Characteristics of the flow field downstream of free and submerged hydraulic jumps

Flow characteristics downstream of free and submerged hydraulic jumps with and without blocks were experimentally studied for Froude numbers ranging from 3·48 to 6·85. The streamwise variation of the mean longitudinal velocity, turbulence intensity and turbulent kinetic energy as well as bed shear stress and water surface fluctuations were studied and compared for different flow regimes. Empirical equations are presented for longitudinal variations of the bed shear stress and water surface fluctuation for free and submerged jumps with and without blocks. The length required for the bed shear stress and water surface fluctuation to attain asymptotic magnitudes was used to define new characteristic lengths for hydraulic jumps. The results of this study show the effects of blocks in determining the longitudinal extension of hydraulic jumps. It was found that the presence of the blocks damped the streamwise variation of the studied flow parameters in a significantly shorter distance. It was also found that the deflected surface jet regime that occurred in submerged jumps with blocks had streamwise characteristics similar to those of free jumps with blocks. The results of this study confirm that this flow regime of submerged jumps can effectively be used as an energy dissipator within a stilling basin with a length approximately equal to that required for free jumps.