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<br />Avenue. Tw<ryear flows in this seWer range from 19 to 38 .fs. A 30- and 48-inch
<br />diameters.w.. is proposed for the syslem extension.
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<br />c, CuffmanStr<<! System
<br />llispropll!lC<.!th:lln'torm5Cweri>eCOllSI11lCledfrom 15th Avenue at Coffman Slreet
<br />to the Ath1clic Ficld Detention (see Drawing ]3). Thc cxi'ting inlets along Coffman
<br />SU'ccljUSl south of 15th Avcnue will be connected 10 rn., bc:ginning of the 36--ioch
<br />,;ewer. The existing inlet contle<:tions to the sewer in 15th Avenue will be
<br />eliminated. The 36.;0.h sewer will cominue along Coffman Sired to Mountain
<br />View Avenue, At Mountain View Avenue the 3/i..inch pipe will transition to a
<br />concrele box.scctionduc to low slopes required to pass OVer sanitary sewers. The
<br />box section will be aligned along Mountain View Avenue between Coffman and
<br />Kimbark Street., At Kimbark Slreer the box 'ectinn will transition to a 4R.inch pipe.
<br />The 48.inch storm ""..ver will then be aligned along Kimbark Slrect from Mountain
<br />View Avenue to the Athletic Field Dctcmionjust ,outh of lllh AVenue.
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<br />d, MainStreetll1th Avenue Outf.l!,
<br />To provide an outfallfo'thce\i'tillg 36-iru;h"orm ",werunder Main $Ir ectat 11th
<br />Avenue. it i'propo<-ed that a 34-inchby 53-inch storm.ewer becon<truetcd along
<br />t Ilh Avenue belween Maln.nd Kimb"Tk SIre,elS, At Kimbark Street the Main Street
<br />outfall ,ewer will be COlUlC<:te<.! to the proposed 48-inch ,ewer along Kimbark Street
<br />Which outfallsto Ihe Alhletic Field Detention nearby.
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<br />2.
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<br />MMlCrPbnnedSySlem, -C<locepruaIDcsigns
<br />Conceptual design, for the Spring Gulch basin include a <hortlcwer ,cllment along St Clair
<br />A"cnuc mxl a parallel storm .ewer 'y'tem in the lowcr ba,in.
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<br />The SI. Clair Avcnuc scsm<'nt would be a 36,inch ,c','cr from La,llley Sm,ct to the Sprin~
<br />Gulc1.tnainchannc] in,ralledparalleJtuthee,isting 31i-inch Sl",m <ewcr(,ce Drawing 10)
<br />n", addit;onwill ,equircrecunSlructiorloftncc\istingoutf.ll ,tructureatSpring Gulch.
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<br />The propo,ed parallel 'lUrm ""wers for the lower Spring Gulch basin are shown in Drawing
<br />10. Th;'sy'lem;~proposedtobr;nguptofuIl2-yearcapacitythecollcction 'ystemdraining
<br />the west branch of Spring Gulch ",uth of 10th Avenue.
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<br />Approxim'lely 7.400 fect of sewer hne~ r,nging frum 24 to 66 inches in di,mcter will be
<br />needcd lUconvey the 2.year runoff. Alignmem uf the proposed ""'ie.. would be generally
<br />parallel to the exi'ting storm sewers in Ihis are,:u;d optimum ahgnmcnl~ ,hould be
<br />determined at the time of final design.
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<br />c.
<br />
<br />OLIGARCHY DITCH BASIN
<br />
<br />1. LPA IOO-Ycarlmpro"cmenls
<br />]n ,'lew that much. of t~e Oligarchy Ditch Basin nonh of Highway 66 is relatively ,parse)
<br />developed at the present time. there exists,n opportunity lU eonslrucl 'y'tems for the
<br />m3nagcmcm of lOO-year runoff. It i. recommended that north of Highway 66 approximately
<br />603,cre.feetofdetemioncap,city be constructed lU reduce runoff from the 0 hS,rchy Ditch
<br />b..in tu 87 d, at llighway 66 (see Drawing 5), Thi' nuw rme equ,ls the esti,nate<.! C.pa<:ily
<br />of the exi'ling 42.iooh pipc located west of Gay Street between Highway 66 and Oligarchy
<br />Ditch. ThiJ; storage requiremcnt iScompuledwith ,he assumptiun that 280acre-fc et"ffi'Nxl
<br />storage capacity 1'1;11 be secured at Teny lake. The additiun.ll ,tur1lgc ..pacity wilt need to
<br />be constl11Cted as one largcur:<cveral smaller parallcl rcgional detemionfaeih'ies locatedn()(
<br />far from Highway 66. Stormwaltr conveyance 'tructures in are" to be de"clopcd ,hOllld be
<br />siledforIOO-yearcap;lcit)'.
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<br />2 "-1.~A Imprtlvemcn..
<br />W;,hin the MSA, securing of detention capacity and con"ruc(;on uf ,hon storm ""wcr
<br />,egmetusare require<ltohringdrainage,yslem,up '0 near 2-year capacity (sco Drawings
<br />7.8, lOan<.! 12). However, wilhlheseimprovemOlltsinpl>cc.varioosreJchesoftheditch,
<br />including "n,c' crossings. will cominueto h,,'e]oss than a 2-ye', c'pacity. Although;1
<br />wa, recommended in the Alternativcs Evaluation Rcpnrtthat2-yeardctcnlional\dehannel
<br />'mpr",'emcnrs should be implemented. the City determined that" the present time snch "
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