Two-dimensional sediment transport usually does not perform well with the Diffusion Wave equation.

2D sediment runtimes can be get long, so it can be attractive to select the Diffusion Wave equation to try to reduce the runtime.  However, 2D, Diffusion-Wave, sediment models often develop a distinctive pattern, eroding a deep sub-channel and depositing in the rest of the channel.  This is not a credible result.  Most 2D sediment transport models should be run with one of the Shallow Water Flow Equations (SWE). 

Distinctive sub-channel erosion common in diffusion wave 2D sediment models (red is erosion, blue is deposition).  This is a numerical aritfact of the interaction of the Diffusion Wave hydraulics with the transport algorithms.  Switch to SWE.