the month of March with the amount of 5.88mm/day for 24 working

hours (for overall proposed crops).

However, for the designing of the irrigation water application and the flows in the entire canal systems, from

the overall proposed crops the one that has maximum NIWR was used for irrigation duty calculation.

Accordingly, potato has showed the maximum NIWR (i.e. 5.88mm/day); and hence taken for the irrigation

project duty calculation as indicated here below:

For Menna_Dawch River Intake Irrigation Project, it decided to adopt 60% field application efficiency, 85%

distribution efficiency, and 90% conveyance efficiency as the soil is clay textured and the canal systems are

estimated to be line and unlined except small portion of the main canal near head work. Hence, the



overall/project efficiency for the selected surface irrigation method has been estimated to be 46%

(60/100*90/100*85/100) which is rounded to 46%.

For the designing of the project, the GIWR is given as follows:

GIWR = 5.88/0.460 = 12.78 [mm/day]

The GIWR, 12.78 mm/day, represents the daily quantity of water that is required to be applied. This water

quantity is also used for the determination of the canal discharge in consideration of the time of flow and is

defined as the duty, expressed as l/s/ha.

The duty is calculated by:

Duty (D) = GIWR × 1000 × 10 / (t × 60×60)

Where; Duty – the duty [l/s/ha]

GIWR – Gross Irrigation Requirement [mm/day]

t – Daily irrigation or flow hours [hrs]

The duty for the GIWR of 12.78mm/day and20 hours of daily irrigation time (t = 20), is supported to be used

with furrow irrigation method. Hence, Duty for20 working hours, as the site is nearer to farmers’ village and

local farmers have experiences in irrigation, is computed as follows:

D = (12.78 x 1000 x 10) / (20 x 3600) =1.22L/S/ha

4.2.4 Irrigation Methods

Among the different irrigation systems furrow irrigation system is proposed for the project area; and the

irrigation water will be obtained from Menna River and by constructing intake and convoying the water

commonly through lined and earthen canals (MC, SC, and TC) and then leading to field canals; and finally

irrigation takes place mostly in furrows.

For this project, among the various irrigation methods, surface irrigation method has been selected. Of the

surface irrigation methods furrow, border and basin irrigation methods can be used to supply irrigation water

to the plants/crops. However, each method has its own advantages and disadvantages. Care should be taken

when choosing the method which is best suited to the local circumstances, i.e., depending on slopes, soil

types, selected crop types, amount of water available, etc. of the command area.



Based on the above factors surface irrigation method has been proposed for the proposed crops in this

project. The method allows applying light irrigation and can be laid out in sloping fields along the contour.

Furrow irrigation method is best suited for most of the proposed and row planted crops. In general, furrow

irrigation method is simple, Manageable and widely practiced irrigation method. This method is suitable for

row crops that cannot stand in water for long periods. The only thing required to use this method is row

planting of crops. Besides, basin and border irrigation method would be used for the non-row planted crops.

Rotational flow water distribution is also recommended for the project area.

4.3 Irrigation and Drainage System Layout

The irrigation system layout for the project is prepared taking the following points into consideration besides

other factors.

A primary concern in the layout of the system is that it serves the purpose of conveying and

distributing water to the command area.

The excavation and earth fill volumes not be excessive, otherwise the construction costs can be

tremendous.

The selection of longitudinal bed slope is made taking into account the existing slopes of the terrain,

so as to minimize deviations in canal routing.

Curves in canals should not be too sharp.

The proposed irrigation system layout comprises one main canal, four secondary canals and twelve tertiary

canals as shown on the layout Drawings. The main canal runs for most of its length parallel to the contours

and several changes of direction are necessary to follow the topography. It crosses four main gullies, one foot

path. The main canal is masonry lined for a length of 2600meters starting from the intake outlet.

Conveyance System

The conveyance system consists of one Main canal to irrigate total command area of 180ha. The main canal

starts from Water abstraction site on right side and conveys water for a length of 2.6 Km.

Main canal is aligned along contours and supplies to four secondary unit and two turn out.

Design of the Canal System

Flow Depth and Section Capacity

The earthen canals have been designed with a trapezoidal shape and the lined ones with rectangular x-section

using Manning's Formula:



n

xSAxRQ

2/13/2

Where Q = discharge (m3/s)

R = Hydraulic radius (Flow area/wetted perimeter)

S = Hydraulic gradient

n = Manning's roughness coefficient, n = 0.025 is for the earth channels and n = 0.018 for

the masonry lined part of the main canal

4.3.1 Main Canal

The main canal is designed for a discharge of 220l/s and depending on the site specific condition, appropriate

slope is provided. Hydraulic parameters of the main canal are shown below.

Bill 1. GENERAL ITEM

I.

