FLOOD04092

• County: Delta
• Community: Delta
• Basin: Gunnison
• Title: Pre-Disaster Flood Hazard Mitigation Plan
• Date: 2/1/2002
• Prepared For: Delta
• Prepared By: CWCB
• Floodplain - Doc Type: Flood Mitigation/Flood Warning/Watershed Restoration

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4. Current ProblemlIssue Identification

A. Flood Hazard Inventory

The first step in the flood hazard inventory process is to define the flood hazard. To
undertake this process, we have reviewed the flood history of Delta. One important area of focus of
the Flood Mitigation Assistance Program (FMAP) will be repetitive loss areas. The local pre-
disaster flood hazard mitigation plan should focus on such areas because of the often
disproportionate amount of flood damage which occurs here.

1. History of Flooding

Flooding from streams in Delta usually occurs during May through July, with the principal
cause of flood flows being Spring run-off. The community is known to have a long history of
flooding, the earliest occurring in 1884, although the Utes talked about a massive flood in their
history when the trappers first came in 1827. The flood ofJune/July, 1984 is considered the most
severe, recent flood in the Delta area, with an estimated peak discharge of 20,000 cfs on the
Gunnison River. In years prior though, the peak flows have been as high as 50,000 cfs, and
numerous floods in the 20 and 30 thousand cfs range.

The largest flood on the Uncompahgre River occurred in 1941, with an estimated peak flow of
3,730 cfs. In 1993 and 1995, large snow depths in the Gunnison River basin resulted in unusually
high snowmelt flows, inundating both private and public properties even though flows were below
the 100 year flood level.

A U.S. Army Corps of Engineers report describes the 1884 flood as follows:

"Historical references to floods on the Gunnison River extend back to 1884. In that year,
early high temperatures in May and June resulted in the largest known snowmelt flood on this river.
At the City of Della, the Gunnison River was reported to be 10 feet above bankfull stage, with an
approximate 0.75-mile width. Many wooden bridges along the river were destroyed by this flood."

Table 1 - Summa", of Discharlfes
Flooding Source Drainage Area Peak Discharges (cfs)
and Location (Sauare Miles) 10-Year 50-Year 100-Year 500- Y ear
Gunnison River
at Delta 5,628 13,500 18,700 21,200 26,700
below confluence
with Uncompahgre 6,760 16,200 22,000 24,700 30,900
Uncompahgre River
at Delta 1,129 3,100 4,400 5,000 6,600