Response of Density Currents to Sudden Change of Bed Roughness

Because of buoyancy effect، the response of density currents to sudden change of bed roughness is different from that at the water flows in open-channels. In this study، hydraulic behavior of sediment-laden and saline density currents on the bed with conic and cylindrical suddenly changing roughness was investigated experimentally. Velocity and concentration profiles were measured for different flow sections and bed effective roughness، and then bed shear stress and drag coefficient were calculated. Results showed that buoyancy had significant effect on the bed shear stress and effective roughness، as with the sudden change in the bed roughness these parameters changed gradually، especially in the presence of lifting phenomenon. According to the results، logarithmic velocity law had the highest accuracy in the intervals from the bed، located at the 90% and 75% of the maximum velocity distance from the bed for saline and sediment-laden density currents، respectively.