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caused wide spread flooding in the Arkansas River basin. In Colorado alone, damage estimates by a special congressional cOll1T1ittee, total- led $43 million. Damage in Lamar was estimated at $1.2 million. The Tri-State Daily News (Reference 3) reported on June 22, 1965, "The John Martln Reservoir stored some 273,138 acre feet of water which otherwi se woul d have poured down on the staggeri ng towns." A U. S. G.S. report on the 1965 fl ood added, ".... the uncontroll ed tributary inflow below the John Martin Reservoir was so outstanding that towns from Lamar, Colorado to Dodge City, Kansas were exten- sively damaged." The 1965 U.S.G.S. report stated the peak flow for Willow Creek was 24,300 cfs. Flow in the Arkansas River at Lamar was recorded at 72,800 cfs with a maximum gage height of 18.9 feet. A previous flood in 1921 carried 130,000 cfs but the maximum gage height was only 17 feet. Other large floods (greater than 30,000 cfs) on the Arkansas River occurred in 1923, 1929, 1934, 1936, and 1942. The John Martin Dam began flow regulation in 1943. Flood history of the Willow Creek drainage area is limited. 2.4 Flood Protection Measures The City of Lamar has adopted flood plain management regulations determined by FEMA. Along Willow Creek, a levee has been built, and the channel has been dredged to protect the city from frequent flooding. An earthen levee along Willow Creek exists on the left bank from First Avenue to the downstream canporate limits. Field inspection revealed the levee was in good structural condition. The 100-year flood elevation was calculated to be three feet below the top of the levee at each cross-section (A-N). The 500-year flood overtops the levee at approximately cross-section "M", and flows into the city, creating shallow flooding areas. 3.0 ENGINEERING METHODS For the flooding sources studied in detail in this community, standard hydrologic, and hydraul ic study methods were used to determi ne the fl ood hazard data required for this study. Flood events of the magnitude which are expected to be equalled or exceeded once on the average during any 10-, 50-, 100-, and 500-year floods, have a ~2, 1, and 0.2 percent chance, respectively, of being equalled or exceeded during any year. Although the rec urrence i nterv a 1 represents the long term a vera ge peri od between fl ood s of a specific magnitude, rare floods could occur at short interval s or even within the same year. The risk of experiencing a rare flood increases when periods greater than 1 year are considered. For example, the risk of 5