Below is a simulation of transport of a conservative constituent. Velocities from the channel bathymetry simulations were used to drive an advection-dispersion (AD) model (description in preparation). In order to capture transport that occurs in the open water versus that in the porous layer, the model's vertical domain is broken into two layers. The surface that separates these two layers is dynamically determined by the maximum intrusion of the free surface into the porous layer. This approach allows constituents (such as NH₄) to be modeled in both the open-water and the porous sub-layer.