Laboratory Study of Effect of Hydraulic Parameters on Sediment Transport Capacity in a Compound Channel with Lateral Floodplain Slope

Study the soil erosion process, sediment transport capacity plays a vital role in the physical description of soil erosion processes. In recent years, researchers examining the sediment transport capacity under different laboratory conditions have shown that hydrodynamic parameters, especially shear stress and unit stream power have a significant effect on sediment transport capacity. Despite the studies, the effects of sediment size on sediment transport are still not well understood and considering that previous studies have been done in direct channel, the effect of longitudinal slope and transverse slope change by changing sediment particle size in composite channel is investigated and not well understood. Therefore, recognizing and investigating the factors affecting this case is of special importance in hydraulic science. One of the influential factors in the hydraulic and hydrodynamic conditions of floodplains is the lateral slope of floodplains. However, qualitative and quantitative study of the parameter requires the presentation of appropriate laboratory research methods. In this study, by aiming at the effect of lateral slope of floodplain on hydraulic and hydrodynamic conditions of flow, as well as the effect of granulation and hydraulic parameters on the amount of sediment output, an experimental design was presented to investigate this parameter. In this study, the effect of granulation and changes in hydraulic parameters in the combined flood section (with flood plain on one side of the main channel) was investigated. Two laboratory models of compound cross-section with the first model of the lateral wall slope of the flood plain zero and in the second model, the value equal to 50% was considered. In addition, in order to investigate the effect of longitudinal slope on the washed sediments, the longitudinal slope was changed in three steps: 0.002, 0.004 and 0.006. In order to investigate the effect of the average diameter of sediments on the scouring process, sandy sediments with a diameter of 0.9 and 3 mm were used during the experiments. By comparing the changes of hydraulic parameters (velocity, shear stress, ratio of main channel depth to depth of plain flood, discharge and Froude number) with changing sediment granulation, the results showed that by reducing the grain size and at zero transverse slope, the amount of hydraulic parameters increased. The results showed that increasing the longitudinal and transverse slope has a great effect on increasing the volume of leached sediments along the channel and by increasing these longitudinal and transverse slopes in the channel, more sediment transfer volume occurs. By examining the changes in shear stress and unit stream power against sediment transfer capacity, the results showed that with increasing the longitudinal slope and in the transverse slope of 0.5, the sediment transfer capacity has increased. As the shear stress increases at different longitudinal and transverse slopes, the sediment transport capacity increases. These findings indicate that the slope has a positive effect on shear stress. The results show that the transverse slope has a significant effect on the increase and change of shear stress with sediment transfer capacity and in the transverse slope of 0.5 and in different longitudinal slopes, increase in sediment transfer capacity is more and washed sediment increased. With increasing depth of flow in main channel to depth of flow in floodplain, more sediment is removed from the flume and the least amount of sediment washed is when the longitudinal slope is equal to 0.002, transverse slope 0.5, and median particle diameter is 3mm, occurring in discharge of 1.6 l/s. As the Froude number increases, the amount of sediment output will increase more when the size of the sediment particle decreases. Also shear stress varies in longitudinal and transverse slopes.