Effects of the angle between the rock strata and slope on flow hydraulics and sediment yield in karst trough valley: laboratory scour experiment

The angle between the exposed bedrock and slope in a karst trough valley strongly affects overland flow behavior, thus, altering the generation of runoff and sediment. However, the directions and magnitudes of these effects remain unclear. The current study aimed to investigate the effects of the angle between the rock and slope on flow hydraulics, runoff, and sediment yield, as well as their linkages. A laboratory flume scour experiment was done under different combinations of angles between rock strata and slope (0°, 30°, 60°, 90°, 120°, and 150°), flow discharge rates (5, 7.5, and 10 L/min) and slope gradients (10°, 15°, and 20°) to simulate the field environment in a karst trough valley. The flow hydraulics (Reynolds number, flow velocity, flow depth, and Darcy-Weisbach friction factor), sediment yield, sediment concentration, and runoff rate were determined. The results showed that with increasing scour duration, the Reynolds number and flow velocity decreased but the flow depth and Darcy-Weisbach friction factor increased. The angle between the rock strata and slope significantly affected the flow velocity and Darcy-Weisbach friction factor, while slightly affecting the flow depth and Reynolds number. Over the scour duration, the runoff rate first increased and remained at a steady state but the sediment concentration and sediment yield rate first increased and then sharply decreased to a steady state. The sediment concentration and sediment yield rate both significantly decreased as the angle between the rock strata and slope increased. The runoff rate was closely linked to the flow velocity and Darcy-Weisbach friction factor as well as the sediment yield rate and sediment concentration. The current results indicate that the angle between the rock strata and the slope should be considered an important parameter when developing a soil erosion prediction model for karst trough valleys.