Autogenic controls on the depositional architecture of big multi-channel rivers: the
Rio Paraná, Argentina
Ashworth, P.J.1, Amsler, M.L.2, Best, J.L.3, Hardy, R.J.4, Lane, S.N.4, Nicholas, A.P.5, Orfeo, O.6, Parsons,
D.R.7, Reesink, A.J.H.1,8, Sambrook Smith, G.H.8, Sandbach, S.D.4,5and Szupiany, R.N.2
1School
of Environment and Technology, University of Brighton, UK, email: p.ashworth@brighton.ac.uk
Nacional del Litoral, Facultad de Ingeniería y Ciencias Hídricas, Centro Internacional de
Estudios de Grandes Ríos, C.C. 217 - (3000) Santa Fe, Argentina
3Departments of Geology and Geography and Ven Te Chow Hydrosystems Laboratory, University of Illinois,
Urbana-Champaign, IL, USA
4Department of Geography, University of Durham, Durham, UK
5Department of Geography, University of Exeter, Exeter, UK
6Centro de Ecologia Aplicada del Litoral, Consejo Nacional de Investigaciones Cientificas y Tecnicas,
Corrientes, Argentina
7School of Earth and Environment, University of Leeds, Leeds, UK
8School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham, UK
2Universidad
Little is known about the processes, dynamics and deposits of the World’s largest multithread 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 groundtruthed 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, highangle, 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.