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<br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />I. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br />. <br /> <br />There are several current USGS gaging stations within Montrose County located along the major <br />rivers and tributary streams. In addition, there are several sites that have collected data but are no <br />longer active. However, most of these gaging stations do not contain enough data to calculate <br />peak discharges. The five gages for which adequate data available for peak discharge <br />calculations are shown in the following section of the report. There are also several gaging <br />stations upstream and downstream of Montrose County along the Dolores River and Gunnison <br />Rivers. <br /> <br />Floodinl! Problems and Floodinl! History <br />Floods in the subject watersheds normally occur during the months of late summer and early <br />autumn and are caused primarily by intense localized cloudbursts or thunderstorms. Typically, <br />these floods have high peak discharges with low volumes over short durations and there is <br />usually a very short window of opportunity for flood waming and evacuation once a major <br />storms hits the area. Less damaging floods can also result from rapid melting of mountain <br />snowpack in the spring and early summer months, especially on the larger drainageways. A <br />combination of rainfall and snowmelt can sometimes prove to be the worst flooding scenario for <br />Colorado's mountain streams. <br /> <br />The PIS reported flooding along the San Miguel River in 1909, 1911 and 1942, with the highest <br />recorded peak discharge of 7,100 cfs occurring at the Naturita stream gage. The PIS report <br />estimated a 20-year recurrence interval associated with this event. This event was caused by <br />heavy snowmelt. The most recent event occurred in 1983, when the Uravan gage peaked at <br />8,050 cfs. <br /> <br />The PIS reported flooding along the Uncompahgre in 1921, 1927, 1938, 1941, 1944, 1947, 1957, <br />1973 and 1975. The PIS reports that the highest flow recorded at the Colona gage is 5,140 cfs <br />during 1921. Examination of the streamflow records shows that the peak flow did occur during <br />1921, but the peak flow was 4,080 cfs. High flow events also occurred in 1983 and 1984, when <br />flows peaked at 3,900 cfs and 3,460 cfs, respectively. Flood damage has occurred to agricultural <br />lands, bridges, diversion structures and agricultural property. Ridgway Reservoir was <br />constructed on the river near Ridgway in 1987. The highest recorded discharge at the Colona <br />gage since its completion was 2,230 cfs in 1995. The PIS mentions that the project will reduce <br />the standard project flood of 7,000 cfs to a flow of 3,700 cfs at the dam site. <br /> <br />Peak discharge on the Gunnison River have primarily occurred during the early part of the <br />century, primarily due to the completion of Blue Mesa, Morrow Point and Crystal Reservoirs on <br />the river in the 196Os. The highest recorded flow of 19,000 cfs occurred in 1921. However, <br />since the completion of the reservoirs, the peak recorded discharge is 11,000 cfs in 1983. <br />Discharges exceeding 11,000 cfs occurred during more than 40 percent of years prior to <br />completion of the reservoirs. <br /> <br />Flooding has been reported in several of the smaller tributary streams, notably in 1938, 1964 and <br />1967. <br /> <br />3 <br />