Comparative study of erosion processes of thawed and non-frozen soil by concentrated meltwater flow

Abstract

Investigating the erosion processes of freeze–thaw-affected soils caused by concentrated snow/glacier meltwater flow can be challenging. Experimental data can help improve our understanding and modeling of the phenomenon. Laboratory experiments were conducted to assess the effects of slope gradient and flow rate on soil erosion by concentrated meltwater flow over thawed and non-frozen soil surfaces. Flumes were filled with the silty–sandy soil materials collected from a watershed delta formed by deposited sediments before being saturated and stored in a freezer to freeze the soil. After the soil was completely frozen, the flumes were taken out of the freezer and placed in the experimental hall to thaw the soil for a period of sufficient length until all the soil materials were thawed. Similarly, flumes which were filled with the same soil in the same procedures without undergoing the freezing and thawing process were used for the comparative experiments. Meltwater was simulated with a tank filled with ice water mixture to supply water flow at a temperature of 0°C. The erosion experiments involved four slope gradients of 5°, 10°, 15°, and 20° and three flow rates of 1, 2, and 4L/min, with seven rill lengths of 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, and 6.0m, as determined by the distance between the water inlets and exit sill. Sediment concentrations at the seven locations formed a rill erosion process, which increased exponentially with rill length to approach a limiting value. The sediment concentrations were positively correlated with flow rate and slope gradient. However, the effect of flow rate on sediment concentration was not as significant as that of slope gradient. The effect of flow rate on sediment concentration decreased with the increase in slope gradient. The maximum sediment concentrations in water flow over thawed slopes were higher than those over non-frozen slopes. Results from these experiments will be useful for estimating erosion model parameters for predicting erosion by meltwater.