Tidal Marsh Mitigation in Connecticut - Challenges, Successes, & Lessons Learned

Christopher Samorajczyk, Connecticut Department of Transportation
Jeffrey S. Simmons, PWS/NHCWS, Stantec Consulting Services, Inc.
Topic Area
Mitigation for Transportation Projects

Mitigation for impacts on tidal wetlands in highly developed areas is a challenge facing many State DOTs in the northeastern US. As these DOTs strive to make infrastructure improvements required to improve safety, traffic flow, and operational efficiency within their transportation systems, impacts on wetlands and other sensitive resources are inevitable. This results in the need to find and develop compensatory mitigation opportunities to offset impacts. Because of the density of development, cost of real estate in many locations, and dwindling quality of remaining potential candidate compensation sites, finding appropriate mitigation to offset impacts on wetlands and other critical resources has become a serious challenge. This is particularly true with regard to mitigating impacts on tidal systems.

The Connecticut Department of Transportation (CTDOT) has completed 3 tidal wetland mitigation projects over the last 7 years. All of these sites encountered similar hurdles in design and construction. The 3 sites included one in southwestern CT along the Housatonic River totaling 2 acres in size, and a second 1.5-acre location along the West River in West Haven, CT. The third and largest site is located at Groton-New London Airport in Groton, CT. The Groton project was initiated by the CTDOT to provide compensation for unavoidable wetland impacts associated with regulated activities required to construct an expanded Runway Safety Area (RSA) at Runway 5-23. The RSA improvements required construction of a 2.5-acre tidal wetland creation site consisting of high/low marsh, open water, and mudflat areas. In addition, adjacent to the compensatory mitigation site 0.25 acres of Phragmites was eradicated to restore an existing Spartina high marsh.

This paper will describe the challenges encountered in developing all three project sites, as well as other tidal wetland mitigation sites the Department has undertaken. In addition, common solutions to these challenges were identified by CTDOT, that helped to reduce risk and improve overall project success. These solutions were implemented during the planning, design, and construction phases. Among the topics to be covered will be:
- Site selection and screening;
- Design modifications made during construction;
- Invasive species removal/control measures;
- Temporary vegetation storage and transplanting approaches;
- Construction methods and sequencing unique to tidal mitigation areas;
- Preservation of existing habitat as a component of the mitigation effort, and;
- Opportunities for habitat improvement from a landscape level perspective.
An emphasis will be placed in this paper on the numerous changes made during construction, the rationale for those changes, and post-construction observations regarding their effectiveness at achieving the desired goal. A discussion of the lessons learned, and results of post-construction monitoring will also be provided.

Abstract Keywords
wetland mitigation
tidal
transportation