Comparison of rill flow velocity over frozen and thawed slopes with electrolyte tracer method

Abstract

Summary Freeze–thaw erosion is the primary soil water erosion form in high altitude and/or high latitude regions. The water flow velocity along an eroding rill over frozen and thawed slopes is vital to understanding of rill erosion hydrodynamics. This study experimentally measured rill flow velocity over frozen and thawed slopes using electrolyte trace method under Pulse Boundary Model. The experiments used three flow rates of 1, 2, and 4 L min −1 , three slope gradients of 5°, 10°, and 15°. The temperature of the rill flow water was supplied at 0 °C as controlled with ice–water mixture. Seven sensors were used to measure flow velocity by tracing the solute transport process at 10, 110, 210, 310, 410, 510, and 610 cm distances from the electrolyte injection position. The measured velocity became steady at a distance of about 3 m from the electrolyte injection location, where the effect of the pulse boundary condition on the analytic solution to the partial differential equation becomes negligible. Results showed that flow velocity increased with slope gradient and flow rate on frozen slopes. A significant effect was observed on the steepest slope or at the highest flow rate over the thawed slope, which changed slightly on the gentle slopes and low flow rates. Flow velocity was about 25%, 30%, and 40% higher on the frozen soil than on the thawed slope at 5°, 10°, and 15° slopes and about 30% higher over the frozen slope at all flow rates. This study demonstrates that water over a frozen slope flows much faster than over a thawed slope. This study helps in the study and further understanding of the hydrodynamics of soil erosion and sediment transport behaviors of frozen and thawed slopes.