Energy Dissipation Assessment in Flow Downstream of Rectangular Sharp-Crested Weirs

Sharp-crested weirs are commonly used in hydraulic engineering for flow measurement and control. Despite extensive research on sharp-crested weirs, particularly regarding their discharge coefficients, more information is needed via research on their energy dissipation downstream. This study conducted experimental tests to assess the influence of contraction ratio (b/B) of rectangular sharp-crested weirs (RSCWs) on energy dissipation downstream under free flow conditions. Five RSCWs with different b/B equals 6/24, 7/24, 8/24, 9/24, and 10/24 were used. The results showed a consistent decrease in relative energy dissipation (ΔEr) with an increase in the head over the weir. Furthermore, as the discharge per unit width (q) increased, the relative energy dissipation (ΔEr) decreased, indicating more efficient discharge over the weir. A higher b/B further reduces ΔEr, suggesting that wider weirs are more effective in minimizing energy losses. The maximum relative residual energy (E1/E0) and relative energy dissipation (ΔEr) occurred at b/B = 10/24 and 6/24, with values of 0.825 and 0.613, respectively. Additionally, the maximum discharge coefficient (Cd) of RSCWs is found at b/B = 6/24, with an average value of 0.623. The results support the accuracy of the proposed equation with R2 = 0.988, RMSE = 0.0083, and MAPE = 1.43%.