No Descriptions Unit Qty

Rate

(Birr)

Amount

(Birr)

1 Genral Items

1.1 Allow for mobilization Ls 1.00

220,000.00

220,000.00

1.2 Allow for demobilization Ls 1.00

176,000.00

176,000.00

1.3 Allow for contractor's camp and facilities

-

1.3.1

Allow for constraction camp and facilities = 4*5 m2,

living rooms for construction key personnel, CIS and

internally painted chip wood wall, masonry floor

cement screend and well ventilated room complet with

doors and windows., cafteria,shawor &toilet.$ from this

two class's 4*5m^2 to consultant living $office

Ls 1.00

450,000.00

450,000.00

1.4 Allow for temporary acess road to site for15km Km 7

250,000.00

1,750,000.00

1.5 Dewatering of open trenches and excavation of

temporary diversion of the river flow and pumps. Ls 1

158,100.00

158,100.00

1.6 Provide project indicator post starting from the

construction time. Ls 1.00

9,500.00

9,500.00

1.7 Provision of as built drawings for the project. Ls 1.00 28400.00

28,400.00



Total Carried to Summary for General Item 2,792,000

Bill 2. Head Work Structures

I.


Rate

(Birr)

Amount

(Birr)

2.1 Bed Bar

2.1.1 Earth Excavation Ordinary Soil m3

522.83

45.00

23,527.35

2.1.2 Back fill m3

367.25

110.00

40,397.50

2.1.3 Concrete (C25) m3

121.13

2,900.00

351,262.50

2.1.4 Lean Concrete (C20) m3

7.55

1,500.00

11,325.00

2.1.5 Reinforcing bars ф 12 including Off take Kg

1,951.77

50.00

97,588.50

2.1.6 Plasterig(1:2 ratio) m2

161.50

120.00

19,380.00

Total Carried to Summary for Bed Bar 543,481

2.2 Right Side Retaining Wall

2.2.1 Earth Excavation Ordinary Soil m3

650.00

45.00

29,250.00

2.2.2 Back fill m3

260.00

110.00

28,600.00

2.2.3 Masonry(1:3 ratio) m3

800.00

1,650.00

1,320,000.00

2.2.4 GABION m3

252.33

1,300.00

328,029.00

Total Carried to Summary for Right Side Retaining Work 1,705,879

2.3

Off take canal gate and installation, 4mm thickness

sheet metal, 40mmX30mmX4mm angle iron, ∅12mm

bar for anchorage square iron tube with 2mm thickness

No

1.00

13,994.15

13,994.15

Total Carried to Summary for Off take 13,994

Total Carried to Summary for Head Work 2,263,354

BILL 3. INFRASTRUCTURE

I.


Rate

(Birr)

Amount

(Birr)

3.1 Main Canal

Earthworks

3.1.1 Common Soil Excavation to a any depth including

haul to a distance not exceeding 200m. m

3 5775.49 45 259,897

3.1.2 Filling with selected material from excavated material

including compaction. m³ 921.20 110 101,332



Masonry Work 0

3.1.3

Basaltic or equivalent stone masonry canal wall

erection well bedded in cement sand mortar of 1:3 mix

ratio .The thickness of masonry wall will be as

indicated in the drawing. The work should be to the

satisfaction of the Engineer

m3 1612.56 1650.00 2,660,724

3.1.4 Internal plastering for the masonry wall m2 2805.92 120.00 336,710

Total Carried to Summary for Main Canal

3.2 Secondary Canal

Earthworks


haul to a distance not exceeding 200m. m

3 1377.00 45 61,965

3.2.2 Filling with selected material from excavated material

including compaction. m³ 921.20 110.00 101,332

Masonry Work

3.2.3






m3 956.77 1650.00 1,578,677


3.3 Turnout/ Division box 0

Concrete 0

3.3.1 Supply and cast lean concrete quality C-10 filled in to

formwork and vibrated. m³ 18.54 2100.00 38,929

Masonry Work 0

3.3.2

Basaltic or equivalent stone masonry retaining wall





m3 8.36 1650.00 13,794


3.3.4 40cm Cemented Stone Pitching as per the engineers

interest m

3 24.05 1200.00 28,858

Gate 0

3.3.5 15cm thick Precast concrete for Walk way, detail is

presented in the drawing m

2 152.60 400.00 61,040

3.3.6 Spindle for vertical lift and its handling Pcs 35.00 6000.00 210,000

3.3.7 Angle iron for shuttering and for stiffening m 24.66 800.00 19,728

3.3.8 Sheet metal 8mm thick m2 2.32 1000.00 2,320



3.4 Drop structure 0

Concrete 0

3.4.1 Supply and cast lean concrete quality C-10 filled in to

formwork and vibrated. m³ 3.79 2100.00 7,959

Masonry Work 0

3.4.2






m3 20.56 1650.00 33,924


3.4.4 40cm Cemented Stone Pitching as per the engineers

interest m

3 21.09 1200.00 25,308

Total Carried to Summary for Secondary Canals 0

3.5 Tertiary Canal Earthworks 0

3.5.1

Common Soil Excavation in trapezoidal Canal to a any

depth including haul to a distance not exceeding

200m.

