Road Ecology Center

The California Department of Transportation (Caltrans) provided funding to help restore and enhance 0.48 hectare (ha) (1.19 acre (a)) of tidal marsh, 0.56 ha (1.39 a) of native wetland and upland habitat, and improve public access at Triangle Marsh in Corte Madera, Marin County, California. This restoration work mitigates for impacts to 0.015 ha (0.038 a) of wetland/tidal marsh habitat resulting from the Highway 101 widening at nearby Corte Madera Creek. The goals of this restoration are to increase the habitat for marsh-dependent species such as the California clapper rail and the salt marsh harvest mouse and to provide wildlife-viewing opportunities for the public while maintaining a suitable buffer from the restored tidal marsh. In 2000, the Marin Audubon Society (MAS) purchased the 13 ha (31 a) Triangle Marsh, which is located along Paradise Drive in Corte Madera adjacent to San Francisco Bay. Triangle Marsh is a remnant of a larger area of historical marsh of the Marin Baylands. At some unidentified time within the past 100 years, a portion of Triangle Marsh was filled, creating large upland areas with pockets of wetlands where differential settling of fill material occurred. This restoration occurred within three areas of the site: the eastern, middle, and western. Upland areas were excavated to tidal marsh elevations. An upland berm was constructed along the boundary between the marsh and Paradise Drive to provide a physical barrier between the public pathway and the middle restoration site. In the larger eastern section, this berm has more gradual slopes on its northern (restored marsh) side to provide wetland-upland transitional refugia habitat. The existing levee in the western section was lowered to provide additional transitional refugia habitat. Grading and contouring of the site began in January 2004 and was completed by January 2005. MAS began planting the upland areas with native species after the grading was completed. Caltrans biologists obtained pre-restoration information on plants and wildlife and took photographic records of the Triangle Marsh in January 2004 before the site was graded and contoured. Caltrans biologists will take photographic records in the same locations annually during the five-year monitoring period to document the restoration progress. Caltrans biologists will conduct spring and summer plant surveys to detect early and late-seasonal species and will map the extent of the vegetation cover using a Global Positioning System (GPS). Surveys will include a minimum of 20 vegetation sample plots, each measuring 3 x 3 meters (m) (10 x 10 feet (ft)), to estimate plant coverage and dominance in the tidal marsh and upland areas. Caltrans biologists will measure wildlife usage of Triangle Marsh on an opportunistic basis. During the June 2005 monitoring, biologists observed pickleweed, marsh gumplant, and California cordgrass naturally recruiting into the margins of the graded and contoured tidal marsh sections. At the end of the five-year monitoring period, Caltrans expects that the restored areas will have at least 70% coverage of native species typical of local tidal marsh habitats and native wetland and upland areas.