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<br />t <br /> <br />. <br /> <br />69S <br /> <br />HYDRAULIC ENGINEERING '94 <br /> <br />shape variations from those of roughness elemenls. The determination of wetted <br />perimeter and cross sectional area in torrents is based on suhjective assumptions. <br />This paper deals with the quantitivc evaluation of torrent shaj?C and roughness <br />using the Strickler equation. The evaluation procedure may easlly be adapted It) <br />Manning's law or even to Darcy~Wcisbach's friction factor. The new approach tn <br />representatively calculate extreme roughne~o;; is based on averaging the, im~l!ular ht.'11 <br />geometry and tmnslating it into a geometrically well determined ideal channel. Th~ <br />aim is to express these average values numerically in terms of the hydraulic radius <br />and the Strickler coefficient. <br /> <br />1. New approach <br />The new approach mainly consists of replacing <br />cross sections by 'horizontal' sections, represented by water surfaces on a short <br />(but possibly representative) reach as system responses to the actual discharge, <br />through averaging the size of water in motion, e. g. the derivation of the surface <br />widlh B of a shon reach by phologrammetry (Slorchenegger. 1988). <br />B..A,Il <br />current meter measurements by the dilution method through averaging <br />velocity over the reach <br />velocity..area-pronte by the concentralion graph of tracer to detennine the <br />discharge Q <br />the esllmallon of Strickler coefficient from Ih. grain size distrlbullon cu..e <br />(IineMby.number analysis) by evaluating the system response <br />kSI ~ vlR2I3*lln <br />The new approach assumes <br />effects due to expansions and contractions of cros5Mscction to be included in <br />roughness <br />.. the widly varying bed of lorrenls to be presented by an ideaH7.ed 'mean' cross. <br />section which smoothly varies on sire only along reaches between bifurcations. <br /> <br />3. Data acquisition <br />3.1. Photogrammetrie Image data acquisition at selected to......nt reaches <br />Photographs of the water surface were taken at suitable test segmenls 01' <br />&elected torrents with two Rollei metric 6006 cameras (50 mm lens) using very <br />photosensitive 6.6 cm' slide films (Kodak Ektachrnm 400 ASA), while the <br />measure-ment of the discharge was simultaneously performed by the salt~dilulion <br />method. For the photogrammetric image acquisition, a special manufactured <br />suspension for the cameras was placed above the torrent. To facilitate the orienlatiun <br />of the acquired stereo pair for the subsequent photogrammetric analysis on the <br />Analytical Plotter Wild ACt, signali7.ed plates were positioned in the photographed <br />area of the torrent. The signalized points were used a.~ pass points for the orientation <br />of the photos. Therefore, the signals were solidly fixed on firm ground and their <br />positions were determined by geodetic measurements with a precision of 2 rom ill <br />planimelry and 1.5 mID in height. <br />Durmg the measurement of the torrent' di!<<:harge by the sall~dilulion method, <br />two or three stereo photographs were simultaneously acquired relea.~lng the shutter <br />of the synchronized cameras through an infrared remote control. Thus, a clear <br />temporal assignment of the discharge measurements and the related photos was <br />warranted, which is essential for the funher data analysis. <br />In the southern Swiss Alps, in Canton Valais (between Simplonpass anll <br />Slmplon- Village) two torrent reaches were selected, which fulfill the hydrologil.al. <br />geodetic and photogrammetric requirements a.. discussed in Hodel et a/., 199/. I.ur <br /> <br />., <br /> <br />--- <br /> <br />. <br /> <br />EXTREME ROUGHNESS ESTIMATE-NEW <br /> <br />6'J9 <br /> <br /> <br />Torrent <br /> <br />Figure I: Photogrammetric camera sctMup at torrent segment I <br />Both cameras rigidly mounled on th I dd I . . <br />sele<:lnble distance on Ihe ladder (up. ]' 8 e a jr n:: d be posHlOned wilhin a <br />Ihe requesled posilion above .he rorre~i. mete.rs. la~~er ~ould be placed on <br />he~vy swinging of the cnmera~ due to thcb~j~~II:~ :~poslh~n,!n~ rope. To avoid <br />uSlOg two ropes at each end For lhe . a er was 'Ixed on the ground <br />facilitatcd the installation oi the stceit;e(:ond th,rch't reae~, a Sleep, narrow V ~vallcy <br />Sides of the valley. . rope, W Ie was fixed on Ihe ground at hOlh <br /> <br />3.1. Phologrammetrk measurements of lhe waler surface <br />In IOla', 60 color pholos per c '. <br />Howcver. for the halo fa~m ~mera were acq~lred at different discharge levels, <br />selected, which ~ the g,wo st~~~a ~afa .IPr~esslRg, .only 9 stereo photos were <br />imn d. the d J r en ena: suffiCient number of pass po' ( <br />The~~el:ted i:~g:s ~~a~~o .strdng C~nlrdSIS of. fight and shadow in the Obj~~l~ <br />Aflerthedeletminafionoflhejn:~~r:~dl ~nalYll~al PI~tler Wild Aviolyt ACt, <br />the bank Jines could be measured . a .tile .oflentatlo~ of each stereo photos, <br />joint bank lines were plolled and lJ:,"lnl by /,O,:.nl In 3-D obJecl space. Fioally, lhe <br />mined surfaces ufthe water at differenalredfl OL t sl'urralce wa.... calculated. The deterM <br />Iscnarge eve are summarized in Table I, <br /> <br />No. I 1 3 4 5 6 1 <br /> 8 9 <br />torrent 1 I <br />reach I 2 2 2 2 2 2 <br />dgcnarge 519 529 549 220 <br />(Vsl 220 241 247 247 342 <br />water <br />....urface 44.49 44.86 45.60 30.15 30.31 19.50 30.01 <br />A</m21 29.81 36.96 <br /> <br />TabJe J: Re..liulls of the photogrammefric dcterminalion of lhe waler surface <br />