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<br />Tdbl ~ V-2 ~re5er1ts d SU"'"dry of the v.dous storm sewer 5Jste111S
<br />'~i thin the City. The 1 i,nit in!! ~art of each is ident i fied, <15 well dS
<br />resultant capacity.
<br />3. MdjorDrdinagewdYs
<br />The capdcities of the yar;ous crossings for the three study
<br />strealllsllavebeeneXd"lincd, and areprc,enled in Tdble V.3. TableV-3
<br />also indicates the frequellcy storm which a given croSoiny iscdpdlJleof
<br />passir1!1withoutovertopping. FigureV-2shows the loccltion of these
<br />crossings. As Tab] e '1-3 indicates. the crossings dre dde~udte lhrou':Jh
<br />the City of r-Iontrose generally for the 5-ycar frequency storm flo~. As
<br />a result, large portions of the City dre susceptible to :;ignificant
<br />flooding during lhe less frequent storms, pdrticularly if blockage of
<br />the crossings occurs. The degree and location of this flooding is
<br />dependent on>lhen, where, and to what extent the crossing is blocked.
<br />Tabl es V~3 and V~4 priorit i ze upgrading of the cross i ngs within
<br />the urban area which are inadequate for the lOO-year storlllf1ow (ttle
<br />lQO-yearstorfllwas analyzed, as~o~ertoppingwill reS'llt indalllage
<br />through th e City of ~~ont rose) . TIle pr i or i ties a re as s i 9 ned to sin gl e
<br />crossings ora series, inorderofincreasingade'1uacy. The
<br />crossing(s) with the lowerlJriority nUlllber, then, has a greater poten-
<br />tial forfloodingthandoesonewithahighernUlllber. If Montrose
<br />chooses to elrob~rk upon a cros~ing improvelll.mt program, those crossfngs
<br />\fit~ the lower ~riori ty nUllrucrs should be !Ii ven attent ion first.
<br />Outs i de the City. where dal~age potent ial from overtoppi WJ is less,
<br />priorities are not assigned. Table V~4 lists the inadequate crossing
<br />locations. and tile requi red cross in<; fac il ity to fully convey the 100~
<br />year star", flow. Other alternat ives are a~ai 1 able asi de frOIll replacing
<br />or augll\enting the inadequate crossing,Jith the facilityshov;n in Tablc
<br />V_4, including a surface dlannel for the excess, and d diver,i()n of
<br />Inajorflow,frolllMontroseArruyo. Thesca1terlldtiveSart:furtller
<br />discussed in tile section floodplain Oeline<1tion-Rccoll1lllendat ions-
<br />Corrective Measures.
<br />
<br />potential to tile extent of the ddequdcy of tht: unir";Jrov~d cuhl!rts.
<br />Thus, if all CJl verts with a pri ority of 1 ~e,'e UIJgrilded, da"laue j.!oten-
<br />t i a I waul d then be I~i ni,ni zed for ~ 11 stornlS whose r"Jrloff di d 10t exceec
<br />tile C<ll,acity of the crossings >lM5ej.lriority nUldber i5 2.
<br />The pres~nt cross ing inade~uacy situat ion i~ the City of ~Orltrus('
<br />results in the potenti~l for large ~r;Iounts of da'''ilgcs, CO"lr:c~cin~ wi~h
<br />the 5~yedr frequency st or",. Are~s pa rt i cul arly s~scej.lt i b lei nc 1 ud~ the
<br />apart:nentcomplexin.nediatelydownstrea:10ftheHospitJl. ThellOsj.!ital
<br />b~ilding itself is not in tlie lOO-year floodplain, ho",ever, the bJse-
<br />ment issuscej.ltibletosubstantidl floodinS due to the location of the
<br />rear ent ry. Access to tile hospita 1 woul d a 1 so eff~ct i ~e ly be c~t -off
<br />by the surrounding depth of flooding and areas of ,~iftly flowing
<br />water.
