Oak Island Marsh Tidegate Restoration Project
Weston & Sampson designed a new tidegate to help restore Oak Island Marsh, part of a 1,800-acre coastal wetland area known as Rumney Marsh in Revere, Massachusetts. Although heavily impacted by adjacent urban development, Rumney Marsh has been designated as “one of the most biologically significant estuaries in Massachusetts north of Boston” by the U.S. Fish & Wildlife Service, and an “Area of Critical Concern” by the Commonwealth of Massachusetts.
Oak Island Marsh and Rumney Marsh were once connected by a single culvert with a standard “flap” style tidegate, which prevented tidal flow into Oak Island Marsh. As a result, salt marsh habitat was lost as the plants adapted to the lack of salt water inundation. In hopes of encouraging natural restoration of salt marsh species, a second parallel culvert equipped with a self-regulating tidegate (SRT) was installed to allow tidal waters to flow up into the Oak Island Marsh. Unfortunately, problems with adjustment and maintenance of the SRT resulted in it being operated in a “flap” style mode, which again, led to a loss of tidal backflow into the marsh.
Weston & Sampson was retained by the City of Revere to evaluate the operation of the existing SRT and develop a solution to balance the need for flood protection and the desire to restore the environmentally significant salt marsh. After review of alternatives, and discussion with stakeholders and permitting agencies, Weston & Sampson recommended replacement of the existing SRT with an electrically-actuated sluice gate so that the City could have greater confidence in the frequency, duration, and elevation of tidal flows supplied to Oak Island Marsh.
Weston & Sampson’s unique design for the Oak Island Marsh tidegate is a combination sluice and flap gate. It was designed to operate as a sluice gate under normal operating conditions, allowing the free flow of tide waters in both directions, but closing on the incoming tide at the predetermined set point to prevent further flow of incoming tide waters and flooding of properties abutting the marsh. Unlike traditional SRTs, the Oak Island tidegate was also designed to operate as a conventional top-hinged flap gate under emergency conditions. When the head pressure behind the gate rises to the emergency set point, such as during an electrical failure or extreme storm events, the flap function automatically releases accumulated tidal and storm flow.
Operation of the tidegate is controlled based on the elevation of the tide on the ocean side of the tidegate structure. Water levels are measured by a differential pressure transmitter system. The level control system consists of a Programmable Logic Controller (PLC) and Mission Dialer, which controls the gate operation, indicates water levels, and relays alarms conditions to City personnel.
Since installation of the new combination sluice and flap tidegate, the City of Revere has been able to protect abutting properties and allow restoration of Oak Island Marsh to begin. Operation and maintenance needs for the new tidegate have also been reduced.