m3 526.6 60 31,596

3.5.2

Filling with selected material from borrow pits

including compaction (hauling distance not exceeding

5km)

m³ 1294.7 110 142,421

Total Carried to Summary for Tertiary Canals 0

3.6 Flume 0


haul to a distance not exceeding 200m m3 48.0 45 2,160

Masonry Work 0

3.6.2






m3 24.0 1650 39,600

Concrete 0

3.6.3 Supply and cast mass concrete quality C-20 filled in to

formwork and vibrated. m3 20.3 2500 50,641

Reinforcement 0

3.6.4 dia 14 kg 219.8 50 10,991

3.6.5 dia 12 kg 225.4 50 11,270

Total Carried to Summary for Flume 0

3.7 Supper passage 0

Masonry Work 0



3.7.1






m3 41.0 1650 67,683

Concrete 0

3.7.2 Supply and cast Reinforced concrete quality C-20 filled

in to formwork and vibrated. m

3 16.4 2500 41,000

Reinforcement 0

3.7.3 dia 8 kg 129.3 50 6,466

3.7.4 dia 10 kg 279.5 50 13,976

Total Carried to Summary for Supper Passage 0

3.8 Road crossing 0

Masonry Work 0

3.8.1






m3 15.6 1650 25,740

3.8.2 Supply and instalation of precast Reinforced concrete

quality C-20 with dimenstion of 0.2m*1.2m*1.5m m

3 1.7 2500.66 4,251

Total Carried to Summary for Road Crossing 6,385,729

Total Carried to Summary for Infrastructure



Table 4-1: Hydraulic Parameters of Main Canal

CHANN

EL Area(ha) Chainage(m)

Q required

(m3/s) B(m) D(m) FB(m)

Adopted

depth(m) A(m2) P(m) R(m) Z S n V(m/s) Qdesign(m3/s)

MC-1

180 0+000-0+269 0.21 0.6 0.6 0.3 0.6 0.36 1.8 0.2 0 0.001 0.018 0.60 0.216

180 0+269+0+0+296 0.21 0.6 0.6 0.3 0.6 0.36 1.8 0.2 0 0.0013 0.018 0.67 0.242

180 0+296-0+428 0.21 0.4 0.4 0.3 0.4 0.40 1.84 0.22 1.5 0.0013 0.025 0.51 0.204

104.8 0+428-0+724 0.19 0.4 0.4 0.3 0.4 0.40 1.84 0.22 1.5 0.0013 0.025 0.51 0.204

104.8 0+724-0+774 0.19 0.4 0.4 0.3 0.4 0.40 1.84 0.22 1.5 0.0013 0.025 0.53 0.211

104.8 0+774-1+312 0.19 0.55 0.53 0.3 0.55 0.29 1.61 0.18 0 0.0013 0.018 0.65 0.189

98.1 1+312-1+448 0.17 0.55 0.53 0.3 0.55 0.29 1.61 0.18 0 0.0013 0.018 0.65 0.189

98.1 1+448-2+595 0.17 0.45 0.36 0.3 0.4 0.36 1.75 0.20 1.5 0.0013 0.025 0.51 0.180



4.3.2 Secondary Canals

Table 4-2: Hydraulic Parameters of secondary canals

Channel Area(ha) Chainage(m)

Q

required(m3/s) B(m) D(m) FB(m)

Adopted

B(m)

Adopted

D(m) A(m2) P(m) R(m) Z S n V(m/s) Qdesign(m3/s)

SC1-1 9.45

0+00-0+40

0.01673

0.2 0.1 0.3 0.3 0.1 0.02 0.4 0.1 0 0.01429 0.018 0.9012 0.018024

0+40-0+107 0.2 0.1 0.3 0.3 0.1 0.02 0.4 0.1 0 0.02273 0.018 1.14 0.022734

0+107-0+244 0.2 0.1 0.3 0.3 0.1 0.02 0.4 0.1 0 0.01961 0.018 1.06 0.021116

SC2-1

27.28 0+0-0+257 0.04829 0.2 0.15 0.3 0.3 0.15 0.03 0.5 0.1 0 0.03571 0.018 1.61 0.048273

18.57 0+257-0+323 0.03287 0.2 0.2 0.3 0.3 0.2 0.04 0.6 0.1 0 0.02041 0.018 1.30 0.052195

