Subsurface flow and transport in tidal wetlands: marsh plain equations

Subsurface flow and salinity patterns in a tidal marsh plain determine the character and health of the wetland ecosystem. The presence of a flow field with both saturated and unsaturated regions requires that the governing equations and the associated equations of state transition smoothly between the two regions. The fluid density in the marsh plain is not constant; it responds to changes in both pressure head and salinity. These considerations lead to the development of the marsh plain equations, the coupled field equations for subsurface flow and salinity transport in the continuous saturated/unsaturated flow domain of a tidal wetland.