Theoretical and Experimental Study of Circular-Crested Trapezoidal Side Weir in Subcritical Flow Regime

Side weir is one of the diversion structures, which widely used in irrigation and drainage networks, flood protection, urban sewage systems and water level control. The flow over the side weirs is a typical case of the spatially varied flow with decreasing flow discharge. In this study, the flow characteristics over the circular-crested trapezoidal side weir located in rectangular channels is experimentally investigated under subcritical flow conditions. In this research, the conventional weir theory with three different reference depths (y1, yavg and ycenter) for computing the weir head was used to evaluate the proposed discharge coefficient and discharge equations. Based on the experimental results, the discharge coefficient is a function of upstream Froude number, the ratio of upstream flow depth to the crest diameter, and side slope of the weir. The comparison between the experimental data and computed results indicated that the conventional weir theory with the average flow depth as the reference depth with an average error of 3.6% is the best relationship for assessing the discharge coefficient. Thus, this method is suggested for practical purposes.