• All the waters entering the reservoir carry some amount of silt.
  • The amount of silt in the water coming into the reservoir depends upon the topography, nature of the soil, vegetation cover over the catchment, and also upon the intensity of rainfall.
  • If soil in the catchment is soft there is always possibility of sheet erosion and amount of silt in the water coming to reservoir will be more.
  • If catchment has large slope, it will cause rain water to flow with greater velocity and possibilities of increas amount of slit in the water will occur.
  • Similarly higher intensities of rain fall also cause greater run off and greater erosion and consequently increas amount of silt in water approaching the reservoir.
  • If catchment has good cover of vegetation, the amount of silt in water would decrease.
  • The silt load held in river water approaching the reservoir may be classifi into two categories namely (a) bed load and (b) suspend load.
  • The large size particles comprising bed load, remain concentra near the bed of the stream.
  • The smaller particles remain suspend in water in upper layers.
  • The bed load is actually dragged along the bed of the stream.
  • Bed load is generally very small (hardly 10 to 15%) as compard to suspend load.
  • When this silt laden water reaches a reservoir in the vicinity of a reservoir the velocity is generally considerably reduce.
  • Fine particles may travel some more distance and may finally deposit farther down in the reservoir.
  • Some very fine particles may remain in suspension for much longer time and even finally escape from the dam along with the water discharged through sluice ways, spill ways etc.
  • This deposition of silt in the reservoir, inform of bed load and suspended load is know ‘Reservoir sedimentation’ or ‘reservoir silting’.

Reservoir sedimentation