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<br />IIYlltt^IIU('I~N(ilNEElUN(j 't)4
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<br />!,,,clars Affectina Disch"rae-Measuremenl Accuracv
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<br />The accuracy uf .he slopc~arca discharge measurement nf Ihe Kaven Fnrk tlHOtl
<br />Ikpemlcll larg.ely UII SUililhilily uf the selL"Clcd reach alld, in p.trlku)..lr. lhe proper
<br />sdcl"Iiun of Millllling's roughness cocffidenls, iOlcrprclalion Ilf the high~wa'cr nmrks,
<br />m..~nitUllc uf Ihe fall. plul.:emCIII and number of cross sectiuns. pn::St:m;c uf large
<br />t"\.llansitms ur COllll,...t.:liun!i. and presence uf slalc~uf-now lrOlnsitiolls. I:or slope~jtrca
<br />lIU";j'\urcnlCnls in Sleep lItuuntain rivers in general. sOllie uf Ihc-sc fal:lOrS l:UIt n\lllrihutc
<br />HI l!rcalcr um:CrlililUics IfI.." olhcl~
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<br />A dischilr~c value- compulcd by Ihe slupe-area methud is inversely I1roporliollilllu
<br />Manning's" value, thus making roughness cucfficicnt sclC\:lilUl a very impunant
<br />lltnsidcmliun, 'Ille sclet:tiun uf Manning's" illllillural channels lradilionally hilS hecn
<br />al leas. parUy suhjeclive, although sevend guides (Chow, 11.)59; Dames; Il.)ti7) iue
<br />useful in rcdut:ing :-iubjcctivily, Most references nlilke no dislinction between the
<br />cU\.'t:ts uf sleep and nal gradienl streams 011 ~Iet:lioll of It values.. Jarrell (19M)
<br />()fcsentell .1 n....themalicallechnitlueforL:UIIl.lUling roughness coertidcnls for hi~h-
<br />~mdicnl slreams Ihal fC4.uircs Ihe field-measured characlerislic.:s nf watcr-surfa\:e slupc
<br />and hydraulit: filllius, Jarreu'!i lel:hniquc yields roug.hness t:oeffil.:icnls for the main
<br />l.:h..nll....1 of Ihe sludy reil\:h of 0'<<144 to .t05ti. whit:h rangL' from 3 to 20 pert'enlluwer
<br />Ihan Ihose sdcl;lL"d in Ihe lield, lIse of Ihese values resullL"f.1 in a computed disi:hafl.!l~
<br />IhiU was 10 llercenl higher Ihan Ihe di~harge I:ompulcd frum the" values chosen in
<br />Ihe liclll.
<br />
<br />The uUerprelalion of high-water marks fur develupmenl of waler-surface prufiks
<br />is anuthcr suurt:c of variahility for slope..uea measurements in l!.cncral. illltl fur slt'l'll
<br />IIllilll1lain streams ill punleular, Mounmin streams usually havc slcel" rlll..:ky hiUlks thill
<br />dn nnl relain high-water marks well, .l1lC only cvidclli:c ut lilt.' heighl of f1nodllow Ihal
<br />usually remains along Sleep banks is wash liues, whit:h generally indicate il Iluod
<br />c1cvalinn higher Ihan Ihe al.:lual hillh-watcr elevalion. In addition. the higher flnw
<br />velodlY 01" mountain streams U\.';,lCS more inslaoces of waler pile-up condilious ill
<br />Uces and rocks where high-WOller marks nUl'" he deposited, Use of these marks itlsu
<br />could result in ;'10 over.cMimatioll ul" high-water le'vd. The clTe!..:1 u[ IIlt.'Sl'
<br />diSl:rcpam..'ies on lhe discharge compulation depends perhaps more 011 how the watl'r.
<br />surfal.:c slope hctween sUl.:cessivc ..'ross sL"Clions l.:hlln~cs rather lhan on h'lW thc ..'W'>\
<br />sct.:tional area and conveyance me idTC'i:lcd. Perhaps Ihe reduc.':lion of t111t.:el1i1illly
<br />g..incd from Ihe generally l'IlL"CllCr walcr-surface slnpcs cuuntcrs lhe (li~rellilUt.:il.'
