Hydraulic jump over an adverse slope controlled by different roughness elements

Hydraulic jump that frequently occurs downstream of hydraulic structures reduces the excess energy of the incoming flow. This study tested two different heights of discontinuous roughness elements over the horizontal bed and two adverse slopes of -1.5% and -2.5% in the stilling basin. In total, 280 data were collected in laboratory conditions to assess the impact of adverse bed slope with a variation of roughness elements height on hydraulic jump characteristics, with Froude numbers ranging from 4.9 to 12.4. The results showed that the average value of the bed shear coefficient on the adverse slope of -2.5% with relative roughness elements of h/d1 = 1.33 was 12.4 times that in a smooth bed. The observation showed that the bed shear stress caused by the bed roughness reduced the sequent depth ratio and consequently increased the energy dissipation by generating large eddies and more turbulence. The reduction was more prominent when roughness elements and adverse bed slope height increased. On the other side, a semi-theoretical solution was presented based upon momentum analysis to assess the sequent depth ratio by considering upstream Froude number, roughness element height, and bed slope. The computed values were compared with the experimental measurements. Empirical predictive relationships were proposed to estimate hydraulic jump characteristics over adverse-sloped and rough beds.