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Divide wall, under sluice, fish ladder functions
Short answer
Fish ladder lets fish bypass the weir via a baffled slope. Divide wall separates the quiet pocket from weir flow, preventing cross-current damage and scour interference. Undersluices are low-level gates that scour pocket silt, maintain a clear channel to the head regulator, and pass low floods without dropping shutters.
Describe briefly the key functions of fish ladder, divide wall and under sluices in a diversion headworks.
- Fish ladder. A fish ladder is a sloping channel (generally 1:10 to 1:15) with baffles or steps, built beside the divide wall at the weir. It lets fish swim upstream past the weir to their breeding places. The baffles slow the flow and form resting pools. It is necessary wherever fish migration must be protected, as in Nepal's rivers.
- Divide wall. A masonry or concrete wall built at right angles to the weir axis, between the weir and the undersluices. Its functions: (i) separates the quiet pocket in front of the head regulator from the weir flow, so that the silt in the pocket can be scoured by the sluices; (ii) keeps the cross-currents from the weir away from the sluices and the regulator; (iii) prevents the high-velocity flow over the weir from damaging the sluices; (iv) acts as the side wall of the fish ladder, if provided; (v) separates the weir floor from the undersluice floor, which is at a lower level.
- Undersluices (scouring sluices). Gated openings in the weir, next to the head regulator, with the crest at a low level (river bed). Functions: (i) scour out the silt deposited in the pocket by opening the gates; (ii) maintain a clear, deep channel in front of the canal head regulator; (iii) pass the low floods without dropping the weir shutters, so the pond level is kept; (iv) induce a curved flow so that the bed silt goes to the sluices and the canal gets the clearer upper water; (v) pass part of the high flood.
✓ Answer checked by Claude Opus 5.5 (high effort)
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