The influence of snowmelt in evaluating small hydropower generation potential

The amount and time of runoff from mountain watersheds is a critical factor in the small hydro development that is currently underway in the Cascade Mountains of the Pacific Northwest. The main source of runoff in this region is the mountain snowpack, therefore, the total snowpack volume and its rate of melt are important considerations in hydroelectric plant design. A model is proposed that is designed to predict the discharge of small ungauged, mountain watersheds for the purpose of assessing small hydro feasility. Both watershed yield (total annual runoff) and timing (the daily distribution of flows throughout the year) are determined by this technique. The two main inputs to the model are the observed runoff for several adjacent watersheds, plus the area-altitude distributions for these watersheds. The model is designed to explain the observed runoff at the gauged sites on the basis of each watershed's area-altitude distribution. The resulting rational runoff-altitude distribution is applied to the area-altitude distribution of the ungauged sites.