Sizing Up Progress on Nature-Based Infrastructure

A highway on piles, standing at 35 feet in elevation in some cases, was the focus of an afternoon session on the Bay Area’s northern crossing. For years now the region has grappled with how to reduce both traffic and flooding on State Route 37 as it crosses from Novato to Vallejo. They not only have to take into account the lower income workforce using the route to get to jobs in Marin County from more affordable homes in Solano and Contra Costa counties; they also need to keep channels and floodplains open to nourish tidal marshes surrounding and underlying the highway. These same marshes will be a critical sponge for the North Bay as flooding increases with warming temperatures. The soaring spans of the new SR37 are designed to remain above water through 2130.

Geomorphologist scientist Jeremy Lowe, who works for the SF Estuary Institute, gave an overview of planning progress to date, saying “collaborative planning, coordinated strategies, and regulatory innovations” will all be key to success in rescuing the low-lying highway. He highlighted three specific projects prime for more immediate attention while long range solutions and funding coalesce. The first project would not only widen but lengthen the bridge over Tolay Creek, creating a larger channel connection between the Bay and the watershed and restoring 337 acres of baylands and alluvial fan habitat. The second project would improve the tidal drainage of 900 acres of the strip marsh south of SR37, enhancing the habitat and further protecting the road. The final project would develop a landscape-scale restoration strategy for the Novato Creek baylands, over which the new elevated roadway will be built.

The Strip Marsh East project proposes construction of nearly six miles of new tidal channels and a variety of other actions which, collectively, would restore 900 acres of tidal marsh lost since 2000, and sustain a stretch of natural shoreline that protects 3.5 miles of SR37. Map: Siegel, Gillenwater, Baye

Beyond these three building blocks, the overall rescue operation for the 21-mile-long stretch of 37 is “a first of its kind in California’s highway system to factor in environmental linkages early on in the planning process,” said the second speaker, David Ambuehl from CalTrans. 

Up next, Larry Goldzband, executive director of the SF Bay Conservation and Development Commission, asked the audience whether they were surprised to hear a senior Caltrans official speak about their plans to integrate environmental restoration and public access into the project, as opposed to talking about possible mitigation. With so many highways threatened by sea level rise in the Bay Area, many adjacent to valuable creek mouths and marshlands, CalTrans’ collaboration on environmental concerns around adaptation will be critical, said Goldzband. So, too, will be considering climate equity issues, such as how to pay for new roads without penalizing low-income drivers with new tolls. “We need ideas that mean something to all of us, ways to make roads work for every reason,” he said. A familiar rallying cry for multi-benefit approaches to gnarly infrastructure challenges. 

While the final fix will take more time and much more money, others are working on interim solutions to the congestion and flooding that don’t get in the way of future goals. Here too there are some unprecedented hook ups between environmental and transportation agencies in the Bay Area. 

Kevin Chen talked about a new plan for the eastern part of the highway between Sears Point and Mare Island that adds an HOV lane and room for buses. This engineer from the Metropolitan Transportation Commission pointed out that there is no public transit option for the 37-corridor because it is too congested for buses to be competitive. If not buses, at least more people in each car, the thinking goes with the HOV lane.

Proposed HOV and transit lanes for interim upgrade to SR37. Art: MTC

The interim plan will also include some “means-based” tolling including lower tolls for lower income travelers. The toll would also help create a needed local match for state and federal funds to save the sinking highway.

As part of the same interim project, the Regional Water Board’s Xavier Fernandez talked about how nature-based infrastructure is being incorporated into the Tolay Creek Bridge and the other projects along the bayfront edge (between the Pond 1/1A intake and Mare Island) in ways that innovate regulatory approaches for nature-based climate adaptation projects. “It’s better to integrate before you mitigate,” he said. The bridge lengthening component of the interim plan, for example, will remove old fill to allow more water under the bridge, reducing the mitigation requirement for environmental impacts and improving the Bay-watershed connection. The strip marsh component will also reduce the mitigation requirement because it reestablishes wetland vegetation and marsh elevations that both protect SR37 from storm surges and wave erosion, and also improves habitat for protected species, such as the Ridgway’s rail and salt marsh harvest mouse. 

