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<br />lIYDRAULlC ENGINEERING '94
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<br />the portion of the now affecu:d by . now separation or an IBL. Within. now
<br />separation, the slope of the bouom velocity profile segmenl and the velocities arc
<br />negative. thereby ",n""tiog the upstream direction of the now ill the recirculating cell.
<br />Within an IBL, the gen~e positive velocity gradical ",ne.:.. the adjuslmenl of the now
<br />10 graill roughness a1l1ne. Above a near-bollOm knol. the velocilY gradical duldla z
<br />is generally sleeper because the now is affe<:ted by both grain roughness and form
<br />drag due 10 large bed obslaCles such as boulde.. and cluster bedforms. .
<br />To date. velocity profile measurements in gravell><d streams were mainly obtained
<br />usillg Price-Iype current meters and Marsh-McBimey EMCMs model 511. Jle<:ause
<br />of their large size, these currenl meters did 1I0t allow velocily measurements 10 be
<br />taken near the bed. As a ",s"It, segmenu:d velocity profiles were observed only ia
<br />streams whe", large bed particles caused the near-bottom kaol of velocity profiles to
<br />be locau:d far enough from the bed to be in the measuring range of these inslrUmenlS.
<br />10 this sludy, the use of . Marsh-McBirney EMCM model 523 allowed velocilY
<br />measurements lO be made as close as 1.9 em above the bed. 1l1e exlendc::d range of
<br />this inslrUmeol permilu:d the finding thai segmeau:d velocity profiles ate nol confined
<br />to streams with very coarse bed material but Iha1 they also occur in streams wilh
<br />",Iatively small bed particles.
<br />I ,)2 ~ If IS
<br />
<br />l )J) R) J l I
<br />
<br />~ I II lZ
<br />, .
<br />;., ~'M' .:o"~"'20~"io 1M *'m'Z4D'ao'2_'*~Ml~
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<br />
<br />HorilOf\bll d1stanclO, em
<br />
<br />!L
<br />. ..
<br />,,...,,
<br />Fig... 2. Velocily profiles and bed microtopography althe study site.
<br />
<br />TllllboDommarkll'ldoalleSltl8pllUllIRalthlJ't'IIIl:dtJlfOfllllIlllI~.u_tMildjlfOlilll.
<br />Tl\lllOpmMIllKllelhlS.lhIIoloe8llDllalU1ll".,......OC8ll$b'~~pulIIle.
<br />fQf~pro"'~. ..1. and 15,Q/ogI..'*uwIhtIllllllonhll.,.....-w..
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<br />Rererences
<br />Bergeron, N.B. (1994) An analysis o/flow velocity profiles, stream bed rOllghness. anJ
<br />resistance to flow in nalural g,ayel bed Ilrealll!. Ph.D. dissertation. l1epartment of
<br />Geography, SIaIe Unive..ily of New York at Buffalo. Buffalo, New York. 163 p.
<br />I"",,u, R.D. (1989) Hydl1lulics research ia mllunwn rive.., P,oc. oj,h.ln'. Coll!..
<br />Cltilnnel Flow and CalcltmenJ Runoff- Centennial oj Manning's Fo,.."la and
<br />Kuildling'l Rational FOrl""la. Univ. of Vir,inia. May 1989. p. 599.608.
<br />MiddlelOn, G.V. and Southan!, I.B. (1984)M.chaniC$ o/S.d....n, Mo.....nl. SocielY
<br />of &:<>nomic PaIeonlologists and Minel1llogislS, Short Cou..e no. 3. 2nd ed.. 200 p,
<br />Robert, A. (1990) Boundary roughness in coarse-grained chanoels, P,og'''' i.
<br />Phys;cal a.og,aphy, vol. 14, I, p. 42-10.
<br />SAS Instilute Inc. (1991) $AS Sys/e..jo, R.gress;.n, S.cond Ed;';.n, Cary, NC:SAS
<br />Instilute Inc., 210 p. .
<br />Smith, P.L. (1919) Splines as a useful and convenienl SlatisticallOOl, Th. A...ric..
<br />Stalistician, vol. 33, p. 57-62.
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<br />A new approach for the estimation of extreme roughness in torrents
<br />by Hydraulic and Photogrammetry
<br />
<br />Hanspeter Hodel I, Thomas P. Kersten 2. Isidor Storchcneggcr 3
<br />
<br />Abstract
<br />
<br />.. In this paper we pre~enl an approach to estimate extreme roughness in torrents
<br />based o~ the tnmsfonnatl~n of. an Irregular bed geometry of a torrent reach into it
<br />gcnmclncally wel.1 delennmed 'J~alized' channel. One ha.'iic parameter is the surface
<br />uf the. waler, which wa~ determmed by a phologrammctric method using stereo
<br />photos on the ~nalYllcal Ploner WILD ACI. Two torrent segments were
<br />rh~tographed With two syn~hronized Rollci 6006 metric camerdS, which were
<br />IDst~~led ~boye the torrent while t.he mean wl~ily was .simultaneously measured by
<br />Ihe sah.dllullo~ melhod., The Strickler coeffiCients derived from our studies at two.
<br />torrcnt reaches m the SWISS Alps are also given in this paper.
<br />
<br />I. Background - Basics - Problem
<br />w.e s,till need calculations of walerlevcls or streamflow velocilies in natural
<br />mounlam fivers or tOrrents based on the Chezy equation for different applications.
<br />
<br />v ~ C*(R*S)O.5 wilh R ~ AlP
<br />
<br />. .T~is equat!on, is theoretically based OR considerations of momentum
<br />equll~b~lum (gravity/friction) of a turbulent uniform flow. Gravity is represented by
<br />A, fncllon (shear stress) by P and C. The hydraulic radius is obviously affected by
<br />lhe channel shape and the fullfilling of discharge,
<br />The Chezy coefficient C is usually expressed by:
<br />
<br />k*R1/6
<br />I/n*Rl/6
<br />
<br />k: Strickler's velocity coefficient
<br />n: Manning's roughness factor
<br />Hydraulic calculations in torrents or mountain rivers are based on information
<br />a~ut channel ~hape, roughm.."SS and hydraulic radius. AI the moment, there exist no
<br />mcthod~ to esllmate the complex geometry of torrent beds which is es~cntial for
<br />c.al~ulatmg the .hydraulic r.adius. Hydrolgical invesligalions'in small calchments in
<br />SWIl,zer~and pomt out lhat now velocity in steep headwalers of moumainous river
<br />ba."isIRS IS usually lower than in the mean slream (Stort:helJegger, 1984,. HOI.Jd. 1993:
<br />/lodel ~"'d Sw,.cJlfmegger, /994). I.R lorrenls. Ihe channel shape varies in u wide
<br />mnge, and even on short reaches. It IS often hard to separale the inOuence of channel
<br />
<br />I Swis.s. National Hydrological and Geolugical Survey. eH . 3003 Berne
<br />21' ,'Good
<br />] ~~IIIulC 0 esy and Photogrammelry, Swiss Fcderallnstilute o(Technology, eH . 8093 Zurich
<br />Lmdenslrasse 23. eH. 8307 EIJrclikon. Switzerland
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