Intake components and site factors

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.

Factors governing the 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.