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<br />I. INTkOOUI.1'ION
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<br />AUTHORIZATION
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<br />The City of Longmonl Urb..n Slorm.....,ucl Man'4lcmcnl Master Plan (Master Plan) study wos
<br />JUlhorizc<J under the (",ms of tbe Contra"! between the City of Longmont (City) and WRC
<br />Engineering, lnc, (WRC). The smdy c""erro hydrologic modelling oflribulary basins and hydraulic
<br />evaluation of stormwatcr management facilities in tlIe Longmont area. :>Iolice to Procccd was given
<br />effective OcIOI:>c, I. 1992. The draft Hydrology Report (Reference. 2) was ,ubmilled on October
<br />8. 1993. The Alternmives Evaluation Report (Rcference. 3)was submined for review On November
<br />8. 1993, and the tinal hydrology report was submincdon November 30. 1993. The draft Collection
<br />System M.Sler Plan was .ubmined for review on November 17, 1995. The final Collection System
<br />Masler Plan was submined on Dccembcr5. 1995.
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<br />PURPOSE AND SCOPE
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<br />The purpose of this Master Plan project wa, 10 evaluate lI1e adequacy of existing 'lO,mwater
<br />management fac;!itic, to accommodate e~i!ting and fmure ~lOrm ruuoff and 10 defi,lC the mo,t fea,ible
<br />alternatives for needed !ystem improvemems. To achieve the project objective ,Ile study w,,, divided
<br />into four phase!, hydmlogieandhyd,aulicanalysisoftribularyalC.lSJndexi,ting'y,tems, rreId
<br />in"emory of e~;sl;ng .tructurcs along m.tjOl dra,nageways, development and evalualion of alternative
<br />system improvements, and preparation of the final Ma.'ter Plan report including recommrndcd system
<br />improvements.
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<br />In addition to tile Master Plansrudics. the projcctconlrnctalw incIudcdlransfcning stormwater
<br />management system diagram. and rdatc<l information from .xi.ting hand-drafted drawing, on aerial
<br />pllotograph! to computer-baM:d CAD formal. Also. e~is{ing HEC.2 wate, surface profile models
<br />werewmpilcd. bascd on the availahle prcvious Sludies by WRC and others. and run on a personal
<br />computer platform to provide 10 the City working models for the major drainageways that p.ass
<br />through the study arc:!, Finall~'. a community oUlreach program was implememed to lolici{ from
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<br />local rcsidenlS;uformationandconcems regarding drainagecondit;on. in the S1udyarea.
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<br />Separate documents were produced for each of the four project phases. The Hydrology Repor!
<br />includes one repor! volume and 17 volume. of appendiees, The Hydrology Rcport volume contains
<br />a description of the hydrolugic sludy. assumptions used for modelling purposes, and modclresultl;
<br />summaries ofrunuffealculated for tbe various drainage sub-basin' and conveyanceclemcms; and
<br />figures and drawings dCl'ieting oo!in boundaries, hydraulicoonncctivilY. basin imperviou.ness and
<br />soil types, and mnoffhydrugraph.fo,seleelCddesignpoims, The 17 vol umcsofappendieeseomain
<br />a full listing of Colorado Urban Hydrogr"1'h Procedure (CUllP) and Slormwatcr Manaj!cmem Model
<br />(SWMM) output for all basins and systems modelled.
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<br />Dala ohtaincd through the drainage.trueture inventory program areeonta ined in two volume. tilled
<br />DrainageStruelureInvcntory(Rcfcrencc.4). These "olumes includedata.heels and phOlographs for
<br />each of llle structures identified along Ihe major drainageways through the srody arca. The
<br />drainageway. invemoried include Sprirg Gulch, $1 Vrain Creek, 1.eft Hand Creek. Dry rrcck No,
<br />I and the Oligarchy Ditch.
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<br />The Altemalive. Evalu'ti"" Report is a lingle volume {hat prelems a brief !ummal)' of runoff modcI
<br />results. descriptiuns of ex is ling system, and are.1,ofinadequatesj' !temeapacities.descriptinnsof
<br />alternative system impro\'ementsand cost,. and an evaluation discussion ot"each !<:lufalternative,
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<br />presented. Drawing. arc aI,o included to describe potential system improvements and alignmems.
<br />TIle final MaSler Plan rcpon, th;! volume. iocludes a general dh;eussiunufsrudy methodologYJlld
<br />prclents preliminary and conceptual designs and cost e!!Imates of Tec"Ommendcd sYltcm
<br />;mpruvemems. AI!o included Arc diagTJms of basin and ,ub.basin boundaries and a !et of dr.wings
<br />depicting existing drainage system' thruughout,heCit}"
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<br />MAPPING Al"D BACKUP INFORMATION
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<br />The primary mapping u,",1 r"r the "udy consiSletJ of CAD.hased aer;al mapping nown hy GEONEX
<br />in April 19</2 Thil mnpping was provided to WRC hy tbe City on prinletJ copies at a scale of
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