Hydraulic Efficiency of Crump Gabion Weirs under Submerged Flow Condition

Weirs are usually constructed by concrete and are impervious so that the water can only flow above the crest. In this between, Gabion weirs with instinctive characteristics including stability, conductivity and economic justification are strongly advised. In this study, the effects of material size, upstream and downstream slopes were investigated on the discharge reduction factor of gabion crump weirs under submerged flow conditions. For this purpose, 8 models of gabion weirs and 3 models impervious weirs constructed in a horizontal flume with 15m long, 0.3m wide and 0.5m deep. The tests were carried out for different variables, including discharge, upstream and downstream depths, material size and upstream and downstream slopes. The results showed that the flow reduction factor decreased as the ratio of the upstream depth to the downstream (Y2/Y1) increased. For a constant ratio of Y2/Y1, the flow reduction factor decreased when upstream or downstream slope increased. It was found that the material size has no significant effect on the flow reduction factor. Based on regression analysis, an empirical equation was developed for estimation of the flow reduction factor which its correlation coefficient variation was in the range of 0.79 to 0.96.