<br />
<br />Eo IdentHicd Drainage Problern Are~s
<br />In the process of performing the urban drainage analy;is, specific
<br />drainage problCl1l locations were identified by the City or 10cJte dby
<br />LheEngineer. Sixteendrainagc problem areas are shOlln 011 rigureV-3,
<br />and SUllllJari zed or: Table 1'~5. The tri butary drainage area to each i,
<br />shown on Figure IV-8.
<br />TypicJlly, theproble"'s are the result of d street QrgJtter
<br />seglllent which does not drain, in~dequate number or size of inlets b
<br />the storm s~wer. inadequate storm sewer. or no croinage pro~i5ion.
<br />
<br />] n arri ~jny at reco,~nended sol ut i OriS to tlw vJrio~s I'roblc II"
<br />where installation of new inlets is required, it is dssurr;edthatthe
<br />net open drea of such j n 1 ets fs greater than 2 square feet. Th i s wo~] d
<br />resul t in J capacity (sump condition) of ~Pilrcximately 7 cfs for ~dch
<br />inlet. It lS recu"'Lende<Jtllattllesmdlleststornr,e"ersizewhicl1
<br />snoul<l be installed is a l~~lncll diameter. Tne cost aifferent j~l bet-
<br />wee~ dn 3~inch dialileter j.lipc install at ion Jnd a 15- inch di~"'eter pi~e
<br />i nst~ll ~t ion is ,"inor, especially wilen rnaint~ndnce dnd capacity ~spe'ts
<br />are considered.
<br />
<br />It 'lLust be redl ize<l that repl acing it si ngle cross i n~ withi r. the
<br />Ci ty of 110ntrose ,nay itctually result in 1 ittle or 110 reductio~ in
<br />darr>ilUepotential resu1ting fro'.I it lOO-yeor event. This isbecdusedn
<br />inadequatecrossingupstreamwhichCJuses overtopping r€sults in the
<br />Sll; 11 d\le trd~el i ng through the street sjste'TI Jnd urbani zed areas
<br />through the City. Si nce this fl ow is not confi ned with-in the ch~nnel
<br />JreJ. its potent idl for ddm~ge is riot reduced significant 1y by
<br />upgrading a downstream culvert. Conversely, ilnproYingupstrearn
<br />cul~ert~ without illlpro~ing downstre~:n cul~erts mJj' result in ]ocdl izec
<br />da'ndge reduct i on in ~Me vi c i nity of the improved cross i n~; 110He~Qr. the
<br />overtopping situation H the r10wnstrearl clll~erts would not De rQduco'd.
<br />
<br />The ~drious sol ut ions LO tIle sixteen probl e n <lrea5 discussed l>elclW
<br />are IlIeant to provide a 5-year frequency le~el of prot~ction. Good
<br />desi~f1, howe~er, in~olves r:ldkin5 pro~ision for the less fre~Ller.t storm
<br />flows tr1butary to the 10cati on, such J, by pr()~fdi rig audit iondl sur-
<br />face ai :ches or channels to pre~ellt loco] i nundat ion. SUCtl add it i o~a 1
<br />;Jrotect i on, as well ~s an integratea deS1 gn ot tac1l1t1eS to alle~Iate
<br />all dr;! i rlage prolil"IL' ar~d s itudt ions should be e~a:,1ined it! a fJtur~
<br />dra i nage study of a I~ore loca I i zed nat u re.
<br />
<br />ProblelllAreal
<br />
<br />For' this redson, so,."e 0'OS5 i I)g priuri ~ ies "eno "5S i ~!led in grClJps
<br />'.;here Jegree of i"ade~udcy was cOld,'arabl e. Rerl acing crossi1gs with
<br />the lower pri orily nUflberi n~ will resu I ~ j n a r~duct i Or! of dar;Iit~e
<br />
<br />Proble;TI Area 1 is located lleJr tl:e Cibsons ",o"~ on Rcs~ Lane.
<br />Present pldns ln the area cdll fo'-extendingthestreetto[ed<jrCr'eek.
<br />Th;, ~111 trdl1S"er the araindgc ~ro:Jlen; t~ the e1~ 0' I\ose ~JnL', ddJd-
<br />
<br />-25-
<br />
<br />-24*
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