Our ability to numerically predict the interaction between complex
topography and three dimensional flow at large scales (similar to 1 km)
has yet to be fully developed. This is the result of our inability to
design numerically stable meshes for complex topographies at these
spatial resolutions. This paper deals with the numerical simulation of
flow over a natural dune field located in the Rio Parana, NE Argentina.
The methodology is based upon the development and application of a new
five term porosity algorithm that modifies the mass conservation
equation within a regular Cartesian mesh. Bathymetric measurements were
made in the field using a multibeam echo sounder which provided an
unparalleled topographic dataset to test this new numerical modeling
approach. Measurements of flow were made using an acoustic Doppler
current profiler and are used as inlet boundary conditions and
validation data. The results demonstrate simple flow acceleration due
to topographic forcing over the dune stoss and expansion and
deceleration over the dune lee.