National Hydrology committee of National Hydrology committee of Afghanistan (NHCA)Afghanistan (NHCA)

Sedimentation in Sedimentation in ReservoireReservoireOCt.2007OCt.2007

Prof. Mohammad Prof. Mohammad QasemQasem SeddeqySeddeqy KPUKPU

بسم اهللا الرحمن الرحيمبسم اهللا الرحمن الرحيم

وجعلنامن الماءکل شئء حیوجعلنامن الماءکل شئء حی

3030واز آب هر چيزی رازنده گردانيدیم سوره انبيا ایه واز آب هر چيزی رازنده گردانيدیم سوره انبيا ایه

Classification of Rivers Classification of Rivers accordingaccording to to the topography of the river basinthe topography of the river basin

Upper reaches in the hilly regionUpper reaches in the hilly regionLower reaches in the alluvial plainLower reaches in the alluvial plain

Rivers on alluvial plains may be broadly classified in Rivers on alluvial plains may be broadly classified in to three types:to three types:

1.1. The meandering typeThe meandering type2.2. The aggrading typeThe aggrading type3.3. The degrading typeThe degrading type

Sediment is fragmental material, Sediment is fragmental material, primarily formed by the physical primarily formed by the physical and chemical disintegration of and chemical disintegration of rocks from the earth crust.rocks from the earth crust.

The process of moving and The process of moving and removing from their original removing from their original source or resting place is called source or resting place is called erosionerosion

Why a good understanding of sediment Why a good understanding of sediment transport processes is indispensabletransport processes is indispensable

1.1. Morphological boundary condition for Morphological boundary condition for design of Hydraulic structure and river design of Hydraulic structure and river training workstraining works

2.2. Sedimentation in reservoirsSedimentation in reservoirs3.3. Sediment problems at IntakesSediment problems at Intakes4.4. Environmental Impact assessment Environmental Impact assessment

Origin and types of SedimentOrigin and types of Sediment

Cohesive Cohesive Non Cohesive Non Cohesive

Cohesive sediment Cohesive sediment –– the physicalthe physical-- chemical chemical interaction between particles plays a interaction between particles plays a significant role.significant role.

Non Cohesive sediment Non Cohesive sediment –– there is no there is no physical and chemical interaction between physical and chemical interaction between individual particles .individual particles .

Sediment Control PlanSediment Control Plan

E=(Q+A E=(Q+A -- B)(1 B)(1 --αα）） -- C C -- DD

Q

E

AB

（Q+A-B)*α

C D

Control Point

Target Area

Sediment Control PlanSediment Control Plan

E=(Q+A E=(Q+A -- B)(1 B)(1 --αα）） -- C C -- DDEE : Design allowable sediment discharge: Design allowable sediment dischargeQ : Design sediment discharge at the design Q : Design sediment discharge at the design

control point of the upstream end of the control point of the upstream end of the subject subsubject sub--basinbasin

AA : Design sediment production: Design sediment productionBB : Design reduction of sediment production: Design reduction of sediment productionαα : Ratio of volume of channel sediment : Ratio of volume of channel sediment

mitigation mitigation CC : Design reduction of sediment discharge: Design reduction of sediment dischargeDD : Design mitigation volume of sediment : Design mitigation volume of sediment

dischargedischarge

Sediment Control DamSediment Control DamFunction 1:Function 1: To Stabilize To Stabilize Hillside Slopes Hillside Slopes Scouring force

becomes less than before；Shallower in depth, Slower in velocity

Sediment Control DamSediment Control DamFunction 1 To Reduce Sediment Function 1 To Reduce Sediment DischargeDischarge

Initial Sediment Capacity

Sediment Capacity for Flood Period

Sediment Control DamSediment Control DamFunction 2: To Mitigate Streambed Function 2: To Mitigate Streambed Erosion by milder bedErosion by milder bed--slope with slope with Stepwise DamsStepwise Dams

1n

1m

h

L

m>n

L=((m*n)/(m - n))*h

Sediment Control DamSediment Control DamFunction 3: To Mitigate Sediment Function 3: To Mitigate Sediment RunoffRunoff

