Effects of Climate and Dam Operations on Reservoir Thermal Structure

Abstract

Recently, the United States Bureau of Reclamation agreed to increase spring releases from Upper Colorado River Basin reservoirs to create a more natural flow regime in the lower Gunnison River and Upper Colorado River. Fishery managers have expressed concern that new operations could change reservoir conditions and jeopardize popular and economically important reservoir sport fisheries. This study attempts to predict how one aspect of reservoir conditions, thermal structure, might respond to new dam operations at Blue Mesa Reservoir aimed at addressing downstream ecological concerns. A one-dimensional thermal model ~CE-THERM! is applied to simulating thermal effects of ''traditional'' and proposed ''new'' dam operation scenarios. To evaluate the relative importance of climate and dam operations a sensitivity analysis of hydrologic ~i.e., inflows and starting reservoir elevation ! and meteorologic ~i.e., air tempera- ture, cloud cover, and dew point temperature! inputs was conducted along with an ''extreme'' dam operation scenario. Results indicate that reservoir managers at Blue Mesa Reservoir have considerable latitude for new operations without negative thermal consequences. The natural variability of climate and hydrology appear to exert stronger control over reservoir thermal structure than reservoir operations at Blue Mesa.