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<br />ar-eas ar-e negligible. 'I'he folloldng Table 10 identif~es IOU-year <br />event detention pond volumes, locations and maximum depths. <br /> <br />resulting inundated area ~s very wido with very shallow sheet flow <br />conditions resulting. <br /> <br />TADLE 10 <br />EXISTING DETENTION PONDING AREAS <br /> <br />. . , <br /> <br />Effect of Recommended Improvement~ <br /> <br />LOCATION <br /> <br />VOLUME <br /> <br />MA_XIMUM DEPTH <br /> <br />Flow through the overbank areas occurs dlonq the majority of <br />the Creek's length. Fortunat.ely, there ore limited or-eas in whi",h <br />structures are affected. width of flow in the over-bonks r-anges <br />f'rom several hundred feet to over: 1500 feet. Heaches that develolJ <br />a very wide floodplain (1000' - 1500') arc from Drake Road through <br />Rolland Moore par-k and Arthur's Ditch th~.ough College Avenue. <br />Overbank flow through the~e ~tretches gener-ally has a velocity of <br />less than 2 feet per second. <br /> <br />, <br />i <br />, <br />I <br />, <br />I <br />[ <br /> <br />Channelization of the Creek in the two locations called for <br />in the Recommended Improvements Plan will have a mUJor beneficial <br />impact with regards to overbank flow thICou<Jh residential and <br />commercial areas. The channel to be con~tructed west of College <br />Avenue will confine the lOa-year event, thereby removing a <br />significant residential and commercial area from the lOa-year <br />floodplain. The proposed lOa-year channelization and bridge <br />improvements through Stuart and stover Streets will also remove a <br />significant residential area from the 100-year floodplain. Cross <br />flow over streets will be eliminated by the crossing improvements <br />at the C & S Railroad, WelCh Street, Drake HO>ld, ilnd Taft Hill <br />Road. The C & S Railroad culvert improvements will also eliminate <br />sheet flow throuqh a large area east of Timberline Road. <br /> <br />Upstream of Taft Hill Rood <br /> <br />74 Ac-Ft <br /> <br />15 feet <br /> <br />Upstream of BN Railroad <br /> <br />165 Ac-Ft <br /> <br />13 feet <br /> <br />Upstream of C & S Railroad <br /> <br />50 Ac-Ft <br /> <br />11 feet <br /> <br />Overbank Flow Areas <br /> <br />4.4 Burlington Northern R~ilroad Stability ~nalysis <br /> <br />Sheet Flow Ea~t of Timberline Road <br /> <br />studie'" conducted during the pr-eparation of the Ginqery Master <br />Plan indicated that the Burlington Northern Railroad embankment <br />factor of safety against failure during the 100- and 500-year <br />events was somewhat less than the recommended filcto~' of silfety of <br />1.5 for a water impoundment dam. The Gln<jery master plan <br />recommended stabilization of the railroad emuankment such that the <br />factor of safety \"ould meet recommended criteria. In order to <br />account for a possible failure of thp r'lilro'ld pmh"nkm"'nt anel the <br />asso",iaL",j ..ff(lcts on downstream bilsoline flood di.lI:lClgc", IIEC-l d..m <br />breach analyses for lOa-year <lOci 500~year events "'ere conducted. <br />Fat. a dct.:liled description of this procedun' ",,{pr tl' thf' Te("hnic,~l <br />AddendUm. <br /> <br />Overbank flLJ'~' (rom Collcge 1\"/cnue dO'dnc:tre"t:'. to the c I. S <br />Railroad bridge is generally less than 1000 feet wille. Except for <br />the Stuart and Stover street sections, this length is c.::haractel'iz<lll <br />by greenbelt area with nlQdenlLely slovin<) overuallk are,.,;. Ov"rbank <br />velocities generally range from 2 - 5 feet per second '~'ith.in thIS <br /> <br />ilr..a. <br /> <br />Approximately 75 cfs overflows Timberline Road and leaves the <br />channel during the 100-year t'VE'nt. Th i s flow, '~'h ich ,-ep,'"'",,nl" tlw <br />peak: of the hydrogr-<lph at Timberline, dmuuuLc; Lu l,-,>!>! Uk'" 10 ,1<:1"'- <br />feet total volume. Due to the topogrClphy ea::::t of 1'imborlino, the <br /> <br />35 <br /> <br />H <br />