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. ?AST FLOODS FLOOD SITUATION Sumrna~y of Historical flood~ Definitive data on velocities, magnitude, and duration of past floods in i...'l. V;;,t" are not available. rnterviews with local citizens disclosed that flooding did occur in 1923 and 1946. The 1923 flood was reported as being caused by the fa11- u.reof the Mill Lake Dam, and was reported to have been "very had" in La Vet.... The only partieul".. damage that could be rern"mbered was that the railroad bridge was washed out. The 1946 flood occur- red during April or ~y. The highway bridge was washed out and the railro..ct bridge Wa3 saved by placing loaded railroad cars on the bridge, however, the railroad bed at each end of the bridge was washed out. it was reported that considerable water from the Dyer Ditch flowed down Main Streot (Colorado State Highway 12). A sBarch of newspaper files and hi~torical documents did not reveal any additional information on the~e two floods. Flood Season and Flood Characteristios The study arQd is divided into separate areas governed by two different types of runoff. The Middle Creek and tributacies and the Hayes Reservoir tributaries, and the aCea around La Veta are lower in elevation and more open to intrusion of rainstorms. Flows from these areas are pred~inantly from rainfall. The Cu- charas River Basin rises up to 13.000 feet and is surrounded on three sides by high llIO\lIltains thus preventing any ll\a:Jer stoB frO<n entering the basin. FIO'ols from this area are predominantly from snowmelt runoff. Storms characteristic of the Cacharas River Watershed are usually of the thunderstom or cloudburst type, which are of short duration and cover only a small area. Moisture-laden winds coming in contact with the mountain slopes, Or conventienal air currents over the plains areas, are forced upward causing rapid cond~nsation with the resulting terrential precipitation. Storms of a general character are infrequent and there are few instances of storms of several days duration. ~he greatest precipitation nermally occurs in the late spring ar.d sun:ne:r lllOnths. Factors Affecting Flooding and Their Impact Obstructions to Floodflow. Obstructions. natural and man-made, within the floodways impede floodflows, creating back- water and increased heights. Debris washing downstre= during floods often collect against bridges, reducing the waterway open- ings and impeding the floodflow. ~his creCltcs a d=ing effect and Causes greater backwater depths with increased overbank flooding. Water pressure on bridges and embankments can result in stress dam- age or destruction of the structure involved. A proneunced in- creas.. in flow volocities usually occurs downstream from obstruc- tions,thuseo<tendin9thcfloodd=gcpotcntial. , ,