Theories of Closure of Rockfill Dams

To proceed with construction in a river bed, a dam must be constructed and the flow diverted. If the dam is composed of rock and other loose material dumped from both banks towards the center of the river, a time may come when the material in the gap is scoured away because the flow velocity in the gap increase as the gap width decreases. Using two analyses, two methods of determining this critical gap width are described and compared with practical examples. It appears that the Logarithmic Method is more reliable, but working backwards from these results it is possible to improve the reliability of the Critical Velocity Method which is much easier to use. It is possible for the designer to determine the critical gap width at which scouring will just occur for a particular mean nominal diameter of the dumped material. In addition, the size of material needed to complete the construction can then be determined.