Woods Hole Group was contracted to evaluate the impact of temporary storage (approximately 14 months) of a tunnel tube section on current and sediment transport processes within the Fort Point Channel.  The study focused on the influence the temporary storage has on the Gillette Pump Station Intake, as well as the dredged channel bottom immediately above the MBTA’s twin subway tunnels.  A two-dimensional, depth averaged numerical model was applied to describe the circulation and flow patterns in the Fort Point Channel.  The hydrodynamic model was driven by tidal elevation data collected at Deer Island.  The Gillette Pump Station Intake was simulated by specifying a time-varying boundary condition at the intake location.

Utilizing the circulation results of the hydrodynamic model, a sediment transport analysis was performed to determine the potential impact on the environment and the use of the industrial water.  Based on the bottom shear stresses, local sediment samples, and physical properties of water (kinematic viscosity, density, etc.), the analysis indicated areas of potential erosion and deposition.  The results of the sediment transport analysis show not only the location of the potential sediment movement within the channel, but also when the movement occurs in the tidal regime.

The results of the study indicated that only minor changes in velocity and sediment transport occur during the temporary storage of the tunnel section.  The Gillette Pump Station Intake should be unaffected by the storage and no lasting or significant environmental impact to the Fort Point Channel will occur.  In addition, sediment transport in the center channel area above the MBTA tunnels, which extends longitudinally beneath the center of the channel, consists either of no effect or of minor deposition of sediments transported from the area of the stored tunnel section.