FLOOD06852

• County: Larimer
• County: Weld
• Community: Fort Collins, Greeley
• Stream Name: Cache La Poudre River
• Basin: South Platte
• Title: Flood Hazard, Dam Safety, and Flood Warning
• Date: 10/1/1981
• Prepared For: Larimer County / Weld County
• Prepared By: US Army Corps of Engineers
• Floodplain - Doc Type: Floodplain Report/Masterplan

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llilll1s"" 1l.es~rvQlr, built "" the ~onh ,or~ C,,,,he la Poudre Riocr,

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ha. attenuation effec~" down"trnam.

Althnughther".etvo!rdoesnot

have s~ecHlc flood cO<lnQl storage, flondOo",. are delayed by ~hetr
p~"s"ge thro"sh th~ r"anno!r sp1.11""1 .,nd "re, thu9, redur_cd.

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On the plat,,", the eumulati~e incidental flood c"ntrol effects of
reB~rvolr. can be significant S8 water is div~rted from strea~s to fill

stor"ee tnthe reservoirs.

Peak dischatges on the Cache la Poudre

River are attenuated considerably by these diversions.

Peak discharges

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are a180 attenuated by valley storage. Discharges are reduced as
floods spread out to fiU the broad Cache la Poudre River Valley. On
the s~aller tributaries, diversion da~. or canals aay absorb normal
high flows and result in complacency about flooding.

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Under the provisions of the Watershed Protection and Flood Preven-
tion Act, Public Law 566, a Soil Conservation Service watershed project
for Boxelder Creek is under construction. The project includes land
tre8t~cnt measures together with con8~ruction of five .ingle-purpose
floodwater-retarding structures and one grade-stabili~ation attucture.
Th~ SolI Conservation Se~vice e~tlmates that th~ project may reduce
floodwater d"",agea tn the ...atc<"h~J by $171,310 annually.

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REGULATION
Fiood plain land uae within the city 11m1ts of Cree1ey ,nd Fort
CoilIns is regulated by the resp"ctlvedty. All other floodplain
lund use h regulat~d by Larimer 'H Weld County.

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The city "f Gre..ley "rl,,!>ted a ~onln" or<l1n"nc.. In July 197& whlch
tCGulre. consttuction of detention ponds in ne... subdivi~ions designed
to assure that dcvel~pment of the subdivis10n ...iil not (ncre"s~ runoff.
The city, ho....e'.er, h,,~ n<lt .."acted flood piai~ ordinance" sufficient to
~ tn..luded tn the ~"ttonal Flood Insur""ce progr"", a" of thts report.

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