Effect of slope gradient on the subsurface water flow velocity of sand layer profile

Abstract

Subsurface water flow velocity influences the hydrodynamic characteristics of soil seepage and the interaction between subsurface water flow and surface runoff during soil erosion and sediment transport. A visualized method and equipment was adopted in this study to observe the subsurface water flow. Quartz sand was used as the test material of subsurface water flow and fluorescent dye was used as the indicator for tracing subsurface water flow. Water was supplied at the same flow discharge to the three parts at the bottom of the test flume, and the subsurface water flow were determined with four slope gradients (4°, 8°, 10°, and 12°). The results showed that the seepage velocity gradually increased with increasing slope gradient. The pore water velocity at different depths of sand layer profile increased with increasing slope gradient, whereas the thickness of the flow front gradually decreased. For the same slope gradient, the pore water velocity in the lower layer was the largest, whereas the thickness of the flow front was the smallest. Comparative analysis of the relationship between seepage velocity and pore water velocity at different depths of sand layer profile showed that the maximum relative difference between the measured pore water velocity and the computational pore water velocity at different depths of sand profile in the experiment was 4.38%. Thus, the test method for measuring the subsurface water flow velocity of sand layer profile adopted in this study was effective and feasible. The development of this experiment and the exploration of research methods would lay a good test foundation for future studies on the variation law of subsurface water flow velocity and the determination of flow velocity in purple soils, thus contributing to the improvement of the hydrodynamic mechanism of purple soils.