Discharge Coefficients for Rectangular Broad-Crested Gabion Weirs: Experimental Study

Abstract

Weirs are commonly used for making discharge measurements in irrigation canals. There are several types of weirs that are categorized based on their geometric shape or hydraulic properties. A gabion weir is a porous weir that can pass flow through its body in addition to the flow that passes over the weir. This study focuses on determining the discharge coefficients (Cd) for rectangular broad-crested gabion weirs using fabricated physical models. Dimensional analysis was carried out for finding the most effective parameters that govern the flow. Results show that the Cd of gabion weirs is 10.5% greater than that of similar solid weirs. In addition, the Cd for porous weirs in free flow conditions is 17.2% greater than that for submerged flow. For H/L>0.45 (where H is the water depth over the weir crest and L is the weir length) a porous weir acts similar to a solid weir and the effect of porosity (n) nearly vanishes. For a specified value of H/L, the ratio of submergence (Sr) for a solid weir is higher than that for porous weirs. Porous weirs with 50% porosity have lower values of Sr compared with solid weirs and weirs with lower porosities, of 45%, 41%, and 30%. Regression equations for the flow through gabion weirs were generated for free and submerged flow conditions. The derivations of equations were carried out using multivariable nonlinear regression and genetic programming (GP). Finally, a comparison of Cd in the present study with the other studies was carried out.