An artificial channel into which water is let by a sluice; specifically, a trough constructed over the bed of a stream, so that logs, lumber, or rubbish can be floated down to some convenient place of delivery.

conduit that carries a rapid flow of water controlled by a sluicegate

Vertical slots, generally located near the bottom of a dam, which can be opened to release water from the upstream reservoir without passing it through the turbines. When the water at a dam is too low to reach the spillway, the sluiceway can be used to release water faster than it can flow through the turbines.