The rule of the front and behind top edges of weirs on their hydraulic performance and working efficiency

The geometry of weirs is a prime factor influencing hydraulic performance and accuracy. One of the geometric components of weirs, is the situation of its top corners, are they sharp or rounded, and what is the most suitable radius of such rounding curves? The present study was conducted to examine the effect of using five different radius of curvature for both the upstream and downstream top corners of a clear over-fall weir on its hydraulic performance and accuracy. Eleven models of wooden weirs were shaped and prepared with five different values of rounding curvature. The prepared weir models were located in a laboratory tilting flume of 13.50 m length, 0.30 m width, and 0.30 m depth. The study was carried out in the Irrigation and Hydraulic Laboratory of the Civil Department, Faculty of Engineering, Assiut University, Egypt. A discharge ranging from 2.0 to 22.0 dm3 s−1 was used, and through 66 experimental runs, all the necessary hydraulic parameters were measured, and recorded. The obtained data were tabulated, analyzed, plotted, and technically discussed. The main results and obtained conclusions proved that when the front weir top edge is curved the discharge coefficient increases up to 8%. Also, when both front, and behind weir top edges are curved the discharge coefficient increases up to 14%. At the same time the discharge coefficient has a maximum value when the radius of curvature in upstream and downstream top corners equals 20% of the height of the weir