Types of intakes and their suitability

An intake is the structure at the head of a water conductor system that draws the required discharge from a river or reservoir while keeping out floating debris, ice, and as much sediment as possible.

1. Side (lateral) intake

Opening in the river bank at an angle to the flow, usually upstream of a diversion weir.

• Suitability: most common in Nepalese run-of-river projects on medium and large rivers. Placing it on the outer bank of a bend reduces bedload entry.

   river flow ---->
 =========================
     |         | weir   |
     |  intake |========|
 ====|  gate   |=========
     v
  to gravel trap / canal

2. Frontal intake

Intake facing the flow directly, with the river bed upstream and a sluice for flushing.

• Suitability: where the river carries little bedload, or in canal-type schemes; strong flow towards the intake but more sediment entry.

3. Bottom (drop, Tyrolean or trench) intake

A trench with an inclined trash rack set in the weir crest; water drops through the rack into a gallery.

• Suitability: steep mountain streams with boulders and coarse bedload, small and micro hydro (common in Nepal's hilly streams).

  flow -->  ___rack___
 ~~~~~~~~~/\/\/\/\/\/\~~~~~~
 =========|  trench  |=====> to canal
          |__________|

4. Tower intake

A vertical tower in a reservoir with ports at several levels, connected to a tunnel.

• Suitability: storage dams with large fluctuation of water level; allows drawing water from different depths.

5. Shore/face intake (dam intake)

Opening in the dam face or reservoir bank, with trash rack and gate, leading to the penstock/tunnel.

• Suitability: concrete dams and pondage schemes (e.g. Kulekhani).

6. Siphon intake

Uses a siphon over the dam crest. Suitable for small heads and small discharges.