Search

The occurrence of snow and soil frost influences hydrology and, in turn, the mechanisms of soil erosion processes in cold regions. For these regions, reliably modeling the dynamics of snow accumulation and melt, and soil frost formation and melt, is necessary prior to accurately predicting runoff and erosion. Only then will methods for predicting the rates and amounts of soil erosion by water be established on a firm hydrological footing. This article examines the potential of an energy budget approach to simulate the magnitude and variations of snow and soil frost depths. It is assumed that the net sum of all energy components in the environment is consumed or compensated by water phase change occurring near or under the ground surface, such as snow melting or soil freezing and thawing. Testing indicates that this energy budget approach demonstrates promise to simulate winter hydrology and to be adapted to erosion prediction models.

Sensitivity analyses conducted on hydrologic models are useful for understanding the complicated interactions of hydrologic processes and for demonstrating the potential errors resulting from incorrect estimation of input parameters. The effects of typical changes (measurement errors or natural variability) in input parameters on soil freezing as simulated by the Simultaneous Heat and Water (SHAW) model were investigated. The SHAW model simulates the interrelated heat and water transfer within snow, residue, and soil using estimated or measured weather data. Simulated frost depth was found to be very sensitive to small changes in air temperature (1° C) and initial snow depth (10 cm). Simulated frost depth was also potentially sensitive to the specified soil temperature for the lower boundary depending on the proximity of frost depth to the depth of the simulated profile. Site, residue soil characteristics having the greatest impact on simulated frost were slope, thickness of the residue layer, thermal conductivity of soil particles, soil bulk density, and a surface roughness parameter. Soil hydraulic parameters had little effect on frost depth, but had a large impact on water movement toward the zone of freezing and ice content of the frozen soil.

A heat flow based model is developed to predict the rate and depth of soil frost development and disappearance under various tillage-residue management systems. The model is compared with observed results under six tillage residue systems consisting of fall plow, fall chisel and no till with and without residue. The model uses constant values for soil water, thermal conductivity for frozen and unfrozen soil and snow, hydraulic conductivity and heat capacity and is driven by daily inputs of air temperature and snow depth. The assumption is made that mean daily air temperatures are reasonable estimates of the mean daily surface temperature of snow or soil. Predicted and observed frost depth values are in good agreement. Thaw depth predictions show the correct trends but do not match observed values.

SOIL freezing induced movement of soil water in the top 1.5 m of a Barnes loam soil (fme-loamy, mixed, Udic Haploboroll) was studied over the winters of 1982 to 83 through 1986 to 87 under fall plow, fall chisel, and no till systems each with and without residue. Measurements consisted of frost depth, snow depth, soil water content, air temperature, snowfall, and precipitation. Changes in soil water were determined relative to soil water content just before freezing. Changes in water content were related to depth of soil freezing and initial fall soil water content. Frost penetration was inversely related to snow depth. However, early season snowfall has a greater effect than later snowfall. Fall plowing traps the least snow and has the deepest frost. No till-residue plots trap the most snow and have the least frost. Uniform frost penetration was measured over all treatments in a year with virtually no snowfall. Initially dry soil grained water. Initially wet soil lost water. Greatest accumulation of water was measured 14 days before complete thawing, which is after maximum frost penetration when surface melting had started. In both wet and dry years water accumulated in frozen soil zones. Accumulation roughly coincided with arrival of the freezin front. Accumulation below the frozen zone occurred at the beginning of spring thaw or during mid-or late winter periods of snowmelt. Apparently water from snowmelt or surface soil thaw passed through frozen soil to unfrozen soil beneath.