from The Century Dictionary.
- noun A gate, sluice, or valve placed in a dam, reservoir-wall, or pipe-system, to be opened when desired to flush out the reservoir, the channel below the reservoir, or the pipe-system.
Sorry, no etymologies found.
The forebay, at which the head-race canal ends, is again a concrete structure, perhaps a bit oversized, with a perpendicular overflow weir and a bottom flush-gate for flushing out sediment (refer to fig. 68).