General requirements of functional RoR headworks

A RoR headworks takes the design discharge from the river without storage, so it must work reliably in both floods and low flows. The minimum standards of a sound headworks are:

1. Stable and safe structure: designed for the 100-year flood (check for a higher flood); stable against sliding, overturning, uplift and piping; strong foundation with cut-offs and protection against scour.
2. Adequate flood passage: spillway, undersluice and gates must pass the design flood with an acceptable afflux, without overtopping the banks or the flood walls.
3. Dependable water supply: the intake must deliver the design discharge during the dry season, with the intake always submerged and no air entry or vortex; an environmental release is also kept in the river.
4. Control of sediment: bed load is excluded by a high-level intake sill, an undersluice, a gravel trap and river training works; suspended sediment above the design size is removed in the settling basin. The sediment must not accumulate in front of the intake.
5. Control of floating debris and trash: trash racks, trash booms, and a raking arrangement.
6. Hydraulic efficiency: small head loss in the intake, a smooth flow transition and a low-turbulence approach.
7. Operation and maintenance: gates and hoists easy to operate in floods, safe access, provision for flushing and inspection, and the arrangement for fish passage.
8. Environment and economy: minimum impact on the river and fish, and a low cost relative to the energy produced.