In 2015, Cullinan Ranch crews breached levees, bringing tidal flows back to 1,200 acres. 11 years later, migratory birds and fish now use the restored Napa River habitat in California

Wetlands are constantly changing landscapes where water, land and wildlife interact. Along coastal regions, tidal marshes are shaped by the movement of water and provide important places for plants and animals to live. They also perform natural functions that benefit people, from helping protect shorelines to supporting fisheries. Yet these environments have been extensively changed by human activity, making restoration a major part of safeguarding the remaining habitat.

Two restoration projects in the San Francisco Bay area, Cullinan Ranch and Dotson Family Marsh, feature how former or damaged wetland areas can be reconnected with tidal waters. Their restoration has created habitat for wildlife while also increasing opportunities for people to visit and enjoy these natural regions.

Pressures Facing Tidal Wetlands

Many elements threaten tidal marsh habitat. Expanding coastal development can increase impervious surfaces and lead to runoff and pollution. Other concerns are rising sea levels, invasive and non-native species, the environmental effects linked with commercial and recreational fishing mainly overfishing and climate change.


The San Francisco Bay area features some of these pressures. Urban development surrounds portions of the bay, positioning nearby wetlands at greater risk from runoff and pollution. The development pressure map identifies urban regions in the counties surrounding San Francisco Bay in red. Wetlands next to or surrounded by extensive urban areas are mainly exposed to these pressures.

Sea level rise creates another concern. As per the National Oceanic and Atmospheric Administration, 10-12 inches of sea level rise is likely by 2050. Wetlands located in the yellow areas could experience the threat of drowning if water nears those levels.

As per the projections from NOAA and the Intergovernmental Panel on Climate Change, around 1-3 feet of sea level rise is likely by 2100. Wetlands situated within the orange areas experience the threat of drowning if water levels rise to that extent.

A Dramatic Reduction in San Francisco Bay Wetlands

The San Francisco Bay Estuary is home to California’s largest tidal marsh ecosystem. However, the region has experienced substantial wetland loss since the Gold Rush. More than 90% of coastal wetland habitats have been lost or transformed. Losing habitat is only part of the challenge. When remaining wetlands become separated from surrounding habitats, a condition known as fragmentation, species can also be impacted.

Using Restoration to Address Environmental Damage

When contamination from an oil or chemical spill damages natural resources, federal, state and tribal agencies use a process known as Natural Resource Damage Assessment and Restoration, or NRDAR.

Through this process, agencies responsible for natural resources analyze the damage caused by contamination and find the restoration needed to compensate for those injuries. The public can offer input as agencies select suitable restoration projects. The agencies also seek damages from the parties responsible for the contamination. The restoration work at Cullinan Ranch and Dotson Family Marsh resulted from this type of process.

Cullinan Ranch: From Farmland Back to Wetland

Cullinan Ranch had originally been a tidal marsh. That changed over many decades. Beginning in the 1880s and continuing into the 1940s, sloughs at the site were filled or blocked with dikes. Without their connection to tidal waters, the wetlands were changed into upland areas and used for farming.

The property later became the focus of a development dispute. In 1987, many conservation groups challenged development proposals for Cullinan Ranch and defeated those plans. Four years later, in 1991, the U.S. Fish & Wildlife Service purchased the property so it could become part of San Pablo Bay National Wildlife Refuge.

Restoration eventually started in 2015. Dirt levees were breached, allowing water from the Napa River and San Pablo Bay to flow back across 1,200 acres.

That reconnection has already changed the site. Several bird species that included migratory waterfowl, as well as fish now use the restored habitat.

The returning wetland is also providing vegetation significant to wildlife. Pickleweed and salt grass, which are important food sources for the endangered salt marsh harvest mouse, are currently growing in higher-elevation areas.

As the restoration continues, conditions at Cullinan Ranch are anticipated to encourage the return of tidal marsh habitat capable of supporting threatened and endangered species, that includes the salt marsh harvest mouse, California clapper rail and salmonid fish.

Reversing the Effects of Farming

The restoration of Cullinan Ranch is not a rapid transformation. Farming had changed the physical elevation of the land.

Decades of agricultural activity involved removing groundwater, which caused the land to sink in a process named subsidence. Some regions of the ranch dropped by around 6 feet.

Restoring tidal circulation and enabling natural sedimentation to happen will gradually help address this loss of elevation. The marsh plain will need decades to reach its former elevation. Nevertheless, the transition from agricultural land toward a functioning wetland has already begun.

The project has advantages beyond ecological restoration. The natural region is open to the public for activities that include hiking, fishing and kayaking, alongside other activities supported by the San Pablo Bay National Wildlife Refuge.

Protecting the Land Around Parchester Village

The second restoration effort happened at what is currently known as Dotson Family Marsh.

In 2008, the East Bay Regional Park District purchased the Breuner property. The purchase brought a conclusion to a decades-long dispute regarding the future of the 150-acre property located between San Francisco Bay and Parchester Village.

The history of Parchester Village is closely linked to the story behind the marsh's name. The community was among the first planned communities in Richmond to sell homes to African-Americans following World War II.

The Rev. Richard Daniel Dotson and his family became residents in the 1950s. He subsequently helped organize the local community and fought against development proposals that threatened the open space next to Parchester Village.

In recognition of the family’s contributions, the District gave the wetlands the name Dotson Family Marsh in 2016.

Rebuilding Dotson Family Marsh

The East Bay Regional Park District undertook the Dotson Family Marsh Restoration Project with two objectives: enhancing public access and helping restore a wetland ecosystem capable of sustaining itself.

The property had already faced extensive human alteration. During the early to middle part of the 20th century, soil was placed on portions of the site as fill. This eliminated tens of acres of tidal marsh. Other human activities later destroyed much of the habitat that remained.

Material positioned in the interior of the property has formed transitional habitats. As sea levels rise, those places are anticipated to develop into additional tidal marsh.

Signs of progress were visible in images taken in 2019, five years after restoration started. Tidal water had reached all parts of the created wetland, and there were no obvious indications of significant erosion.

Restored Wetlands and Public Access

Both restoration projects illustrated the gradual process of bringing altered landscapes back toward tidal wetland conditions.

At Cullinan Ranch, reconnecting the land with tidal waters has enabled birds, fish and marsh vegetation to return while natural sedimentation begins to address the impacts of subsidence. At Dotson Family Marsh, removing fill and debris, reshaping the land and establishing channels has reconnected the restored wetland with San Francisco Bay.

Projects like those explained here help support the ecosystem services (i.e. natural processes that benefit people) that tidal marshes provide as well as common and endangered species that rely on these environments.

Restoration also creates places where people can experience these environments. Cullinan Ranch is open for hiking, fishing, kayaking and other activities supported by the San Pablo Bay National Wildlife Refuge. Dotson Family Marsh is also open to the public, offering trails, a picnic area and other recreational activities supported by the marsh.

The restoration of these sites is a long-term undertaking. At Cullinan Ranch, returning the marsh plain to its previous elevation will take decades. At Dotson Family Marsh, continued monitoring will help track the development of the restored wetland. Together, the projects represent an ongoing attempt to restore tidal habitat, enhance ecological value and maintain opportunities for wildlife and the public.

Source: Restoration Success Stories in the San Francisco Bay

FAQs:

Q1. What is a tidal marsh?

A tidal marsh is a coastal wetland affected by the regular movement of tides. It can be salt, brackish or freshwater depending on its salinity.

Q2. Why are tidal marshes important?

Tidal marshes provide habitat for plants and animals and support several natural processes that benefit people. They can also help filter polluted water, protect against flooding and support fisheries.