Cold Regions Engineering
U.S. Army Engineer Research and Development Center, Hanover, New Hampshire
Inclusion of FreezeThaw-Induced Soil and Bank Erosion
in CoE Planning, Engineering, O&M, and Model Development
Soil freezethaw (FT) processes directly affect soil erodibility and bank-failure susceptibility (Fig. 1) (Gatto et al. 2001,
Simon et al. 2000) and thus have substantial impact on shoreline or bank evolution, system-wide sediment management,
reservoir infilling, levee stability, and sediment-bound contaminant transport within watersheds. This technical note outlines
how FT cycling affects overland soil erosion and bank failure. In so doing, it alerts Corps planners, designers, O&M person-
nel, and water-resources modelers to the importance of knowing the magnitude of these effects on sediment detachment,
failure, and transport in such cold-climate, navigable systems as the Mississippi, Illinois, Ohio, Missouri, Susquehanna,
Delaware, Columbia, and Sacramento Rivers, and the Great Lakes and their connecting channels.
Freezethaw processes
During freezing, ice crystals form within
a soil, tightly binding soil particles and
keeping the soil highly resistant to erosion
and failure. However, that ice also pushes soil
particles apart, reducing interparticle friction
so that thawed soils are less cohesive, dense,
and strong (Gatto 2000). One FT cycle can
reduce soil shear strength by 50% or more
(Formanek et al. 1984, Van Klaveren 1987).
Also, the soilsurface geometry of
thawed soil is often changed by frost heaving
during freezing, unit weight is often increased
by the soil water drawn into the freezing soil,
and infiltration is reduced because water
content is usually high. The magnitude of
these effects is variable and depends on soil
Figure 1. Banks are highly susceptible to failure upon thaw.
type, water content, and freezing intensity.
Soil FT cycles are generally inferred from surface air temperature records. According to Hershfield (1974), a FT event
occurs when the air temperature drops below freezing in a calendar day. The presence of frozen ground, which confirms FT
processes, is noted over most of the United States (Fig. 2). The most frost-susceptible soils are cohesive, silty sediments. Silts
absorb water rapidly because they have particles small enough to provide comparatively high capillary rise and large enough
to furnish voids of adequate size to allow rapid flow of water (Jumikis 1962). These characteristics lead to rapid saturation of
the soil voids. Coarser-grained soils do not retain a significant volume of water after wetting, and finer-grained soils do not
absorb water rapidly. However, sand may become frost susceptible if it is well compacted (Janson 1963), and needle ice will
form in almost any soil type (Chamberlain 1981).
FT effects increase soil erodibility and instability such that overland runoff and floods in the spring often erode signi-
ficantly more thawed upland and bank soil than at other times of the year (Renard et al. 1997). Research shows that in areas
where seasonal frost forms, processes related to soil FT contribute to 40 to 85% of overland soil erosion (Zuzel et al. 1982,
McCool 1990) and 30 to 90% of bank failures (Thorne 1978, Sterrett 1980, Gardiner 1983, Reid 1985, Lawler 1993, Chase et
al. 2001). When rills (Fig. 3) are present on hillslopes they transport 80% of the sediment eroded from that slope (Mutchler
and Young 1975). Thus, rill flows are far more important in hillslope erosion than overland sheet flow.
ERDC/CRREL Technical Note 04-2
April 2004
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