Two-dimensional (2D) hydraulics models have been widely used in engineering practice for flood simulation, bridge design, habitat restoration, and many other purposes. As in any other modeling efforts, the results from 2D hydraulics models have to be mesh independent. Otherwise, different results will be obtained with different meshes and there is no way to trust any of them. Typically, to show mesh independence, a modeler has to successively refine the mesh, while holding everything else constant, until the result does not change significantly. However, most 2D hydraulics models are based on the depth-averaged shallow water equations (SWEs). In SWEs, there are at least two terms that are dependent on the mesh resolution, namely the bed slope term for the gravity and pressure forces and the Manning’s n in the flow resistance term. Because of this, strictly speaking, there is no mesh independence for 2D hydraulics modeling. We will show with some analysis and demonstration examples. In the 2D modeling practice, mesh independence study has to be performed in conjunction with Manning’s n calibration.
