Dry river intake with sketch

Need for an intake structure

Water cannot be taken directly from a river, lake or reservoir in a safe, controlled way. The intake is needed to:

• draw the design quantity in all seasons and draw it from the best level;
• keep out floating matter, silt, fish and debris with screens;
• protect the supply from floods, scour and erosion;
• allow valves to control and isolate the flow;
• provide a stable base for pipes and pumps.

Dry type river intake

A dry intake is a tower built on the river bank (or just inside it) whose interior is kept dry. Water enters through ports in the wall, flows into a separate sump by a connecting pipe, and only the valves and pipes are in the dry chamber. The operator can work inside it at any time.

 Foot bridge ===+
                | operating floor
 HFL ~~~~~~~~~ ||   gate valves
              ||[=]---+
 NWL ~~~~~~~~ ||[=]---+--> pipe to
              ||[=]---+    sump/pump well
 LWL ~~~~~~~ ||  dry chamber
   ///////// ||____________ screens at ports
   river bed  |   (water-tight walls)

Operation

• Water flows from the river through the screened ports, then through the valves in the dry chamber, to the sump or directly to the pump.
• The operator selects the port at the best level and closes the others.
• Valves and screens can be inspected, cleaned or repaired from inside, in dry conditions.

Merits and demerits: Operation and maintenance are easy, but it needs stronger water-tight walls and a heavier, deeper foundation (to resist floatation when it is empty), so it costs more than a wet intake.