- It is also call an open channel or trough spillway.
- It consists of a steep-sloped open channel which is call trough or chute.
- It is place in the dam abutment, or in a saddle.
- The discharge flown over the chute, is carrie to the D/S of the
- dam through a natural channel which may be meeting the river on D/S side.
- The channel may be forme artificially or by excavating the trench, if natural channel does not exist.
- This spillway is provid for earth or rock fill dams and is always isolated from the main dam.
This spillway has following advantages.
(i) It is simple in design and construction.
(ii) It is adoptable to almost any foundation condition.
(iii) It is economical.
- In this spillway a close channel is used to convey surplus water from U/S to D/S of the dam.
- When the close channel is carrie under the dam, it is know conduit spillway.
- Conduit spillway is suite best for darn in wide valley.
- Tunnel spillway is considere best when dam site is narrow canyon.
- This spillway is designe to flow partly full.
- Full flow is not allow it will develop siphonic action and negative pressures may be create in the conduit.