A Natural Fix for Flooding

In February 2025, scientists, engineers and community organizers from around the United States gathered at a National Academy of Sciences conference center in Irvine, California to discuss using nature to protect people from natural disasters. One major theme of the event was applying these nature-based solutions over large areas. “Twenty years ago, oyster reef restoration projects were the size of this stage,” UC Santa Cruz professor Mike Beck told over 500 attendees at the meeting. “Now they are miles long.”

With a warming planet intensifying fires and floods, Beck highlighted the urgency of scaling up nature-based projects even further. “Climate change is here now and we are spending billions on it,” he said. “Most of those funds are destined toward gray infrastructure that will further degrade nature unless we can show that nature-based solutions are effective.”

Beck, who is the director of the Center for Coastal Climate Resilience at UCSC, has spent nearly two decades showing how natural ecosystems protect people from natural disasters like floods and hurricanes. Sea level rise caused by climate change is requiring many communities make massive investments in fortifying the coastline, and the field of nature-based solutions aims to solve this challenge and others with nature.

One example of this approach in action is along the edges of Redwood Shores, California. Just feet from San Francisco Bay, the community relies on levees to stay dry. But new research co-authored by Beck suggests the salty, swampy grasslands that lie just offshore serve as the region’s first line of defense by bogging down waves and storm surges before they even reach the levees.

The swamps in question are called salt marshes, a habitat defined by specially-adapted grasses that spring up in areas that flood with the rising tide. Salt marshes are a type of tidal marsh, a catch-all that include riverside grasslands that flood when high tide pushes freshwater back upstream. Fish, otters and wading birds enjoy the protection of these safe havens from the ocean. In addition to blunting floodwaters, tidal marshes provide millions of dollars of value in the form of improved fishing, recreation opportunities, and storage of planet-warming carbon dioxide.

Credit: Natasha Pascal

Beck now is taking a major step to scale up tidal marshes as a form of protection from coastal floods. He published a set of methodologies this year to estimate the dollar amount of flood protection offered by any tidal marsh on Earth based on the sea level, number of people living in a flood-prone area, and 42 other parameters. Assigning monetary flood-protection benefits to habitats will make them eligible for infrastructure funding, which could inundate marsh restoration projects with billions of dollars.

“Mike Beck’s work fuses a deep knowledge of natural systems and an understanding of policy and economics to offer tangible, sustainable solutions to the challenges facing coastal ecosystems and the communities that depend on them,” said Anne Kapuscinski, director of the Coastal Science and Policy Program at UCSC. She made the comment in a 2020 press release announcing that Beck would receive a $1.2 million research grant from the prestigious AXA Research Fund to study how restoring coastal habitats like marshes reduces flood risk.

Bogging Down Floodwaters

Beck in 1998 began serving as the lead marine scientist at the Nature Conservancy, a nonprofit that protects land and water from development. But it was not until seven years later that he began realizing the enormous role marine life plays in keeping the ocean away from dry land.

In 2005, Hurricane Katrina brought a wall of water to New Orleans that reached nearly 20 feet in height. The surge crumbled flood control levees, filling the low-lying city with water and killing 1,833 people. The U.S. Secretary of Homeland Security at the time, Michael Chertoff, described the flood as “probably the worst catastrophe, or set of catastrophes” in the history of the country.

Flooding in New Orleans following Hurricane Katrina. Credit: U.S. Coast Guard.

Subsequent investigations revealed much of the flooding stemmed from the paltry state of the city’s levees, and engineers began researching what could be done to reinforce them. Beck turned to the city’s sprawling swamps, wondering if more robust wetlands could have bogged down the storm surge before it ever reached the city. In the decade leading up to the hurricane, Louisiana had been losing a football field’s worth of wetlands every 100 minutes. “Hurricane Katrina was that galvanizing event where people said: ‘We’re losing these wetlands and they must be really important,’” he said.

Beck spent the following years showing that cities benefit from their neighboring reefs, marshes, and mangroves, a type of seaside tropical forest.

While the ecosystems differ, the underlying mechanics are the same. Coastal flooding occurs when large waves push water into areas that normally stay dry. Coastal ecosystems form the first line of defense against the ocean by dampening the waves that travel through them. Storm surges that slog through through healthy habitats before reaching dry land are smaller and move more slowly than waves that move through open water.

