Reservoir intake for an earth dam

Components of an intake

1. Intake opening / port with a bell-mouth entry, placed at one or more levels.
2. Coarse screen (trash rack) with bars 20 to 50 mm apart to stop large floating objects, and a fine screen (6 to 12 mm mesh) to stop small debris.
3. Intake well / tower / chamber that houses the gates and valves and lets water settle.
4. Sluice gates / valves to regulate or cut off flow.
5. Conveying (intake) pipe or conduit from the well to the pump house or main.
6. Sump or pump well (for pumped schemes) and a foot bridge for access.
7. Protection works: pitching, groynes, wing walls, embankment, guard rails, and a flushing / scour pipe for removing silt.

Wet reservoir intake for an earth dam

In an earth dam the intake is not placed inside the embankment (which would cause leakage and settlement). Instead a wet intake tower is built in the reservoir upstream of the dam, near the upstream toe, connected to the crest by a foot bridge, and the outlet conduit (a pipe in a trench, or a tunnel through the abutment or under the base) passes under or beside the dam.

  Foot bridge =======+     Earth dam
 HFL ~~~~~~~~~~~~~~~ |   /\
 NWL ~~~~~~~~~~~~[T] |  /  \
        ports --> [ ]| /    \
 bed ///////////[ ]-+------\--/////
              conduit with cut-off collars
                          ---> outlet / plant

Operation and characteristics

• Ports at different depths (top, middle, bottom) with screens and sluice gates let the operator draw the best quality water at all reservoir levels.
• Gates are lifted by stems from the service platform; the lowest port is above the silt level.
• Water flows to the well, then through the outlet conduit to the downstream valve house and plant.

Factors ensuring stability and safety of the intake works

• The tower base is founded on a firm stratum, with a foundation wide enough to resist overturning and sliding under water pressure, wave and ice loads.
• Check stability against overturning, sliding and floatation (empty well) and against the earthquake load, with the foot bridge as a hinged or sliding support.
• The conduit through the dam has cut-off collars (anti-seepage collars) to stop piping and leakage along the pipe, and is laid on firm ground, not on fill.
• Keep the gate and valve control house above flood level, and the tower top above the maximum water level plus wave height (freeboard).
• Provide a flushing pipe to remove silt, a trash rack and a fine screen, and pressure-test the conduit.
• Build the tower of reinforced concrete, or of masonry in waterproof cement mortar.