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It 37 would require evacuation of portions of the canyon, and outflows of 5,000 ft3/S are expected to overtop Highway 34, restricting evacuation routes. Because of this, the storm time at which outflows exceed these values were used to develop the decision criteria discussed later in this document. Fisher Criteria A HEC-1 rainfall-runoff model was developed to obtain an estimate of the runoff from rainfall depths using various basin infiltration scenarios. The model also computed the impacts on the reservoir level from those inflows. The model was developed using the subbasin delineation and runoff parameters from the PMF study dated May 7, 1981. After an initial calibration model were made for various rainfall events at the drainage basin for dry and wet soil Ramfal runs locations in process, different [ . centered conditions Establishing the rainfall criteria required determining the one-hour and three-hour precipitation values, and comparing the time at which these values occurred with the time that the reservoir outflows exceeded 2,000 ft3/S and 5,000 ft3/S for each model run. A spillway release of 2,000 ft3/S impacts many homes and bridges across the river, and a spillway release of 5,000 ft3/s begins to overtop Highway 34 potentially blocking evacuation routes. An estimate of the criteria was determined by establishing a precipitation value that would keep the frequency of false alarms low, while still providing as much warning time as possible. The 25-year, one-hour precipitation value areally reduced for 150 square miles is 1.2 inches, and the 25-year, three- hour precipitation value is 1.7 inches. This rainfall depth has a 4 % chance of occurring in any given year, which implies a frequency of false alarms of once every 25 years. The 100-year, one-hour precipitation value areally reduced for 150 square miles is 1.5 inches, and the 100-year, three-hour precipitation value is 2.2 inches. This rainfall depth has a 1 % chance of r occurring in any given year, which implies a frequency of false alarms on the average of once every 100 years. The tradeoff in selection of rainfall decision criteria is warning time versus frequency of false alarms. A search of the historical precipitation data for Estes Park rain gauge shows the maximum rainfall amounts were 0.70 inches in one hour, and 0.80 inches in three hours from 1978 to 1993. A search of the historical precipita- tion data for nearby gauges at similar elevations as the Estes Park rain gauge shows the maximum rainfall amounts were 1.60 inches in one hour, and 3.00 inches in three hours. This event occurred on July 22, 1991, at the Allens- park Lodge rain gauge located at an elevation of 8,450 feet. This gauge has