In 2023, Beck co-authored a federal policy that designates coral reefs as infrastructure, letting authorities use flood control money to fund the rebuilding and restoring of coral reefs. The first funded by this policy is a 38.6 million effort to restore a 5-kilometer (3-mile) long reef off the coast of San Juan, Puerto Rico that will make waves crest and break before reaching dry land.

Just last year, Beck co-authored a World Bank report estimating that the world’s mangrove forests provide $855 billion of flood protection – a figure that is only increasing as sea levels rise and storms intensify. He hopes demonstrating the staggering value of these ecosystems will show communities around the globe that protecting their mangroves is smart—environmentally and economically.

Most recently, Beck and his colleagues are focused on calculating the value of coastal marshes. He worked with an international team of university and nonprofit researchers to create a standard method to measure the dollar amount of flood protection offered by any coastal wetland on Earth, which will make tidal marsh restoration eligible for flood mitigation funding.

Nature Bats Last

Beck’s research is helping to turn the tide against centuries of destruction of coastal ecosystems.

When a French priest named Pierre François Xavier de Charlevoix visited the swampy settlement that eventually became New Orleans in 1721, he described it as “a malarious wet thicket of willows and dwarf palmettos, infested by serpents and alligators.”

Over the centuries that followed, that perception became practice. Settlers throughout the United States diked and drained the country’s wetlands to make room for farms and cities. While large-scale data is limited, researchers have found that San Francisco Bay has lost 80% of its tidal marshes in the past few centuries, while New York has lost 85%.

All the swampy destruction and human construction has come at a cost. “Nature bats last,” said Julie Beagle, Engineering with Nature Coastal Practice Lead at the Army Corps of Engineers. “All the places that flood are places that we filled.” Most of New Orleans lies below sea level, which made it fill like a bathtub when the levees cracked.

Hurricane Katrina highlighted a drama that is unfolding across the country. One trillion dollars’ worth of property on all coasts of the United States is currently at risk of coastal flooding when storms and high tides push seawater onto dry land, according to the Environmental Protection Agency. Scientists expect this figure will grow dramatically in the coming decades as melting polar ice caps make the ocean rise.

“Hurricane Katrina was that galvanizing event where people said: ‘We’re losing these wetlands and they must be really important,’” he said.

Preparing for that future is very expensive. Just to adapt to the projected sea level rise, communities around the San Francisco Bay Area will have to spend $110 billion to fortify the coastline by 2050, said Rylan Gervase, Director of Legislative and External Affairs at the Bay Conservation and Development Commission (BCDC), a state agency that coordinates management of San Francisco Bay.

Around the world, there is an urgent need to adapt, and Beck is showing that much of this work can be done by restoring nature. He employs biologists and engineers alike in his lab to build complex computer models showing how these habitats reduce the size and intensity of waves that hammer the coast.

His methodologies use a series of equations that show how to calculate the wave energy bogged down by a marsh, and how much that will blunt the economic losses of coastal flooding. These equations show the dollar amount of flood reduction that any coastal marsh in the world provides, helping engineers and scientists make an economic case for protecting and restoring tidal wetlands.

Solutions in Action

In San Francisco Bay, longstanding habitat restoration projects are combining with sea level rise adaptation, turning the region into a hotbed for nature-based solutions. One marsh that defends Redwoods Shores is on nearby Bair Island, a former salt evaporation pond whose decades-long restoration into a salt marsh was completed in 2015. Although flood protection was not the original intent of the project, researchers have found it has had that effect.

Bair Island in 2014. Credit: formulanone on Flickr.

Last year, Beck and his colleagues published a study estimating that each football field-sized section of Bair Island and its surrounding wetlands can provide $450,000 in flood protection, but costs just $100,000 to restore. The researchers predict that in 2100, when sea levels in the Bay will be more than 18 inches higher than they are today, the protection offered by a healthy marsh could be worth as much as $5 million.

“San Francisco Bay has a huge amount of momentum already supporting nature-based solutions, and this paper has added quantitative justification for it,” said study author Rae Taylor-Burns, a postdoctoral researcher at UCSC.

