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1411 (ref. 14). A 30-minute computat:ion interval was used in the HEC-l model for this rainfall. DISCHARGE FREQU:E:NCY. Peak discharges for the J.OO-, :;0-.., 25-, and 10-year floods were determined using the HEC-l computer program. The 500- year flood was determined by extrapolation. The values are shown in the following table: '-- FREQUENCY 500-YR -- - 100-YR -- - 50-YR -- - 25-YR 10-YR REGFESSIC~N ANALYSIS This portion of the report describe!; the attempt to develop a regional relationship correlating basin area to frequency flood discharges for tributaries of the Arkansas River in the vicinity of Florence, Colorado. A final relationship was not generated because the lack of stream gage data for foothill streams in the Arkansas River basin precluded the development: of a statistically sound predicting equation from a regional regression analysis. USGS STREAM GAGE DATA. The regional st:Udy required an analysis of stream flow data from U.S. Geological Survey (USGS) gages located on t:~ibutaries to the Arkansas River. The USGS National \^later Data Stor3oge and Retrieval System (\^lATSTORE) retrievEld annual discharge data from gaged basins in the area of inten,st havin'J similar physical characteristics to the watershed under study. Oak Creek is a foothill stream, and an attempt was n~de to retrieve gage data for streams located in the foothill areas of ~he Arkansas River basi~; however, very few such gages exist. To enlarge the data base, gage information was also retrieved for streams located in the plains region adjacent to the foothills and streams located in the South platte River basin directly north of the Arkansas River basin. Annual peak discharge records for all USGS stream gage" which lie in the Arkansas River basin within the coordinates J70 to 390 north latitude and 1020 and 1060 longitude have been analyzed for their applicability to the regional study. Foothill str,eam gages in the South Platte River basin Here obtained from USGS Water 4