INVESTIGADORES
ORFEO Oscar
congresos y reuniones científicas
Título:
Autogenic controls on the depositional architecture of big multi-channel rivers: the Rio Paraná
Autor/es:
ASHWORTH, P.; AMSLER, M.; BEST, J.; HARDY, R,; LANE, S.; NICHOLAS, A.; ORFEO, O.; PARSONS, D.; REESINK, A.; SMITH G, SAMBROOK; SANDBACH, S.; SZUPIANY, R,
Lugar:
San Francisco, USA
Reunión:
Congreso; American Geophysical Union (AGU) Fall Conference; 2009
Institución organizadora:
American Geophysical Union (AGU)
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) channels. This paper reports on a combined field and numerical modelling study of the sandy Rio Paraná, Argentina – the World’s 6th largest river. Bathymetric and 3D flow data were collected in a 38 km long, 4 km wide, reach using single-beam echo sounding, acoustic Doppler current profilers and RTK dGPS. Results demonstrate that the main channels of the Rio Paraná at low flow are dominated by dunes up to 3.5 m high, and less commonly by braid bars 2-5 m high with some up to 10 m high. The subsurface architecture of eight, kilometre-scale, mid-channel bars was characterised by 43 km of Ground Penetrating Radar (GPR) with penetration down to 10 m, and ground-truthed using 28, ∼4 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, high-angle, bar margin sets, and (iii) decimetre-thick ripple sets, most commonly, but not exclusively found at the bartop. Re-activation surfaces on bar margins are common. Numerical modelling of flow, sediment transport and morphological change in the 38 km study reach using a reduced complexity modelling approach, shows 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). We will use these field data and modelling output to highlight the role of autogenic processes in shaping the internal architecture of large river deposits. Bathymetric and 3D flow data were collected in a 38 km long, 4 km wide, reach using single-beam echo sounding, acoustic Doppler current profilers and RTK dGPS. Results demonstrate that the main channels of the Rio Paraná at low flow are dominated by dunes up to 3.5 m high, and less commonly by braid bars 2-5 m high with some up to 10 m high. The subsurface architecture of eight, kilometre-scale, mid-channel bars was characterised by 43 km of Ground Penetrating Radar (GPR) with penetration down to 10 m, and ground-truthed using 28, ∼4 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, high-angle, bar margin sets, and (iii) decimetre-thick ripple sets, most commonly, but not exclusively found at the bartop. Re-activation surfaces on bar margins are common. Numerical modelling of flow, sediment transport and morphological change in the 38 km study reach using a reduced complexity modelling approach, shows 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). We will use these field data and modelling output to highlight the role of autogenic processes in shaping the internal architecture of large river deposits. th largest river. Bathymetric and 3D flow data were collected in a 38 km long, 4 km wide, reach using single-beam echo sounding, acoustic Doppler current profilers and RTK dGPS. Results demonstrate that the main channels of the Rio Paraná at low flow are dominated by dunes up to 3.5 m high, and less commonly by braid bars 2-5 m high with some up to 10 m high. The subsurface architecture of eight, kilometre-scale, mid-channel bars was characterised by 43 km of Ground Penetrating Radar (GPR) with penetration down to 10 m, and ground-truthed using 28, ∼4 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, high-angle, bar margin sets, and (iii) decimetre-thick ripple sets, most commonly, but not exclusively found at the bartop. Re-activation surfaces on bar margins are common. Numerical modelling of flow, sediment transport and morphological change in the 38 km study reach using a reduced complexity modelling approach, shows 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). We will use these field data and modelling output to highlight the role of autogenic processes in shaping the internal architecture of large river deposits.