FLOOD04204

• Designation Number: 179
• County: Ouray
• Community: Ouray
• Stream Name: Uncompahgre River, Ouray to Dallas Creek
• Basin: Gunnison
• Title: Floodplain Information Report - Uncompahgre River, Ouray to Dallas Creek, Ouray County, Colorado
• Date: 4/1/1978
• Designation Date: 12/1/1981
• Floodplain - Doc Type: Floodplain Report/Masterplan

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lI'lthin Ouray, the creeks flew through small concrete flu",<>s, er c"annels,
~hich traverse the alluvial fan in a westerly direction, as sho~~ on
Plate 18, The flumes are generally located at high points On the alluviure,
such that flows exceeding the tops of the flumes flow a'."y from the chan-
nelratherthanbeingcontainedinalargerfloodplain. In the case of
the violent cloudbursts carrying debris, the boulders frequently clog the
channel, thus creating flows out of the flumes at varying locations. The
flows th<>n seek their own paths through town to the Uncompahgre River, frc-
quently leaving a boulder strewn pathway behind,

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As the nature of flooding of Portland and Cascade Creeks was studied, it
became increasingly apparent that the flooding did not follow patterns
~hich could be evaluated by norlllal hydra...llc methods. After evaluating
other techniques which might be applied to rivers carrying high loads of
silt or debris, a basic conclusion waS reached -- the flood~lains of Po,t-
land and Cascade Creeks ~ere variable, un~redictable, and could not be de-
fined.

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As a result, it was decided that envelopes deacribing the "Area of High
Hazard due to Flooding" would be illustrated on Plate 18, Thesesreas
were delineated through use of photographs of past floods, discussions
with residents. and the topographic mapping. It is unlikely that a single
flood would pose a hazard to all areas within the envelopes for the de-
scribed reasons. On the other hand. all areas within the envelopes are
likely to be exposed to flash flooding during so~e future flood eveot.

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~pp.roximate Study Areas

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Da]l~~_~nj Pleasant Valley-C!~e~~

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Outlines of flooding were deter:nined along D(lllM Creek for a <I;stM'Ce of
approximarely5.7.,ilesupstrea..frOnl.lts confluence "..ith theUnc ompahgr<>
Riv<>r, and along Pleasant Valley Cr"ek for a distance of 3.9 miles upstn_'''"
from its confluence with Dallas Creek. These outlines were d"lineated us-
ing an "approximate ",ethod" which is suitable for defining gene".l "reas
of flood hazard but <Ioes not provide the detail which is generated by a
study such as that pcrfotmcd on the Uncompahgre Rivet. The"approxireate
analysis" was made ~ith the assIstance of "Technical Man"al 1>0. 1, Manual
for Estimating Flood Choracteristics of Natural-Flo~ Streams In Colorado,"
pr~pared in 1976 by the Colorado ~ater Conservation Board. The basic st~ps
jn~luded drawing profiles of the channels, selecting typical cross aections
ut 3000 to 6000 foot intervala. estimating depths of flo~, and plotting
flooded areas at the cornputed flow depths, s."cIl...seofthcopproxi",ste
nature of the results, th~y are not reprodoced in this report, but they are
available from the Colorndo\o,'ater Conservation Board and th<>L and AUl1,lnls-
trator'sofficeofOurayCounty. All work was based cpon the use of the
topegraphic ~aps,

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The tollowing pictures sho'" the Un~ompahgrc Riv~r sl,,~"i' ~h"-ta~te. at seve.
,,1 pnintt..

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CASCADE CREEK - CONCRETE FLUME

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UNCOMPAHGRE CHANNEL NEAR DALLAS TOWNSITE. STATION 10+

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