flood bypass; floodway; discharge channel; diversion channel
Civil engineering term for a channel or waterway built to divert excess water, especially during floods.
During heavy rain, the town would be flooded without the diversion channel.
This floodway was built to prevent the river from overflowing.
水路 is a broad term for any waterway or canal; 放水路 is a specific type designed for flood control.
Compound of 放 (release, discharge) and 水路 (waterway, channel).