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SUMMARY AND RECOMMENDATIONS The Arkansas River at Las Animas, Colorado, has had a long history of floods caused by intense rainstorms on the high plains. Since 1939, the U.S. Geological Survey has maintained a gaging station at Las Animas and, during that period, flood peaks have exceeded 20,000 cfs four times. The flow in 1955 was 44,000 cfs, which was the second largest flood in recorded history. The largest flood occurred in 1921 with a discharge of 187,000 cfs. This is the only flood which inundated the City of Las Animas. A log-normal frequency curve based upon flood peaks since 1939 indicates a lOa-year flood discharge of 66,000 cfs at Las Animas. The recent completion of Pueblo Darn will produce partial flood control for the Arkansas River and modify the flood- frequency distribution. The resulting modification of the frequency curve indicates the lOa-year flood to be 47,000 cfs. Flood-routing calculations of this lOa-year flood indicate a water surface elevation of 3894.8 feet at the highway bridge, north of Las Animas, and a backwater slope of 1.2 feet per 1000 feet upstream. The flood will be contained by an irrigation ditch embankment located 1200 feet north of the city. The Town Ditch at the north edge of the city provides a back-up levee, resulting in no flood inundation of the City of Las Animas by the lOa-year flood. It should be emphasized that this analysis was based upon the assumptions of the existing channel condition and no debris- clogging at the highway bridge. Any decrease in channel or bridge capacity will produce higher water elevations and some inundation at the north edge of the city along Highway 50. The following recommendations should be considered by the City of Las Animas. 1. File an appeal with the Federal Insurance Administration to remove the City of Las Animas from the flood hazard area. The following recommendations apply until the Corps of Engineers completes the Las Animas levee project. 2. Inspect and maintain the Town Ditch embankment and make emergency plans to fill the existing cuts in the ditch. 19 . .