The detailed grain-scale dynamics of sediment erosion are very complex and not yet well understood. To capture
the essential aspects of this phenomenon, we employ the simplified model of2. While this empirical model does
not resolve the turbulent motions near the bottom boundary, it does provide the erosional inflow of particles into the
current as a diffusive flux ( 1), which may capture the true dynamics more closely thanalternate approaches, such as
the somewhat arbitrary distribution of the eroded particles over several computational grid spacings adjacent to the
bottom boundary employed by other authors.