18.57 0+323-0+382 0.03287 0.3 0.25 0.4 0.3 0.25 0.075 0.8 0.1 0 0.02 0.018 1.62 0.121605

18.57 0+382-0+572 0.03287 0.2 0.15 0.3 0.3 0.15 0.03 0.5 0.1 0 0.04 0.018 1.70 0.051087

SC3-1

71.6 0+00-0+290 0.12673 0.25 0.21 0.3 0.3 0.2 0.0525 0.67 0.1 0 0.05556 0.018 2.40 0.125885

62.5 0+290-0+410 0.11063 0.25 0.25 0.3 0.3 0.25 0.0625 0.75 0.1 0 0.03846 0.018 2.08 0.129917

50.63 0+410-0+560 0.08962 0.3 0.2 0.3 0.3 0.3 0.06 0.7 0.1 0 0.0303 0.018 1.88 0.112804

36.35 0+560-0+620 0.05016 0.3 0.2 0.3 0.3 0.3 0.06 0.7 0.1 0 0.04 0.018 2.16 0.129602

18.23 0+620-873 0.02516 0.25 0.21 0.3 0.3 0.25 0.0525 0.67 0.1 0 0.04 0.018 2.03 0.106817



4.3.3 Tertiary canals

In the layout system there are 19 tertiary canals, the designed discharge is determined based on the duty of irrigation. The sections of the canals are

determined by using manning’s formula, and they are trapezoidal section. The hydraulic characteristics is Presented in Table 4.3 below.

Figure 4-1: Typical Cross Section of tertiary canals

Table 4-3: Hydraulic Parameters of Tertiary Canals

Area(ha) Chainage(m)

Q

required(m3/s) B(m) D(m)

Adopted

B(m) FB(m) A(m2) P(m) R(m) Z S n V(m/s) Qdesign(m3/s)

TC1R-1-1 2.63 0+00-0+302 0.004655 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.002353 0.025 0.3 0.010688

TC1L-1-1 2.58 0+00-0+56 0.004567 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.003333 0.025 0.4 0.012721

TC2R-1-1 0.72 0+00-0+138 0.001274 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.003333 0.025 0.4 0.012721

TC2L-1-1 2.02 0+00-0+145 0.003575 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.0025 0.025 0.3 0.011017

TC1R-2-1 3.77 0+00-0+245 0.006673 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.003333 0.025 0.4 0.012721

TC1L-2-1 3.56 0+00-0+96 0.006301 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.002857 0.025 0.3 0.011778

TC2R-2-1 6.58 0+00-0+246 0.011647 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.003333 0.025 0.4 0.012721

TC2L-1-1 4.66 0+00-0+275 0.008248 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.003333 0.025 0.4 0.012721

TC3L-2-1 3.53 0+00-0+94 0.006248 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.003333 0.025 0.4 0.012721



Area(ha) Chainage(m)

Q

required(m3/s) B(m) D(m)

Adopted

B(m) FB(m) A(m2) P(m) R(m) Z S n V(m/s) Qdesign(m3/s)

TC3R-2-1 4.77 0+00-0+217 0.008443 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.003175 0.025 0.4 0.012415

TC1R-3-1

4.88 0+00-0+80 0.008638 0.2 0.2 0.3 0.3 0.1 0.9 0.1 1.5 0.001333 0.025 0.3 0.03324

4.64 0+80-0+229 0.008213 0.2 0.1 0.3 0.3 0.035 0.6 0.1 1.5 0.002222 0.025 0.3 0.010387

TC1L-3-1 4.57 0+00-0+213 0.008089 0.25 0.2 0.3 0.3 0.11 1.0 0.1 1.5 0.001 0.025 0.3 0.032574

TC2R-3-1

6.92 0+00-0+180 0.012248 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.001538 0.025 0.3 0.019495

6 0+180-0+338 0.01062 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.002 0.025 0.3 0.022228

TC2L-3-1

4.6 0+00-0+100 0.008142 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.003333 0.025 0.5 0.028696

3 0+100-0+249 0.00531 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.002857 0.025 0.4 0.026567

TC3R-3-1

9.45 0+00-0+217 0.016727 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.003333 0.025 0.5 0.028696

8.12 0+217-0+260 0.014372 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.002222 0.025 0.4 0.02343

6.34 0+260-0+418 0.011222 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.003333 0.025 0.5 0.028696

TC3L3-1 4.83 0+00-0+195 0.008549 0.25 0.2 0.3 0.3 0.11 1.0 0.1 1.5 0.001176 0.025 0.3 0.035331

TC4R-3-1

9.23 0+00-0+124 0.016337 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.00125 0.025 0.3 0.017573

7.06 0+124-0+191 0.012496 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.003333 0.025 0.5 0.028696

