Abstract
A jet that passes through dam gates or forms downstream of a chute can cause scouring to the riverbed. This scouring can pose a risk to the structural integrity of the dam. Therefore, understanding the scouring processes is of great practical importance. This study deals with the depth of scour at the location of impact between the free falling jet and the riverbed. The present study is based on extensive laboratory experiments that were designed to mimic full-scale behavior. The falling height of the water jet (H) is 3.5 m for three different sizes of riverbed material (d). Results showed that with increasing downstream water depth (h), the impinging jet causes increasingly turbulent currents and large vortices that increase the scour of the riverbed. Increasing the average diameter of the riverbed materials and discharge per unit width (q) enhances the relative scour depth (D/H), where D is maximum scour depth. With increasing F-r (particle Froude number), the relative scour depth indicates an almost linear increasing trend. The maximum width of the scour (W) was evaluated to the maximum depth of the scour (D). The ratio of W/D is in the range of 3.4-6. Regression shows that a fractional form of the nonlinear multivariate regression equation has reasonable agreement with observed data. The derived nonlinear equation can be used for predicting scour depth with a determination coefficient R-2 = 0.825 and root mean square (RMSE) 0.1308.