FLOOD07531

• County: Ouray
• Community: Ouray
• Stream Name: Uncompahgre River
• Basin: Gunnison
• Title: Floodplain Information Report
• Date: 4/1/1978
• Prepared For: Ouray County
• Prepared By: A & S Consultants
• Contract/PO #: &&
• Floodplain - Doc Type: Floodplain Report/Masterplan

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STUDY AREA DESCRIPTION

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Draina~e Basin Characteristics

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The Uncompahgre River is located in southwestern Colorado approximately
70 miles east of the western boundary of Colorado (Reference Plate 1 _
Vicinity snd Basin Maps). It's head waters rise On the northern slopes of
the San Juan Mountains west of the Continental DiVide at elevations higher
than 13,000 feet. The rivet then flows In a northwesterly direction
through Ouray, Montrose and Delta Counties for approximately 70 miles to
its confluence with the Gunnison Rivet near the City of Delta. The Un-
compahgre Rivet drains approximately 1,100 square miles at its confluence
with the Gunnison River and contributes an annual average of approximately
200,000 acr~-f~~t of water to th~ Gunnison RiVer.

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Most of the Uncompahgre River basin is se~i-arid, but rainfall and temper-
ature vary widely ss a function of elevation. The prevailing wind is from
the west, but a wide range of surface wind conditions exists as influenced
by speCific topographic features. Av~rag~ annual precipitation ranges
from 8 inches at Delta and 13 inchea in the Colona-Ridgway Srea to as much
aa 40 inches in the mountainous areas, with approximately 30-40 percent of
the precipitation being from anowfall. The frost-fr~~ p~riod (consecutive
o
days with minimum temperatures above 32 F) averages about 127 days annual-
ly and varies from 112 days at the higher elevations to 148 days in the
valleys.

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The San Juan Mountains at the south end of the Uncompahgre basin are a well
defined group of high peaks, many of which ris~ above 14,000 feet in eleva-
tion. The Uncompahgre River heads in these mountains and has eroded a deep
canyor, varying greatly in width as it flows nGrth tojGin the Gunnhon Riv"r
at Delta.

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The valley bottom alGng the Uncompahgre River south of Ridgway and along
Dallaa Creek to the west is slightly rGlling because of irregulnr surface
weathering and strea~ erosion of the soft underlying Mancos Shale. Relative-
ly smooth, flat terrsces of alluvium up to One mile in width parallel these
two streams. The terraces are from 5 to 50 feet above the stream channels.
Near the confluence of Dallas Creek and the Uncompahgre River, a large term-
inal morraine marks the northern extremity of the glacial advance which .form-
ed the valley bottom north from Ridgway.

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North of Ridgway at the confluence of Dallas Creek and the Uncompahgre River,
the valley consrricts to form two subdivisions separared by a canyon which
extends to a point near Colona.

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The soils in the study area are coarSe grained, mostly of alluvial orisin,
in the valleys, to heavy rocks on thedrelnage slop..s.

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The vegetation in the Uncompahgre River baSin ranges from desert shrubs in
the lower valleys to alpine plants in the river headwaters. The basin con-
tains five general vegetative zones which can be defined by elevation. These

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,8,

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indude: (1) desert shrubs (4,900-5,500fect), (2) pinon, juniper, sage-
brush (5,500-8,500 feet), (3) oak brush, ponderosa pine, sagebrush (8.500-
9,500 feet), (4) spruce, fir, aspen (9,500-12,000 feet) and (S)alpine
plants (over 12,000 feet). Within each zone, vegetative variations occur
as a result of localized differences in topography, precipitation, and
land use.

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Study Reach Description

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The portion of th~ Uncompahgre River basin included in the detailed portion
of this study has its lower limit (Plate 1) at rhe County Road Bridge 1.8
miles downstream from the Town of Ridgway which coincides with the southern
edge (upstream) of the proposed Ridgway storage reservoir of the Dallas
Creek project. Construction of elements of this project are scheduled to
begin in 1978.

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The detailed study area has its upper limit at the southeast edge of the
Town of Ouray at an elevation of approximately 7,800 feet MSL. The total
length of the detailed atudy reach of the Uncompahgre River is approximate-
ly 14.4 miles. Total contributory drainage area to the detailed study reach,
is approximately 150 square miles.

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All streams tributary to the Uncompahgre River within rhe study area drain
minor areas and while many are subject to cloudburat type flooding, none
drain areas large enough to individually materially affect the peak flows in
the main channel of the Uncompahgre River.

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Two streams, Canyon Creek and Red Mountain Creek are tributary to the Un-
compahgre River above the upper limits of the study with a combined drainage
area of approximately 45 square m11es. Table 1 shows contributing drainage
areaS to the Uncompahgre River at selected locations referr~d to stationing
on the floodplain maps, Plates 3 through 18.

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The channel of the Uncompahgre River through the study reach follows a nar-
row valley in the upper 5 miles, beginning at the Town of Ouray, then breaks
out into a wider valley where the flows are at time.s divided bd"~~,, the
present main channel and an older channel shown on the floodplain maps as
the "West Arm" which extends to 4~ miles south of Ridgway. The flows then
arc confined to One channel and enter a natrower valley which cont1nues to
the lower limits of the study reach.

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Development within the derailed study reach has been limited to the areas in
and near the Towns of Ouray and Ridgway with the exception of ranch type
dwellings and buildings in the wider valley south of Rid~ay. Lately, some
mobile homes have been locared in the wider valley ~st of Highway 550 which
parallels the Uncompahgre River on the eaat. The 4-3s Trailer Park on the
west side of the river at Ouray lies partially within the 100-year floodplain.
The Radium Springs Swim:ning Pool development at the north end of Ouray Uea
within the 100-year floodplain of the Uncompahgre River and is also subject
to damage from flash floods from Skyrocket Cfeek. Minor gravel operations
exist near the stream channel at Ridgway.

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