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<br />The fl0Odod ~ro~s shown on ol~tes 2 through 5 indiCJte <br />the width or extent of flooding correspondinG to the flood elovatlons <br />shown On thepro+iIGs. The flooded areas Jre not preclso becausll of <br />the Ilmihtion of the topographic mapping, but do indicate tM <br />generai nature 01 a flood. Forilmoreprecisedeterrninationof <br />flooding, the elevation of all aredsof COnCern should bedoterml"od <br />and cornpJrod to the flood olovations Shown on thIC profiles. <br />Except In 11 very goneral way, the flooded areas have not <br />been shown for that portion of Left-HandCreekbetweenLJ. S.Hlghway <br />287andtheSt.YrainCroek. The flood plain widens In the shapeot <br />a delta as it merges with tho St. Vraln. The overbank flows are <br />carried by I Ittlo drainage courses that diverge from the creek sep- <br />ar<:lting the \oI<:lter intoshallo\olindependentstreams,each\ollth its <br />own profile. The flood profiles are not valid in this reaCh and apply <br />only to are<:lS Jdjacent to the stream. Another location of indeter- <br />~Inate flooding Is ~nown by the cross hatChed area below State HighwaV <br />li9. Goththehighwi)yandrailwJybridges,lItthls locatlon,have <br />adoquJte capacities tor the Intermediate Regional Flood, but the left <br />upstream ovorbank is low and flo\ols are diverted ncrTheasT along the <br />hi9h"<:lY, The tops of both the rood and r1lllroademb1lnkrnentssIOlle <br />In <:l northeasterly directLon and u!timately the water overto~s th~. <br />Oncoacrosstheerrbankrnents,the\olater1ollowsvJrioussnallowp"thS <br />backtothostroam. <br />Ten cross sdctlons portraying various Channel "ndvalley <br />characteristics are provided on plates 8 and 9. Thev sho\ol the depths <br />of overbank flooding, and "hen used with the flooded are<:l maps and <br />the pr0111es help complete the picture of the Leff-~<:lnd Creek'S flood <br />potential. <br />In <:lddltTon to damages from inundation, othdr d<:lmJgos <br />c~ld be caused by fast-flowi~ \oIater. During an Intermediate Regional <br />Flood, the velocities inthechannol will be In The range of six to <br />Ten feotpcr second but at The bridges lInd OTher loc;JllzedarOIlS, <br /> <br />they will ba much higher. These velocities lire erosive but the extent <br />of erosion is limited by a number of fllCTor5. Considerable lateral <br />erosion has been obsorved In similar streams even during JI1inor flood Ing. <br />Buildings located close to the stream, although aoove the flood stage s, <br />have been damaged from undercutting as the channel banks were eroded. <br />BeSides erosion, the force cr61lted by the s\olift-flo\oling \oIater against <br />buildings can result In structural damage especially If floating debris <br />Is present. A similar hazardous condition exists at 16 of the 18 <br />bridges, whiCh can be flanked or overtopped. People often attempt to <br />cross submerged road~ays. In serne c<:lses, cars have been swept of1 <br />the roads, but the usual case Is for the cars to become stalled ~nd <br />the occupants s\olept Into the flood afTer they emerge from their cars. <br /> <br />19 <br /> <br />20 <br />