Brief Description: Replacing a section of the Dingley Island causeway with a small bridge will restore the natural water flow and halt the ongoing silt buildup caused by construction of the solid barrier in the 1940s. Feasibility studies are required to ascertain the effects of restoring tidal flow on the clam-flats, including a seed clam bed located about 400' north of the causeway. A hydrodynamic study will predict current velocity and direction of water flow and provide a recommendation on depth and width of opening. A geologic sedimentation study will predict rates of erosion and deposition of accumulated sediment near the causeway. It will predict where existing silt will move and its depth, how long it may take, and how it will affect the habitat for soft-shell clams. These feasibility studies are critical to the project. Their results will determine whether it is environmentally sound to reopen a section of the causeway. If the recommendation is to proceed, the studies will provide a basis for engineering and design. A biological survey will provide baseline data on the shellfish population on either side of causeway as far as current population boundaries (~300'). Post-construction surveys are planned; these may be conducted by Bowdoin College students and Harpswell shellfish harvesters.

Resource Values: The Dingley Island clam-flats comprise 45 acres and are among rural Harpswell's richest resources. The average harvested value of the annual clam harvest in these flats is $225,000. The 6 acres adjacent to the causeway on both sides would be impacted by the restoration of tidal flow. Expected long-range benefits for the flats include improved water quality, circulation, and flushing. Reopening the waterway also would allow the passage of small boats at high water, thus increasing recreational opportunities in Harpswell.

Cost/Budget: The total project costs for construction of a small bridge in the causeway is estimated at $174,000. The value of the preliminary studies has been estimated at $12-15,000.

Schedule: The feasibility studies should be conducted this year, 2001. Based on the findings, engineering and design for reopening a section of the causeway would take place in 2002, with construction by the Seabees through an IRT partnership in summer, 2003.

Permit Status: The construction phase requires a full permit from DEP; we have corresponded with Doug Burdick (DEP) and Jay Clements (ACE). We have received notice from the Maine Historic Preservation Commission that "this project will have no adverse effect…"

List of Partners: Town of Harpswell, US Navy IRT, Dingley Island residents and neighbors, Bowdoin College students/faculty, New Meadows River Watershed Project, CWRP.

What is requested from the ME-CWRP: This project requests services from ME-CWRP in the form of the critical feasibility studies and the biological baseline study. These studies and recommendations will determine the future of the project and its outcome.

Point of Contact: Elsa Martz

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