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. VI be used for flood control and floodplain management activities for the Sulphur Creek Basin. This recommendation is based on the findings of the detailed investigation using 1991 basin conditions and the USDA-SCS TR 20 rainfall-runoff model. TABLE VI SULPHUR CREEK BASIN 1991 HYDROLOGIC CONDmONS FLOOD DISCHARGES (in cubic feet per second) FLOOD FREOUENCY Discharge 10-year 25-year 50-year 100-year 5OD-year 345 690 975 1325 2450 It was discovered that the 1969, 1976, and 1977/1978 hydrologic studies previously listed were performed under criteria/procedures which cannot be re-constituted. However, . these respective criteria/procedures may have been state-of-the-art at the time of study. A summary of the review of those studies is listed below: o For the 1969 study, a study procedure was used by the SCS which has been replaced by their TR-55 procedure. It is recommended this method not be used for homogeneous basins which are larger than 5 square miles. The Sulphur Creek Basin is 22.2 square miles. o For the August, 1976 study, a hybrid procedure was used which included portions of a Bureau of Reclamation procedure and basin parameters from the SCS's 1969 study. It is difficult to determine how the frequency values were computed. o The June, 1978 study was prepared in draft form in April, 1977. There is some comparability of the study procedure described in that draft to the SCS TR 20 model. However, a number of the input parameters are referenced to the 1969 study. Some changes were made after the April, 1977 draft. Those changes appear in the floodplain study itself. No final hydrology report could be located. Since the final report can not be retrieved, it is difficult to determine the study procedure. . 10