Hydraulic Characteristics of Concentrated Flow Relative to Angle between Rock Strata and Slope in the Karst Trough Valley Area

Abstract: Outcrops of rock strata in the Karst Trough Valley Area often form angles with slopes, thus making micro landforms complicated and altering significantly paths of concentrated flows, and consequently bringing about great changes in characteristics of the flows. So, it’s important to study hydraulic characteristics of the concentrated flows relative to angle between rock strata and slope. To that end, a flume experiment, designed to have combinations of three slope gradients (10°,15° and 20°), three flow rates (5, 7.5 and 10 L·min-1) and six angles between the rock strata and slope (30°, 60°, 90°, 120°, 150° and 180° (0°)), was carried out. Results show that hydraulic characteristics of a concentrated flow varied significantly with the angle between the rock stratum and slope. Reynolds number (Re) of the concentrated flow changed with duration of the scouring in a complicated trend, but exhibited a significant trend of increasing with rising flow rate, and an insignificant one of changing with slope gradient. And it varied in the range of 517~3343 in the experiment. Darcy-Weisbach friction coefficient (f) of the concentrated flow increased with rising slope gradient and with scouring going on, but decreased with rising flow rate. And it varied in the range of 0.62~5.70 in the experiment. The relationship of Re with angles between rock strata and the slope was not significant, but that of f varied with combinations of slope gradient and flow rate. The coupling relationship between f and Re was influenced significantly by the angle between the rock stratum and the slope. It could be better described with a logarithmic equation when the angle between the rock stratum and the slope was narrower than 90°, and with a power function equation when the angle between the rock stratum and the slope was wider than or equal to 90°. In the experiment, when Re<1791, the relationship between f and Re was not apparent, but when Re>1791, it was significantly positive. To sum up, f and Re and their relationship vary with the angle between the rock stratum and the slope. The findings in this experiment may provide strong data support for establishing soil erosion prediction models in the Karst Trough Valley Area.