Paraná River Project - Background: Methodology 3

Living with the river Downstream view of the Paraná River

Numerical modelling to simulate flow, sediment transport, braid bar evolution and sedimentology

  1. CFD: High resolution (c.0.5m in the horizontal) CFD modelling will be conducted using existing code which solves the Reynolds-averaged Navier-Stokes equations to quantify 3D flow structure through multi-km-scale reaches of the Paraná. Sediment transport modelling will be carried out using a nested strategy at two scales. First, by applying Discrete Particle Modelling (DPM) to quantify particle step length distributions (including their possible conditioning by location within the dune field). Second, by combining an existing approach to modelling dune migration based upon entrainment and deposition (bed deformation) and step length, with turbulent suspended sediment transport represented using an advective-diffusive treatment. The coupled hydrodynamics-sediment transport code will be modified to include the effects of turbulence modulation by sediment.
  2. RC Modelling: A new RC model of flow, sediment transport, morphological change and subsurface sedimentology will be developed. CFD model output will be used to determine the relative magnitude of each component of the local momentum balance and quantify spatial patterns and gradients in energy slope. The influence of bedforms on flow and sediment transport will be parameterised using existing process knowledge and theory. Dune dimensions will be modelled using theory for equilibrium bedforms, reformulated for non-equilibrium conditions to include a simple treatment of bedform evolution. Bedload transport formulations will be based on existing theory suitable for sand-bed rivers, and MBES data quantifying transport by migrating dunes. Additional processes that will be modelled will include bank erosion and the effects of vegetation on the stabilisation of channel bars and margins.
  3. The model will be implemented on a 3D mesh with horizontal (downstream and cross-stream) and vertical (subsurface) grid resolutions of c.10m and 0.1m, respectively. RC simulations will be conducted at three timescales: (1) for particular flow stages at which flow and sediment transport datasets have been collected; (2) over periods of less than 100 years to evaluate bar evolution and sedimentology within the contemporary channel system; and (3) over periods of 1000+ years, to examine the controls on the long-term preservation of deposits.