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<br />2.3 Principal Flood Problems <br /> <br />Floods in the study area generally result from rapid melting of <br />the mountain snowpack from mid-May through early July and from <br />general rainstorms that normally occur from July through October. <br />Snowmelt flooding is characterized by moderate peak flows, large <br />volume, long duration, and marked diurnal fluctuation of flow. <br />Snowmelt runoff may occasionally be augmented by rain. Rainfloods <br />are characterized by high peak flows of moderate volume and duration. <br />Flooding is more severe when antecedent rainfall has resulted in <br />saturated ground conditions or the ground is frozen and infiltra- <br />tion is minimal. Convective-type cloudburst storms, sometimes <br />lasting for several hours, can be expected to occur in the Montrose <br />region during the summer, Runoff from these storms is characterized <br />by high peak discharge, short duration, and small volume. Because <br />of the small areal extent of cloudburst storms, they would have <br />little effect in the study area unless they occurred concurrently <br />with rapid snowmelt or runoff from general rain. <br /> <br />Historical records show that floods occurred on the San Miguel <br />River in 1909, 1911, and 1942 (Reference 2). The September 5, <br />1909, flooding was caused by severe rains on the headwaters of the <br />San Miguel River that caused the failure of two small power reser- <br />voirs of the Telluride Power Company. Middle Reservoir failed on <br />September 5, 1909, and a sudden release of approximately 700 acre- <br />feet of water raised the level of Trout Lake, located approximately <br />1.5 miles downstream, nearly 2 feet above the crest of the dam. <br />This caused a failure of that dam and the release of approximately <br />2,000 acre-feet of water, A local newspaper account estimated the <br />crest of the flood down the river as 20 to 45 feet above low water, <br />depending on the width of the channel (Reference 3). <br /> <br />The October 5, 191', flood was caused by continuous rain over the <br />previous 10 days associated with a large rainstorm on October 4, <br />1911. No stream gage records of high-water marks are available <br />for the 1909 and 1911 floods at Naturital therefore, estimates of <br />their recurrence intervals are unavailable. <br /> <br />The 1942 flood has the highest recorded peak discharge on the San <br />Miguel River during the period of operations of U.S, Geological <br />Survey (USGS) stream gage No. 09175500 (1917-19291 1941-present), <br />The April 1942 flood was caused by a heavy snowmelt and had a peak <br />discharge of 7,100 cubic feet per second (cfs) as recorded at the <br />Colorado Highway 97 stream gage. Based on the results of the study, <br />the 1942 flood has an estimated recurrence interval of 20 years. <br /> <br />The earliest reference to a flood on the main Uncompahgre River <br />came from the settlers who founded Delta, Colorado, in the early <br />1880s. At that time, an Indian squaw, Chipeta, wife of the famous <br />Ute Chief Ouray, stated that within her lifetime of then approxi- <br />mately 50 years, she had seen the Uncompahgre Valley at Delta <br />"flooded from bluff to bluff" (Reference 3). <br /> <br />8 <br />