“This is huge! These integrated projects open up new funding for nature-based infrastructure as part of transportation projects,” said Fernandez. The whole North Bay shore could benefit.

Elevated route envisioned for western end near Novato. Art: CalTrans

Most of the current flooding impacts on SR 37 are further west, however. Final speakers Jeanette Weisman of the Metropolitan Transportation Commission and James Muller of the SF Estuary Partnership described the elevated causeway planned between Highway 101 and Atherton Avenue. The work is funded in large part through the Bipartisan Infrastructure Law that explores a multi-benefit approach to the highway project, in coordination with the strategy for protecting the underlying Novato Creek baylands and the SMART line railroad.

“It’s a bear,” said Muller, “but luckily most of the land is owned by the public.”

“Like water, like air, sediment is incredibly important to everything we do,” said the first speaker, Brenda Goeden of the SF Bay Conservation and Development Commission. This statement framed a conference session focused on the particles of clay, silt and sand that have become as precious as gold in the Bay Area fight to raise our shores faster than rising sea levels. Gold because moving the 450 million tons of sediment needed for survival, according to research by the SF Estuary Institute, will be expensive. Session talks focused on letting nature do most of the heavy lifting. 

Eroding edge of Whale’s Tail marsh near Eden Landing courtesy David Hasling.

What everyone is most worried about are drowning marshes that the region and its taxpayers have worked hard to preserve and restore — marshes that also provide a critical buffer between rising waters and the roads, bridges, airports, cities, industries and homes of the Bay Area’s urbanized shores. According to speaker Scott Dusterhoff from SFEI, the region currently has about 80,000 acres of tidal marshes and mudflats, and is planning or restoring 24,000 acres more. While these wetlands have enough sediment supply to keep pace with the current rate of sea level rise (via natural accretion and plant growth), once that rate accelerates dramatically around 2040 they’ll need much more. About 30% of the 450 million tons of projected need is readily available from dredging or natural processes, his team’s research shows. The remaining 70% needs to be sourced, moved or managed to keep our marshes from going under. “The good news is we think we have this sediment in the region already,” he said.

Steps to releasing that hidden supply including reconnecting creeks to the habitats and shores at their mouths, finding ways to reuse the 200,000 tons of sediment cleared each year from flood control channels, tapping construction sites (already a success story: one million cubic yards of excess construction soil from building sites made its way into South Bay Salt Ponds restoration projects in the past several years), and releasing supplies trapped behind small, historic dams in reservoirs (150 in the region’s immediate watersheds). “The trick is to match local sediment need with local sediment supply,” said Dusterhoff, pointing to his team’s OLU work as a scientifically vetted guide for how to set priorities for where to invest this brown gold. 

The most obvious source of the stuff is the maintenance dredging undertaken in the Bay by the US Army Corps of Engineers to keep shipping channels and ports navigable (5,700 acres of projects). But beneficial use of dredged sediment in upland and wetland restoration projects has been hampered by Corps policies favoring the least cost alternative, namely an in-bay or an ocean disposal site. The more costly projects, therefore, often require local dollars to be invested. 

“We’re comfortable with failure in grey infrastructure, but much less comfortable with the idea of failure with green infrastructure, so we have to build projects now that buy us time and leave the door open for learning,” said Beagle. 

Two speakers from the Corps, Tessa Beach and Arye Janoff, described important recent policy shifts allowing for more ways to approve beneficial use, either within the standard “least cost alternative” or to cost-share the additional expense if it is beyond that. “We’re excited to have more flexibility and an increased ability to cost share,” said Beach. Instead of requiring local sponsors to pay 100% of incremental costs associated with beneficial use, the Corps can now pay 65%, she said. 

Not only have national priorities for the Corps shifted to supporting more beneficial use, so have those of the local Corps District. “We want to change the paradigm by regionalizing our approach and optimizing beneficial use in the Bay Area,” said Arye Janoff. Janoff is trying to apply this new paradigm in the District’s Regional Dredged Material Management Plan in San Francisco Bay. 

