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.
silt extractor
silt extractor
  • 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.