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During the first stage of the present study tha historic flow data for the Arkansas River <br />above John Martin Dam were evaluated. This historic information was obtained from the United <br />States Geologic Survey's (USGS) web site and imported into a spreadsheet program, The data <br />set covers the period from 1903 through 1999, although the data have been gathered from five <br />separate gage locations over that time. <br />The study area includes an approximately 80 -mile reach of the Arkansas River from just <br />downstream of Pueblo Dam, near Avondale to just upstream of John Martin Reservoir near Las <br />Animas, Colorado. Five gages will be studied which include; three stream gages owned by the State <br />and two U.S. Geological Survey (USGS) stream gages. These are listed in Table 3.1. <br />TABLE 3.1 <br />STREAM GAGES <br />Gage Name <br />Gage ' <br />Drainage Area <br />Gage <br />Period <br />Number <br />(Square Miles) <br />Elevation (ft) <br />Of Record <br />Arkansas River near Avondale, CO <br />07109500. <br />6327 <br />4510 <br />1939 to 51, <br />65 -1999 <br />Arkansas River near Nepesta, CO <br />07117000: <br />9345 <br />4385 <br />1903,12,14- <br />1999 <br />Arkansas River at Catlin Dam near Fowler, CO <br />07119700 <br />10901 <br />4246 <br />1965 to <br />1999 <br />Arkansas River at La Junta, CO <br />07123000; <br />12210 <br />4040 <br />1894,1903, <br />12 to 1999 <br />Arkansas River at Las Animas, CO <br />07124000 <br />13976 <br />3884 <br />1921 -72 <br />1974 -99 <br />A Discharge Rating Curve was developed for the Lai �Junta stream gage-at the request of the <br />CWCB (Refer to Plate 1), <br />The Albuquerque District investigated discharge- frequency relationships for the stream <br />gages on the Arkansas River from just downstream of Pueblo Dam, near Avondale to just <br />upstream of John Martin Reservoir near Las Animas, Colorado, <br />The current study utilizes data from an earlief Corps of Engineers flood control study by <br />reducing the actual flow by a percentage due to the assumption that Pueblo Dam was operating <br />prior to 1975. The 1967 Hydrology DM #1, developed for the Las Animas Local Protection <br />Program, Table 13, page 22, used data from the Las Animas stream gage to describe existing <br />conditions preceding the construction of Pueblo Dam in 1975. We compared the flows at the <br />other four stream gages and interpolated based on the percentage of decrease in flows for each <br />year. The adjusted data were placed into an Excel spreadsheet and incorporated into an input file <br />for the Flood Frequency Analysis (FFA) program. The Corps then performed a Log- Pearson <br />26 <br />G ' <br />1 <br />n <br />r <br />t <br />I. <br />