The Study Impact of Effective Factors in Sediment Transport in Unsteady Flow

The role of floods in sediment transport and river morphology has been proven. In this study, the effect of different parameters on the transfer of sediment bed load under flash flood has been investigated. The input flood hydrograph of the symmetric triangular type with the base time of 90 sec and peak flow rate 30 and 45 lit/s were considered. Sediment particles of quartz type with a moderate diameter of 1.2 and 3 mm and two bed slopes of 0.006 and 0.014 were tested. In this study, changes in water surface profile, rate of bed load in steady and unsteady conditions, and unsteadiness parameter relative to total work done of flow and sediment rate were investigated. By using dimensional analysis, the parameters affecting sediment transport were determined and evaluated in experiments. The results showed that the unsteadiness parameter in unsteady flow had a significant effect on sediment transport. On the other hand, the work done by the flow has a greater impact on sediment transport than the unsteadiness number. In this regard, the effect of channel slope on sediment transport should be considered. The role of channel slope in the transfer of bed load is very important so that by doubling the bed slope, the total amount of sediment transferred to the downstream increases almost 5 times. Also, with increasing the sediment flow rate, the unsteadiness parameter increases and it plays an effective role in the whole work. In general, in high-value hydrographs, the amount of transfer sediment increases and there is a large relationship between the amount of transfer sediment and the total flow work. Reducing the time of the rising arm of the hydrograph shows the effect of increasing the flow rate, which is effective in these waterways, so that with the faster the flood peak time, the more sediment is transferred and the probability of damage and destruction increases.