6.21 0+191-0+353 0.010992 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.001818 0.025 0.3 0.021193

5.74 0+353-0+502 0.01016 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.0025 0.025 0.4 0.024851

TC4L-3-1 8.39 0+00-0+390 0.01485 0.2 0.2 0.3 0.3 0.06375 0.7 0.1 1.5 0.001538 0.025 0.3 0.019495

TC5L-3-1

14.41 0+00-0+426 0.025506 0.2 0.2 0.3 0.3 0.1 0.9 0.1 1.5 0.001176 0.025 0.3 0.031223

6 0+426-0+605 0.01062 0.2 0.2 0.3 0.3 0.1 0.9 0.1 1.5 0.001538 0.025 0.4 0.035705



4.3.4 Design of Division box

At different points of the main and secondary canals division boxes are provided which divert the flow to the

secondary canal and tertiary canals. Gate should be provided at the outlet of the boxes. For detail refer the

drawing.

Figure 4-2: Typical Division Box plan

Using broad crested formula,

Q= CL (h)3/2

Where; Q= discharge over rectangular intake (opening), m3/s

C = discharge coefficient, c= 1.7

L= effective length of crest form in m

h= over flow depth, m

Assuming equal discharge coefficient & sill height for two or three dividing canals, the proportion becomes.

Q1/ Q2= Q2/ Q3 =L1/ L2 = L2/ L3



Where Q1= is flow in canal 1

Q2 = is flow in canal 2

Q3 = is flow in canal 3

L1= is effective crest length of intake sill across opening to canal 1

L2= is effective crest length of intake sill across opening to canal 2

L3 = is effective crest length of intake sill across opening to canal 3

Q1= CL1 (h) 3/2

,

L1 = Q1/Ch3/2

L2 = L1*Q2/ Q1

L3 = L1*Q3/ Q1

The depth of (height of) the division box,

D = d + fb

The width of the division box,

B = b + 2*m*D

D = total canal depth of the incoming canal

B =Width of Incoming Canal



Table 4-4: Hydraulic Parameters of Division Boxes

Canal

name

Chai

nage

Q00

((LL//

ss))

Q11

((LL//ss))

Q22

((LL//ss

))

Q33

((LL//ss))

B,

m d(m) D ((dd++ffbb))

L,

m W00,, mm W11,, mm

W22,,

mm W33,, mm H0 H1 H2 H3 Hs1 Hs2 Hs3

L0,

m

L1,

m

L2,

m

L3,

m

DV1-1 0+458

20

4 204 17 0 0.4 0.4 0.7 1.80 0.50 0.50 0.30 0.00 0.40 0.39 0.10 0.00 0.01 0.30 0.00 1.30 1.30 1.10 0.00

DV2-1-1 1+936

18

1 181 48 0 0.45 0.4 0.7 1.85 0.50 0.50 0.30 0.00 0.40 0.36 0.21 0.00 0.04 0.19 0.00 1.30 1.30 1.10 0.00

DV3-1-1 2+591

18

0 0 130 0 0.45 0.4 0.7 1.85 0.50 0.00 0.40 0.00 0.40 0.00 0.33 0.00 0.00 0.07 0.00 1.30 0.00 1.20 0.00

DV1-1-1 0+20 17 17 0 13 0.3 0.1 0.4 1.10 0.40 0.40 0.00 0.30 0.10 0.08 0.00 0.09 0.02 0.00 0.01 1.20 1.20 0.00 1.10

DV2-1-1 0+40 17 17 10 0 0.3 0.1 0.4 1.10 0.40 0.40 0.30 0.00 0.10 0.08 0.07 0.00 0.02 0.03 0.00 1.20 1.20 1.10 0.00

DV3-1-1 0+234 21 21 11 12.7 0.3 0.1 0.4 1.10 0.40 0.40 0.30 0.30 0.10 0.10 0.08 0.09 0.00 0.02 0.01 1.20 1.20 1.10 1.10

DV1-2-1 0+30 48 48 13 11.7 0.3 0.15 0.45 1.20 0.50 0.50 0.30 0.30 0.15 0.15 0.09 0.08 0.00 0.06 0.07 1.30 1.30 1.10 1.10

DV2-2-1 0+246 48 48 13 12.7 0.3 0.15 0.45 1.20 0.50 0.50 0.30 0.30 0.15 0.15 0.09 0.09 0.00 0.06 0.06 1.30 1.30 1.10 1.10

DV3-2-1 0+429 51 51 13 0 0.3 0.15 0.45 1.20 0.60 0.60 0.30 0.00 0.15 0.14 0.09 0.00 0.01 0.06 0.00 1.40 1.40 1.10 0.00

DV4-2-1 0+572 51 0 0 12.7 0.3 0.15 0.45 1.20 0.60 0.00 0.00 0.30 0.15 0.00 0.00 0.09 0.00 0.00 0.06 1.40 0.00 0.00 1.10

DV1-3-1 0+10

13

0 130 33 10 0.3 0.2 0.5 1.30 0.90 0.90 0.30 0.30 0.20 0.19 0.16 0.07 0.01 0.04 0.13 1.70 1.70 1.10 1.10

