Hydrology analysis of the Colorado River floods of 1983

Despite an extensive system of river regulation works, the mainstem of the Colorado River in 1983 experienced the highest flows on record, resulting in severe flood damage. The high flows were due to an abnormally late season mountain snow accumulation, an accelerated snowpack ablation, and high initial reservoir levels. Forecasts of April-July inflow to Lake Powell, the major Upper Basin reservoir, nearly doubled from early May to late June.The report evaluates the efficacy of runoff and inflow prediction methodologies utilized to formulate reservoir operational responses during the winter and spring of 1983. Given the restrictions inherent in the forecasting network, the reservoir release schedule followed during the period by the US Bureau of Reclamation (USBR) is then reviewed. Two alternative reservoir release schedules are also presented, and their hypothetical impacts on flooding assessed. In light of the 1983 flooding, recommendations are made to increase the reliability of flood predictions for Colorado River reservoirs and to reduce the extent of future damage to and destabilization of the biological and physical resources of Grand Canyon National Park.A brief epilogue provides an update on the evolution of the Colorado River reservoir operations policy. The new policies helped to attenuate 1984 peak reservoir discharges, even though the 1984 total tunoff exceeded that of 1983.