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lateral extent of the IntermedIate RegIonal and Standard Project Floods, are shown on Plates 19 and 20. OBSTRUCTIONS There are five bridges crossIng the Colorado River In the study area. None of these bridges cause any serious obstruction to flood- flow. AI I cause a small rIse In the water surface upstream. Although debris lodging against the piers can cause additional rise In the water surface, the lIkelihood of debrIs blockIng the waterway to any extent Is very remote. There Is only one brIdge crossIng the Gunnison RIver In the study area and It has no pIers. No obstruction to flows I santi cl pated. VELOCITIES OF FLOW The magnitude of flows for Intermediate Regional or Standard Project Floods are shown in Table 2. During an Intermediate Regional Flood the average velocity of flow would be about 7 to 9 feet per second in the main channel and 2 to 3 feet per second in the overbank area of the Colorado River. On the Gunnison River average velocitIes would be about 5 to 6 feet per second in the channel and about 2 feet per second in the overbank area. It is expected that slightly higher velocities of flow would occur during a Standard Project Flood. Water flowing at about 2 feet per second or less wll I deposit debris and silt. RATES OF RISE AND DURATION OF FLOODING The Colorado and Gunnison Rivers are major streams with large drain- age basins above the study area. The stream channels are large and wel I defined. Smal I volume runoff such as that produced by cloudburst storms has a neglIgible effect on the streams and no effect on flooding. Flood- flows are produced by snowmel~occasional Iy augmented by rain. High temperatures over an extended period, usually occurring in late May and early June, produce maximum flows of large volume. Rates of rise are relatively slow but duration of flooding is prolonged. Table 3 gives the typical rate of rise, height of rise, and duration of critical stage 19