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<br />heavy rainfall over large areas and are characterized by high peak <br />flows of moderate duration. Flooding is more severe when antecedent <br />rainfall has resul tE!d in saturated ground conditions or when the <br />ground is frozen and infiltration is minimal. Cloudburst floods <br />characteristically have high peak flows, high velocities, a short <br />duration, and a small volume of runoff. <br /> <br />Mesa County has a long history of flooding from SUIlUUer cloudburst <br />storms and from sno~melt runoff. Cloudburst flood events, however, <br />have virtually gone unrecorded due to the rural nature of flood plain <br />areas affected. From records, limited ne,."spaper coverage, and inter- <br />views with local residents and officials, it is known that seven <br />major flood events have occurred on the Colorado River, four on the <br />Gunnison River, and four on the Dolores River. Floods occurred in <br />l884, 1917, 1920, 1921, 1935, 1952, and 1957 on the Colorado River; <br />in 1884, 1920, 1921, and 1957 on the Gunnison River; and in 1884, <br />1909, 1911, and 195B on the Dolores River. Most known floods in Mesa <br />County resulted froITl snowmelt, sometimes augmented by general rain. <br /> <br />In 1884, snowmelt flooding was widespread in Mesa County. All major <br />streams were overflowing in May, June, and July, and flow on the <br />Colorado River at Fruita reached an estimated l25,000 cubic feet per <br />second (cfs) on July 4. The largest snowmelt flood runoff of record <br />on the Colorado River occurred in June 1921. Heavy rain on June 14 <br />and 15 augmented runoff to produce a peak flow of 81,100 cfs near <br />Fruita. Flooding from general rain occurred on the Dolores River in <br />September 1909 and October 19l1. Snowmelt flooding on the Dolores <br />River in April 1958 inundated 1,lOO acres in the Gateway area and <br />resulted in damage estimated at $230,000. Recorded cloudburst floods <br />occurred on Indian Wash (Grand Junction area) in June 1958 and on <br />West Creek (Gateway area) in July 1940. The West Creek cloudburst <br />covered approximately 25 square miles of the drainage area and <br />produced a peak floW' estimated at 11,700 cfs. <br /> <br />The most recent serious floods on the Colorado and Gunnison Rivers <br />occurred in June 1957. Approximately 4,000 acres were flooded along <br />these streams and damage totalled approximately $430,000. Peak flows <br />on the Gunnison and Colorado Rivers were 27,800 cfs and 56,800 cfs, <br />respectively. <br /> <br />Studies show that the 1884 flood on the Colorado and Gunnison Rivers <br />had a frequency of approximately once in 300 years. With considera- <br />tion given to upstream regulation, the most recent flood on those <br />streams (June 1957) had a frequency of approximately once in 12 <br />years. The flood of June 1921 on the Colorado River had a frequency <br />of once in 25 years. Data to estimate realistic flood frequencies <br />for the Dolores River are not available. <br /> <br />10 <br /> <br />~\;.:"<t~_ <br /> <br />~ <br /> <br />'- <br /> <br />~ <br />