Figure 1-3. James Brook Tide Gate
Loss of Tidal Marsh in Cohasset Harbor/Cohasset Cove
James Brook Tidal Marsh James Brook, a tributary of Cohasset Cove, is identified as a High Priority Tidal Restriction Restoration Site by the Metropolitan Area Planning Council, 2001. This designation was made based on the size of the area affected, the potential for an anadromous fishway, proximity to shellfish resources, potential for upstream benefits, and a high feasibility rating. . A Self Regulating Tide gate (SRT) was installed in 2003 to promote wetland restoration of James Brook and Jacobs Meadow marsh. A horizontal float located at the base of the gate holds the gate open on an incoming tide allowing tidal water to enter the Brook and Jacobs meadow. When a predetermined tidal level is reached the two floats on the top of the gate closes the flapper preventing further salt water from entering the Brook. During ebb tide water flows from the Brook to the Harbor and the gate resets. The Town of Cohasset is working with CZM, NOAA/NMFS, EPA, and the ACOE to determine optimal gate management to balance wetland restoration of the Jacobs Meadow marsh while preventing flooding of area properties. Other potential restoration efforts such as enlarging the culvert between the Brook and the Harbor and Open Water Marsh Management techniques to reduce phragmites and restore native salt marsh vegetation are being evaluated.
The design/build drawings for the Greenbush Commuter Rail Restoration Project have caused several culverts over James Brook (a tributary of Cohasset Cove) to be either replaced or abandoned. Stormwater runoff is now being discharged into a culverted portion of James Book from the proposed replacement parking facility near Pleasant Street (Maguire 2005). The proposed Greenbush changes to the James Brook culverted section, permitted by the Wetlands Program have been completed with deep sump catch basins and vortex style separators that provide water quality treatment.
Treats Pond is a culverted but often blocked tidal pond that drains to Sandy Cove. Congress authorized $200,000 to the Army Corps of Engineers to conduct a feasibility study (currently underway) for reconnecting a hydrologic link with the Cove. The feasibility study will include surveying, hydrolic modeling, site assessment and the development of a restoration plan. Restoration of East Harbor (Truro MA) to address bacterial pollution by the reintroduction of tidal exchange has demonstrated that reconnecting a hydrologic link increases flow velocities resuspending sediment and bacteria which are carried down the culvert during the ebb tide. Once fine sediments were flushed from the system, bacteria counts at the culvert outlet decreased greatly (Progress Report on Estuarine Restoration at East Harbor, May 2005 John Portnoy, Stephen Smith & Evan Gwilliam).
South Coastal Watershed Action Plan 9/12/2006 Watershed Action Alliance