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Wet and dry river intake

Short answer

A wet river intake is a tower in the river with interior flooded to river level; water enters through screened ports and exits via a bottom pipe, gates operated from a top bridge. A dry river intake is on the bank with a dry interior; water enters ports, passes through valves in the dry chamber to a sump, allowing easy maintenance. Wet intakes are cheaper but harder to maintain; dry intakes cost more but offer easy access.

Define wet and dry river intake with neat sketch and briefly describe their operation and maintenance, showing all major components in the sketch.

Wet river intake

A wet intake is a tower (or well) built in the river, with its interior filled with water up to river level. Ports at different levels admit water, and the intake pipe leaves from the bottom of the well. The valves are operated from the top, since they are underwater.

  Foot bridge =====#=====
        Stem (control rod) |
  HFL ~~~~~~~~~~~~~~~~~~~~ |
  NWL ~~~~~~[port + screen]|  <- water inside
  LWL ~~~~~~[port + screen]|     well = river level
  bed ///////[port]--------|
              |   intake pipe
              +---------------> to pump well / plant

Operation and maintenance: The tower is filled with water and the pipe is always flooded. Gates at each port are operated from the bridge by a stem. Screens must be raked and cleaned from above, and divers or stop-logs are used when the tower has to be examined. It is cheaper than a dry intake, but harder to maintain.

Dry 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.

✓ Answer checked by Claude Opus 5.5 (high effort)

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