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I I I I I I I I I I I I I' I I I I I I - 4 - in the Breckenridge area. One station, Hoosier Pass, is located on the Continental Divide south of town. Two other stations are located at different elevations down through the basin. A U.S.G.S. continuous recording gage is located on the Blue River below the town. A review and correlation of the precipitation gages with streamflow records gave an indication as to the type of hydrology that existed in the area. For example, shown in Table 1 are the dates of peak discharges on the Blue River and the amounts of precipitation that occurred on that day and three days preceding the date of peak discharge for the period 1951 through 1972. From the table it could be seen for the most part that very little relationship exists between the peak discharge and the amount of rain that fell in the basin. This relationship suggests two things: the storms that caused the events are of small areal distribution or the flood peaks were due almost entirely to snowmelt runoff. To duplicate the type of storm that is most likely to occur and cause a flooding event, it was necessary to have an understanding of meteorological factors that govern the occurrence of storms. Accordingly, a series of reports on the climatology of the Blue River Basin was prepared by Mr. G. V. Mulvey of Colorado State University Department of Atmospheric Sciences. In his reports, Mr. Mulvey describes the rainfall producing events for the la-year, 25-year, IRF and SPF. These reports are shown in Appendix A and were used in the computer model to synthetically derive flood flows. The relationship between snow course data collected at Hoosier Pass . and peak discharge in the Blue River basin recorded at the U.S.G.S. recording gage helped define the dependence of peak flows on snow- melt. Figure 1 shows the relationship between snow course data and peak discharge. A statistical analysis was run on the two sets of data and a regression coefficient of 0.88 was found to exist. The equation defining the relationship is also shown on the Figure. Similar type investigations were made for the lower snow course stations; however, lower regression coefficients were found to exist. This indicates that the peak discharge on the Blue River occurs primarily when the upper basin is contributing snowmelt and most of the snowmelt in the lower basin is gone. " ~ Leonard Rice Consulting Water Engineers. Inc.