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I I I I I I I I I I I I I I I I I I I where peak flows are not affected by regulations and diversion. The locations of selected gauging stations are shown in Figure B. Stream ga~ging stations used are listed in Table 1 and Table 2. Since the annual peak discharges published in the u.S. Geological Survey's Water Supply Paper (References 6, 7, and B) and the U.S. Geological Survey's Surface Water Records (Reference 9) were a mixture of flood flows caused by snowmelt and rainfall events, the regional relationship established by using these annual peak dis- charges does not reflect intense rainfall produced flooding. A more detailed method was used for each gauging station to develop regional relationships for an individual river basin. The procedures are described as follows: (1) separating the rain and snowmelt data at each gauging station, developing statistics for each type of event, and statistically combining the two frequency curves (stream flow records were obtained from the u.S. Geological Survey, Denver Federal Center); (2) adjusting short period statistics to reflect long period values if they are closely correlated; (3) outliers and historical data were considered during the development of flood flow frequency realtionships for each gauging station; and (4) developing regional relationships relating basin area to peak discharge for the 10-, 50-, 100- and 500-year floods by regression analysis. The accuracy of the station frequency-discharge relationship de- rived from a short record can be improved by comparing the short record with nearby long-term record and adjusting the short record. \ statistics accordingly if they are closely correlated during the -12-