Woods Hole Group conducted a study to evaluate the hydrodynamic and biological impacts of culvert installation at the Menauhant Road bridge on the Green Pond ecosystem.  To assess the impacts that the culverts would have on the circulation and resulting water quality of Green Pond, a one-dimensional numerical model was used to accurately simulate the Pond’s hydrodynamics.  In support of the numerical modeling, a field data collection program was completed in which tidal data and bathymetry were obtained.  To develop information on tidal forcing and damping within the Green Pond system, tidal elevation data were collected at three locations for a 29-day period.  The bathymetry was measured using a high-precision fathometer linked to an integrated navigation system.  All data were stored directly using a portable PC.  The bathymetry data were collected along a series of predetermined transects as required for the numerical modeling.  Data from the tide gauges were used to correct the bathymetry for tidal fluctuations, and to adjust the data to a common datum.

The bathymetry data were used to set up the numerical model grid, and the tidal elevation data were used to calibrate and verify the model.  The purpose of the numerical model was to evaluate impacts of the culvert and to optimize the culvert design.  The model was used to calculate flushing rates, water elevations, and current velocities both with and without the proposed culverts.  A number of culvert designs were evaluated incorporating different widths, elevations, and locations.  Changes in the tidal hydrodynamics for the alternative designs were modeled and compared with the existing conditions.  Woods Hole Group also performed the environmental permitting for the bridge reconstruction and culvert modifications.  All necessary local, state, and federal environmental permits were obtained.