Fighting Sea Level Rise with Nature: Nature-Based Adaptation in San Francisco Bay

The San Francisco Bay is far more than a beautiful backdrop to call home. It is the centerpiece of our regional identity and a vital protector of our communities and environment. With sea levels rising, the Bay’s natural defenses, its living shoreline, are as much at risk as our built environment. Squeezed between shoreline development and rising seas, the Bay’s living shoreline is at risk of drowning. Yet we all depend on its invaluable ecosystem services and will increasingly need it as a core asset in our response to sea level rise and climate change. Through nature-based adaptation, we can harness the power of the environment to build resilience, protect communities, and preserve critical ecosystems that we all depend upon. Let’s explore how this approach works and why it’s essential for the Bay Area’s future.

What are Nature-Based Solutions? 

Nature-based solutions (NBS) leverage natural processes and habitats to address a variety of environmental challenges, including sea level rise. Unlike “grey” infrastructure—like sea walls and levees—which rely solely on engineering, NBS use elements of the natural environment to enhance resilience, offering sustainable ways to mitigate intense storms and rising tides while providing a host of additional benefits. It is imperative we safeguard our current shoreline habitats and surrounding undeveloped and lightly developed lands suitable for habitat migration to maintain the feasibility of these strategies for the future. The use of NBS is vital to protecting our communities, economies, and fisheries from risks along our coasts. 

The Sierra Club’s Bay Alive Campaign advocates for these solutions at the regional and local levels, working to protect the Bay’s tidal habitats to ensure their resilience—and by extension, our own—in the face of sea level rise. 

Why Do Bay Ecosystems Matter?

Nature has been adapting to subtle changes in the environment since the beginning of time. The San Francisco Bay’s marshes and tidal wetlands possess several key attributes that we, as Bay Area residents, increasingly depend upon for a variety of “ecosystem services” that are essential for the health and safety of our communities. These services include: 

• Water Purification. Wetlands filter stormwater runoff, wastewater discharge, and pollutants, improving water quality.,
• Carbon Sequestration. Wetlands capture and store carbon at a rate 10 times higher than tropical forests, helping combat climate change. 
• Temperature Regulation. Wetlands can lower surrounding temperatures by up to 10 degrees Fahrenheit, 
• Storm and Flood Protection. Marshy soils act as sponges to absorb floodwaters and reduce the impact of storm surges, protecting inland areas. 
• Biodiversity Support. The Bay and its shoreline ecosystems provide essential nurseries for growing fish and crab that support California’s commercial fisheries and a critical stopover for birds on the Pacific Flyway. 

If we allow our critical shoreline habitats to drown, we will lose these critical ecosystem services. Such an outcome would not only harm our environment, but also put local economies and community health at risk.

How Do Nature-Based Solutions Work?

In planning for regional sea level rise, we must remember each part of the Bay’s edge is unique. As you follow the shoreline from San Francisco down to the South Bay, you’ll see rocky, deep waters become shallow marshes with extensive tidal wetlands. Nature-based solutions can be implemented in various ways, each tailored to the unique characteristics of different parts of the Bay shoreline. For instance, while tidal marsh restoration might work well in the shallow waters of the South Bay, other areas like the North Bay might benefit more from beach restoration. 

As sea levels begin to rise, it's crucial we take inventory of our shoreline’s natural features and plan how we can best utilize and amplify their attributes to generate community and ecological resilience. NBS, while productive on their own, can also be mixed with grey engineered approaches. 

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  Restoring or protecting shoreline wetlands and shallow water habitats. 
  • Protecting and Augmenting Marshes:  Tidal marshes and wetlands serve as natural buffers against storm surges and floodwaters, filter pollutants, and provide habitat for teeming wildlife. 
  • Oyster Reefs: The Bay’s historic Oyster Reefs are critical habitat for breaking waves before they reach the shore, as well as water filtration. Reefs are made of thousands of oysters, and each tiny organism filters an estimated 50 gallons of water daily.
  • Eelgrass Meadows: Eelgrass grows in shallow, sunlit waters and supports a critical and incredibly vibrant habitat. It also captures carbon and releases fresh oxygen. These long grasses slow down waves, protecting shorelines and helping to reduce the need for more extensive flood defenses 
• Using protective beaches along unprotected shorelines. The coarse gravel of beaches can absorb energy and break up waves before they reach the shore, reducing damage to shoreline infrastructure.