<br />arising from misinterpreHuion of high-wah.'r marks, hlr thc Ravcn Fmk UlllllllllilliulI,
<br />inclusiun uf Ihe sedion thai wa~ rcjct.:ted becausc of iUl:ondusivc high.walcr lIliU~'
<br />would have luwcrcd the final diSl:harl-!,c l'umpul.uiulI by 3 to IS pcn:cnt, deJleudin~ lill
<br />whit.:h wall'l-surfal'c dl'vation Was used allhe climimlted t.:russ St.'l:tiun,
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<br />'Ibe ovcmll leat.:h len!!.lh must salisfy hilsit: t.'[1!t',ia IDalryml'k illld Ikn'lI!l
<br />11)67), Thc readl should be lonl! enuugh tn pruvidl." ~uUi~'icnl fall In lIIil.imil.l.' l'lIl1l'
<br />ill waler-surface profil.., intcrpll.'lillion, Spedr....ally. nnl~ ur more of Ihe fulhl\\illF
<br />"'lIIulitiuns shuuld he mN:
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<br />(I) the ICII~lh o[ Ihe reach should he l1.IUill to or vrciller limn 75 limes till'
<br />lI!Can depth
<br />(2) Ihe fall uf Ihe rc.u.:h should l~ cqulIllo or greah:I' than the vclodly head
<br />(3) Ihe fall of Ihe reach should he elfuill to or ~realcr Ihan 0,15 In
<br />The Raven Fork measurcment clIsily mcllhe st:t.:und autllhird nf Ihl'SC cUlllliliUlI'i.
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<br />11)1)2 ':IJ)()I)-NOkTlI ('AkOJ.JNA
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<br />Ilnwt.'~l'r~ l~c fac;t thallhc rei.ll'h Icn 'Ih ,. '
<br />f~1I cnlerla III mountain riven.; can ~ 1~,s.(U~ly 34 !hllHCS the mean depth indica.e,It ,h."
<br />rlVcrs, III a mUt: shOrter reat.:h Ihan in lowland
<br />, ,( :ross st~l:liuns are t.:hosefl to he re ' ,', .
<br />1,lUht:alcd prcviou,ltJy, LTO:':S .oret:';OllS ar~~~~n~all~c ollhe geometry uf .he ..'hunnel. As
<br />lall between sel:liuns. 'l11e differc'~e i~' UsI be far enough apalt 10 allow suflidt'III
<br />was ver . II I' conveyalwc hetwt.'CI1 su " " "
<br />"' '" Y, SlIljJ ',.m the expanding p.lff (If .hc " .' ct:esslv~ I:ross set:JjoJl...
<br />hc.lwcel} s~t.:(...esslVe cross sections were onl J rea~~. Ih.e d'fference~ m convcYi.IIll'C
<br />flflrd and fourth l'ruSS secliolls was ani H Y, pen;~nl. ll1e COOlrucllOIl between rhe
<br />I~~~cen sut.:cCss.ive individual s~bfCiJ~he,~~i:C~I.,f)lsdlUr1=C computaliun diffcrenl'cs
<br />rd~lIvely slIIi.l1I pcrt:emage for a ll<tlunll . . .mge~, (rom 4 to 15 pcn.:cOl, whit:h is a
<br />vanable llolxl plains along s.leep mo c,~~nn~1. ~ hc cuslum~ry ahscnl:c of wide and
<br />'cache" , 'h un &1111 streams. 1;0",1" d "I h "
<br />" are s ont'r. cnhances Jhe Probabilil .:' ,Ill.' WlI ~ I c filt:1 Ihal
<br />:>lrc~l~l:> J~lnre so 111;111 in tlatler.sloped SlfC4J':;,'t~f fuu.hng it umfonn rcadl in llIountaill
<br />I he utctll slope-area re.u,:h shuuld nol c ' . , ,
<br />itnd supcrt.:rilical now This situatin " ol~lalU any lrdnslllons belwcC'n :>ubcrilicill
