Morphology and flow fields of three-dimensional dunes, río Paraná, Argentina: results from simultaneous multibeam echo sounding and acoustic Doppler current profiling

PARSONS D,; L BEST, JAMES; OSCAR ORFEO; HARDY R,; KOSTASCHUCK R,

JOURNAL OF GEOPHYSICAL RESEARCH

American Geophysical Union

Año: 2005 vol. 110 p. 1 - 9

0148-0227

Morphology and flow fields of three-dimensional dunes, Rio Parana´, Argentina: Results from simultaneous multibeam echo sounding and acoustic Doppler current profiling D. R. Parsons,1 J. L. Best,1 O. Orfeo,2 R. J. Hardy,3 R. Kostaschuk,4 and S. N. Lane31 J. L. Best,1 O. Orfeo,2 R. J. Hardy,3 R. Kostaschuk,4 and S. N. Lane3 Received 24 August 2004; revised 20 September 2005; accepted 4 October 2005; published 10 December 2005. [1] Most past studies of river dune dynamics have concentrated on two-dimensional (2-D) bed forms, with constant heights and straight crest lines transverse to the flow, and their associated turbulent flow structure. This morphological simplification imposes inherent limitations on the interpretation and understanding of dune form and flow dynamics in natural channels, where dune form is predominantly three-dimensional. For example, studies over 2-D forms neglect the significant influence that lateral flows and secondary circulation may have on the flow structure and thus dune morphology. This paper details a field study of a swath of 3-D dunes in the Rio Parana´, Argentina. A large (0.35 km wide, 1.2 km long) area of dunes was surveyed using a multibeam echo sounder (MBES) that provided high-resolution 3-D detail of the river bed. Simultaneous with the MBES survey, 3-D flow information was obtained with an acoustic Doppler current profiler (ADCP), revealing a complicated pattern of dune morphology and associated flow structure within the swath. Dune three-dimensionality appears intimately connected to the morphology of the upstream dune, with changes in crest ine curvature and crest line bifurcations/junctions significantly influencing the downstream dune form. Dunes with lobe or saddle-shaped crest lines were found to have larger, more structured regions of vertical velocity with smaller separation zones than more 2-D straight-crested dunes. These results represent the first integrated study of 3-D dune form and mean flow structure from the field and show several similarities to recent laboratory models of flow over 3-D dunes.1] Most past studies of river dune dynamics have concentrated on two-dimensional (2-D) bed forms, with constant heights and straight crest lines transverse to the flow, and their associated turbulent flow structure. This morphological simplification imposes inherent limitations on the interpretation and understanding of dune form and flow dynamics in natural channels, where dune form is predominantly three-dimensional. For example, studies over 2-D forms neglect the significant influence that lateral flows and secondary circulation may have on the flow structure and thus dune morphology. This paper details a field study of a swath of 3-D dunes in the Rio Parana´, Argentina. A large (0.35 km wide, 1.2 km long) area of dunes was surveyed using a multibeam echo sounder (MBES) that provided high-resolution 3-D detail of the river bed. Simultaneous with the MBES survey, 3-D flow information was obtained with an acoustic Doppler current profiler (ADCP), revealing a complicated pattern of dune morphology and associated flow structure within the swath. Dune three-dimensionality appears intimately connected to the morphology of the upstream dune, with changes in crest ine curvature and crest line bifurcations/junctions significantly influencing the downstream dune form. Dunes with lobe or saddle-shaped crest lines were found to have larger, more structured regions of vertical velocity with smaller separation zones than more 2-D straight-crested dunes. These results represent the first integrated study of 3-D dune form and mean flow structure from the field and show several similarities to recent laboratory models of flow over 3-D dunes. Citation: Parsons, D. R., J. L. Best, O. Orfeo, R. J. Hardy, R. Kostaschuk, and S. N. Lane (2005), Morphology and flow fields of three-dimensional dunes, Rio Parana´, Argentina: Results from simultaneous multibeam echo sounding and acoustic Doppler current profiling, J. Geophys. Res., 110, F04S03, doi:10.1029/2004JF000231 Parsons, D. R., J. L. Best, O. Orfeo, R. J. Hardy, R. Kostaschuk, and S. N. Lane (2005), Morphology and flow fields of three-dimensional dunes, Rio Parana´, Argentina: Results from simultaneous multibeam echo sounding and acoustic Doppler current profiling, J. Geophys. Res., 110, F04S03, doi:10.1029/2004JF000231