A flexible collapsible dam for a watercourse is provided with one or more conduits for carrying water from upstream to downstream of the dam and thereby regulate the depth of water flowing over the dam to reduce vibrations of the dam caused by the water flowing over it. The water which is conveyed around the dam is discharged immediately downstream of the dam to prevent the deposit of objects on the bottom or banks of the watercourse where the collapsed dam contacts said bottom and banks.
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