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<br />caraci ty v;lried from apprcximately 100 cis at ~lir.detJ:ll're
<br />Street to 50 cfs at Po~ers Park. The storm sewer on the
<br />South Tributary ,.-as installed in many segments v;lryin[: from [I
<br />i2-inch COnCTl'te pipe to an IS-inch metal pipe. This storm
<br />se~er system has limited capacity in the segment at the
<br />intersection of Powers Avenue and \'Ii:H.!ermere Street. The
<br />system capacity is approxir.-.atcly 60 cfs at thi:; pOLnt.
<br />Limitations include, inadequate pipe slope, insufficient
<br />surface inlets and insufficie:lt panding depths.
<br />
<br />SECTION V
<br />
<br />HCGD DH!!\GE - BEKEFI"I A~ALYS[S
<br />
<br />These calculated sel,'er capacities \o'cre subtracted from the
<br />total computed flows used to calculate the flood plain
<br />through these read:es. The flood plain limits will be :;hOI"11
<br />on the preliminary plan drawi~gs prepared for the selected
<br />alternative.
<br />
<br />Th,' flood darf.'lgro> or ber.efit C'l'lalysis is one part of the benefit!
<br />cos t ,',-;\lu(\ t ion ccmplctcd if' this illi t ia] pha50 of the S laughtcr ~
<br />l'cuse GUlch planning liQrk. Benefits arc generally described as
<br />the reduction in potential ~ama~e resulting from improvements
<br />or actions taken to improve the facility under consideration.
<br />In cunnection with Slaughterhouse Gulch, the benefits considcrcd
<br />arc those which would be derived from tr.e expenditure of a
<br />certain sum of money in il~.prOVef\ents which, in effect, ~ould
<br />reduce tile potenti,,1 tl_anage ,lue to f]oodinr. under the cxistinr,
<br />channel conditions.
<br />
<br />The theory behind tho benefit evaluation and the total benefit!
<br />cost analysis procedure, as well as the application to urban storrr.
<br />drainap~ projects is well c(')v'n-ed in the tcxt, fcor.ol'lics of
<br />hater Resuurces Planni~~, by L. Douglas James and :':'obert 1. Leo,
<br />publlshe(f[)}T ~:cGra\"..I-rr in 1971.
<br />
<br />The first step in cu;n~letiJlg a benefit evaluation is the deter-
<br />mir,,1tion of the existing dJm;]~e potential fcr a stream. This
<br />is done by computing the water sllrface pTofih's for a minil.'um
<br />()f th-ree fleod event~.. Us i.r.g depth -Call'_<1-&f Tf' l:,t ion~hirs
<br />ChaliJcteristic of the area within the noad plaIn, tI-,e dollar
<br />dam:lgr, figures for each storm event arc c"lcui:ltcd ar.d plottc((
<br />on a graph of dollar da::-:;lf,O versus peT~el,t probabili ty or rettltrl
<br />frequency of the store. event. tivaluatir,g th~ ar~a b<Jp..,,,t]~ th~
<br />plotted curvo gives the aveTJp,e annual dama~c potential ch;]ra~ter-
<br />istic of the ell'''l'!"l ,..,"ch under considc.ration. Thi~ W<l" th(:
<br />procedure followed in tb.J detorrr:in;.tior: of the dam"ge potential
<br />,');aruct.eristic of Slaugr.ternol:se l;ulch.
<br />
<br />TQ simplify the determination of property d.lIhlges Jssoci"tcd
<br />",ith flooding, one depth-daJ:"iage curve for single J:Jmily rcsider-
<br />t-i<<l flTopert)" was dClri"ecl. The typic(!l h0t:.Se type Wi'S con"iden,d
<br />to b,: " mul ti-Ievel ut:s igr; ... i t h 11 w,,-lk-~,t.:t l1useJ~ent level and 11
<br />foV\,r (,n'~ rrtnce. fro::1 a5.""'..sP(\ eva IU;lt ion;; avai lab 1(' in the arcas
<br />~ldJ oining the ~lIl en, the av{'r<lgc va Ill" of t.he houses and
<br />i'rc","rt). l!:i.f a~su"~ed tc b..' ~32,200. Subtfcctin.g ~l1, """",,"",J
<br />Jot v!\lue of $7,000 from thf' ;Jssc5sed evalliaticn galiC all avcr".ge
<br />structural value of approxinately $25,200. Sir.\ilar figure5 "ere
<br />"etel.c.~inecl for 3-[Jiirtm,'nt rcuuscs and cGmmerc:i,d ~tn\ctt;rl'5.
<br />
<br />Ti,e contents (J[ e~eh bOl:~lng I,dt weft: S0t (It $.E,GOG peT tmit.
<br />L';;in" ! hesp v;t1 \I~~ and the dt"rth-t'!'\rr_"g.. (:lJrvc's d'-'Vl'] "P~(! ;'Y the
<br />r:OTp~ of Engincers fur tl:" Federal Ins\lriln:e t,dminis!ration as
<br />,I L,ts is, a Sj"K_ ial dept!' -ll_'ll:::!!',e cu't"ve liftS d"term illeet for ~;~ a\\g~.tor-
<br />i:o\l~c L;1,;,.,h. CO,~;)U!i:lg d'Jmat'l's h',J, t'lt'll 3 Inatter or dH"rminillf;
<br />the numher ot" ho\\sc~s flooded JIl..! tbt" dcptr o{ inundat ion.
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