Meltwater erosion process of frozen soil as affected by thawed depth under concentrated flow in high altitude and cold regions

Changes in thawed depth of frozen soil caused by diurnal and seasonal temperature fluctuations are commonly found in high altitude and latitude regions of the world. These changes significantly influence hydrologic and erosion processes. Experimental data are necessary to improve the understanding and modeling of the phenomenon. Laboratory experiments were conducted in Beijing to assess the impacts of thawed soil depth, slope gradient, and flow rate on soil erosion by concentrated meltwater flow over an underlying frozen soil layer. Soil samples from watershed were filled in flumes, saturated before being frozen. After the soil was completely frozen, flumes were taken out of storage to thaw the frozen soil from top to the designed depths. Meltwater flow was simulated using a tank filled with water and icecubes at approximately 0 degrees C. The erosion experiments involved four thawed soil depths of 1, 2, 5, and 10cm; three slope gradients of 5 degrees, 10 degrees, and 15 degrees; and three flow rates of 1, 2, and 4l/min; and seven rill lengths of 0.5, 1, 2, 3, 4, 5, and 6m. Sediment-laden water samples were collected at the lower end of the flume for determination of sediment concentration. The results showed that sediment concentration increased exponentially with rill length to approach a maximum value. The sediment concentrations were closely correlated with thawed soil depth, flow rate, and slope gradient. Shallower thawed depths delivered more sediments than deeper thawed depths. Slope gradient was the primary factor responsible for severe erosion. The effect of flow rate on sediment concentration which decreased with increasing slope gradient, was not as significant as that of slope gradient. Results from these experiments are useful for understanding the effect of thawed soil depth on erosion process in thawed soils subject to freezing and for estimating erosion model parameters. Copyright (c) 2017 John Wiley & Sons, Ltd.