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<br />, pinon Carten flows. dire'(,t}ythr>ough:'a..p0'rtion of the city of Trinidad
<br />'before 'enterihg the pui-gatoi.re!j.iver. The wat'ers.hed is shown on plate 1
<br />~nd,:the :projEict:100a'ti6fi'i's sh6wnon:plate 2..; ...
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<br />..4~02. .Existing floGd. contrbl"wO:rks:,-Flows ''f;POrll Pinon Canon at
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<br />the present.time.are. conveyed through the City of .Trinidad to Purgatoilre
<br />River by means of a drainage ditch and 11 large eulverts, including one
<br />concrete box culvert 400 feet long. The capacities.. of this drainage
<br />'. ditCh. an,d:'p~rticillarlf>: tne . culv~rts are'wholly ih~d~qua:t:e. t9,. handle flood
<br />flows . Flash. ,floods from . :LDten~e thunderstorm ramfall. have
<br />greatlor efceetled the6apaei:t:Les.iofthes~:'.drainage.facl1it:ies thereby
<br />eausing overflows and flood dam~ge to 'the. city. Rehab:i:litation of the
<br />ditch and reconstruction of theiculverts to adequately pass flood flo,iS
<br />. q~ot\lde~~\cons~derablY in~~e th~n the,pr~posEOdsm~ll d~tetltiondam.
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<br />4-03; Watershed;~. Pinon danon Arroyo, a tributary of the Purga-
<br />toire Rive:i-j-draihs i. p'recipito~s area of about .1.1.(square miles north-
<br />west of the ..city of Trinidad.. Fjlash fl6odsfrom this area are severe
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<br />because of stEOepcanyon.slopes .~nd .sparse'.vegetal.ClJver. The only out-
<br />let of p'inoti Canon to Purgatoir~ Rivef 1:S through a: highl;; developed
<br />residential :arid 'commerCial area -io:i:'.'.Trinid!J:d~. Small flows from .the arroyo
<br />are adequately handled by the priesent ditch. and euiverts but overflows
<br />from flash floods cause dama"eto this portion of the city.
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<br />.4"04~ . Area. prote'eted. - A:n :a~ea of! about 40 a.cres would be protee-
<br />ted :in .tne:cH;yof ilS::inidad. The pr6tected'area lies in the northwestern
<br />. 'a:i')dCentral'Sectionsof tbe cit~. ': 8i tu,g.ted :i,.n this px:otected area are
<br />r<'!sidences: and busines:;; and j.nd:ustrial estab1ishIi1ai.t~. . TbeAtchison,
<br />T~peka: and: S8,ntaF e Raihiily is.tix:idgedacro:;;s the Pinon...Ollnon dra inage
<br />. ditch but 'physi6al. fl60d damage.:totheproperty ismiti6r. . .Tbe total
<br />property valuation in the. area p;rotectad.' is: approx:iJriately $1;860,000.
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<br />v'~. PRO~ECTPJ;A}J
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<br />5-01. .General. - The general plan is ~hown on plate 3 and would
<br />provide for an earth-fill detentioD dam ~ith ungated outlet to control
<br />floods from Pinon Canon Arroyo. I This proposed earth-fill dam would detain
<br />all flood discharges and provide: sedllnent.Tetentionf'rom a drainage area
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<br />of about 1. 2 square miles. The plan of impr~vement wpuld not e1i;ninate
<br />all flood damages because of the; small uncontrolled area below the dam
<br />which would produce minor flood:,!,g during ;'eryititen.~e storms. .
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<br />5-02. Hydrologic cri1;:er~.i - . \l;[drologic and other engineering design
<br />criteria utHized in planning th~ proJect,iorks have.peen based on the
<br />fact that assurances of eompletej safetya~ainst failure of the dam is
<br />necessary beeause .of the distinc~ hazard to life and 'property created by
<br />loeating the ,dam .apQve..a pOPL\lat~d. ar~a q:f :the.ci ty. of TrJ.nidad. The
<br />hydrologic chata.cteristics ..of 'th~ region .and dt-ainage basin of Pinon Canon
<br />Arroyo are di/jcussed in detail i:n appendix.r, The detention dam is
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