Patterns of Soil Loss and Snowmelt from an Intermountain Rangeland Site
Wildland areas in the Intermountain Area are being more heavily utilized in recent years for energy and mineral development, grazing of livestock, forest products, and recreation. Management and planning agencies require techniques to assist in the prediction of soil erosion from these and other land uses. Most erosion prediction methods apply to agricultural situations, and application to wildland areas has met with many problems. The objective of this study was to determine the magnitude of soil loss due to spring snowmelt from a mountain snowpack, and attempt to develop a snowmelt-erosion relationship. The Universal Soil Loss Equation was tested on four .01-acre bordered plots, each 72.6 feet long and 6.0 feet wide. Snowmelt runoff and soil loss were measured on a daily basis throughout the 1978 and 1979 spring snowmelt periods. Rainstorm soil loss was measured after each event during 1978. Average soil loss in the snowmelt period of 6.0 and 10.3 pounds per acre were measured from plots on 11 and 32 percent slopes, respectively. Snowmelt runoff averaged 1.1 percent from a maximum snowpack water equivalent of 13.9 inches. The Universal Soil Loss Equation rainfall-runoff factor as modified for winter precipitation would have predicted soil loss of approximately 10 and 55 tons per acre from the same slopes, during the winter months. Highly permeable stalactite soil frost and slow melt rates resulted in minimal overland flow from the snowpack. Insignificant soil loss due to spring snowmelt from a deep continuous snowpack makes the use of the modified rainfall-runoff factor unwarranted during winter months in the Intermountain Area. The Universal Soil Loss Equation applied on a per-storm basis drastically overestimated the soil loss from summer rainfall events at the study site during 1978. The measured seasonal storm erosivity was 24 percent of the average annual value derived from published isoerodent maps. Soil loss from the 32 percent slope was 1.6 times that of the 11 percent slope. The degree-day method was more accurate for daily snow melt prediction than a simplified energy balance method. Maximum daily air temperature provided a more useful degree-day factor than did mean daily air temperature.
Loomas, Steven A. (1984). Patterns of soil loss and snowmelt from an Intermountain rangeland site. MS. 95p.