CECOAL   02625
CENTRO DE ECOLOGIA APLICADA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The processes and dynamics of a large multi-thread river: the Rio Paraná, Argentina
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:
Durham University, UK
Reunión:
Simposio; British Society for Geomorphology (BSG) Annual Conference; 2009
Institución organizadora:
Durham University
Resumen:
Little is known about the processes, morphology and dynamics 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 with mean daily discharge ∼12000 m3 s-1, channel width ∼4 km, mean depth of 5-12 m and D50 grain size ∼ 0.25 mm. Bathymetric and 3D flow data were taken in a 38 km long, 4 km wide reach from boat surveys 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 that scale with flow depth. Unit bars are less common than observed in other rivers and are typically 2-5 m high, with some up to 10 m high, and can possess very low-angle lee slopes. The 3D flow field at low stage is dominated by topographically forced flow over and around bars and no secondary flow even in the main 10 m+ deep channels. The Paraná study reach should be highly dynamic and active because there is evidence of relatively recent lateral migration as preserved in the adjacent floodplain, there is little clay in the system, there are regular bartop floods and the bed sediment is available for transport at nearly all stages. However, mid-channel bars in the Paraná are extraordinarily stable over decadal time-scales and bank erosion rates are negligible. Examples are shown to suggest that because the controls and drivers on the flow field are relatively simple, the resulting channel change is mostly confined to moderate thalweg shifting and repositioning. Bathymetric and 3D flow data were taken in a 38 km long, 4 km wide reach from boat surveys 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 that scale with flow depth. Unit bars are less common than observed in other rivers and are typically 2-5 m high, with some up to 10 m high, and can possess very low-angle lee slopes. The 3D flow field at low stage is dominated by topographically forced flow over and around bars and no secondary flow even in the main 10 m+ deep channels. The Paraná study reach should be highly dynamic and active because there is evidence of relatively recent lateral migration as preserved in the adjacent floodplain, there is little clay in the system, there are regular bartop floods and the bed sediment is available for transport at nearly all stages. However, mid-channel bars in the Paraná are extraordinarily stable over decadal time-scales and bank erosion rates are negligible. Examples are shown to suggest that because the controls and drivers on the flow field are relatively simple, the resulting channel change is mostly confined to moderate thalweg shifting and repositioning. th largest river with mean daily discharge ∼12000 m3 s-1, channel width ∼4 km, mean depth of 5-12 m and D50 grain size ∼ 0.25 mm. Bathymetric and 3D flow data were taken in a 38 km long, 4 km wide reach from boat surveys 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 that scale with flow depth. Unit bars are less common than observed in other rivers and are typically 2-5 m high, with some up to 10 m high, and can possess very low-angle lee slopes. The 3D flow field at low stage is dominated by topographically forced flow over and around bars and no secondary flow even in the main 10 m+ deep channels. The Paraná study reach should be highly dynamic and active because there is evidence of relatively recent lateral migration as preserved in the adjacent floodplain, there is little clay in the system, there are regular bartop floods and the bed sediment is available for transport at nearly all stages. However, mid-channel bars in the Paraná are extraordinarily stable over decadal time-scales and bank erosion rates are negligible. Examples are shown to suggest that because the controls and drivers on the flow field are relatively simple, the resulting channel change is mostly confined to moderate thalweg shifting and repositioning.