Various causes for the reservoir sedimentation
1. Nature of soil in the catchment area
If the soil is sandy, loose and easily erodible, the river will have a large amount of sediments.
2. The topography of the catchment area
In case of catchments having steep slopes, the sediment load is large because of high velocity of flow of water.
3. Vegetation cover in catchment area
The catchment areas having poor or practically no vegetation cover will be more easily eroded and hence rivers having such catchment areas will carry more sediment.
4. Intensity of rainfall in catchment area
If the intensity of rainfall is higher the total runoff will be more so the sediment carrying capacity will be more and so the sediments in the stream will be more.
Control of the reservoir sedimentation
1. Proper selection of reservoir site
The reservoir site should be so located that the sediment inflow is low. The reservoir should not be built on the downstream of the confluence of a tributary carrying a large quantity of sediment.
2. Proper reservoir design
A reservoir of a small capacity on a river which has larger inflow rate will have lesser sedimentation than a larger size reservoir on the same river. So, if the capacity of the reservoir is increased in stages, the sedimentation proportion will be reduced.
3. Control of sediment inflow
The inflow of sediments in the reservoir can be controlled by constructing check dams and by providing vegetation cover over the catchment area. These will decrease the soil erosion and hence sediment inflow is reduced.
4. Control of sediment deposit
The sediment deposit in the reservoir can be controlled by designing and operating outlets in a dam and by proper operation of the gates of scouring sluices and the head regulators of the canals etc.
5. Removal of sediment deposits
The sediments which have been already deposited in a reservoir can be removed by excavation or by scouring through sluices. Both the methods are costly and need have some structural changes.
6. Control of erosion in the catchment area
For erosion control methods commonly used are terraces, strips cropping and contour farming. These methods reduce the velocity of flow of water and hence erosion. Other methods used are afforestation, control of deforestation, control of cultivation, regrassing, control of grazing etc.
