CONCORD, Mass. – The town of Duxbury, Department of Public Works, is seeking a permit from the U.S. Army Corps of Engineers, New England District to conduct work in waters of the U.S. in conjunction with replacement of a seawall that was damaged by storms in 2018 in Duxbury, Massachusetts.
The work, proposed on Duxbury Beach in Duxbury, involves the replacement of a 950-linear-foot section of seawall that failed during the March 2018 winter storms. The replacement seawall will have an elevation of 24.5 feet above mean low water (MLW), which is 4.8 feet greater than the current average seawall elevation. The work is proposed to begin in the fall of 2019 and conclude in the spring of 2020.
The replacement seawall will be constructed with a deeper and wider footing than the existing seawall in order to accommodate for the additional height. The proposed footing will include a 2-foot deep by 12-foot wide concrete base supported by a 1-foot-deep by 12.5-foot-wide crushed stone area and 950 linear feet of 12-inch steel sheet piles. These sheet piles will be driven to a depth of 10 feet, and remain beneath the seawall, in order to reinforce the seawall and prevent undermining.
Increasing the size of the seawall will have 1,381 square feet of permanent impacts and a seaward encroachment of 17.15 inches beyond the existing footprint, below the high tide line. This encroachment will occur below grade only, and the replacement wall slope will match the existing wall slope.
The work also will include the construction of drain pipes through the wall. The drainage system will involve a continuous crushed stone trench along the top of the footing with 4-inch PVC pipes through the wall at 10 feet on center along the trench and at existing grade level behind the wall. This will alleviate hydrostatic pressure on the back side of the wall, as well as allow for water return during storm overtopping. Work will also include the replacement of the damaged staircase with a new staircase in order to maintain safe beach access. The replacement staircase will have concrete stairs on the landward side of the seawall and removable steel stairs on the seaward side.
This project will impact 0.69 acre of Essential Fish Habitat (EFH). This habitat consists of sand and cobble that periodically changes in composition due to the strong wave action observed at the project site. Loss of this habitat may adversely affect species that use these waters and substrate. However, the Corps has made a preliminary determination that the site-specific adverse effect will not be substantial. Further consultation with the National Marine Fisheries Service regarding EFH conservation recommendations is being conducted and will be concluded prior to the final permit decision.
There is an additional 2,850 linear feet of seawall that will need to be repaired in the future. These repairs will require additional permitting from the Corps.
The application for the federal permit was filed with the Corps in compliance with Section 10 of the Rivers and Harbors Act, which provides for federal regulation of any work in, or affecting navigable waters of the U.S.; and Section 404 of the Clean Water Act, which regulates the discharge or fill of material in U.S. waters, including wetlands. The public notice, with more specifics on the work proposed by the town of Duxbury, Department of Public Works, can be viewed on the Corps website at www.nae.usace.army.mil/Missions/Regulatory/PublicNotices.aspx.
Public comments on this work proposed by the town of Duxbury, Department of Public Works (file # NAE-2018-02614) should be forwarded no later than Aug. 30, 2019 to the U.S. Army Corps of Engineers, New England District, Regulatory Division (ATTN: Katelyn Rainville), 696 Virginia Road, Concord, MA 01742-2751. Additional information is available from Permit Project Manager Katelyn Rainville at 978-318-8677 or toll free 800-343-4789 or 800-362-4367 (if calling from within Massachusetts) or by email to: katelyn.m.rainville@usace.army.mil.