<br />thai' 'I ' ' , . n IS ,"ore Ikely 10 occur' t
<br />I m s rearns m nUller terrain and b' .' In !i eep Illounti.lin Slrt'.lIlll-i
<br />mc~h~1II now call1lol .llways idcnffO ~~~atl(~1I ~.f,lhe slope-area reach during low or
<br />lOn~ IS nol identified um;, tbe SIO;':' J'i ~se. trallSlh~Q Z?nes, Genenllly. a transitiol1
<br />pr.cV~{)lIsly, rhe fanhesl duwll."i;n.'.am :::" ~o~l~~lallon IS performed, As ll1el1lioned
<br />ehnun,llcd from Ihe coml,uta,' l..._,..' S foicxl,fon of Ihe Raven Fork rCilch was
<br />sun., .'," I n lOll uct:ause 01 a lr'ms'" I" "
<br />: 1.':~CIIIL:a ow. .lbe,greaterprcv'l ' i., . ,IIO~. rom sub.:ritical to
<br />III IIsmg Ihe slopl' .area melhOl.I "", Ihot, ~m.:C? foirate'of~t1ow transitIOns is iI disadvilOla"c
<br />S IS environment ~
<br />_ummary
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<br />, A severe n~sh flood swepl throllgh Raven Fork ne
<br />dunng Ihe evenlOg of September 10 IW2 .. " .' ~r Smokemont. Norrh ('urolina,
<br />~'arnpgrounds. tft!UI ponds, and ma'incena',:~u;~~~/~n~us damage (0 hridges, hlimes,
<br />aboul 3 hours O' inlense rain from a smaJ at:1 lUes. The nood was the re~alll of
<br />11~11(~Walers of Raven "ork. The Nalion~' I ,but st~on~ lhun~erslorm cell over Ihe
<br />rillll~all fr~)m md,lr dala and bucket !iurvey~eather Service eSUmated 13 to 22 cm of
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<br />''he 1;,1~lors Ihal Probably contributed nos _
<br />sft~I~-a~cil dlst,.harge measurement for the nl)(~ '(:ff~l fhe uncerlalnly of thc computed
<br />w~_rc Ihe roul-thncssnteffidcn.s .mrl thee" . , _ Seplcmber 10, 1992, on Raven Fork
<br />III "',' ." , . . '1I11t1alfoo of Cwo er()...' "
<br />" dllSIlIOllllllllt~ Slillt:-uf~n l ' I I "s SCCllonsuone becuuse
<br />III!!h'~~ncr murks. Fitt:wrs Ihi!; ~;~~~~,~:~~~her beL:a~se_~funcertuinly in interprcli;lg
<br />Ihe umlurmity uf Ihe reach and ,he " " " 10 the rehUblhlY of Ihe eSlinultc included
<br />R f lagnltut c of the fall,
<br />_ e erences
<br />Uaruc,'t., JI II JI '," I R
<br />. " '. I "..- nuglll1cs.s c; l rr ,- f
<br />, Survt'y Warcr-Supidy Paper 'IH4~ e 2:~lenls 0 nalllntl t:hanncls: U,S, Ueologit:al
<br />(hHw, V,T" J<)51) Opt.on dmnncJ h .- I:.,
<br />('U11~liIUY, 6KO p, YI rau ICS: New York, Mdiraw-Ilill Huuk
<br />I JafrYIIII)1 "'"
<br />..'. l.Ilt.", and Bensun M A 1%7
<br />sItIJ}(.'.,lrCi.l mClhOl.I" IJ ,. 'C' " I"'" " S' Measuremem of peak dis.charuc by ,I,e
<br />I' ' ,.J. 'co ogu..-a <<trvey'" 'I ' l"
<br />1l\"i'~llgali(Jlls, hook 3 t.:h'lp A2 12 Cl: 1I11ques of Waler-Resourccs
<br />J;lrH'U k IJ I<)~P II ',I. , p.
<br />. .' , :., ..,. ydraullcs of high.grilflit'"nt s ' .,
<br />thlslUn, Amcrit:an Society I' C' .1.... ,Ireams. Journal of Ihe hydrOlulks
<br />o IVI :nglllcers,v. 1IIJ,Ilo, II.p, 151l)~15.N. '
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