Unstable Sediment Deposition

Design Sedimentation Line to Cover the Unstable Sediment Deposition

3D VIEW OF KABUL RIVER BASIN

Oulet basin

KabulNaghlu

dam

3D View of Alingar River Basin

DaruntaDam

Other view from agriculture land of Gulbahar –Panjsheer desert

3D view of Sorobi and Nagludams

Naghlu dam

Sorobidam

3D View of from Kunar River

Kunar river

Daruntadam

Pakistan

satalite Landsat 7 Date : 2002-09-22

3D View of Darunta Dam

Daruntadam

3D View of Panjsheer river Basin

Gulbahardesert

Daruntadam

Naghludam

Darunta Reservoir 24 years ago

satalite Landsat 3 Date : 1979-06-20

••SedimentationSedimentationIntensive soil erosion has been causing Intensive soil erosion has been causing rapid sedimentation of reservoirs with rapid sedimentation of reservoirs with an important loss of irrigation lands, an important loss of irrigation lands, power generation capacity and life time power generation capacity and life time of reservoirsof reservoirs

AfganistanAfganistan is facing annually with 150 is facing annually with 150 million m3 sedimentation in the million m3 sedimentation in the reservoirs and 400 million m3 reservoirs and 400 million m3 sedimentation to downstream of dam sedimentation to downstream of dam reservoirs and irrigation networksreservoirs and irrigation networks

Causes of sedimentationCauses of sedimentationDesertificationDesertification

1.1. Continued deforestation from logging and fuel wood needs : In Continued deforestation from logging and fuel wood needs : In South,eastSouth,east and northeast of Afghanistan.and northeast of Afghanistan.

2.2. overgrazing:Theovergrazing:The grazing lands used by grazing lands used by KochisKochis ((nomads)havenomads)havebeen dried out due to the lack of sufficient rainfalls & convertbeen dried out due to the lack of sufficient rainfalls & converting to ing to cultivable land causing considerable reduction in livestock and cultivable land causing considerable reduction in livestock and livelihood.livelihood.

3.3. Destroying land covers bush used for fuel woodDestroying land covers bush used for fuel wood4.4. Soil erosion due to flood and wind Soil erosion due to flood and wind 5.5. Unsustainable agriculture :Unsustainable agriculture :SalinizationSalinization of soil ,over use of of soil ,over use of

agricultural inputs.agricultural inputs.6.6. Drought :Started in 1969,getting up to a critical status in 1997Drought :Started in 1969,getting up to a critical status in 1997--

2002 ,causing hydrological circulations of the soil 2002 ,causing hydrological circulations of the soil

Lack of river Lack of river mangementmangement and training workand training workLand useLand usesteep drainage basin slopes and reliefsteep drainage basin slopes and reliefhigh rainfall magnitudes and frequencieshigh rainfall magnitudes and frequenciesLack of Reservoir maintenance Lack of Reservoir maintenance

Extensive Extensive destruction of destruction of forest over the forest over the past 25 yearspast 25 years

Sedimentation and erosion Sedimentation and erosion problems affect the following problems affect the following

sectors.sectors.Health(drinkingHealth(drinking water , domestic )water , domestic )Society Society Economy(Economy(WaterWatersupply,Irrigation,Hydropower,Maintenancesupply,Irrigation,Hydropower,Maintenanceand operation of and operation of Reservoir,Reservoir,NavigationNavigation,,FloodFloodProtectionProtection,,FisheryFishery ))Environment Environment

Flash flooding is a direct Flash flooding is a direct consequence of land cover consequence of land cover degradation in Balkh river degradation in Balkh river

26 March, 200326 March, 2003

Sediment deposition into reservoirs Sediment deposition into reservoirs has several major detrimental has several major detrimental

effects. effects. Loss of storage capacity.Loss of storage capacity.Damage to or impairment of hydro equipment.Damage to or impairment of hydro equipment.Bank erosion and instabilities.Bank erosion and instabilities.Downstream channel modification. Downstream channel modification. Reduced downstream suspended sediment load.Reduced downstream suspended sediment load.Upstream aggradations.Upstream aggradations.Effect on water quality. Effect on water quality. Effect on waste assimilation. Effect on waste assimilation. Effect on navigation and recreation. Effect on navigation and recreation. Effect on aquatic life. Effect on aquatic life.

