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<br />ANNUAL SNOWMELT AND RAINFALL PEAK-FLOW DAT~ ON <br />SELECTED FOOTHILLS REGION STREAMS, SOUTH PLATTE RIVER, <br />ARKANSAS RIVER, AND COLORADO RIVER BASINS, COLORADO <br /> <br />By John G. Elliott, Robert D. Jarrett, and John L. Ebling <br /> <br />ABSTRACT <br /> <br />Peak flows in the foothills region of Colorado are attributable to two mete- <br />orologic sources--snowmelt and rainfall. As part of a study of the hydrology of <br />foothills streams in Colorado, charts from streamflow gages on unregulated streams <br />were examined to determine the source of peak-flow events. Snowmelt-runoff peaks <br />were distinguished from rainfall-runoff peaks on the basis of daily and seasonal <br />occurrence, hydrograph shape, and local weather conditions. Peak-fiow data for <br />snowmelt runoff and rainfall runoff are presented for 69 streamflow-gaging sta- <br />tions in the South Platte River, the Arkansas River, and the Colorado River <br />basins. <br /> <br />INTRODUCTION <br /> <br />A realistic determination of the magnitude and frequency of floods is essen- <br />tial in the design of structures, land"use planning, identification of flood- <br />hazard areas, and studies involving streamflow characteristics. Peak flows for <br />ungaged watersheds or those with short periods of record are estimated with a re- <br />gional flood-frequency analysis which utilizes data collected in gaged watersheds <br />of similar climatic and geomorphic setting. Regional flood-frequency analysis has <br />been performed for Colorado streams by Patterson (1964; 1965), Patterson and <br />Somers (1966), Matthai (1968), McCain and Jarrett (1976), and Livingston (1970, <br />1981). <br /> <br />The foothills region of Colorado is defined as the rugged terrain between <br />high mountainous areas and plains, or plateaus, areas. Peak-flow events in this <br />region may be produced by either melting of the snowpack or rainfall runoff, This <br />mixed population of flood events complicates flood hydrology and attempts at con- <br />ventional flood-frequency analysis. For this reason a study to identify the unique <br />character of the foothills region flood hydrology has been undertaken. The study <br />was conducted in cooperation with the U.S. Army Corps of Engineers, Albuquerque, <br />Omaha, and Sacramento Districts; the U.S. Bureau of Reclamation, Salt Lake City, <br />Utah; the Colorado Water Conservation Board; and the Urban Drainage and Flood Con- <br />trol District, Denver, Colo. <br />