Estimation of the Coefficient of Discharge of an Orifice Spillway - A Basic Research Study

摘要

Estimation of the coefficient of discharge (Cd) is a key parameter in determining the discharge capacity of a spillway. The Cd of an orifice spillway is governed by many parameters such as bottom and roof profiles, head over the spillway crest, upstream depth of the spillway's crest from the river bed, width of piers, shape of pier nose, width and height of the orifice opening, and approach flow conditions. Assessing the Cd for an orifice spillway is a complicated task due to variation in the above parameters from site to site. In the present basic research the aim is to estimate the discharge capacity of an orifice spillway using both physical and numerical models. The bottom and roof profiles of the orifice spillway have been designed considering all possible practical heads and heights of an orifice. Based on the results, an equation has been developed for estimating Cd. It is expected that this equation can be used at the initial design stage of an orifice spillway. The developed equation has been used to estimate the discharge capacity of 22 real life orifice spillway projects. The estimated values of Cd are compared with Cd values obtained through physical model studies of these projects. It is seen that the Cd estimated from the proposed equation is much higher than the one obtained for a particular real life case, as the equations of the bottom and roof profiles were not designed properly. Therefore, it can be concluded that the design of these profiles are of extreme importance in order to achieve maximum discharging capacity.