The crest gate is fitted to the crest of an ogee spillway on a dam or weir to increase storage capacity. The variable buoyancy crest gate is empty and buoyant to close while water levels upstream are below the designed opening water levels. Inlet weirs are mounted on the abutment of the reservoir or on the piers and are connected via ducted pipes and upstream facing radial arms to the gate.
As water levels rise to open fully, water flows in at the inlet weir and floods the buoyancy tank. Two smaller diameter drain pipes drain the tank at a lesser rate than the inflow. As the tank fills it sinks against the ogee of the spillway and water and debris is discharged over the gate. Only once the water level drops below the inlet weir level and the drain pipes drain the tank does the gate empty and float back into its normal closed position to retain the additional storage.
These gates actuate automatically based on water levels upstream and have been fitted to many weirs and dam spillways in South Africa and abroad.
The crest gate works well with scour gates to control flooding and sediment build up in river weirs.