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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.llit 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 />th~ crossings occurs. The degree and Jacat ion 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 ng, within
<br />the urban area which are inadequate for the lOO-year storlllf1ow (ttle
<br />laO-year storfll>ldS analyzed, as~o~ertopping >lill reS'llt in dallla!!e
<br />through th e City of ~~ont rose) . TIle pr i or i ties a re as s i g ned to sin gl e
<br />crossings ora series, lnorderofincreasingade'1uacy. The
<br />crassing(s) with the lawerlJriority nUlIlber, then, has a greater poten-
<br />tial forfloodingthandoesonewithahighernUlllber. If Montrose
<br />chooses to elrob~rk upon a cros~ing impravf.'lIl.mt program, those crossfngs
<br />\fit~ the lower ~riori cy nUllrucrs should be !Ii ven attent ion first.
<br />Outs i de the Clty. >lhere dal~age patent ial frOJll uvertolJpi WJ is less.
<br />priorities are not assigned. Table V~4 lists the inadequate crossing
<br />locations. and tile requi red cross in<; fae il ity to fully convey lhe 100~
<br />year storm flow. Other alternat ives are a~ai 1 able asi de from repldclng
<br />or augll\enting the inadequate crossing,Jith the facilityshov;n in Tdblc
<br />V_4, including a surface ctldnnel for the excess, and d diver,i()n of
<br />InajorflowsfrolllMontroseArruyo. Thesedlterlldtivesdrt:furtller
<br />discussed in tile sectior;f1oodpldinOeline<1tion-Rccollllllendati ons-
<br />Corrective Measures.
<br />
<br />potenticll to tile extent of the ddequdcy of tht: unir;';Jrov~d cuh!!rts.
<br />Thus, ifall colvertswithclpriorityofl we,'eUIJgrilded, da"lauej)oten-
<br />t i a I woul d then be I~i ni,ni zed for a 11 stornlS whose "'onoff di d 10t excecc
<br />tile C<ll>acily of the crossings "hose j)riority n~ldber i5 2.
<br />The pres~nt crossing inade~uacy situ~tion in the Citj of ~o"tr~s('
<br />results in the potent i~l for large dr;Iounts of da'''ilgcs, cO"lr:encin~ l-li~h
<br />the 5~jCdr frequency st or,,'. Areas Pcl rt i cul ar11 s~scej)t i b 1 e i nc 1 ude the
<br />apart:nent complex in.nediately downstre~:' of the HospitJl. The IIOSj)i lal
<br />b~ilding Hse1f is not ln tile IOO-ye~r floodplain, ho",ever, the bJse-
<br />ment issuscej)tibletosubstantial floodinS oue to the location of the
<br />rear ent rj. Access to tile hospita 1 woul d a 1 so effect i ~e ly be c~t -off
<br />bj the surrounding depth of flooding dnd aredS of 5~iftly flowing
<br />water.
<br />
<br />Eo IdentHied Drainage Problem Are<'ls
<br />In the process of performing the urban drainage analysis, specific
<br />drainage problCl1l locations were ldentified by the City or 10eJte dby
<br />ehe Engi ~eer. Sixteen drai nage problem areas are shOlln 011 rigure 1'-3,
<br />and SUllllJar1 zed 01: Table 1'~5. The tri butary drainage area to each i5
<br />shown or. Figure IV-S.
<br />TypieJlly, theproble"', are the result of a 5treet orgJtter
<br />seglllent wh1ch does not drain, inadequate 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 Froble 115,
<br />where install at ion of new inlets is reGuire~, it is dssurned that the
<br />net open area of such j n 1 ets fs greater than 2 square feet. Th i 5 wo~] d
<br />resul t in J cdpacity (sump conditioll) of ~pprcximJtelJ 7 cfs for ~dch
<br />inlet, It lS recu"'Lende<Jtllattllesmdlleststornr,e"ersil<=whicl1
<br />snoul<l be installed is a l~~lncll diallleter. Tne cost oiff~rent idl bet-
<br />ween dn 3~inch dialileter lJipe install at ion Jnd a 15- inch did",eter pi~e
<br />i nstdl1 dt ion is lei nor, especially wilen rnaint~ndnce alld capJcity aspects
<br />are consid~red.
<br />
<br />It 'ILUSt be re<'ll iled that repl dcing a si ngle cross i n~ withi ~ the
<br />City of!1ontrose Inay actually result in little or no reduction in
<br />damage potential resu1ting fro'.I a lOO-yeor event. This isbecousedn
<br />i nadequdte cr05sing upstrecllr. which causes o~ertopping results in the
<br />Sll; 11 a\le trd~el i ng through the street syste'TI Jnd urbani zed i1rblS
<br />through the City. Since this flow 1s not confined with-in tile cl1annel
<br />areJ, itsrotential forddma.geis IlotreducedsignifiCdntlyby
<br />IJp~radi ng a downstredm cul vert. Conversely, ilnproYing upstredrn
<br />cul ~erts without illlpro~ing downstred:n cul ~erts maj' result in lOCal iz..ct
<br />odlndge reduction in ~h~ vicinity of the impro~ed crossin~; I1OHe~er. the
<br />overtoppin~ situation H the r1ownstrea.rl clll~erts would not De reduCE'd.
<br />
<br />The ~Jri()us sol ut ions La tIle sixteen probl e n <lrea5 discussed 1.>0;101'1
<br />are Illeant to pra~ide a 5-year frequency le~el of protection, Good
<br />des i gn, howe~er, in~olves r:lakin5 pro~is ion for the less fre~Ller.t storm
<br />flows tr1butary to the 10cati on, such d, by pr()~fdi ng audit ional sur-
<br />fdce di :ches or channel s to pre~ellt local inundation. SUCtl additional
<br />;Jrotect i on, as well d5 an integratea des1 gn ot lac1l1t1eS to dlle~Ia.te
<br />dll dra i "a~e probl"", ar~a $ ituat ions should be e~a:,1ined in a fJtur~
<br />dra i nage study of a I~ore loca I i led nat u re,
<br />
<br />ProblelllAreal
<br />
<br />For' th i s redson, so,."e 0'OS5 i ng pri ori ~ i es He"e "55 i ~!led in grClJps
<br />'.;here Je~ree of i"ade~uacJ was cOld,'arabl e. Rerl acing crossi1gs ~i,h
<br />the lower ~riority nUflberin~ will resul~ in d r~ductio" of dar;Ia~e
<br />
<br />Proble;TI Area 1 is located near tl:e Cibsons "'o,'~ on Rcs~ Lane,
<br />Pres<<nt plans lnthedreacdll fo,-enendingthestreettoCed<jrC'-eek.
<br />Th;5 ~111 ,ralls"er the arainagc ~ro:Jlen; t~ the e1~ 0' I\ose ~JnL', JdJa-
<br />
<br />-25-
<br />
<br />-24*
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