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3,0 FLOODING PROBLEMS 3,1 Surface FloodinQ The hyd ro logy for the Ri to Seco, wh i ch f lows through the Town of San Luis, has been provided by the U,S, Soil Cons,ervation Service (SCS), The hydrology work is based on a U,S, Army Corps of Engineers report which included some regional hydrologic curves, The basin at San Luis is divided into two drainages. The SCS has labeled thesE? two drainagE's as the North Drainage and the East Drainage, The North Drainage drains 1,\ to 4,5 square miles at the point of its confluence with the East Drainage (see Figure 1), An emerqency levee. built by the Corps of Engineen:" has a controlling effect on the East Drainage, The SCS September, 1980, "Close Out Report, Rito Seco 1~latershed" did not include any discussion of hydrologic investigations for the East Drainage due to the controlled discharge of the 24" Corrugated Metal Pipe installed in the levee at the Rita Seco, The following is a summary of SCS hydrologic findings for both drainages:5 North Drainag~ Upstream Limit of Study (3,98 sq, mi,) pownstream Limit of StU('!y, (4.52 sq, mi.) 10 yr, flow 50 yr. flow 100 yr, flow 500 yr. flow 111 cfs 157 cfs 175 cfs 223 cfs 118 cfs 168 cfs 189 c[s 245 cfs East Drai~!,,- Upstream of San Luis (in the foot hills) (28.12 sq, mi.) Jmmediatel~ Upstream of San.1.uis 38,44 sq, mi.) 10 yr, flow 50 yr. flow 100 yr, flow 264 cfs 460 cfs 560 cfs 290 cfs 550 cfs 680 cfs According to the SCS report, the potential flood threat to the Town of San Luis has been reduced considerably by construction of the Corps of Engineers levee.l SCS states that some flooding from the East Drainage will undoubtedly continue along pasture lands, roads. and ditches west of the levee, -3 -