In some cases, a combination of natural and engineered solutions, referred to as hybrid, or green-grey infrastructure, will provide the most effective protection. These hybrid solutions can provide broader and longer lasting benefits than purely engineered approaches, making them more cost-efficient over time.

• Constructing eco-tone levees. Also known as horizontal levees, this hybrid solution combines flood protection and habitat resilience. These levees feature a longer (less steep), vegetated slope on the Bay side of a flood protection levee that allows wildlife to retreat inland during very high tides, and enables wetlands to gradually migrate to higher ground as sea level rises. These vegetated levees also have proven effective as a final filtration method for removing pollutants and harmful, algae-promoting nitrogen from treated wastewater. 

Why are NBS important? 

A growing body of science, including by the U.S. Army Corps of Engineers (USACE), recognize the benefits of natural habitats and NBS to provide sea level rise resilience.  According to their “Engineering with Nature” webpage, USACE states that their initiative, “...enables more sustainable delivery of economic, social, and environmental benefits associated with infrastructure [i.e. green and green-grey infrastructure].” 

If we do not utilize NBS now, we will have no choice but to use unsustainable grey solutions against sea level rise. Sea walls may protect one jurisdiction, but can worsen flooding for neighboring communities as excess water is diverted. Grey infrastructure prevents the movement of shoreline habitats upland and will result in the drowning of these habitats. The loss of these habitats and their ecosystem services will diminish our ability to reduce sea level rise flooding and other climate change impacts and to manage environmental pollution from our growing communities, effects that will be felt by community members throughout the region. A healthy Bay needs an expansive living shoreline of tidal wetlands and shallow water habitat. NBS are also estimated to be cheaper in the long run than investing in engineered solutions. 

This is not to say there is no place for grey infrastructure. We recognize there are some regions in the Bay where there are simply no other options. However, it is in the best interest of our communities and Baylands to assess our current natural defenses first, and prioritize giving them the resources they need to protect us before we lose them to accelerating sea level rise. 

How do we know where and how to use NBS? 

In planning for regional sea level rise, we must remember each part of the Bay’s shoreline is unique. As you follow the shoreline from San Francisco down to the South Bay, you’ll see rocky, deep waters become shallow marshes with extensive tidal wetlands. Due to this astounding variance, it is no surprise certain NBS are better suited for different points in our shoreline. For example, while revitalizing marshes is a suitable strategy for the South Bay and its extensive tidal wetlands, it would be unsuitable for the rocky shorelines of the North Bay, where beach restoration would be more effective. 

The Adaptation Atlas, published by the San Francisco Estuary Institute (SFEI) and SPUR, was created to assess our natural infrastructure and how best we can adapt to changes in sea level. The document breaks the Bay shoreline into 31 distinct segments, called Operational Land Units (OLUs), each with distinct biological and geological characteristics. This resource helps communities identify the best NBS strategies for their specific shoreline. When faced with a problem such as sea level rise, we must base our adaptation plan on the Bay’s natural ecologies, not just human-drawn jurisdictional lines. The Bay is one interconnected system, so actions taken in one area will impact the Bay as a whole. 

What can you do to promote NBS? 

The future of San Francisco Bay and Bay Area communities depends on concerted action now. Join our Bay Alive Campaign to speak up for NBS and make sure they are prioritized in our region-wide planning for sea level rise resilience! 

Under a new state law, every shoreline community in the Bay is required to make a plan for sea level rise. The Bay Conservation and Development Commission (BCDC) is responsible for approving these plans and recently released a draft Regional Shoreline Adaptation Plan (RSAP), including strategic regional priorities, minimum criteria and  adaptation standards that must be addressed in local plans. BCDC is accepting public comment on the draft RSAP until October 18 and will adopt a final version by the end of this year. 

The Bay Alive Campaign has been actively engaged in this process, and is hosting a webinar series to encourage community participation. Watch part one, or register to join us for part two on October 9, 2024, when we will review the public draft. You can also follow the campaign on AddUp, a Sierra Club activism platform, to stay up to date on action items related to this effort.

Along with our regional work, the Bay Alive Campaign also works on several local projects around the Bay promoting NBS for community and ecological resilience. Check our campaign page for more information on these projects. 

Finally, you can learn more about your home’s natural resources. The aforementioned Adaptation Atlas also features interactive mapping. Explore this resource to find out which OLU you live in, which NBS are best suited for your community, and other characteristics of your home to better educate yourself to become a local advocate for NBS.