Quantifying the Effect of a Freeze-Thaw Cycle on Soil Erosion, Laboratory Experiments

摘要

In this paper we quantitatively tested the hypothesis that soil freeze-thaw(FT) processes significantly increase the potential for upland hillslope erosion during runoff events that follow thaw. We selected a frost- susceptible silt to obtain an upper bound on FT effects, and completed three series of six experiments each to quantify differences in soil erodibility and rill development for bare soil following a single FT cycle. Each series represented a specific soil moisture range: 16-18%, 27-30%, and 37-40% by volume, with nominal flow rates of 0.4, 1.2, and 2.4 L/min and slopes of 8 and 15. Each experiment used two identical soil bins, one a control (C) to remain unfrozen, the other to be frozen and thawed. Standard soil characterization tests did not detect significant differences between the FT and C bins. Experimental results were closely related to conditions of the experiment, imposing a requirement for minimum differences in soil weight, bulk density, and soil moisture through each series. We measured cross-sectional geometry of an imposed straight rectangular rill before each experiment, sediment load during, and rill cross sections after. Changes in cross section provided detailed measures of erosion at specific locations along the rill, while sediment load from time series runoff samples integrated the rill erosion. Several parameters, including average maximum rill width, average maximum rill depth, rill cross-section depth measures, and sediment load all followed similar trends. Each was greater in the FT than in the C, with values that generally increased with slope and flow. However, soil moisture was the only parameter that affected the FT/C relationship. For example, average sediment load grouped by soil moisture provided FT/C ratios of 2.4, 3.0, and 5.0 for low, mid, and high moisture, respectively. In contrast, a 'dry' experiment at 4.4 soil moisture had FT/C of 1.02 for sediment load.