A Simplified Method for Marsh Inundation Modeling in Hydrodynamic and Water Quality Models With Application to the Cooper River Estuary (SC)

摘要

A simplified method for incorporation of the marsh inundation effects on the circulation and transport within an estuary is proposed, with the use of a special marsh boundary condition. The marsh boundary has two basic features; determination of flow in and out, and storage of water, salinity, heat and constituent in the marsh. A particular marsh is specified by a set of physical parameters that include the surface area, front elevation referenced to mean sea level (i.e. when the marsh will flood), back elevation (affects marsh volume), flow length and porosity (growth density) of the marsh. Flow in and out of the marsh is modeled with a reduced momentum equation, which varies dependent on flow regime and is influenced by the specified Manning friction factor, marsh flooding length, and predicted values of marsh water elevation. Test cases run indicate that the two more sensitive parameters in the marsh boundary cell calculations are the marsh surface area and the marsh gradient length (from the reduced momentum equation in the boundary condition). For short gradient lengths the discharge is significantly larger than for the longer values. In addition increasing the marsh surface area has little effect on the discharge after an initial increase in response at small surface areas, whereas the concentration of salt or constituent will respond more slowly for the larger areas. An example application is presented where the marsh boundary was used to model the impact of extensive salt marshes and former rice paddies along the Cooper River, South Carolina. Model predicted surface elevations at the head of estuarine Cooper River, are over-predicted where no marsh boundary cells were used. When marsh boundary cells are used the effect is to damp the tidal amplitude, by draining off large volumes of water, thereby matching observations.