Intake, its functions and site factors

What is an intake?

An intake is a structure built in or near a water source (river, lake, reservoir, canal or spring) to draw water safely in the required quantity and send it to the conveying main, pump well or treatment plant.

Functions of an intake

• Withdraw the required quantity of water from the source throughout the year.
• Keep out floating matter, debris, fish and coarse silt by means of screens and gates.
• Draw the best quality water (away from pollution, silt and bottom deposits).
• Protect the supply from floods, scour, silting, ice and damage.
• Allow control and isolation of flow (valves, sluice gates) for repair and maintenance.

Factors affecting site selection

1. Water quantity: the source must give the design flow even in the driest season; the minimum flow must exceed the demand.
2. Water quality: the site should be upstream of towns, sewage and industrial discharges, and away from tributaries that bring silt or pollution.
3. Stable bank and bed: choose a stable, non-eroding reach, preferably on the concave (outer) side of a bend where the water is deep and the current scours silt away.
4. Depth of water: enough depth at all stages so the intake port stays submerged at low water.
5. Flood level: the structure must stand above the highest flood level (HFL) or be safe against it, and the site should be free from flood and drift damage.
6. Foundation: sound strata for the foundation of the intake tower and pipes.
7. Navigation: the site must not obstruct navigation and should not be in a navigation channel.
8. Distance and elevation: close to the treatment plant and consumers (shorter pipeline, lower cost); for gravity schemes, enough head.
9. Accessibility: access for construction, inspection and maintenance in all seasons, and nearness to power for pumping.
10. Future expansion and ownership of land/legal rights at the site.
11. Ice and silt: the site should not be affected by ice formation or heavy sedimentation.