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, . .~;: 67. The month of Apr i I 1942 was one of the wettest months of Colorado history. Heavy snowstorms fol lowed by widespread rainfal I, which hastened the melting of the snow deposits, produced a peak dis- charge of 23,600 c.f.s. on the Arkansas River at Las Animas and 60,000 c.f.s. from the Purgatoire River. Transportation faci I ities and agri- cultural improvements suffered the most damage from overflow. 70. Even with the regulation of the Arkansas River afforded by the Pueblo Reservoir, Las Animas sti I I wi I I be menaced by overflow from floods generated by storms over the large uncontrol led drainage area of 9,747 square mi les between Pueblo and Las Animas. A discharge- frequency relationship for the Arkansas River at Las Animas was deter- mined for two conditions, as follows: (al existing conditions, with Barrier Dam in operation; and (b) with the authorized Pueblo Dam in operation. The computed flood frequencies are I isted in table 2. 68. The largest flood at Las Animas since 1921 occurred on May 20, 1955. A general storm over eastern Colorado, northeastern New Mexico, and western Kansas, which began on May 17 and persisted through the 19th, produced major flooding al I along the Arkansas River downstream from Pueblo. Floodflows in the lower reach of the Purgatoire River were the largest of record with a peak discharge of 70,000 c.f.s. at the mouth. The peak discharge on the Arkansas River at Las Animas measured 44,000 c.f.s.; but widespread flooding of the city was pre- vented by a very wel I-organized flood fight. 69. FLOOD PROBLEM.- The problem area under consideration includes the city of Las Animas and the rural areas adjacent thereto which are subject to flooding from the Arkansas River and which would be protected by the project described under SELECTED PLAN OF IMPROVEMENT. Cultivated lands on the north side of the river are not subject to overflow; how- ever, the river banks on the south side are quite low and the val ley floor is comparatively level from the river to the sandhi I Is. Channel clearing and straightening by the Corps of Engineers, under the con- tinuing authorities, and by the city of Las Animas have afforded temporary flood protection to the town from low median f loodf lows on the Arkansas River. The extent of this work is. indicated on plate 2. Downstream from the State Highway 101 bridge crossing, the Purgatoire River has banks simi lar to the Arkansas River; however, upstream from the bridge the river flows in a val ley with moderately high banks and Las Animas is further protected from Purgatoire River floods by the sandhi I Is which form the divide between the rivers. There has been no recorded incidence of flooding in Las Animas from the Purgatoire River. 21