DV2-3-1 0+190

13

0 130 29 19.5 0.3 0.2 0.5 1.30 0.90 0.90 0.30 0.30 0.20 0.19 0.15 0.11 0.01 0.05 0.09 1.70 1.70 1.10 1.10

DV3-3-1 0+410

13

0 110 35 28.7 0.3 0.25 0.55 1.40 0.70 0.60 0.30 0.30 0.25 0.23 0.17 0.15 0.02 0.08 0.10 1.50 1.40 1.10 1.10

DV4-3-1 0+690

11

0 110 20 17.6 0.3 0.2 0.5 1.30 0.80 0.80 0.30 0.30 0.20 0.19 0.11 0.11 0.01 0.09 0.09 1.60 1.60 1.10 1.10

DV5-3-1 0+860

11

0 110 0 31 0.3 0.2 0.5 1.30 0.80 0.80 0.00 0.30 0.20 0.19 0.00 0.15 0.01 0.00 0.05 1.60 1.60 0.00 1.10



4.3.5 Road Crossing Structure

Three road crossing structures are provided on the main canal, at the Chainage of 157m, 0+874,

1158m,1588, 2+076 and 2802m. The road crossing structures are rectangular reinforced concrete slab. The

slab is reinforced with 12mm @ 200mmc/c the length of the slab is 4m which is the same as the respective

canal bed width, its width and thickness is 1.2m and 15mm respectively.

4.3.6 Drop structure

The drops are provided at places where the ground slope is steeper than the canal bed slopes. For irrigation

canals, vertical drop structure of U.S.B R type standard is selected to convey water from higher to lower

elevation of the ground. The design procedures are shown below:

a. Critical hydraulic

Design discharge, Q (m3/s)

Height of drop, h (m)

Width of drop, bc = )(

734.02/3

md

Q

Where d = water depth of the canal, m

Critical discharge, q = Q/bc

Critical depth, dc =

3/12

g

q

Lip height, a = dc/2, a 0.15

b. Stilling basin

Basin width, B =

mQ

Q,

91.9

46.18

Basin length, L =

mhdch

dc

h

dc,7.0

1.15.2

3



The standard drawing for all the drops to be constructed is found in the irrigation infrastructure drawings on

which the above parameters are used to code each of the dimensions of the drops.

All the hydraulic parameters computed using the above procedures with the type of canals are shown



Table 4-5: Drop Hydraulic Design

Canal

name

Chainage

(m)

D1,

(m)

b,

m

Q

(m3/sec)

h,

m bc, m

q

(m3/s/m) dc, m a, m L, m B, m

Lup

(m)

Head Above

Crest, m

Ldp

(m)

Dc U/s,

m

Dc

D/s,

m

tb, m tp, m PW1,

m

PW2,

m

SC2-1 0+200 0.45 0.30 0.048 0.60 0.30 0.16 0.14 0.15 0.79 0.41 0.45 0.11 3.00 0.30 0.30 0.40 0.30 0.45 0.45

SC3-1 0+30 0.50 0.30 0.130 0.90 0.30 0.43 0.27 0.15 1.40 0.66 0.50 0.15 3.00 0.30 0.30 0.40 0.30 0.50 0.50

TC3R-3-1 0+217 0.45 0.30 0.029 0.60 0.30 2.00 0.74 0.37 3.46 1.36 0.45 0.22 3.00 0.30 0.30 0.40 0.30 0.45 0.45

TC1L-3-1 0+00 0.45 0.30 0.011 0.30 0.30 1.00 0.47 0.23 2.57 0.99 0.45 0.17 3.00 0.30 0.30 0.40 0.30 0.45 0.45

TC2L-2-1

TC3R-2-1

0+00 0.40 0.30 0.012 0.30 0.30 1.00 0.47 0.23 2.57 0.99 0.40 0.17 3.00 0.30 0.30 0.40 0.30 0.40 0.40

0+00 0.40 0.30 0.012 0.55 0.30 1.83 0.70 0.35 3.31 1.31 0.40 0.21 3.00 0.30 0.30 0.40 0.30 0.40 0.40

