The default option for silt and clay simply applies the selected transport function for the fine material as well. The transport equation will extrapolate well outside its derived range and usually compute enormous (often unreasonable) transport potentials. These transport potentials should not be considered remotely representative. They can be useful, however, to model fine sediment as wash load. With huge transport potentials, even a tiny amount of silt and clay in the active layer will produce essentially unlimited sediment transport capacity. This method can route fine wash load through the system, treating fine material as throughput load.