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ISIS 2D outputs represented in the area of the proposed water control structure

A geomorphological study using the Flood Modeller 2D solver was undertaken for the Trinational Committee for the Development of the Pilcomayo River basin. This technical assessment supported the development of water management strategies, and associated structural measures, that could provide secure access to Pilcomayo water resources for both Argentina and Paraguay.

The Pilcomayo River is over 1,000 km long and has one of the largest sediment loads in the world. Its source is at an elevation of 3,500  m in Bolivia and it descends to 250 m near Misión La Paz in Argentina. Major lateral migration of the channel over a large alluvial fan causes significant water stress and economic losses for Argentina and Paraguay.

The study focused on the full characterisation of fluvial dynamics in the catchment together with an options assessment for a water control structure to share water resources.

The Flood Modeller 2D ADI solver was a key component of the multi-scaled modelling strategy to quantitatively assess the dynamics of the geomorphological process and support the development of engineering design options. The modelling consisted of:

  • ŸRegional 1D-2D hydraulic modelling for the entire Pilcomayo river system to develop an understanding of fluvial dynamics and to support broad scale screening of options.
  • Local 2D hydraulic modelling at a much finer resolution around the selected location for the water control structure to assess long term performance of the water resources strategy devised for both countries.

The development of the regional model permitted a rapid and early assessment of potential strategic locations of water control structures.

The broad scale 2D model (150 metre grid size) was developed to approximately represent the hydrodynamic processes on the floodplains. The model covers an area of 190 kilometre x 130 kilometre. Grid elevation values were taken from the broad scale Digital Elevation Model (filtered Shuttle Radar Topography Mission, NASA-USGS).

The 150 metre resolution broad scale model helped provide an initial understanding of catchment dynamics and initial screening of locations of possible alignments for water control structures.  However it is too coarse to represent the details of the flow dynamics around the selected location for the water control works. For this, a local two-dimensional hydraulic model was developed with a cell size of 60 metre in a domain of 100 kilometre x 100 kilometre.

The local model was quick to set-up and run. Typical simulation times were 12 hours to represent a hydrograph lasting 1,400 hours (using a 10 second timestep).

The resolution was fine enough to adequately represent the topography and simulate the flood dynamics.

The local 2D model was coupled to the SED2D sediment transport model in order to predict changes in patterns of sediment erosion and deposition in the region near to the proposed water control structures.

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