Overland erosion due to freezethaw cycling
3
Several investigators have used controlled laboratory experiments to define
the magnitude of the FT effects. Formanek et al. (1984) found that the shear
strength of a silt loam was reduced to less than half its original value after one
FT cycle, but second and third cycles resulted in little additional change. Van
Klaveren (1987) suggested that critical shear strength of soil might be half of its
normal value after one FT cycle. Edwards and Burney (1987) used a laboratory
rainfall simulator to determine that FT of a bare soil increased sediment loss by
90%, and that this loss increased significantly when overland flow was added.
Laboratory experiments by Van Klaveren and McCool (1998) on rill erosion
following a single FT cycle revealed that rill erodibility of thawed soils was
slightly higher than that from an unfrozen soil test. Edwards et al. (1995) con-
ducted similar laboratory tests except that four diurnal cycles of freezethaw
were performed prior to a final 12-hour freezing cycle. Erosion of this cycled and
initially frozen soil produced a mean sediment yield 25% greater than a similar
soil that had never been frozen.
These field and laboratory experiments did not use a control, which is
required to define and model the quantitative differences caused by FT cycling.
Still, this previous work suggests that FT is a primary process contributing to
upland soil erosion and that inadequate modeling of FT effects could cause
significant underprediction of soil losses in cold climates. However, further
investigation is needed to build a more complete and quantitative understanding
of FT effects and to accurately account for FT weakening in soil erosion predic-
tion models applied to hill slopes and watersheds. Without this understanding,
the effects of FT cannot be explicitly modeled and must be lumped with other
processes, thereby prohibiting incorporation of future scenarios of varying
temperature regimes into soil-erosion predictions. Good regional sediment
management requires accurate modeling of all important processes, including
soil-FT cycling.
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