Relocation of Ellisville Inlet Plymouth, Massachusetts


The purpose of the Ellisville inlet relocation was to address the on-going severe coastal bank erosion along the west side of the Ellisville Harbor entrance channel. Episodic coastal erosion has been occurring at an average rate of between 19 and 29 feet per year. Since April 2000, the inlet channel has continued migrating landward and the remains of the coastal dune system have rapidly disappeared.

The configuration of the Inlet was causing erosion of the beach and dune at the shoreline along Lookout Point Road. The growth of the barrier spit lengthened the tidal inlet channel, and forced it to run alongshore approximately 1,400 feet.  In addition to the southward migration of the inlet entrance, the inlet channel is slowly migrating landward due to periodic over-washing from surge and waves during storms. The movement and curvature of the inlet channel began eroding the coastal bank between the termination of Salt Marsh Road and the first groin south of the inlet. As tidal currents in the inlet channel cut away at the beach/dune system, resulting in a substantial dune scarp (~10 feet from dune crest to base) along this part of beach until the coastal dune had been completely eroded and the channel was undermining the coastal bank fronting two residences.  Immediately prior to the inlet relocation, the top of the coastal bank was within 50 feet of the nearest dwelling.

Applied Coastal designed, permitted, and managed the inlet relocation to its pre-1991 position.  Breaching of the inlet at the pre-1991 location provided the most appropriate erosion protection solution, without adversely affecting the environmental resources.  This was a critical consideration of this project because of the Area of Critical Environmental Concern (ACEC) regulations governing Ellisville Harbor. The channel excavation required dredging approximately 210 feet of channel through the barrier beach and plugging the existing inlet channel.  Since relocation of the inlet channel returned the system to the condition described in the late 1980’s, it has been anticipated that the barrier will gradually elongate to the south of the jetty structure. This process continues be monitored on an annual basis and used to predict future project re-location windows. 

An added benefit of the inlet relocation project is the improved tide range and estuarine circulation within Ellisville Harbor. Tide gages deployed through the inlet relocation effort indicated an increase in tide range of approximately 1 ft. Photographs of the marsh plain indicate that historic Spartina alterniflora stands had been “drowned” by the inefficient inlet system, monitoring post construction has shown recovery of the marsh system following inlet relocation.