Planners around San Francisco Bay are required to use nature-based approaches as a first line of defense, according to the Regional Shoreline Adaptation Plan. Human-constructed seawalls, otherwise known as gray infrastructure, are permitted only in areas where natural solutions are ineffective. Aside from flood protection, nature-based solutions offer numerous benefits for communities, said Jaclyn Perrin-Martinez, Senior Climate Adaptation Planner at BCDC. “They draw down carbon, they support our commercial fisheries, and they draw people to the region to spend money on tourism and other things.”

Nature-based solutions often cost less than conventional infrastructure. A recent, global review of nature-based projects found that coastal ecosystems including marshes were at least as economical flood barriers as conventional engineering projects 73% of the time.

“Hardened infrastructure is not regenerating itself,” Perrin-Martinez said. But restored natural habitats “can be self-sustaining, providing the benefits of flood risk reduction without the same type of maintenance.”

Racing Against a Rising Tide

With sea level rise due to climate change, marsh restoration has become an even more nuanced process. Draining is no longer the dominant destroyer of tidal marshes, but rather flooding.

Tidal marsh grasses only grow at a Goldilocks elevation — low enough to flood during high tide, but high enough for their roots to breathe fresh air during low tide. A rising ocean is pushing the habitable zone landward, forcing these ecosystems to migrate or drown.

This is already happening around Chesapeake Bay, where ocean currents have caused sea levels to rise about a foot and half — twice the global average. Satellite images from NASA revealed that a massive area of salt marsh disappeared between 2015 and 2019, likely as a result of the region’s accelerated sea level rise.

Salt marsh lost from the east coast of Maryland between 2000 and 2019 is shaded in blue. Credit: Campbell et al. (2022)

The drastic change hasn’t gone unnoticed. In the Chesapeake Bay of Virginia, 70% of seaside farmers surveyed at an agricultural conference reported they had to stop farming parts of their land that recently became persistently wet. “One-third of the acreage that I farm could be directly affected by sea level rise,” said Virginia farmer Sands Gayle in a 2021 interview with PBS. For years, he and his father had watched wet, salty patches of land slowly expand on their family farm, creating areas where crops cannot survive. In place of soybeans, marsh plants are beginning to appear.

Virginia, like San Francisco Bay, requires planners to consider nature-based solutions as a first line of coastal defense. One current project is restoring a struggling salt marsh on Cedar Island, which lies near the Gayles’ family farm. It has the goal of protecting local communities from surges and rising seas.

But even without our help, marshes are finding ways to cope with a changing world. High tide drenches these wetlands with silt-laden water, and some of those sediments remain when the ocean recedes. Over the years, dirt piles up and the marsh grows higher, a process called accretion. While many wetlands in the Chesapeake are struggling, marshes in San Francisco Bay have so far kept pace with rising waters.

But the accelerating rate of sea level rise is raising concerns that eventually the ocean will overtake tidal marshes in San Francisco Bay and around the world. A 2023 study from the University of Chicago’s Marine Biological Laboratory estimated that more than 90% of the world’s salt marshes will meet this fate by 2100.

Their ability to adapt still gives marshes a significant advantage over human-made structures, Beck said, but it’s often left out of consideration when evaluating potential solutions. “Marshes can actually grow,” Beck said. They’ve actually kept up with sea level rise in the past. You got any hard infrastructure that’s doing that alone?”

Beagle, the Army Corps branch chief, is looking at ways to accelerate marsh accretion in San Francisco Bay. One way, she said, is to use the muck siphoned up while dredging boat channels to reinforce marshes. The rising tide will carry more sediment into the wetlands, causing them to build themselves up faster.

But this approach requires a pre-existing marsh, and sea level rise is making new ones harder to build. “If we want tidal marshes to keep pace with sea level rise so that we can incorporate them into our flood risk management approaches, they need to be in the ground and implemented by 2030,” Beagle said. “That’s when the sea level rise curve picks up and it’s going to be much harder to establish new marshes.”

With their increasing urgency and scientific support, nature-based solutions are attracting high-profile supporters. Last year then-Secretary of the Interior Deb Haaland visited Bair Island to announce that San Francisco Bay will receive $2 million in federal funds to improve its wetlands. From a podium placed on a raised trail through the island’s salt marshes, she told local media: “investing in our landscapes and expanding nature-based solutions are critical to maintaining the connection to the land for future generations.”

© 2025 Mark DeGraff / UC Santa Cruz Science Communication Program