Sesuit Marsh is located along the southern coastline of Cape Cod Bay in the town of Dennis, Massachusetts. The upper portion of the system is divided from the lower marsh by a roadway embankment. There is a small culvert under the road that connects the upper marsh to the lower marsh and allows limited tidal exchange to occur. As a result the health of the upper marsh system has suffered significantly. The project examined various culvert alternatives to restore the natural tidal exchange to the upper marsh in order to assist in the restoration of the marsh system.
A data collection program was conducted as the initial phase of this study. The goal was to collect the necessary data to construct and calibrate the hydrodynamic model. The collection program included bathymetry and topographic measurements, ADCP survey, and tidal water surface elevation measurements.
The next phase of the project was the development of a numerical hydrodynamic model of the existing Sesuit marsh system. Using the bathymetry data, a finite element model grid mesh was generated for use with the RMA-2 hydrodynamic code. Tide data collected in the lower section of the marsh was used to define the open boundary condition that drives the circulation of the model, and data from tide gages within the system were used to calibrate and verify model performance to ensure that it accurately represents the dynamics of the physical system. Once the model was calibrated, several culvert alternatives were modeled to examine the influence of various openings had upon the tidal exchange and resident times within the upper marsh. This provided the necessary tools for evaluating the impacts to the system and ensuring the restoration of the marsh will be successful. The recommend culvert solution allowed the town to recreate the historic “bridge” opening across the marsh and was so successful that the project won the 2008 Coastal America Partnership Award for excellence in marsh restoration.