Investigation of water and sedimentary deposits in the Paraná-Paraguay river

The drainage basins of the world’s ten largest rivers amount to 17 per cent of the global continental drainage area and deliver ~33 per cent of the sediment load transported into the oceans. The way this vast sediment load moves through km-wide rivers is hugely important in determining flooding, bank failure, infrastructure collapse and ultimately creates the deposits that host some of the most lucrative mineral and hydrocarbon reserves.

Despite the global importance of these rivers, our present knowledge-base relating to the morphology, dynamics and sedimentology of large rivers is wholly inadequate. A central weakness relates to how evidence derived from small rivers has been applied uncritically to rivers many orders of magnitude larger. We have good theoretical reason to question this transfer, since force balance considerations suggest a dependence on width-depth ratio that does not scale linearly with flow discharge. Furthermore, evidence is now emerging that the dominant processes and deposits of large rivers may be fundamentally different to currently accepted wisdom.

In this project we investigated one of the World's largest rivers, the Paraná-Paraguay in Argentina to understand:

> what controls water and sediment movement and river channel changes over time; and
> what this means for the formation and preservation of river sedimentary deposits.

We addressed these issues by

> using state-of-the-art field instrumentation to map river bed morphology and its evolution through time, and measure the three-dimensional patterns of water and sediment movement around and over channel bars;

> using Ground Penetrating Radar to map the three-dimensional sedimentary structure of braid-bar deposits, both within the current river and in formerly active areas that have been abandoned over the past few thousand years; and

> integrating Computational Fluid Dynamics models that provide a sophisticated representation of the physics governing water and sediment movement, with innovative Reduced-Complexity models capable of simulating how these processes interact to determine channel evolution and deposit sedimentology over periods of centuries to millennia.

The result of this work was the world's first comprehensive database on how the morphology of a large river changes through time, obtained concurrently with data on what drives those changes and what this means for the formation of sedimentary deposits.

This project was based on the Rio Paraná in NE Argentina, which is the 5th or 6th largest river in the World in terms of drainage area or mean discharge respectively. The Paraná has a basin of 2.3 x 106 km2 that covers the surface of five countries and has a mean annual discharge of ~20,000 m3 s-1 at Corrientes City (max. ~60,000, min. ~8,000).

The main channels are 2 km wide on average, have mean depths of around 5-8 m (up to ~25 m at constrictions) and a total sedimt discharge of 145 x 106 tonnes yr-1. Four, 10 km2+ reaches of the Paraná will be monitored in the project - sites upstream and downstream of the junction of the Rios Paraguay and Paraná, a site near Corrientes City about 50 km downstream and a site at Santa Fe 300 km+ downstream.

Papers published

Lewin, John, Ashworth, Philip and Strick, Robert J.P. (2016) Spillage sedimentation on large river floodplains Earth Surface Processes and Landforms, 42 (2). pp. 290-305. ISSN 0197-9337

Nicholas, A.P., Sambrook-Smith, G.H., Amsler, M.L., Ashworth, Philip, Best, J.L., Hardy, R.J., Lane, S.N., Orfeo, O., Parsons, D.R., Reesink, A.J.H., Sandbach, S.D., Simpson, C.J. and Szupiany, R.N. (2015) The role of discharge variability in determining alluvial stratigraphy Geology, 44 (1). ISSN 0091-7613

Lewin, John and Ashworth, Philip (2014) The negative relief of large river floodplains Earth-Science Reviews, 129. pp. 1-23. ISSN 0012-8252

Nicholas, A.P., Ashworth, Philip, Sambrook-Smith, G.H. and Sandbach, S.D. (2013) Numerical simulation of bar and island morphodynamics in anabranching mega-rivers Journal of Geophysical Research: Earth Surface, 118 (4). pp. 2019-2044. ISSN 2169-9011

Reesink, A.J.H., Ashworth, Philip, Sambrook-Smith, G.H., Best, J.L., Parsons, D.R., Amsler, M.L., Hardy, R.J., Lane, S.N., Nicholas, A.P., Orfeo, O., Sandbach, S.D., Simpson, C.J. and Szupiany, R.N. (2013) Scales and causes of heterogeneity in bars in a large multi-channel river: Río Paraná, Argentina Sedimentology, 61 (4). pp. 1055-1085. ISSN 0037-0746

Lewin, J. and Ashworth, P.J. (2013). Defining large river channel patterns: alluvial exchange and plurality. Geomorphology, doi: 10.1016/j.geomorph.2013.02.024.

Nicholas, A.P. (2013). Morphodynamic diversity of the world’s largest rivers. Geology, 41, 475-478, doi:10.1130/G34016.1

Ashworth, P.J. and Lewin, J. (2012). How do big rivers come to be different? Earth-Science Reviews, 114, 84-107, doi: 10.1016/j.earscirev.2012.05.003.

Fielding, C.R., Ashworth, P.J., Best, J.L., Prokocki, E.W. and Sambrook Smith, G.H. (2012). Tributary, distributary and other fluvial systems: what really represents the norm in the continental rock record? Sedimentary Geology, 261, 15-32, doi: 10.1016/j.sedgeo.2012.03.004.

Sandbach, S.D., Lane, S.N., Hardy, R.J., Amsler, M.L., Ashworth, P.J., Best, J.L., Nicholas, A.P., Orfeo, O., Parsons, D.R., Reesink, A.J.H. and Szupiany, R.N. (2012). Application of a roughness-length representation to parameterize energy loss in 3-D numerical simulations of large rivers. Water Resources Research, 48, W12501, doi: 10.1029/2011WR011284.

Nicholas, A.P., Sandbach, S.D., Ashworth, P.J., Amsler, M.L., Best, J.L., Hardy, R.J., Lane, S.N., Orfeo, O., Parsons, D.R., Reesink, A.J.H., Sambrook Smith, G.H. and Szupiany, R.N. (2012). Modelling hydrodynamics in the Rio Paraná, Argentina: an evaluation and inter-comparison of reduced-complexity and physics-based models applied to a large sand-bed river. Geomorphology, 169, 191-211, doi: 10.1016/j.geomorph.2012.05.014.

Parsons, D.R., Amsler, M.L., Szupiany, R.N., Ashworth, P.J., Best, J.L., Hardy, R.J., Lane, S.N., Nicholas, A.P., Orfeo, O., Sambrook Smith, G.H., Reesink, A.J.H., Sandbach, S.D. (2010). Process-product relationships in a large river: the Rio Paraná, Argentina. Proceedings of the 6th IAHR Symposium on River, Coastal and Estuarine Morphodynamics: RCEM 2009. Universidad Nacional del Litoral, Santa Fe, Argentina, 21-25 September 2009. C.A. Vionnet, M.H. García, E.M. Latrubesse, G.M.E. Perillo (eds). Vol. I: 51-56. Taylor & Francis Group, London, ISBN 978-0-415-55426-8.

Sandbach, S.D., Hardy, R.J., Lane, S.N., Parsons, D.R., Best, J.L., Ashworth, P.J., Reesink, A.J.H., Amsler, M.L., Szupiany, R.N., Nicholas, A.P., Orfeo, O. and Sambrook Smith, G.H. (2010). Three-dimensional modelling of a very large river; the Rio Paraná. Proceedings of the IAHR River Flow 2010 Conference, Braunschweig, Germany, September, 2010. A. Dittrich, Ka Koll, J. Aberle, P. Geisenhainer (eds). Vol. 1: 409-417. Bundesanstalt fur Wasserbau, ISBN 978-3-939230-00-7.