Application of Environmental Analysis to Watershed Snowmelt

Abstract

The role of environmental characteristics of elevation, slope-aspect and forest cover in spatially differ-entiating rates of snowmelt is examined over a 43-mi2 northern Vermont watershed. Both energy balance considerations and selected melt observations indicate the operation of an effective natural snowmelt runoff control mechanism. The more spatially diverse the watershed combinations of elevation slope-aspect and forest cover are, the more effective the natural snowmelt control mechanism is apt to be. Previous snowmelt models developed by the U.S. Corps of Engineers are modified to fit topographic and forest conditions in New England. The modified model is used to compare average snowmelt rates over a typical upland Vermont watershed, a highly diverse watershed in the White Mountains of New Hampshire, and a watershed of maximum homogeneity in the open flat Champlain Valley of Vermont. The profound role of environment in regulating snow-water release is apparent. Simulated weather sequences of rapid melt days are run through the model to estimate effects of watershed environment on snowmelt. Rapid snowmelt runoff is extremely unlikely except in environmentally homogeneous watersheds or during unusual weather sequences in which sensible heat and condensation heat energy are added rapidly and uniformly to the entire watershed snow cover. As most of the snowmelt in northern New England results from solar radiation over watersheds of great environmental diversity, the region appears to enjoy a highly effective natural snowmelt runoff control mechanism. Although soil types, geology, ground frost and other factors affect runoff, relatively simple analyses of forest, elevation and slope-aspect distributions over ungaged watersheds provide considerable information on their snowmelt runoff characteristics.