TC1L-1-1 0+00 0.40 0.30 0.012 0.70 0.30 0.04 0.05 0.15 0.51 0.30 0.40 0.07 3.00 0.30 0.30 0.40 0.30 0.40 0.40

TC2L-1-1 0+00 0.40 0.30 0.011 0.65 0.30 0.04 0.05 0.15 0.47 0.30 0.40 0.06 3.00 0.30 0.30 0.40 0.30 0.40 0.40

4.3.7 Design of a Typical Flume

Hydraulic Characteristics of the canal

Length of the flume: 40m

Shape of the flume: Regetangular, Roughness coefficient, n = 0.018

From the canal longitudinal profiles, u/s canal bed level (CBL) = 1989.998

D/s Canal bed level (CBL) =1989.66



Table 4-6: Hydraulic Parameters of Flume

Section Location Water depth (m) Change in water level

Elevation of

Canal

bed

Water

surface

A u/s canal 0.36 - - 1989.998 1990.358

B Flume 0.71 drop 0.000 1989.652 1990.358

C Flume 0.71 drop 0.032 1989.620 1990.326

D d/s canal 0.36 rise 0.000 1989.966 1990.326

4.3.8 Drainage System

The drainage system is provided for effective disposal of excess irrigation water and runoff from the

irrigation field during rainy season.

Field drains and catch drain collect from each field units and catchment above the canals will be conveyed

with drainage crossing structure and directly discharge into the river and natural Drainage system.



5 SOURCES OF CONSTRUCTION MATERIALS

During site investigation, natural construction materials required for the construction of the various proposed

engineering structures at the headwork and within the farmland have been assessed, and possible quarry sites

and borrow areas have been identified within the visited of the study area as close to the project site as

possible. In addition to identifying the quality, quantity and accessibility conditions of the construction

materials, ownerships of each proposed production sites have also been studied and described in this report,

on separate sub-sections below. The materials needed for the construction of the structures include rock for

masonry stones, aggregates (both coarse and fine), and water.

5.1 Rock for Masonry and Crushed Coarse Aggregate

During site investigation rocks required for masonry works were identified Masonry stones are highly

required during construction of the project for headwork structure, main canal route structure, cross drainage

structure, and for many other purposes. The aggregates are another required construction material found

during in the construction of the project. The aggregates required for constructions of the project in concrete

work are fine aggregate and coarse aggregate that is sands and crushed stones respectively. Rocks use as

masonry works incorporated in the engineering design and found near the command area at location of

383910E, 1355479N and at elevation of 2014m above sea level near mountain ridges (BOSSENA mender).

In the past time the contractors used this rock for construction of the weir and river bed is additional

construction source, but the rocks occurred as boulders and cobble size. The rock type that exists in the

production quarry site is fine grained volcanic rock within higher quality and the abundance is more than

required amount for both masonry and coarse aggregate and which has 2km distance from headwork site.

The productive quarry sites have no ownerships and accessible in dry season and also which is out of

farmland area.

5.2 Fine Aggregates

Borrow areas for fine aggregate or natural sand have been assessed starting from the project stream itself.

Natural deposits of such materials are during construction process, natural fine aggregate is required for

concrete works and accessing this material in the surrounding area is another issue in the study. Natural

deposits of these materials are found within the beds of MENNA DAWOCH stream itself and the quantity of

sand is more than required amount. The sand deposits are higher in both the upstream and downstream

direction from headwork site and this natural deposit is used by local people for construction purpose in the

surrounding. But the sand source until this study is not used by local contractors due to accessibility problem



of the area. Both visual investigation and laboratory testing of the sand deposits that are found in the

proposed area have been done. The secondary source also found nearby stream called Menna (megenagna)

River and natural deposit of this sand is used by local contractors and also far from project area by 22km

distance towards word town called Arbaya. For secondary sand source area also visual investigation and

laboratory test have been done

The laboratory tests of the sand deposits that are found in the Menna_Dawch and Menna River have been

done. To characterize the gradation of the deposit, a sample has been taken for laboratory testing (especially

for gradation test) the sand deposit from Menna_Dawch River itself has the following gradation:

Gravel (>4.75) = 37.15 %

Coarse Sand (4.75-0.425mm) = 40.25%

Fine Sand (0.425-0.075mm) =16.67%

Silt and Clay (<0.075mm) =5.93%

And the secondary sand source (Menna river locally megenagna river) laboratory result also has the

following gradation:

Gravel (>4.75mm) =26.90%

Coarse sand (4.75-0.425mm) =31.11%

Fine sand (0.425-0.075mm) = 38.01 %

Silt and Clay (<0.075mm) =3.99%

From observation the percentage of fines (Silt and clay) and gravel is higher, because the sample is taken by

local contractors repeatedly so that the sand deposit should be washed before using for construction to

remove fines and in addition, the amount of oversize grains (gravels) are also considerable and sieving with

sieve opening of about 4.75 to 5mm is required.

5.3 Water

Water for construction purposes can be found from the project stream Menna River itself. The stream is

perennial throughout the year that there is some amount of flow along its course. During this field time the

stream flow was more than 280L/second.