The main target of the push for regional optimization is the region’s drowning marshes, as well as the need to continue to restore other areas previously cut off from the tides. Managers have tried barging and pumping sediment onto restoration sites (Hamilton Wetland Restoration in Marin and Montezuma Wetlands in Solano) but this year the Corps tried a different method altogether: strategic placement in the shallows off Whale’s Tail Marsh near Eden Landing on the Alameda County bayshore. They wanted to test whether waves, tides and other natural processes would deliver the sediment to the shore. “We need to let water do the work,” said the Corps’ Julie Beagle in another talk during the sediment session. 

Research vessel takes samples after placement experiment. Photo: USGS

Scientists led by the US Geological Survey are tasked with carefully monitoring the results of this experiment. One group is looking for any immediate impacts on critters living on the bay bottom, where the mud landed, and others are tracking where the sediment ends up. Does it arrive on the intended marsh or not? “We’ve sampled before, during and after the strategic placement,” said scientist Jessie Lacy of USGS. She noted early results, such as spikes in suspended sediment an hour or more after placement, and the gradual decrease in size of the “multiple mounds” left behind by the placement project. 

“We need to do a lot more experiments like this in other places around the Bay before we run out of time,” said Beagle. Sites chosen have to have the right conditions to deliver sediment to the mudflats and marsh, she says. At the moment, she’s looking into Marin’s Bothin Marsh, the Emeryville Crescent, and Hayward’s Arrowhead Marsh, and also considering different techniques for delivering the sediment. Beagle appealed to people with other potential projects to reach out: “As scientists, we don’t do something once and decide whether it worked or not.” Success can’t be announced until results are replicated.

At the end of the panel, BCDC’s Goeden summed up the thrust of recent research and policy shifts around dredged material disposal. “We’re shifting from a least cost view to a most valuable view in evaluating project candidates,” she said. 

With the ambition to do so much more with each and every natural infrastructure project on our shores, the burden of complex and collaborative planning is increasing. Building living shorelines, a task that includes everything from planting eelgrass and crafting oyster reefs in the shallows to texturing seawalls and weeding wetlands, requires both patience and deep pockets to get stuff done. The way Marilyn Latta sees it, however, it would all be easier and quicker to scale up and approve the ten projects now waiting in the wings around the Bay if every single one of them didn’t have to get their own permit. 

Jeanne Hammond plants cordgrass to speed marsh development adjacent to living shorelines oyster reefs (castle shapes) off Point Pinole. Photo: Katie Rodriquez

“Living shorelines are voluntary, non-mitigation related, projects that can help us on the path to climate resilience,” said the Coastal Conservancy’s Latta at the beginning of an afternoon panel on the topic. “The key idea is to link biological and physical goals for improving our shores, but there is no existing guidance on how to do this. Many engineers and contractors don’t understand how to build living shorelines but want to. We need to normalize these kinds of projects.” 

Latta and her partners have raised $6.5 million to develop the desired regional design and constructability guidance for 10 sites within the next year, as well as to conduct more monitoring, information sharing, and workforce development. “We’re hoping to get programmatic permitting,” she said. 

Scaling up will also require a newly trained workforce of people capable of undertaking these projects, said Chela Zabin of the Smithsonian, the second panelist. Zabin is part of the science team testing the habitat results of living shorelines projects like Giant Marsh near Point Pinole, which are very promising. Not only oysters, but also fish and waterfowl are attracted to the installations. 

Modular oyster reef experiment. Photo: Packard Jennings

Zabin described two current frontiers of her work: developing a “lighter, more modular” reef design that doesn’t require contractors with heavy equipment for construction; and monitoring what critters and marine plants are colonizing some textured tiles installed on the San Francisco seawall. The premise is that seawalls don’t have to be smooth concrete, they can include nooks and crannies attractive to seaslugs, macroalgae, crabs, and other marine life. 

Zabin’s excited that the San Francisco seawall project is in such an urbanized environment, where the public can actually see the results. “If we can do it right, this going to be really good for the Bay for a long time,” she said, referring to plans to incorporate some of the textured designs into larger efforts to protect the Embarcadero and the downtown waterfront from rising sea levels. “Nice, habitat-friendly seawalls should be in all the places that need them, not just the places that can afford them,” she hopes. 

The Port of San Francisco, which owns most of the city’s Bay shoreline, is already deep in the throes of a waterfront resilience plan. It’s also partnering with the Army Corps of Engineers to address sea level rise and coastal storm risks. More “engineering with nature” to reduce flood risk is newish Corps priority. 

