Lock-Type Fishway
The lock system fishway help fish to move through the double leaf wheel gates installed on the upstream and downstream sides. As shown below, overflow operation or underflow operation is selected in the fishway.
Overflow Operation
Overflow operation helps floating fishes such as ayu and satsukimasu (a species of trout) to move.
When the gate on the downstream side is lowered, the difference in water level between the lock room and the downstream is decreased. Fish can then get over the gate to enter the lock room.
Next, the downstream side gate is raised to reduce the difference in the water level between the lock room and the upstream. Fish can then get over the gate to exit upstream.
Underflow Operation
This helps bullheads, crabs, etc. that creep along the river bed to move.
The gate on the downstream side is raised to let the fish enter the lock room freely.
When the gate on the downstream side is lowered and the one on the upstream side is raised, the fish can move upstream from the lock room freely.
In flow operation, in the stage shown in Fig.
, water containing salt infiltrates into the lock room. Before switching to the step shown in Fig.
, however, the upstream side gate is put into the overflow state and the downstream side gate into the underflow state to remove saltwater. Thus, saltwater is prevented from intruding upstream.