Conceptual soil moisture accounting (SMA) models distribute available moisture through the soil mantle with assumed percolation characteristics, thus simulating streamflow.
The SMA model breaks the soil mantle into upper and lower zones, each with tension and free water components.
The capacity of the zones and percolation characteristics between zones are determined by parameters.
In the NWS River Forecast System (NWSRFS), about twenty parameters control the direct runoff, surface runoff, interflow and base flow in SMA.