Influence of slope, flow rate, and thawed depth on soil detachment rate in partially thawed black soils

Abstract

The detachment rate of partially thawed frozen soil supplies data sets to compute the soil erodibility and critical shear strength in rill erosion model. This research aims to investigate the effect of slope gradient, flow rate, and thawed soil depth on detachment rate under partially thawed condition. The detachment rates of partially thawed soil rill were estimated under three thawed soil depths (1, 2, 5 cm), four slope gradients (5°, 10°, 15°, 20°), and three flow rates (1, 2, 4 L/min). They were then computed with the sediment concentrations measured along different slope lengths of 0.5, 1, 2, 3, 4, 5, 6, 7, 8 m. Results show that the detachment rates on a partially thawed soil slope as a function of rill length are piecewise functions, which initially maintain a constant value before decreasing exponentially with rill length. In the constant detachment rate section, the constant detachment rate increased with thawed soil depth. After the constant detachment rate section, it increased with slope gradient and flow rate but decreased with the increase in thawed soil depth. The detachment rate decreased fast with the increase in slope gradient and flow rate. The computed detachment rates fitted by stepwise functions produced high coefficient of determination, thereby indicating a good correlation of detachment rate with rill length. The parameters, critical rill length, constant detachment rate, potential detachment capacity, and reduction coefficient of detachment rate in the piecewise function were regressed with stepwise regression method. They determined the effects of those four parameters on detachment rate. The influence of flow rate on critical rill length and thawed soil depth on reduction coefficient of detachment rate was limited. The combined impacts of slope gradient and flow rate were positively related to those four parameters. This study quantified the effect of slope, flow rate, and thawed soil depth on detachment rate and help to quantify the soil detachment rate in cold region.