<br />CHAP'rERVI
<br />HYDRAULIC ANALYSIS
<br />
<br />proceed, in steps, from one cross section to the next. The HEC-2 progrnm
<br />i" also capable of hnndling the effect of the various hydraulic struct~res,
<br />soch as bridge. snd culverts, which re~trict the flow.
<br />
<br />The hydraulcc analysis in this study entailed the compotatcon of ~atcr
<br />s~rface profile" "ithin the study reach for the 10- a"d 100-year frequency
<br />flo"s.
<br />
<br />The results of the 10- and IOO-year frequency flood computations are
<br />pre$ented in Table-5. The flooded arena from a lOO-ye~r frequency flood are
<br />pr~"ented on Plate" 1 thro~gh 4. The flood profiles ore ShOwn on Plates 5
<br />through 7, Plate 8 "ho",s a numlJ"r of typical cro~s Bection. of the strG"m
<br />and valley in the study area.
<br />
<br />Topographic mapping, with a scale of I inch equal to 100 fent ~nd 2 foot
<br />contourintervalo,w"sprClvidedbyElbertCountyinc(X)peratio"",ithth"Town
<br />of Elizabeth. Tbi" topograpbic mapping ",as photo-revi~ed to reflect the land
<br /><Jse conditions in the study ,~ri'a as of June 1979. Channel cross sections were
<br />field S<Jrveyed at intervals along tbc study rn"eh by Elbert COlmty and the CWCB.
<br />Watnr s<Jrface profiles were determined using the croS~ sections, the ch"nnel
<br />and bank rO<Jghnes" coefficients, the bridge bydraulic characteristics, ~nd
<br />tbe flood flo",s for tbe "elected frequencies presented in the hydrologic
<br />anaLysis pba.e of this st<Jdy.
<br />
<br />Water s<Jrface elev~tions presented in Table-5 are based on comp<Jtations
<br />",hich aSS<Jme no red<Jction in tbo State High",ay 86 bridge conveyance capabili-
<br />ties. The bridge has adeq~ate freeboard, long spans, and strenmlined piers
<br />whiCh "ho<Jld minimi~e the acc<Jmulatio" of debris during flood flo~ periods.
<br />
<br />A detniled dnscrip~ion of the hydra<Jlic analysis i. included in tbe tech-
<br />nical addend<Jm.
<br />
<br />rwo field investigations ",ere conducted to determinc tbe hydraulic charac-
<br />teristics of the Hudy reach. D<Jri.ng th~ initial "<Jrvey, pho~og(aph" of the
<br />cb,~"n"l and valley ",ere tak.en. Photograph. of typical sections ate presented
<br />on Pages II thro<Jgh 13. From tl'es~ ph"tt>gtMphH ,",,,I th~ ini tial field "<Jrv"y,
<br />r"" r~'\g~"~~. <,,~a~a('t"Ti~tic" "f th,' Ch,mnd .."J valley ~ere det<,:rmined. The
<br />v"l<Jes for ~he ~~nning R<J<Jghness Coefficient <Jsed in this analysis ranged from
<br />0.028 to 0.034 for the channel and from 0.040 to 0.085 for tbe overbank. ateas.
<br />
<br />Tb" water "<Jrfac~ ~levati""s for th~ 10- "'ld 100-year rec~rrence intervlIl
<br />floods ~"re comp<Jt~d \.lsi"g the Corps of Enl;ineers HEC-2 Step Backwater Comp<Jter
<br />Program. This program t\tiLi~os a sol<Jtio" to the one-dimensional energy eq<Ja-
<br />ti"n to determine the shape of the profile bet",een control s~ctio" ",here the
<br />water "<Jrfllce elevation is known or can be as"<J",ed. The proced<Jr~ for a steady
<br />flow profile ~alC<Jl..tion is ~alled the "Standard Step Method". In this method
<br />the d1stance from a do"",Hream or <Jpsnea"' point, "tH,re the conditio,," are
<br />:<en"""" to the point \Vhere theback",ater effecta are to b" determined, is
<br />divided into rClIcbcs byero"s sections at fixed locations along t he river.
<br />5tarcin~ fro'" ""e cunltol point, cal,,,I..tions of the water surface profile
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