Hydraulics and Design of Fusegates

Fusegates are the mechanical equivalent of a fuse plug. A typical installation consists of multiple gates placed on a spillway crest. When installed, the gates approximate the shape of a labyrinth weir in which each gate represents one cycle of the labyrinth. The gates are held in place by gravity. For a moderate range of reservoir levels, the water flows over the fusegates as it would over a labyrinth weir. If the reservoir level exceeds some predetermined value, the fusegate overturns by rotating about its downstream edge. Each gate is set to overturn at a progressively higher reservoir elevation. For the maximum design discharge, usually equivalent to the probable maximum flood, all of the fusegates tip and the entire crest length is available to pass the flow. Fusegates are supplied by the manufacturer in three standard configurations. The empirically derived discharge coefficients for these configurations are presented. General stability equations of fusegates are derived, and the tipping moments for one configuration is shown. A procedure to design a fusegate installation is outlined and is illustrated with an example. The advantages of a fusegate over a fuse-plug installation are that operation of the system can be controlled to within a few centimeters, it acts like a labyrinth spillway for flows that are less than some critical discharge, and that the entire installation is not lost for floods less than the probable maximum flood.