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<br />The pri;n.ary areas to be protected are the te. [denc~. "rtd camp-
<br />grounds In the Paudre Canyon J.nd the Bellvue, Laporte, and Fort
<br />Collin.ar..a,
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<br />3aseJ on ,,>:pedence In the Big Thompson Rho"r fLoo..!, COmt""t" by
<br />Larimer County officIal. and the ~WS, and ""pertence in other floods,
<br />, " ,> '^~ ,>~"',.,,,. Therefore. all f la,qn
<br />telephone com"",n cat on s cons tie ~u ""
<br />flood detection alt".natlves "..ill be designed uaing radio co","",.~l.c,,-
<br />tian.
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<br />Along th Front Range, the likellhoQd of heavy rainfall decreases
<br />wUh increasing altitude. The clO\.ldblHst ~One "hidl is prone to flash
<br />floodIng is generally con6idered to lte belowelevanon 8000 feet
<br />...s.L The licst edge of the heavy rainfall pHter" of the 1976 Big
<br />Thompson ~iver storm e~peared to 11e at approximately 9,000 feet ~.a.l.
<br />The~efore, in designing flaah flood dHection alternativea, rain and
<br />5tream gages we~e placed only in the area. east of the 9,OOO-foot
<br />elcv~t10n contou~. This 1s app~oxlmately the area ea5t of R~sti~.
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<br />ft'o,"
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<br />In for~lating alte~native$. ~ range of technology ~aa conaidered
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<br />completely volunteer to cOUlpletely ~~tom"ted ayatema.
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<br />explore the effect of fund llmiutiona or phased development, the geo-
<br />graphic .cale of alternatives ~aa a180 varied. Regardles" of scope,
<br />each a.lternative ~as designed to p~~vtde so~ proteeti~n f~~m both main
<br />stem and ~orth Fork floods.
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<br />Stream g,1ge~ should be conf1ned to the ""lin stem 1n the Poudre
<br />Canyon and to the m"in stem of the 1I0rth Fork. The Poud~e Canyon is
<br />the only densely populated flood pl~1n area. The ~orth Fork area 1a
<br />spaesely populated but p~oduces floods that th~e~ten the Fore Col11ns
<br />area. Placing stream gages en trtbutari~. ~o~ld r~qu1re an excess1ve
<br />nu~ber of gage. ~ieh little increase 1n ~ar~1n8 t1me.
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<br />Although the ar..a pdmat'ily aubjece to flaah fl~oda i. ""ot of the
<br />9,OOO-foot elevaeion, local off1ciala are also concerned about dam
<br />failure and sno'>llll..lt floods. Thereare.ev"raldam$upBtreamfrom
<br />Spencerllelg3es. Also, a considerable number of residents have IlIOved
<br />i~to the a~ea up8ttea~ fro~ Ruetic. In order to tdentify tbe costs of
<br />fla~h flood ~ilrning, the cost of a dam hil"re flood "arning wae
<br />computed se?arat~ly.
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<br />The potential ~lze of flood ~ro~ucing stor~s ~ffects the de"ig~ of
<br />"lt~~n~tL'''S. Th~ cor" 0, tMe i976 Illg ThoOl?son ,U..."r ~to,.rn, taken as
<br />ehc a~ea wieh 8 tnch~s or mor~ of total ralnf~ll, ~as ~n ell1pse or
<br />0",,1 approximileely 5 miles ~ide and 10 !lUCS long. FOf other p<l.H
<br />stor",s in th.. ~egion, the cOre of the highe~t rainfall a:reas .1ho
<br />resembled ellipses ranging in dt~~nsion fr",,, abo~t 4 by 8 mile, te 10
<br />hy 30 ~iles. To av01d rnisstng the cor~ of ra1~fall, and thug severely
<br />underestim8tlngthegtor-n, rain gage., ",here used, sho<Jldbespacedno
<br />""'~" than abo~t 5 miles ap.1rt, or about one ga~e for each 25-squ"re
<br />nl1h "rea. Stream gag"', ..h"r~ used, sl,o<J1d ~ho be sp"~ed no :nore eh,,,,
<br />~'bo"t S <liles "-p,,-n. Voh,nteer gage" s!,ould 1'Jeet the req~t'~~.ent ef
<br />bdn" ~( or ".Gar ~ r~~id,'nte. Aul''''8t1e ","ge> "..~'" ,~<'unw~ '0 req';i~e
<br />th" p~d,d"'1ty of .~n acce~S rMd.
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<br />POTENTIAL COMPONENTS OF ALTERNATIVES
<br />Ex1sting Flagh Flood Detection. The NWS ha~ &bout 35 to ~O
<br />volunteer ground observers or "~potter"" in Larimer County. )1o~t of
<br />, . ~ " ,,, The lI'.;S .notteU repo~t to
<br />thes~ are appa~~~t y .~ t..e p+8+nS reg 0.. ~
<br />the Lar1~r County She~lff'a off1ce ~ho tn t~rn report$ eo the NWS.
<br />,.. " 'o~al ,rtvate ~eathe~ con.~ltant
<br />~s an intert~ f oo~ "arn+ng measu e, ~ _ ~
<br />h,l$ be~n retained by Lari~er Co~nty. ;:he conslllt.1nt maint8tns a
<br />~~c:tcr ~~:'~nk of ~bO\lt gO ;erso~". ~a~h h~" """'~ f"rnl.~p~ wHI> d
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<br />pla"tic rain gage.
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<br />They telephone tll<> con"~ltant if 0.50 i"ches ~f
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<br />., , ~ "'~." ,~~~,,',.~. ""0 has" color rad"r,
<br />rain ts rec"lvQ~ +n "'~ "our. "'~ U"3~ He ~ 0
<br />",'lich displays LMj(eg fro", ~VS ,."dns ..t Lt"'ln, Col~n"k' and ChevenM,
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