Quantifying the Effect of a FreezeThaw Cycle on Soil Erosion: Laboratory Experiments
M.G. Ferrick and L.W. Gatto
Environmental Sciences Branch
Cold Regions Research and Engineering Laboratory
Engineer Research and Development Center
72 Lyme Rd.
Hanover, NH 03755-1290
Abstract. In this paper we quantitatively tested the hypothesis that soil freezethaw (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: 1618%, 2730%, and 3740%
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. These results
indicate a dramatic increase in the rate and quantity of bare soil eroded as a result of the FT cycle that is
in direct proportion to soil moisture.
Keywords: Soil erosion, rill development, freezethaw effects, overland flow
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