CECOAL   02625
CENTRO DE ECOLOGIA APLICADA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Process-product relationships in sandy braided fluvial systems: the influence of channel scale
Autor/es:
PARSONS, D.; ASHWORTH, P.; AMSLER, M.; BEST, J.; HARDY, R,; LANE, S.; NICHOLAS, A.; ORFEO, O.; REESINK, A.; SANDBACH, S.; SMITH G, SAMBROOK; SZUPIANY R,
Lugar:
Santa Fe, Argentina
Reunión:
Simposio; River, Coastal and Estuarine Morphodynamics (RCEM) 6th Symposium; 2009
Institución organizadora:
Univ. Nac. del Litoral (Argentina)
Resumen:
Our knowledge concerning the morphodynamics and sedimentology of multi-threaded river channels is primarily based on analysis of small-scale channels (less than 1 km wide), with little known about whether or not such knowledge is transferable to the world’s largest rivers. However, there are good theoretical reasons to suggest such transfer should be questioned. For example, force-balance considerations show a dependence on width-depth ratio that does not scale linearly with flow discharge, and this may then affect the depositional sedimentology. This paper reports on a combined ‘process-product’ investigation in one of the world’s largest multi-thread rivers – the Rio Paraná. Bathymetric and 3D flow data were taken in a 38 km long, 4 km wide reach from boat surveys using single and multi-beam echo sounders (MBES) and acoustic Doppler current profilers (ADCP) linked temporally and spatially with dGPS. Initial results demonstrate that the main channels of the Paraná at low flow are dominated by a sinuous thalweg, which contain dunes up to 3.5 m high that scale with flow depth. Unit bars in the Paraná seem less common than observed in smaller river channels. Deposits of recent, km-scale, mid-channel bars in the Rio Paraná were characterised using Ground Penetrating Radar (GPR), and ~5 m deep cores. The internal structure of these mid-channel bars is dominated by decimetre to sub-m high, stacked dune sets and up to 7 m thick, high-angle, bar margin accretionary sets. Re-activation surfaces on bar margins are common, whereas cross-bar channels are less prevalent than expected. These field observations are used to examine some of the differences in the basic flow processes operating in smaller and larger river systems and help reveal some of the controls on large-scale morphology and bar sedimentology.