For urgently For urgently Dredging, Sub cut, empty washingDredging, Sub cut, empty washingReforestation and plantation for land covering long termReforestation and plantation for land covering long termPreparation of National Strategy and policy for Preparation of National Strategy and policy for erosion and sediment mitigation.erosion and sediment mitigation.Use water resource potential in the country through Use water resource potential in the country through rain and flood water harvesting, construction of rain and flood water harvesting, construction of small, medium, and large depressions, pools and small, medium, and large depressions, pools and dams for flood control and prevention of erosion .dams for flood control and prevention of erosion .Construction of protective structures along river Construction of protective structures along river where sliding may occur.where sliding may occur.

Plans for mitigation of erosion and Plans for mitigation of erosion and sedimentation sedimentation

Immediate ResponseImmediate ResponseGood river management :includes sediment and Good river management :includes sediment and floodplain management floodplain management National Emergency Employment Program, National Emergency Employment Program, National Solidarity Program and National National Solidarity Program and National Hydrology program of Afghanistan (NHCA), Hydrology program of Afghanistan (NHCA), Based Development program and other Based Development program and other Nationwide programs are contributing to Erosion Nationwide programs are contributing to Erosion and sedimentation reliefand sedimentation reliefEmergency Rehabilitation Irrigation Project Emergency Rehabilitation Irrigation Project (Hydraulic structures)(Hydraulic structures)Intermittent meetings by UN and Governmental Intermittent meetings by UN and Governmental and welland well--known nonknown non--Governmental Agencies for Governmental Agencies for assessing response and coordination regarding assessing response and coordination regarding erosion and sedimentation management and erosion and sedimentation management and capacity Buildingcapacity Building

conclusionconclusionThe principal reservoirs of Afghanistan are rapidly losing theirThe principal reservoirs of Afghanistan are rapidly losing theirstorage capacity and day by day exacerbated because of high ratestorage capacity and day by day exacerbated because of high rates s of sediment influx and accumulation.of sediment influx and accumulation.The factors that promote sedimentation in the reservoirs includeThe factors that promote sedimentation in the reservoirs includeland use, steep drainage basin slopes and relief, and most land use, steep drainage basin slopes and relief, and most importantly, high rainfall magnitudes and frequencies and lack oimportantly, high rainfall magnitudes and frequencies and lack of f maintenance due to prolong war.maintenance due to prolong war.connecting reservoirs at high elevations with those at lower connecting reservoirs at high elevations with those at lower elevations, results in an increased drainage area and available elevations, results in an increased drainage area and available water.water. As the upstream reservoirs fill with sediment, however, the As the upstream reservoirs fill with sediment, however, the bottoms reach the outlet structures and sediment is bypassed intbottoms reach the outlet structures and sediment is bypassed into o the lower reservoirs, accelerating the sedimentation rates in ththe lower reservoirs, accelerating the sedimentation rates in these ese impoundments.impoundments.

Reservoirs with small drainage areas loss Reservoirs with small drainage areas loss storage capacity at a faster rate than storage capacity at a faster rate than reservoirs with larger basins, especially in reservoirs with larger basins, especially in developed basins.developed basins.In reservoirs with large basins In reservoirs with large basins however,intensehowever,intense rainfall in a short period rainfall in a short period can transport large amounts of sediment can transport large amounts of sediment into the reservoirs, rapidly depleting their into the reservoirs, rapidly depleting their storage capacity.storage capacity.

Efforts to significantly increase the overall Efforts to significantly increase the overall water resources by simply building more water resources by simply building more dams over time , is proving to be dams over time , is proving to be ineffective ineffective on a long-term basis.

Thank you for attentionThank you for attention