Experimental Investigation of Non-Cohesive and Mixed Sediment Effects on Optimum Thickness of Detention Rockfill Dams

From ancient times, flood and its mitigation methods have been important to human in order to reduce damages threatening people and nature. Detention rockfill dams which are from the structural methods can control the flood risks in downstream by decreasing the maximum discharge of the flood and increasing the total time of its hydrograph. In order to have an efficient design of these dams, the important conditions of sediment transportation through dam body and also the optimum thickness of the dam should be known. The optimum thickness of detention rockfill dam leads into the maximum reduction in flood peak discharge and also causes the increment of flood duration to get minimized. To find this optimum thickness, some experiments were done on a simulated porous media in a lab. Then, the experimental results were utilized in Monte Carlo probabilistic method in order to find the percentage of sediment transportation probability. Results depict that by using mixed sediment with non-cohesive mean diameter of 0.6 mm within the water flow, optimum thickness would be 7 to 8 times greater than the rockfills with mean diameter of 2 cm in the dam body; while using non cohesive sediment with mean diameter of 0.2 mm in the flow causes the optimum thickness of the detention rockfill dam to be 7 times greater than body rockfills with diameter of 5 cm.