Fuse-plug Spillways

Synopsis There are fuse-plug spillways at many large dams around the world. These may be designed to trigger in floods with return periods of, say, 10,000 years but may also trigger in much smaller floods if these are combined with failure of one or more of the main spillway gates to open. The annual probability of the latter combination may be much higher than that of experiencing a flood with a return period exceeding, say, 10,000 years. Earthfill bunds, of conventional appearance, sitting on non-erodible foundations (whether rock or concrete) are examples of such fuse-plugs and typically have sloping clay cores resting against erodible downstream shoulders. Tipping gates in steel or concrete have become popular in the last thirty years and there are several examples in the north-west of England. Various types of rubber dams are also used to hold water until they deflate when overtopped by a critical depth of water.