Taken from the 2015 Mesa County Hazard Mitigation Plan
Previous occurrences
- Mesa County has a long history of flooding from summer cloudburst storms and from snowmelt runoff.
- Seven major flood events have occurred on the Colorado River, four on the Gunnison River, and four on the Dolores River.
- Floods on the Colorado River occurred in 1884, 1917, 1920, 1921, 1935, 1952, 1957, 1983, and 1984.
- Floods on the Gunnison River occurred in 1884, 1920, 1921, and 1957.
- Floods on the Dolores River occurred in 1884, 1909, 1911, and 1958.
- Most known floods in Mesa County resulted from snowmelt, sometimes augmented by general rain.
- The largest snowmelt flood runoff of record on the Colorado River occurred in June 1921.
- Heavy rain on June 14th and 15th augmented runoff to produce a peak flow of 81,000 cfs near Fruita.
- Flooding from general rain occurred on the Dolores River in September 1909 and October 1911.
- Snowmelt flooding on the Dolores River in April 1958 inundated 1,100 acres in the Gateway area and resulted in damage estimated at $230,000.
- Recorded cloudburst floods occurred on Indian Wash (Grand Junction area) in June 1958 and on West Creek (Gateway area) in July 1940. The West Creek cloudburst covered approximately 25 square miles of the drainage area and produced a peak flow estimated at 11,700 cfs.
- The most recent serious floods on the Colorado River occurred in 1983 and 1984.
- Peak flows on the Colorado River at the State Line were approximately 61,000 and 70,000 cfs in 1983 and 1984 respectively.
- Colorado River flood flows in the Grand Junction area inundated streets, lawns, and gardens; deposited sand, silt, and debris; and flooded basements and lower floors in residential areas in the Riverside Park, Rosevale and Connected Lakes area southwest of the City in 1983 and 1984 but has not caused significant damage since these events.
- The flooding events in 1984 resulted in loss of life as did the flooding event that occurred on I-70 when Bosley Wash flooded in 2008 resulting in a drowning.
- The Riverside Park area has experienced repeated flood danger as the erosion and undermining of protective levees has necessitated extensive flood fighting and levee repair.
- This noncertified levee and storm drain system improvements serve to mitigate potential flooding.
- The principle cause of flooding on Plateau Creek and Buzzard Creek is a rapidly melting heavy snowpack during May, June, and July.
- Rainfall on melting snow may hasten the melting process and increase flood flows.
- A major flood occurred on Plateau Creek in 1922.
- Based on the record from a stream gage on Plateau Creek located approximately 6 miles east of Collbran, this flood had an estimated discharge of 3,080 cfs which corresponds to a frequency in excess of 100 years.
Probability of future occurrence
- The probability of future occurrence is highly likely with a near 100% chance of occurrence next year or happens every year.
- Due to the documented cases above and the information collected on events that were smaller in size, Mesa County and the various towns/municipalities will continue to deal with flood related activities in the future.
Magnitude/severity
- The magnitude/severity of a flood event is limited resulting in minor injuries and illnesses, minimal property damage that does not threaten structural stability and/or interruption of essential facilities and services for less than 24 hours.
- Most of the flood events that have occurred in Mesa County over the past 10 years have been limited with respect to injuries and property damage.
