Hydraulic design considerations for orifice spillways

Abstract

Orifice spillways have been widely recognized as the most appropriate especially for run-of-the-river projects for handling both flood releases and flushing of sediments. The present paper discusses various important parameters to be considered in the design of an orifice spillway, evolution of orifice spillway, and structural design consideration. A need for physical and numerical model for modeling spillway flows has been identified. Literature review on physical and numerical model studies of orifice spillway has been reported. Central water and power research station has contributed in evolving the design of orifice spillway by conducting hydraulic model studies for more than 25 projects. However, no guidelines have been developed as the data was site-specific for each case. Based on the data, a need for further research is identified and discussed in detail. Roof profile is found to be an important hydraulic parameter as it affects the discharging capacity of the orifice spillway. However, design of roof profile has not been standardized so far. Hence, basic research studies were taken up to develop the design guidelines for roof profile using physical and numerical models. The important findings obtained from the basic research study have also been discussed in the present paper. An equation was developed to design the roof profile, which will be useful for the engineers at the initial stage of design of orifice spillway.