“It’s really possible to increase nature-based solutions on an urbanized shore. This green infrastructure just has to be more vertical,” said the Corps’ Julie Beagle, the next speaker. “The purpose is not just to make it pretty, she added, running through some examples on screen showing both the textured tiles and ecological armoring Zabin described, but also new seawall profiles. “The trick is to avoid more fill, layer your edges, and add small but mighty features like a perched beach or engineered tidepools,” she said. “But it’s a cultural change for regulators to view nature-based solutions as part of a project plan, rather than as the mitigation for the shoreline project.” 

The last speaker reminded us that even the best laid plans and restoration sites will attract invaders. “You’ve got to build invasive species management into your project even if it isn’t sexy,” said Jeanne Hammond of Olofson Environmental, which manages the region’s Invasive Spartina Project. Under that project, the region’s acreage of destructive Atlantic cordgrass and hybrids was reduced from 805 in 2005 to 22 in 2023. The newest invader on their radar, said Hammond, is a seashore turf grass. 

As climate change increased the urgency of achieving mature wetlands, especially on newly restored sites, Hammond’s team recognized that leaving everything to natural processes wasn’t going to cut the mud. “We now need more rapid habitat enhancement to promote marsh resiliency,” she said. Her teams have been working in interior marshes and upland transition zones near wetlands “to speed up the process” of plant growth and associated resilience to advancing tides. “We choose and add native plant species that act like weeds, species that grow and spread fast,” explained Hammond. 

At the end of the four presentations on living shorelines, conference panelists shared one magic thing they would wish for to lift up their projects. Most mentioned the need for more training and guidance for engineers and contractors about how to make elements of these pilot living shorelines “work on the ground.” More heterogeneity in guidelines can be difficult, they all recognized, because so many nature-based solutions are place-specific. But the important thing is to link grey infrastructure upgrades to nature-based solutions, and also to experiment with more projects before it’s too late. 

Source: USCOE

“We’re comfortable with failure in grey infrastructure, but much less comfortable with the idea of failure with green infrastructure, so we have to build projects now that buy us time and leave the door open for learning,” said Beagle. 

The humpbacked levee — steep on one side but gently sloped and thick with willows and tarweed on the other — is a much-discussed sea level rise adaptation project around the Bay Area, especially for wastewater treatment plants. As these plants confront the need to not only stave off flooding of their facilities, but also to upgrade treatment processes to remove nutrients and other pollutants, the living levee, as it has also been called, has become an increasingly viable solution. Read “multi-benefit” project with superpowers: flood protection, habitat, and pollution control all in a hump of dirt and grit with frills. 

Seven years into the first demonstration project at San Lorenzo’s Oro Loma Sanitary District, numerous treatment plants around the Bay region are developing their own versions of these wastewater-filtering levees. Indeed how to scale up such wonders was the focus of an afternoon panel at the State of the Estuary conference. As is the case with living shorelines, the region now has solid pilot results from its experiments it now wants to try out at larger sizes in more various situations. 

Early experiments at the Oro Loma horizontal levee project showed that passing wastewater through the cells (different mixes of gravel, dirt, water, vegetation) of this highly specialized levee can remove the nutrients that cause harmful algal blooms in the Bay. Further testing suggested the process also works to remove some potentially toxic metals like copper.      The latest round of levee experiments, meanwhile, is tackling treatment of the brine, aka reverse osmosis concentrate, from Valley Water’s water recycling and purification plant. 

Treatment cells of Oro Loma experimental levee.

“We tore out a few old cells in the Oro Loma levee and added new ones that included granular activated carbon in a gravel and woodchip mix,” said speaker Anthony DeSalvo from UC Berkeley. In this presentation, he and fellow graduate researcher Jonathan Uhler described how their tweaks to the levee system helped remove even more contaminants from the wastewater. “We saw pretty robust removal of a suite of PFAS,” DeSalvo said. (PFAS are cancer-causing chemicals found in many common products including fire-fighting foams.) 

The question really is, can the region build bigger versions of the treatment levee at other sewage plants and then connect them to the Bay? Early indications suggest the wastewater they treat could be clean enough for direct discharge, with various tweaks. The more difficult challenge is the footprint such new levees might have in existing tidal marshes ringing these sewage plants. 

