Bed forms resistance dependency on numerical model grid size spatial resolution

Abstract

The selection of an appropriate model grid for large-scale riverine numerical modelling applications is a compromise between the resolution needed to define all of the channel segments and flow features and the consequent execution time required for a certain grid resolution. In this study, three-dimensional numerical modelling of a selected reach of the Lower Mississippi River was used to examine the effect of re-sampling high-resolution (multi-beam) survey data on the simulated bed form resistance. The study showed that the resistance follows a decreasing asymptotic exponential trend where the apparent resistance and bed form steepness decreased with increasing grid spacing. Increasing the grid spacing also created artificial bed form fields which in turn resulted in a grid-dependent resistance that is a logarithmic function of the bed form periodicity and the grid dimensions with respect to the bed form wavelength.

Keywords::

• bed forms
• Lower Mississippi River
• riverine modelling
• multi-beam bathymetry
• 3D hydrodynamics
• spatial resolution

Acknowledgements

Special thanks go to the Danish Hydraulic Institute (DHI) for providing their proprietary models (MIKE 3). This project was partially funded by the LCA Science & Technology Program, a partnership between the Louisiana Department of Natural Resources (LDNR) and the US Army Corps of Engineers (USACE), through LDNR Interagency Agreement No. 2512-07-08.