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During the first stage of the present study the historic flow data for the Arkansas River above John Martin Dam were evaluated. This historic information was obtained from the United States Geologic Survey's (USGS) web site and imported into a spreadsheet program. The data set covers the period from 1903 through 1999, although the data have been gathered from five separate gage locations over that time. The study area includes an approximately 80-mile reach of the Arkansas River from just downstream of Pueblo Dam, near Avondale to just upstream of John Martin Reservoir near Las Animas, Colorado. Five gages will be studied which jnclude; three stream gages owned by the State and two U.S. Geological Survey (USGS) stream gages. These are listed in Table 3.1. TABLE3.! STREAM GAGES Gage Name Gage , Drainage Area Gage Period Number (Square Miles) Elevation (ft) Of Record Arkansas River near Avondale, CO 07109500 6327 4510 1939 to 51, 65-1999 Arkansas River near Nepesta, CO 07117000 9345 4385 1903,12, 14- 1999 Arkansas River at Catlin Dam near Fowler, CO 07119700 10901 4246 1965 to , 1999 Arkansas River at La Junta, CO 07123000. 12210 4040 1894,1903, 12 to 1999 Arkansas River at Las Animas, CO 07124000 13976 3884 1921-72 . 1974-99 A Discharge Rating Curve was developed for the La' Junta stream gage.at the request of the CWCB (Refer to Plate 1). The Albuquerque District investigated discharge-frequency relationships for the stream gages on the Arkansas River from just downstream of Pueblo Dam, near Avondale to just upstream of John Martin Reservoir near Las Animas, Colorado. The current study utilizes data from an earlier Corps of Engineers flood control study by reducing the actual flow by a percentage due to the !\ssumption that Pueblo Dam was operating prior to 1975. The 1967 Hydrology DM #1, developed for the Las Animas Local Protection Program, Table 13, page 22, used data from the Las Animas stream gage to describe existing conditions preceding the construction of Pueblo Dam in 1975. We compared the flows at the other four stream gages and interpolated based on the percentage of decrease in flows for each year. The adjusted data were placed into an Excel spreadsheet and incorporated into an input file for the Flood Frequency Analysis (FFA) program. The Corps then performed a Log-Pearson 26 I I I I I I I I I I I I I I I I I I I