CECOAL   02625
CENTRO DE ECOLOGIA APLICADA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The processes and depositional architecture of big rivers: the Río Paraná, Argentina
Autor/es:
ASHWORTH, P.; AMSLER, M.; BEST, J; HARDY, R,; LANE, S,; NICHOLAS, A.; ORFEO, O.; PARSONS, D.; REESINK, A.; SANDBACH, S.; SMITH G, SAMBROOK; SZUPIANY R,
Lugar:
S. M. de Tucumán, Argentina
Reunión:
Congreso; 9th International Conference on Fluvial Sedimentology; 2009
Institución organizadora:
Univ. Nac. de Tucumán - Findación Miguel Lillo
Resumen:
Little is known about the processes, dynamics and deposits of the world’s largest multi-thread rivers and whether they are different from smaller (less than 1 km wide) rivers. This paper reports on a combined field and numerical modelling campaign on the sandy Rio Paraná, Argentina – the world’s 6th largest river. Bathymetric and 3D flow data were taken in a 38 km long, 4 km wide reach using single-beam echo sounders, acoustic Doppler current profilers and dGPS. Results demonstrate that the main channels of the Paraná at low flow are dominated by dunes up to 3.5 m high and less common unit bars 2-5 m high with some up to 10 m high. The deposits of eight km-scale mid-channel bars were characterised by 43 km of Ground 4~Penetrating Radar (GPR) with penetration down to 10 m, and 28, m-deep suction cores. The internal structure of mid-channel bars is dominated by (i) decimetre to sub-m high, stacked dune sets, (ii) up to 7 m thick, highangle, bar margin sets, and (iii) decimetrethick ripple sets, most commonly, but not exclusively found at the bartop. Re-activation surfaces on bar margins are common. Between 2-7 stacked unit bars make up a mid-channel bar. Numerical modelling of flow, sediment transport and morphological change in the 38 km study reach show a good match between field and model flow distributions. Simulated channel change is characterised by talweg shifting and the formation and migration of low-relief bedforms with  dimensions similar to unit bars observed in the field (height ~3-5 m, wavelength 1-2 km). Field-model data suggest a need to: (i) understand the contribution of unit bars to big river sedimentology, and (ii) establish why the majority of the Paraná channel-belt is stable over decadal time scales.