Snowmelt indexes for small mountain watersheds

Abstract

The area used in this study was the Upper Hourglass watershed which is located on the Little South Fork of the Cache La Poudre River, 26 air miles west of Fort Collins, Colorado. The Upper Hourglass watershed is an area of approximately 1000 acres lying between 10,400 and 12,700 feet above msl on the north side of Comanche Peak. The snowmelt indexes were developed using multiple correlation and regression analyses of runoff and climatic data from the study area. Two dependent variables and 23 independent variables were used in the analysis. In the development of the independent variables the variation of solar radiation between mountain watersheds for the period July-August, 1965, was studied. This analysis showed that there were significant differences in the amount of incoming shortwave radiation between days and between the two general locations studied. Six snowmelt Indexes are presented to fit different situations that occurred during the study year. These indexes indicate that solar radiation and minimum temperature play an important role in indexing snowmelt on the Upper Hourglass watershed. The indexes using the first day's runoff as the dependent variable consistently accounted for more of the variability in snowmelt than did the indexes using total generated runoff. The six relationships presented all appear reasonable when the factors that effect snowmelt are considered.