Bed compaction effect on dam break flow over erodible bed; experimental and numerical modeling

Disastrous floods result in severe loss of human lives and intense destruction to the infrastructure and economic activities. Furthermore, it leads to environmental and ecological damages located at the downstream area of the dam. The present study aims at investigating experimentally and numerically the sediment transport and morphological evolution of the erodible bed induced by dam-break flows. Experimental runs were conducted in a flume, specially designed for dam-break flow process, equipped with a thin vertical gate at its middle. Based upon an initial plane bed, the effect of three different compaction rates of the bed at both up-and downstream of the dam was investigated. The experimental data consistently suggested that increasing the bed compaction rate resulted in decreasing the scouring and sedimentation depth, as well as the sediment transport rate. Further, increasing the bed compaction rate led to increasing the wave-front celerity, reducing the scouring rate and the erosion depth. Both the experimental and numerical outputs highlighted the process of air entrainment at the leading edge of the wave-front. The numerical results showed that the maximum void fraction was associated with the maximum flow velocity at the zone of wave-front. Comparisons were made between the experimental results and those are provided from a numerical study using standard volume of fluid VOF method, where three different turbulence closure schemes; RNG, k-epsilon and k-omega, and three bed load sediment transport approaches, Van Rijn, Meyer-Peter-Muller and Nielson, were applied. Accordingly, by considering the error values in predicting the free surface height and the bed deformation, the k-omega closure model showed the highest accuracy in capturing the turbulence features while the Mayer Peter-Muller formula had the highest performance in predicting the bed deformation in non-compacted (NC) bed. Besides, the RNG closure model and Nielsen bed load formula revealed the highest accuracy in predicting the aforementioned features in a semi-compacted (SC) bed. The k-epsilon closure model and Mayer Peter-Muller formula showed the highest accuracy in reproducing the turbulence characteristics and bed profile in a fully-compacted (FC) bed.