53 Acre Guadalcanal Village Marsh Restoration as Mitigation for a Transportation Improvement Project on a State Highway: Fid-Bau Portal

53 Acre Guadalcanal Village Marsh Restoration as Mitigation for a Transportation Improvement Project on a State Highway

Morton, Chuck / Galloway, Michael

Tidal marsh restoration as mitigation for a transportation improvement project on a State highway can be successful and result in a win-win situation. The California Department of Transportation (Caltrans) is widening a two-lane highway to four lanes to reduce existing and projected traffic congestion along State Route 37 in the City of Vallejo, Solano County, California. In order to widen the highway, adjacent tidally influenced salt marsh will be affected. After extensive coordination and design review, Caltrans has limited this impact to less than eight acres. Portions of this marsh are habitat for the salt marsh harvest mouse (Reithrodontomys raviventris), the California clapper rail (Rallus longirostris obsoletus), and the black rail (Laterallus jamaicensis). These three species are all listed either by the Federal or State governments, as endangered (mouse and clapper rail) or as a candidate for listing (black rail). The San Francisco Bay Conservation and Development Commission authored AB 719 in 1990, which allows Caltrans to fill up to 13 acres of wetlands with the provision that the impact be mitigated at a 4:1 ratio. AB 719 also mentions the use of Guadalcanal Village as an appropriate mitigation location for the impacts resulting from the highway improvement project. Guadalcanal Village, a 53 acres former Mare Island housing site, is located just west of the Napa River on the north side of Mare Island in Solano County. Caltrans, and their consultants, in coordination with the U.S. Fish and Wildlife Service, the San Pablo Bay National Wildlife Refuge, and other federal and state resource agencies, developed a plan to restore this site to a tidally influenced salt marsh. The restoration plan requires the creation of 14.8 acres of mudflats and subtidal sloughs, 29.1 acres of tidal wetland habitat, and 5.6 acres of upland refugia habitat. Creation of this habitat involved grading the site to the desired subtidal and marsh plain elevations. Caltrans then breached the levee between the restoration site and Dutchman Slough, a large tributary of the Napa River, on October 31, 2001. In September 2002, 11 months after the breach, with no planting efforts from Caltrans, pickleweed (Salicornia virginica), salt bush (Atriplex sp.), salt grass (Distichlis spicata), tule (Scirpus sp.) and cord grass (Spartina sp.) have been recorded on the site. The site receives full tidal influence and has begun to show secondary channel development (rills) along the graded slough edges.