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Colorado, to the east; and Dolores County, Colorado, to the north. Dolores River drains approximately 837 square miles upstream from the Town of Dolores. Dolores River has a tributary, West Dolores River, that confluences about 15 miles upstream of the Town of Dolores, whi Ie the Dolores River joins the Colorado River in eastern Utah, about 100 miles northwest of Dolores. At the mouth of West Dolores River, drainage is 167 square miles. The West Dolores and Dolores Rivers flow into San Juan Range, reaching elevations around 14,000 feet. Lost Canyon Creek confluences with Dolores River, south of the Town of Dolores, rising to elevations around 10,000 feet in the western slopes of the La Plata Mountains. At the mouth of Lost Canyon Creek, drainage is 72 square miles. Mancos River drains approximately 83 square miles, excluding the 1.4 square mi Ie tributary to Jackson Gulch Reservoi r. Chicken Creek is north of the Town of Mancos and west of the Mancos drainage area. Mancos River rises to an elevation approximately 13,000 feet at the headwaters, lowering to 6,800 feet. Chicken Creek ranges from 11,200 feet to 6,200 feet above sea level. The headwaters of Mancos River are located about 16 miles upstream of U.S. Route 160. Chicken Creek headwaters are 12 miles upstream of U.S. Route 160. The mean annual precipitation in the Montezuma County area 15 approximately 16 inches. From July to October, approximately 40 percent of the normal annual precipitation results from rain, generally thunderstorms. From November to June, the remaining 60 percent of the normal annual precipitation occurs as snow. Winters are long and cold, with mean daily temperatures of approximately 300F between November and March. Summers are short and hot with mean daily temperatures greater than 900F (Reference 2). According to the U.S. Bureau of the Census, the population in the county grew from 12,952 in 1970 to 16,510 in 1980, an increase of 27.5 percent (Reference 3). 2.3 Principal Flood Problems The nature of flooding problems within the study area include: general frontal type rainstorms, convective type cloudbursts, and snowmelt. Cloudburst storms can constitute a severe flood threat; but, due to small aerial extent, small volume of runoff, and short duration of this type of storm, a significant flood threat is present only in the smaller drainage areas such as Lost Canyon Creek. Frontal type rainstorms present the most serious flood hazard in the county. In May to June the combination of spring snowmelt runoff and thunderstorms perpetuate the potential for severe flooding. Antecedent ground moisture also contributes to flood 4