Wet (typical) reservoir intake

When a reservoir intake is constructed

A reservoir intake is built when the supply comes from an impounding (storage) reservoir or lake, for example when the river flow in the dry season is less than the demand, so water is stored behind a dam and drawn through a tower. It is used when the quality changes with depth and season, and when the supply must be taken at a controlled level.

Typical wet reservoir intake

A reservoir intake draws water from an impounding reservoir (a natural lake or an artificial lake formed by a dam). A wet intake tower is a vertical tower, usually of masonry or concrete, set in the reservoir near the dam, with ports at different depths. The water level inside the tower is the same as in the reservoir.

  Foot bridge ==============+
                            | operating
  HFL ~~~~~~~~~~~~~~~~~~    | stem
  NWL ~~~~~~~[ ]~~~~~~~~~~~ |
       top port + screen    |
  MDDL ~~~~~[ ]~~~~~~~~~~~~ |
       middle port + screen |
       ~~~~~[ ]~~~~~~~~~~~~ |
       bottom port          |
  bed //////|  intake well  |////
            +--------pipe/conduit--> outlet to plant

Characteristics and working

• The tower has ports (usually 3) at different levels. Water is taken from the level of best quality: top water in summer when the deeper water is cold and poor (low oxygen, high iron and manganese), and deeper water in winter when the surface is cold or frozen.
• Water entering the port passes through coarse and fine screens, then the sluice gate or valve, into the well, and from the well by the intake pipe or conduit to the plant.
• Gates are operated from the top by stems and handwheels on the service platform; access is through a foot bridge.
• Low entrance velocity avoids drawing silt and floating matter. The bottom port is placed above the sludge/silt level.