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Posted on January 31, 2019 at 3:52 PM by Elizabeth Dukes
FROM THE TOWN ADMINISTRATOR’S DESK
On Monday, February 4th starting at 7:00PM here at Town Hall, the Selectmen will be hosting a presentation on the proposed replacement of the existing Central Street culvert, dam and tide gate. Consulting Engineers Tighe and Bond, led by David Loring, PE, will provide an update on the design options and ask the selectmen to give guidance on which option should be advanced.
The existing structure over Sawmill Brook as it empties into the Inner Harbor is in poor condition. Temporary shoring was done a couple of years ago to buy us a few more years of use but we need to proceed with a complete rebuilding of the culvert and dam. Voters have approved funding for the project and we have received a $500,000 grant from the state to help pay for the reconstruction. (Additional wall repairs upstream will likely require more funding – grants will be pursued.) Once a final design is chosen and permitting completed we hope to begin the reconstruction work in a couple of years.
The existing tide gate serves to maintain water in the upstream pond. It does not prevent storm surge from moving upstream. The tide gate is at elevation 4.6 NAVD88 while the mean higher high tide is 4.8 feet. Thus, even normal tidal action overtops the existing structure regularly.
A larger culvert needs to be installed to reduce the likelihood of upstream flooding along Sawmill Brook. Flooding is further reduced with the removal of the tide gate. While some property owners fear that removing the tidal gate will cause more storm surge to move up stream, the reality is the existing tidal gate does not prevent storm surge from traveling upstream. To prevent storm surge moving upstream, much of Central Street would have to be raised and a much larger tide gate installed.
To quote from the engineers: “Data and survey results demonstrate that the tide gate does not provide protection from high tide or storm surge and that the impoundment restricts drainage from Central (Mill) Pond causing upstream surface waters to back up. . . . coastal flooding protection must be provided through other methods such as a surge barrier at the harbor entrance.”
In addition to better controlling flooding, another goal of the project is to maintain an aesthetically pleasing pond area. Various options are being explored that would re-establish marsh grasses, eliminating bare mudflats and provide some ponding while still achieving a high degree of flood mitigation.
The details of the extensive analysis and modeling that has been done on Sawmill Brook and the preliminary design of a reconstructed culvert and Dam at Central Street will be presented at the Selectmen’s meeting Monday. The public is invited to attend, ask questions, and provide input about the project.