Take, for example, the “First Mile Levee Project” proposed along the nearby Hayward Regional Shoreline: the first full-scale demo of the horizontal levee concept. “There’s a pretty well-functioning marsh there today, but we need to add fill to build the new levee and protect the marsh for tomorrow,” said Jackie Zipkin of the East Bay Dischargers Authority in her presentation. As with many innovative shoreline adaptation projects, permitting requirements legislated long before adapting to climate change and sea level rise became an urgent priority are getting in the way. “The regulatory framework isn’t set up to support work that mitigates future conditions, it’s set up to require mitigation for impacts today,” she added. 

For the First Mile project, regulators asked Zipkin’s team to consider downsizing the footprint so the marsh was impacted as little as possible, which she found frustrating. Baselines are hard to establish, she says, when you’re comparing habitat today to future habitat lost with no project. Increasing the footprint over time, as sea level rises, is one way to handle it, but then benefits could come too late to prevent flooding. “We’re trying to do a lot with one project,” said Zipkin. 

Future vision for the First Mile levee. Art: Nate Kauffman

Up in the North Bay engineer Emily Corwin also has a lot of balls in the air with her project: a new treatment wetland planned for the Fairfield-Suisun Sewer District. She prefaced her presentation with the good news: “We have more space to adapt to future conditions than most other sewer plants around the Bay.”  

When the District shared their project vision — a combo flood protection levee and wastewater treatment wetland that could also pilot carbon capture techniques — with their neighbors, they got a surprising response. The community asked if the project could include a soccer field, a recreational resource sorely lacking in an area with a high percentage of disadvantaged youth. 

In response, Corwin’s team has been struggling to design a hybrid project. While she hopes to include a trail and some open space, managing a soccer field would require help from the local parks department. “Community access pushes the edge of what a sewer district is all about,” says Corwin. “While we want to shift the perception of wastewater treatment from being dirty and dangerous to it being clean and safe, it can get a little smelly around the plant.” 

Beyond the community interface, Corwin is laser-focused now on the best size and shape for the levee, the wastewater treatment wetland, and associated carbon capture and peat creation functions (where soil, bacterial processes and decomposing plants bulk up the site in the face of sea level rise). “We want to let nature do the work of building up elevations around our plant,” she says. 

The final talk of the panel delved into the engineering and science of what we can do with the concentrate produced by reverse osmosis, better known as Reverse Osmosis Concentrate (ROC). The reverse osmosis process is part of the treatment train at any advanced water purification plant. These plants convert treated wastewater into a highly purified form clean enough for groundwater recharge or potable use. 

Recycling more water is a state and local priority in a drought-plagued state. To that end, Valley Water has been operating the Silicon Valley Advanced Water Purification Center in San Jose since 2014 and is planning another South Bay plant for the future. However, this will translate into more ROC that can’t be simply discharged into Bay. The concentrate will require proper management and disposal. 

“There are no silver bullets,” said Valley Water’s Medi Sinaki in his talk. Valley Water has been exploring various options: physicochemical and biological breakdown processes; engineered treatment cells; floating wetlands; the horizontal levee; and even dilution with residual effluents of wastewater treatment plants. While the physical and chemical treatment options that have been explored aren’t commercially available right now, or use a lot of energy, according to Sinaki, the nature-based solutions approach where ROC passes through engineered wetlands or horizontal levee systems shows a lot of promise.

Testing drainage from engineered wetlands. Photos: Valley Water

The engineered wetlands experiment removed 15-30% of the nutrients and 5-20% of the pharmaceuticals and pesticides from ROC, but failed to remove metals, for example. The new cells at the Oro Loma horizontal levee removed more contaminants and improved other water quality parameters. 

 “These nature-based solutions pilots show the potential for success for ROC management but need to be 5-6 times bigger to get more reliable data,” said Sinaki.

While the end of the day session filled with science produced some dazed looks in the audience, the take home from the panel came through clear enough. The region’s wastewater treatment plants are stepping up to the challenges ahead, and working with new partners and nature-based approaches in the process. Though perceived as dusty, dirty and smelly, they could be our frontline protection from not only rising seas, but also drought and algal blooms.