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<br />B.
<br />
<br />ALHR~i!\TE 2
<br />
<br />Jllternate 2 ~"ould include nn inprovcd conduit fr:l:n the plHte
<br />River to Prince Street, an lIT,proved chao~el through the
<br />Lakeview Knolls PUD, a detention pond just east of the tracks,
<br />v.;locity control structures <<no 10',' flow channel improv...ments
<br />through 'tr.e future park area, right-of-way acquisition and
<br />channellz>lticm from Windermere to Datura, [load plain zoning
<br />to Powers Park and additional sewer l;apacity along the
<br />South Tributary. A schematic of this alternate is shown
<br />in l'ig\'Ye 8.
<br />At th" lower end, the detention pond houl<l be built to
<br />minir.l.ize the improvement costs do\.>'nstrealll. With a flood
<br />ponding volume of approximately 43 acre-feet construc;tcd in
<br />the proposec park area cast of the ATqSF tracks, the struc-
<br />tural improver.:ents downstream can be economically built to
<br />give lOO-year protection. The conduit at Prince ,-'ould be
<br />genet.1_11y the same Si7.0 as presently required for the S-yea:-
<br />storm flow. As sho"'n on l'igure 9, Accumulated Costs <<nd
<br />Benefits for Alternate 2, this benefit-cost ratio at the
<br />detention pond .....ould be approxImately 0.94, nea:dy justi-
<br />fiable based on t~ngible dolla~s.
<br />Above the pond, chanl'.el improvements consisting of velocity
<br />control s~ruc tl.:'res and 10..... flo'" cr.unnol mOdifications "'Otlld
<br />he made to minirr.i7.e eresion in the rhannel and sediment
<br />dcpvsition in tho ponu. ~laxirnum flo'" velocities in this
<br />~each presently r,":lge from 4 fps to 10 fps. The improvements
<br />would be compatible ,",'ith the City Citch flune which nos~es
<br />tr.o gulch in this are:!. Also, consideration would be given
<br />to pro':icti:-.g a relu::f tlverflow at this location for the City
<br />lJitch, to ffilnir-.i::e flooding :!long the ditch. Under present
<br />c;\annel conditions, the channel improver::ent costs woulJ
<br />exceed the benefits gained. However, if park il~p~ovements
<br />He::-c to be lrade along tho channel in this reach, such
<br />t;hanael improy"ments cOHld look pore econo:aically desirable.
<br />
<br />,
<br />,
<br />1
<br />,
<br />
<br />c.
<br />
<br />Above \','intlcr:;lere Street, this alternate \;ould propose to
<br />acquire appnnlmately eight residenr.;es and channBlize the
<br />streal'l through the area with a bridge at IHndermere Street.
<br />These improvements ,,'ould have an irr.m"diate affect of elimi-
<br />nating the high private p~'operty damage potential for this
<br />area. HOh'evcr, the econo::lic hcn"f:its recognized by SllCh an
<br />i::lprQvement cO\Jld be offset by the sociological damages
<br />associated with relocatillf: a number of families.
<br />
<br />Aboye !l:t tu::-a ::>t rL'ct, fl OO~ plain zeni ng "ou ld be i rrp It:men t<~d
<br />to miniml:\;' t)H1 flJLure IHJLcntial flood ,brr.age. Zoning ",{)tlid
<br />requlr.. minir':ll. if a"y, cost and eouid stJ.nu to ..cquire
<br />c:\teI~si..." benefits thNugh the r:criod "hi,:h J.v"rClI!t' anIlu:;.l
<br />d~.;;,,,;;c~ '"rill occur. Also, actiUll ~huulu lJ.. taken ;:0 qua.lifr
<br />th,.) rcsluents of the arlJ<I for flood inslIrm1(..".
<br />
<br />.,
<br />. ~ L.
<br />
<br />Tb", total cost for this alttnnative i~ approximately
<br />~783,OOO. The pot"ntial hcncfi ts range from S930,OCO to
<br />'"I'pr()xir::ately S 1,780,000. Benefi t-cos t ratios for the~e
<br />figures range from l.19 to 2.27. The ac(;umulated costs
<br />and henefits :Ire sho-"n on Figure 9.
<br />
<br />Along tht:: Sou.th T'ributary, an improved sewer 1S rec~m,"ended
<br />h'itL this alternate. The seh'er wou~d extend from the- F.,ain
<br />stream to Littleton Boulevard along liindermere and then
<br />easterly r..1ong Littleton RO!Jl<:var2. to Datura Street.
<br />Inlets \-"ould be provided along the new alignment with a
<br />large inlet provided at natura to collect all street flo,-'s.
<br />Because of the high damage associated with this area for
<br />the full range of events, improvements of this magnitude
<br />are ea.~lly justified, economically. An improvcr:tt!nt designed
<br />for the lOO-year event would cost approximately S579,eoo
<br />while deriving beJ\cfi ts on the order of ~3 ,382 ,000 for a
<br />benefit-cost ratio of 5.84.
<br />
<br />A cost hreilkdo\-,'n summ;try for the alternate is sho\-"n in
<br />Table VI.
<br />
<br />ALTERNAT5 3
<br />
<br />Thi$ alternate 'iO'llrl i.r,COl'J10l'~t.C the SD-me improvements pro-
<br />p,):;ed in A1tern~ te ? for tho "''' i n $1 re~m ,,'i th t.he ~tldit ion
<br />of improve::1ents at PO',,'ers PiJ-rk. J\t lhe park, thu available
<br />ftovd storag{' volu~e would be ir.creasr=d to re-duce the flood
<br />f],n;s In the tiv\>lJ:stream reaches. Schel7,atically, this
<br />alterll:.t.te i~ ShO'A'Il in Figure 10. The Seuth "i'dbutary l'.'ould
<br />be improvl,d along ','.'i.ndermere AvenUt. by l(j;,ering the street
<br />approxim:.t.tely 1.5 feet for approximately 650 fe"'t north of
<br />Powers Avenue a~cl adding additional surface inlets along the
<br />existing storm seller to utilize available pip" capacity.
<br />
<br />On thO' main stream, improving Powers Park Ie detain tiddi-
<br />tio"al flood h'aters fer t.ho lOO-yc~~ event ;,0\11d re,Juce
<br />the degrce of flooding below tht, p,.r:k to approxim:ltcly
<br />the 7-year e'ient t1llder pre~,mt conditions. This improvement
<br />,,'ould reduce the damages along Berry Circle but ,;ould not
<br />totallv eliminate thor.:. Tbe reach abo\'e Datura WOltlrl still
<br />he flood plain ~one~ to qualify thc adjoining Pl'Opt>rt>.
<br />ownf'-rs for flooel insuraJlce.
<br />
<br />The o'/er;!.ll r:<.ain stream cost for this alternate would he
<br />approximately $919,500 with a derived benefit of ~l,172,3nn
<br />or D benefit-tost ratio of 1.28. The cost ;lnd b~nefit
<br />cor.p:Hl~()Jls are sLew;! UII Fi.gurc 11.
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