HYDRAULICS OF SEMICIRCULAR-INLET DROP STRUCTURES

The semicircular-inlet drop structure is used by the USDA-Soil Conservation Service to stabilize grade and control erosion in natural and constructed channels. It has been extensively used to prevent the formation and advance of gullies, where water must be dropped from about 0.61 m (2 ft) to 1.22 m (4 ft). A physical model was used to study the hydraulics of the semicircular-inlet drop structure. Research was conducted in two phases: the free flow tests and the submerged flow tests. The submerged flow tests were designed to determine the effect of tailwater elevation on the discharge capacity. In each phase, the objective of the research was to develop relationships between discharge rate, total head, and the geometric variables of inlet shape, overfall height, and approach channel width. The results of the research were used to develop a comprehensive hydraulic design procedure for the semicircular-inlet drop structure.