Comparison of Fixed- and Moving-Vessel Flow Measurements with an aDp in a Large River

by Ricardo N. Szupiany, Ph.D., Fellow; the Natl. Council of Scientific and Tech. Researches (CONICET), Coll. of Engrg. and Water Sciences, Littoral Natl. Univ., Ciudad Universitaria, C.C. 217, (3000), Santa Fe, Argentina.,,
Mario L. Amsler, Researcher; Natl. Council of Scientific and Tech. Researches (CONICET), Coll. of Engrg. and Water Sciences, Littoral Natl. Univ., Ciudad Universitaria, C.C.217, (3000), Santa Fe, Argentina.,,
James L. Best, Threet Prof. of Sedimentary Geology and Prof. of Geography; Dept. of Geology ang Geography and Ven Te Chow Hydrosystems Lab., Univ. of Illinois at Urbana-Champaign, 1301 W. Green St., Urbana, IL 61801.,,
Daniel R. Parsons, Res. Fellow; Natural Envir. Res. Council, Earth adn Biosphere Inst., School of Earth and Envir., Univ. of Leeds, Woodhouse Lane, Leeds, LS2 9JT, U.K.,,

Serial Information: Issue 12, Pg. 1299-1309

Document Type: Journal Paper

Abstract: A comparison of three-dimensional flow velocity measurements, made with an acoustic Doppler profiler (aDp) from fixed and moving vessels at cross sections of the Paraná River, Argentina, was performed. The purpose was to design a rapid and reliable procedure for quantifying the velocity field, and related parameters such as bed shear velocity and the identification of secondary circulations, in large rivers using an aDp. The fixed-vessel measurements were performed over a period of 10 min at three vertical profiles along two of the sections. These data were then compared with the results of ten moving-vessel repeat transects made at each of the sections, and which intersected the fixed-vessel sampling locations, using a number of different aDp setup configurations. From the velocity profiles obtained with both fixed- and moving-vessel measurements, total bed shear velocity values were computed by applying the law-of-the-wall. The results indicate there can be significant differences between velocities obtained using the moving-vessel method and fixed-vessel measurements averaged over 10 min. These differences in horizontal velocity can be significantly reduced by averaging five, or more, moving-vessel transects, with corresponding shear velocities calculated from five-transect averages showing differences ranging between 10 and 15%, dependent on the aDp configuration. Location of the at-a-point vertical velocity profile in relation to large-scale bed roughness may also be an influential factor, and ideally the bed morphology should be quantified together with the aDp-derived velocities. When using the aDp to identify secondary flow cells, it was found that although one cross-section transect can provide a reasonable overall picture, an average of five cross sections is necessary to resolve the finer details of flow. The implications for applications that use moving-vessel techniques for measurement and analysis of three-dimensional flow structures, including secondary flows, are highlighted.

Subject Headings: Flow measurement | Ship motion | Rivers and streams | Comparative studies | Three-dimensional flow | River flow | Velocity profile | Secondary flow | Shear stress | Argentina | South America

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