Table of Contents
EFFECTS OF CONSTRUCTION OF DIVERSION HEADWORKS ON THE BEHAVIOUR OF RIVERS
Following are the changes that take place in the behavior of the river after the construction of a diversion headworks.
- The silt carrying capacity of river is decreased because heading up of water
- causes flattening of the surface slope on the U/S side of the weir.
- Because of reduction in silt carrying capacity, the pond formed on U/S side starts silting.
- Because of silting on U/S side, the water passing D/S of the weir contains less amount of silt.
- To make up for the deficiency of the silt, the D/S flowing water starts scouring the bed and banks.
- The scouring may lead to undermining the stability of the weir.
- Because of silting of the pond, the afflux goes on increasing and thus more and more areas on U/S are submerged.
- At last, a stage is reached when no more silt is deposited and the normal silt charge is passed on to the D/S side.
- Devices like silt excluder also discharge more silt D/S.
- The silt discharge D/S is more than the silt carrying capacity at low discharges.
- This will cause silting D/S side. In other words where scouring was taking place in the initial stages, silting will start. This process is known as recovery process of D/S bed levels.
- The recovery of levels on D/S, may lead to loss of control on silt excluding devices.
- Because of this, sufficient margin should be left between F.S.L. of a canal and the pond level so that if need be, the crest level of the head regulator could be raised later.