Long-Term Simulation of Thermal Regime of Missouri River

Abstract

Riverine water temperature extremes have typically been analyzed using event-based simulations, for example the 10-year 7-day low flows, combined with record-high air temperatures and other extreme conditions relevant to the location (e.g., maximum power generation). Using this combination of extreme conditions, one can estimate the maximum water temperature that may occur on the river. However, this method does not allow for calculation of, for example, the probability of a given temperature exceedence, or the average duration of such an excursion event. Alternatively, long-term continuous simulation using historical and physically representative reconstructed data records provides a large database of realistic events, which can be used to analyze the thermal regime of a river and its variability under current and changing conditions. This study applies such a procedure to the Missouri River between Gavins Point Dam at Yankton, S.D., and Rulo, Nebr. Along this reach, the thermal regime is influenced by six power installations, which release heated condenser cooling water to the main stem. Several scenarios were simulated numerically with the one-dimensional (1D) CHARIMA model to examine the effects of current power generation, as well as changing operational, hydrologic, and climatological conditions on the river thermal regime. Model simulations revealed that climate change and increased power demand may significantly affect the thermal regime of the Missouri River; however, the scenarios simulated in this study did not result in water temperatures that exceed the current temperature standards.