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<br />Snowmel t flooding is characterized by moderate peak flows, large
<br />volume, and long duration, and is marked by a diurnal fluctuation
<br />in flow. Rainfall on melting snow may hasten the melting process
<br />and increase floodflow. General rainfloods are caused by prolonged
<br />heavy rainfall over large areas and are characterized by high peak
<br />flows of moderate duration. Flooding is more severe when
<br />antecedent rainfall has resulted in saturated ground conditions or
<br />when the ground is frozen and infiltration is minimal. Cloudburst
<br />floods characteristically have high peak flows, high velocities,
<br />short durations, and small volumes of runoff.
<br />
<br />Mesa County has a long history of flooding from summer cloudburst
<br />storms and from snowmelt runoff. Cloudburst flood events, however,
<br />have gone virtually unrecorded due to the rural nature of
<br />floodplain areas affected. From records, limited newspaper
<br />coverage, and interviews with local residents and officials, it is
<br />known that seven major flood events have occurred on the Colorado
<br />River, four on the Gunnison River, and four on the Dolores river.
<br />Floods occurred in 1884, 1917, 1920, 1921, 1935, 1952, 1957, 1983,
<br />and 1984 on the Colorado River; in 1884, 1920, 1921, and 1957 on
<br />the Gunnison River; and in 1884, 1909, 1911, and 1958 on the
<br />Dolores River. Most known floods in Mesa County resul ted from
<br />snowmelt, sometimes augmented by general rain.
<br />
<br />In 1884, snowmelt flooding was widespread in Mesa County. All
<br />major streams were overflowing in May, June, and July, and flow on
<br />the Colorado River at Fruita reached an estimated 125,000 cubic
<br />feet per second (cfs) on July 4. The largest snowmelt flood runoff
<br />of record on the Colorado River occurred in June 1921. Heavy rain
<br />on June 14 and 15 augmented runoff to produce a peak flow of 81,100
<br />cfs near Fruita. Flooding from general rain occurred on the
<br />Dolores River in September 1909 and October 1911. Snowmelt
<br />flooding on the Dolores River in April 1958 inundated 1,100 acres
<br />in the Gateway area and resulted in damage estimated at $230,000.
<br />Recorded cloudburst floods occurred on Indian Wash (Grand Junction
<br />area) in June 1958 and on West Creek (Gateway area) in July 1940.
<br />The West Creek cloudburst covered approximately 25 square miles of
<br />the drainage area and produced a peak flow estimated at 11,700 cfs.
<br />
<br />The most recent serious floods on the Colorado River occurred in
<br />1983 and 1984. Peak flows on the Colorado River at the State Line
<br />were approximately 61,000 and 70,000 cfs in 1983 and 1984,
<br />respectively.
<br />
<br />Studies show that the 1884 flood on the Colorado and Gunnison
<br />Ri vers had a frequency of approximately once in 300 years. wi th
<br />consideration given to upstream regulation, the most recent flood
<br />on those streams, in late May, 1984, had a frequency of
<br />approximately once in 50 years.
<br />
<br />Colorado River floodflows in the Grand Junction area have inundated
<br />streets, lawns, and gardens; deposited sand, silt, and debris; and
<br />flooded basements and lower floors in residential areas in the
<br />Riverside Park, Rosevale, and Connecticut Lakes sections southwest
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