6 OPERATION AND MAINTENANCE

6.1 General

The main objective of the operation and maintenance aspect of an irrigation scheme is to facilitate

the timely delivery of the required irrigation water to farms and to keep the irrigation system in an

optimum operating condition. This section therefore, discusses the main functions of the subject

matter under consideration for the scheme.

6.2 Operation of the Head Works

Operation at the intake mainly focuses on the diversion of a controlled flow of river water, timely

cleaning of floating debris in front of intake and removal of sediment deposits in front of the intake.

6.3 Irrigation System Operation

The operation of the irrigation system depends mainly on the method of water delivery at farm level.

Surface irrigation method is the recommended type of water distribution and application method for

Menna_Dawch intake irrigation scheme.

The farmers would organize themselves and form groups in order to handle the water Management. Since

flow is low Rotational water distribution would be applied within the group. The rotational distribution is

then to distribute water by turn to the whole scheme according to the timely need of crop water requirement.

For better and efficient water Management, crop diversification should be avoided within a group. This

would reduce the complexity of water distribution system of the scheme during one irrigation season. At

farmers’ level of operation, a constant flow and variable irrigation time is advisable.

The operation of the irrigation system is continuous for 20 hours per day in main, secondary and tertiary

canals whereas field canals within a tertiary block are operating in rotational system with each other for

irrigation hours proportional to their size. Since the tertiary canal discharges are within the Manageable

range and the irrigation canal structures are accordingly designed for simple operation, the farmers can open

and close easily whenever they required.

6.4 Maintenance Requirement

The canal system of the project is earthen canal except main canal and secondary canal, which is susceptible

to siltation, erosion, growth of weeds and or breaching problems. Though the canal sections are designed for



non- silting and non-scouring conditions, the above mentioned problems are unavoidable and hence

periodical and yearly inspection and maintenance of canals and structures are obligatory in order to fulfill the

design objective of the project area.

The maintenance tasks are categorized into two types: - routine activities, and repairs. The routine

maintenance activities that are carried out periodically include:-

Regular cleaning of sediments and weeds from canals and drains;

Inspection and lubrication of gates; and

Maintenance of cracked lined canals, regulating and control structures.

Repair works include task carried out more frequently and quickly, and include those tasks that are generally

unpredictable. They also include emergency works. The activities included in this category are:-

Repairing overtopped or breached canals, drains, and flood protection dykes;

Repairing jammed gates;

Filling holes made by wild animals; and

Reduced free board due to walking over by people and livestock.

Regular inspection of the irrigation facilities should be carried out as part of the maintenance activities.

These tasks could be carried out immediately after the end of the main rains in September and during the

rainy season. This could concentrate on the interceptor drains and the flood protection dykes, the main

canal and the field drains. The inspection of the other works like the tertiary canals, field drains, and the

water control and regulating structures could be carried out as part of routine operation activities.

Beneficiaries of the project need to have operation and maintenance budget, For O&M cost incurring

entity area:

Purchase sing of gate lubricate (grease)

Replacing and maintenance of Stolen and damaged gates

Repair Damages on the cross drainage structures.

The expense for O&M should be collected from the beneficiaries. Of course, much of the task is done by the

labor and skill of the community. For cost incurring activities beneficiaries have to collect money based on

the proportion of the command area they owned.



7 CONCLUSION AND RECOMMENDATION

The infrastructure of this project area is designed to irrigate about 180 ha of land by taking its supply

from the Menna_Dawch intake irrigation project. The maximum duty of the command area for 1.22

hours per day irrigation with overall project efficiency of46%. The method of irrigation of the

project area is furrow surface irrigation in which the main and secondary canals are working

continuously whereas the field canals within a tertiary block are working rotational system.

As the dominant soil type is black cotton, silt clay and clay soil, the main canal system is designed

both earthen and masonry

Secondary canals, one, two and three are earthen. But, secondary canal four is lined.

The design of the canal dimensions of the irrigation canal is done by applying the manning’s uniform

flow equation. The variable of the hydraulic parameters are calculated using iteration or flow master

program.

The following recommendations are drown:

1. For better performance and long service year of the project regular inspection and maintenance

is highly required.

2. Farmers training, how to operate and maintain the project structures as a whole and available

and water resources has a paramount important.

3. The irrigation hours per day and per week should be flexible based on base flow amount of each

week or month.

4. Close supervision of the construction should be made to modify (if need be) each Components

of irrigation system based on specific site conditions.



8 REFERENCE

1. FAO (1977) guidelines for predicting crop water requirements. No 24, Rome Italy

2. Applied Hydrology (1988) by Von Tec how David R. Maidment and Larry w.

3. Design of small Canal structures , USBR

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