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~ 84. During the design of each of the three plans, it was found ,that to provide protection against discharges greater than about 140,000 c.f.s. would entail extensive channel rectification and bridge alterations resulting in a disproportionate increase in incremental costs as compared to the potential benefits. Inasmuch as a discharge ofe 140,000 c.t-s. on the Arkansas River atLas Animas has a probable frequency of occurrence of once In about 360 years, it is considered that protection against such a discharge would be adequate and desira- ble. The probable f low on the Purgatoire River coinc ident with a 140,000 c.f.s. flow on the Arkansas River would be about 20,000 c.f.s. Therefore, for the purpose of comparing the merits of the three plans, each was designed for a discharge of 140,000 c.f.s. on the Arkansas River coincident with a flow of 20,000 c.f.s. on the Purgatoire River. 85. Each ,plan inc ludes a short levee on the left bank to prevent Interrupt i on of tratt icon State Highway 194 and U. S. Highway 50 near the bridge. If these two highways were blocked, there would be no feas'i b Ie, access to the north side of the river from Las An i mas and' vice versa. The standard project flood under existing conditions would flood State Hi ghway 194 to a depth of about 6 feet. With the right bank levee of each plan in place, this depth would be increased up to 2,feet. The standard project flood also would inundate State High- way 194 at a point near Adobe Creek to a depth of approximately one foot under existing conditions. However, the depth of flooding at this I ocat i on wou I d not be I ncreased by the right bank levee in any of the plans and the frequency of inundation wou Id be much lower than down- stream near the bridge. Traffic could be detoured easi Iy if the highway is flooded near Adobe Creek but detouring would not be prac- ticable near the U.S. Highway 50 bridge; therefore, the left bank leyee is included as an essential item of the plans considered for flood control at Las Animas and vic inity. -,-.' ,,-- a. P,I an A. - The south bank levee for P I an A, tota I length 7.,0 miles, would begin about two miles southwest of Las Animas, extend northeast across U.S. Highway 50 and the rai Iroad, continue northeast and east around the city, and then turn southeast and tie to high ground near the rai Iroad about It mi les east of the city. The rai 1- road grade at the west snd of the levee would have to be raised about 2 feet. u.S. Highway 50 would require a raise in grade of about 7 feet. ,The left bank levee would be constructed for a distance of about one mi Ie along the south side of State Highway 194, north of Las Animas, and it would cross U.S. Highway 50 at the intersection of the two highways. Plan A would provide protection to 740 acres of urban and suburban land, 2,800 acres of irrigated land, and 1,190 acres of dry farm, grazing, and other lands. The south bank levee would be about 8.4 It mi les farther west than the levee in extend northward across U.S. Highway 50 b.' Plan B.- Plan B would protect a larger area than Plan A. miles long and begin about Plan A. This levee would and the rai Iroad to the river, 28 R 1/28/64