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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lI'lth!n Ouray, the creeks flow through small concrete nu",(>s, or c"annels,
~hlch traverse the alluvial ran in a westerly direction, as sho~~ on
Plate 18. The flumes are generally located at high points On the nl1uviure,
such that flows exceeding the tops of the flumes flow a'.,,>" from the chan-
nelratherthanbeingcontainedtnalargerfloodplain. In the case of
the violent cloudbursts cafrying debris, the boulders frequently clog the
channel, thus creating flows out of the flumes at varying locations. The
flows then seek their own paths through town to the Uncompahgre River, fre-
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 follo~ patterns
which could be evaluated by norlllal hydra...l1c methods. After evaluating
other techniques ~hich might be applied to rivers carrying high loads of
silt or debris, a basic conclusion ~as reached -- the flood~lains of Port-
land and Cascade Creeks were variable, un~redictable, and could not be de-
fined.

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As a result, it ~as decided that envelopes describing the "Area of High
Hazard due to Flooding" would be illustrat"donPlate 16. These areas
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 thc de-
scribed teasons. On the other hand, all areas within the envelopes are
likely to be exposed to flash flooding during so~e future flood event.

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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 det~r:nined along D(lllM Cr~ek for ~ ni ~tM'Ce of
approximat"ly5.7.,il"supstrr"..fronl.ltsconfloence",'ithth"Uncompahgre
River, and along Pleasant Valley Cr"ck for a distance of 3.9 miles upstn_'''"
from its confluence with Dallas Creek. These outlines were d"Hneated us-
Jng an "approximate method" whi,,-h is suitable for defining general "rea~
of flood ha7.ard but nOes not provide the detail which is generatrd by a
study such as that performed on the Uncompahgre River. The"approxi",ate
:>-nalysis" wa.s made with the assist8nce of "T~chnica.l Man"al 1>0. 1, Manual
for Estim~t1ng FlOOd Chotactedstics of Natural-Flow Strea.ms In Colorado,"
ptepared In 1976 by thc Colorado ~ater Conservation Bo~rd. The basic st~ps
jn~luded dr~wing profiles of the ohannels, selecting typioal cross sections
at 3000 to 6000 foot intervals, estimating depths of flow, and plotting
flooded areas at the computed flow depths. g..clluseofthenpproxilllate
nature of the results, they are not Teproduced in this report, but they are
nvail<lble from the Colorndo\o,'ater Conservatlon Board and theL andA(h,1nis-
trator'sofficeofOurayCounty. All work ",as based cpon the use Qf the
topographi"- ~aps.

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The tollowing pictures sho'" the Un~ompahgre Riv~r sl,,~"i' ~harn~ter at sever
"I pointt..

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CASCADE CREEK - CONCRETE FLUME

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UNCOMPAHGRE CHANNEL NEAR DALLAS TOWNSITE. STATION 10+

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