Why Restore Tidal Marsh?
Between 1800 and the late 1990s, about 80% of the tidal marshes in the San Francisco Bay estuary were lost due to diking and filling. These tidal marshes provide many ecosystem services which benefit not only nature, but our society. Here’s how tidal marshes benefit you:
Flood Protection: Improved protection against floods and sea-level rise
Flooding in the Bay Area often occurs where runoff from major storm events collides with a rising high tide. The marshes around the fringes of the bay store water at these collision points, absorbing it like giant sponges, then releasing it during low tides.
Tidal marshes also serve as “horizontal levees” by absorbing the energy of storm waves, thereby reducing the potential for bay waters to flood low-lying areas along the bay during storm events and rising sea levels. Tidal marshes form by trapping sediment until the sediment builds up to an elevation that allows vegetation to grow. At that point, marshes gain elevation in two ways: (1) additional sedimentation, and (2) accumulation of organic matter (such as roots and rhizomes of plants) below the surface of the sediment. Historically, marshes were able to keep pace with sea- level rise by migrating inland to higher elevations. The ability of marshes to keep up with sea-level rise is dependent on sediment availability, the presence and type of vegetation and its organic root zone building capacity, the rate that sea levels rises, and the topography and connectivity of adjacent uplands.
Healthier Ecosystem: Improved water and air quality and fisheries
A marsh acts as a natural filter and improves water quality by trapping and filtering nutrients, sediment and pollutants transported by runoff. This prevents these pollutants from ever reaching the bay and adversely affecting its marine life. The San Francisco Bay Estuary was once teeming with salmon, crab and oysters. The fishing industry thrived, and harvests from the Bay not only fed the region, but much of the west coast as well. Tidal marsh was an essential component to the health of the fishing industry in the San Francisco Bay. With the closure of the herring fishery in 2009, commercial fishing and shell fishing is now prohibited. Restoring our marshes will undoubtedly improve the health of the fisheries in the Bay.
Additionally, tidal marsh can serve to purify the air and reduce a major cause of climate change, carbon dioxide. Marshes tend to be “carbon sinks” because of the amount of carbon dioxide absorbed through photosynthesis by the prolific wetland vegetation. These sinks are especially important in highly urbanized areas, like the San Francisco Bay Area, where carbon dioxide levels are elevated.
Recreational and Educational Opportunities
Restoring tidal marsh also provides recreational opportunities for people to experience the natural world, such as hiking, biking, kayaking, and bird watching. The San Francisco Bay Area is one of the most densely populated metropolitan areas in the United States, and we are fortunate to have such large areas close by that have not been developed. With proper planning and funding, tidal restoration projects present a unique opportunity to provide recreational areas for its residents that are, at times, right outside their front door.
In a similar respect, public access to the marsh provides an educational opportunity to learn about our natural environment and how plants, animals and humans can coexist.
Sustainability: Reduced levee building and maintenance
Most levees along the San Francisco Bay are aging and poorly constructed as they were built with technology and methods from the turn of the 19th century. Further complicating the matter is subsidence. As the land sinks, the water on the tidal side places more pressure on the levees, requiring them to be widened and strengthened to keep from failing. Without constant maintenance, failures are inevitable. Tidal restorations reduce the need for and height of levees and are designed to restore the natural processes and let the site evolve as it needs given the specific conditions of the site. This approach effectively provides a long-term solution to reduce maintenance costs into the future.