FLOOD07844

• County: Montezuma
• Community: Dolores
• Basin: San Juan/Dolores
• Title: FIS - Dolores
• Date: 9/29/1989
• Prepared For: Montezuma County
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

TABLE 1 - SUMMARY OF DISCHARGES

Flooding Source
and Location

Drainage Area
(SQ. Miles)

Peak Discharge (cubic feet per second)
10-Year 50-Year 100-Year 500-Year

Dolores River downstream
of the confluence of
Lost Canyon Creek 567 6,800 11,500 14,500 36,000
Upstream of the confluence
of West Dolores River 270 3,700 6,000 7,500 20,000
West Dolores River at
mouth 167 2,300 3,800 4,800 11,500
Lost Canyon Creek at
mouth 72 600 1,700 2,500 4,500
3.2 Hydraulic Analyses

Analyses of the hydraulic characteristics of flooding from the
riverine sources studied were carried out to provide estimates of
the elevations of floods of the selected recurrence intervals.

For flooding sources studied by detailed methods, other than
shallow flooding areas, water-surface elevations for floods of
selected recurrence intervals were computed through the use of
the COE HEC-2 step-backwater computer program (Reference 1).
Basic cross section input was derived from surveyed cross section
information furnished by the Colorado Water Conservation Board.

Locations of selected cross sections used in the hydraulic
analyses are shown on the Flood Profiles (Exhibit 1).

Starting water-surface elevations were based on the normal pool
elevation of the McPhee Reservoir.

The profiles are used to determine depth of water in the channel
and adjacent flooded areas. It has been determined that the 10-
year flood would be contained within stream channels, and the 50-
year flood would closely follow the pattern of the 100-year
flood. Some areas are subject to sheetflow, broad, overland
flooding less than 2-feet deep on the average, and characterized
by unpredictable flow paths. In sheet flow areas, water-surface
elevations are essentially independent of those along adjacent
streamways, and are affected principally by obstructions and
local topography in the area flooded.

Flood profiles were drawn showing the computed water-surface
elevations for floods of the selected recurrence intervals.

The hydraulic analyses for this Flood Insurance Study are based
on unobstructed flow. The flood elevations shown on the profiles
are thus considered valid only if hydraulic structures remain
unobstructed, operate properly, and do not fail.

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