The Effect of Ground Frost on Snowmelt Runoff
at Sleepers River, Vermont
James B. Shanley1 and Ann Chalmers1
Ground frost has been monitored at the Sleepers River Research Watershed in northeastern Vermont
since 1984. Frost develops every winter, particularly in open fields, but its depth varies greatly from
year to year in inverse relation to snow depth. During the 15 years of record at a benchmark mid-
elevation open site, the seasonal frost depth maximum varied from 7 cm to 39 cm. At the outlet of the
maximum seasonal frost depth for the period leading up to peak flow, and negatively correlated
(p < 0.05) to the maximum seasonal frost depth for the period from peak flow to the return of base
flow. These same runoff-frost relations appeared to be even stronger for 6 years of flow and frost
depth measured at a small agricultural catchment within the Sleepers River watershed. The runoff-
frost relations can be explained by the greater tendency of snowmelt or rainfall runoff to flow over-
land to the stream channel when ground frost is present. In the absence of ground frost, snowmelt
and rain more readily infiltrate and recharge groundwater. Ground frost thus tends to shift runoff
toward an earlier date by increasing surface runoff in early spring and limiting the recharge that
normally sustains high base flows in mid- to late-spring.
Based on analysis of six events, the presence of frost appeared to promote a larger and somewhat
quicker response to rainfall relative to the no-frost case, although snow cover caused a much greater
time-to-peak regardless of frost status. The role of frozen ground in increasing early spring runoff is
important both from a water supply standpoint (less recharge) and a water quality standpoint (ero-
sion and rapid transport of surface contaminants to channels).
1
U.S. Army Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire
03755-1290, USA
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