Adapting to sea level rise and climate change in the San Francisco Bay Area: What can we do?

San Pablo Bay by USFWS
San Pablo Bay
Dr. Letitia Grenier and Jeremy Lowe discuss current projects underway to address adapting the San Francisco Bay’s shoreline for sea level rise and climate change

With sea level rise projected to be anywhere from 2 feet to 5 feet, many projects in recent years have been focusing on how to adapt the San Francisco Bay’s extensive shoreline.  At the May conference, New Approaches to Climate Change in the San Francisco Bay-Delta, Dr. Letitia Grenier and Jeremy Lowe, both with the San Francisco Estuary Institute, discussed some of the current efforts underway to address the impacts of sea level rise and climate change.

DR. LETITIA GRENIER: The Baylands and climate change: What can we do?

Letitia Grenier
Dr. Letitia Grenier

In 1998, the Baylands Ecosystem Habitat Goals project was first completed which outlined a vision for extensive tidal marsh restoration around the San Francisco Bay Area. Recently, the Baylands project was updated to address climate change and sea level rise issues.  Dr. Letitia Grenier, Senior Scientist at the San Francisco Estuary Institute, gave a presentation on the update, noting that the project is a very large collaborative project with over 200 scientists, regulators, restoration practitioners and others who have been working on it over a three year period.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_02Dr. Grenier noted that although her talk today would be focusing on the San Francisco Bay tidal marshes and not necessarily the Delta, this is all one estuary, she said. “We’re all in the same boat here,” she said. “We’ve lost marsh in both places and actually more catastrophically in the Delta, and I think it’s an interesting quirk of island biogeography that in the bay, most of our endangered species were in the salt marshes as you might expect; in the Delta, most of our endangered species ended up in the freshwater aquatic habitats, but that’s really driven a huge difference in how we think about and manage these two parts of the estuary. Nevertheless they started out this way, and I think a lot of what we’ve thought about in the bay probably is relevant in the Delta as well.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_03In 1998, the first iteration of the Baylands Ecosystem Goals set a goal of 100,000 acres of tidal marsh, she said, presenting a bar chart showing the historic, 1998, and current acreage that has been restored. She pointed out that historically, there were 190,000 acres of tidal marsh, and in 1998, when the first Baylands project was completed, only 4,000 acres had been restored. “By now, about 7000 acres and we’ve got another 30,000 planned, so there’s been a huge amount of progress made since the original Baylands goals about 15 years ago,” she said.

However, we now face greater challenges because of climate change and other drivers of change, and sea level is a big one for the long term persistence of the Baylands,” Dr. Grenier said. “There are a lot of other climate change drivers that are affecting the Baylands, and I won’t be able to go into all of those, but I will talk about the reduction in sediment supply because it’s so critical.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_05Hydraulic mining in the Sierras in the 1800s was part of the cause of a large flush of sediment that has come into the San Francisco Bay over decades; there were also other land use changes that caused the sediment pulse, but it was a long sediment pulse, she said. “Based on work from USGS, that now there’s a step change and we’re seeing much reduced sediment loads, and it’s hypothesized that they will continue to be low,” she said. “This is a really big deal in terms of how marshes can accrete and keep up with sea level.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_06Work done with marsh accretion models by Point Blue puts us in the unfortunate situation of probably high sea level rise and low sediment supply, she said. “We’re in the worst case scenario of these four options here that could happen.   Of course there’s uncertainty but we think we are headed in this direction.”

Dr. Grenier noted that in the diagram, the light green is the low marsh, dark green is the mid marsh, and orange is the high marsh, and she pointed out that over time moving across the x axis, the prediction is that we’re going to lose quite a bit of marsh. “For the Baylands goals project, we’re thinking about that in terms of ecological health, which is mainly about supporting native wildlife and other biological processes, but there’s a lot of other ecosystem services that we rely on from these marshes.   So if we lose these, we lose a lot.”

The purpose of the update to the Baylands project was to determine what could be done about the possible impacts of climate change, as well as the effects of other future changes. “One difference between this project and the 1998 one is that we were able to focus more on processes and functions, because now it’s become so critical to be thinking about how those processes and functions support the long-term resilience of habitat,” Dr. Grenier said. “We can’t just talk about static habitat acreages; we actually need to think about the processes that are going to make those habitat acreages continue to be viable and change and evolve over time, and then provide the functions that we want to come out of those habitats.”

The Baylands project came up with recommendations as well as landscape visions to try and help people visualize outcomes, and those recommendations and visions are provided at several different spatial scales. Dr. Grenier said her presentation today would focus on the regional recommendations, but she invited those interested to look at the report for much more detailed recommendations for the different segments of the Bay Area shoreline.

Baylands Goals: Regional Recommendations

1.  Restore estuary-watershed connections that nourish the Baylands with sediment and fresh water.

The first regional recommendation is to restore estuary watershed connections that nourish the Baylands with sediment and freshwater. “In the past, we’ve often had to think of sediment and freshwater as waste products that we’re trying to deal with as they get near the bay, but now we want to actually use them as precious resources to help nourish the Baylands so that they survive,” she said, noting that previous speakers had discussed how the accumulation of both organic matter and inorganic matter relate to the ability of marshes to keep pace with sea level rise.

But what do these connections look like? I realize when I say this to people, people have no idea what I’m talking about, so we’ve got a project now that tries to envision what connections used to look like, what they look like now, and what they could look like in the future,” she said.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_10The connections that we have now tend to be this, which is where water comes off the watershed, it’s shunted between levees and goes out into the bay,” she said. “We’ve lost the connection – we have land and water connected but we lost the wetland in between. We didn’t have the water coming off the land go through the wetland and then be connected to the larger aquatic area.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_11The other kind of connection we have now is no connection,” she said. “The water is shunted into a pipe and it goes somewhere else and from there it gets sent to the bay.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_12Dr. Grenier explained that in the past, there was diffuse seasonal or intermittent flow that would create wet meadows and even large shallow ponds that would transition to salt marsh and then to the tidal flat in the bay; there were also areas of diffuse perennial flow that would create wetland complexes with willow groves, as well as other freshwater marshes.

These were really important for wildlife and provided a lot of complexity,” she said. “With climate change, this is the kind of thing you’re going to want to have. In a dry year, if you have an animal that needs a certain kind of salinity, it can move up more to the fresher area; in a wet year, it could move down farther into the salty area and this is the kind of complexity that we need to retain resilience in our wildlife populations.”

Where there was larger flow, there was direct creek input into tidal channels, but those creeks dumped their water with their sediment into the back of the marsh which went out through a marsh channel into the bay and this helped nourish the marsh, as well as create complexity in the habitat, she said.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_18So what could these look like in the future?,” she said. “Could we rethink how water gets to the bay, and have a diffuse connection – either wastewater or other kinds of stormwater coming out of pipes in a diffuse way to create a transition zone that has more complexity to it? Is there a way to reconnect some of that water directly into the back of wetlands, the way it used to be, and create these zones of brackish to salt marsh, and these big complex areas that we think are going to be very important for wildlife in the future?

Historically, there were different kinds of connections to the bay, some more connected while some other more disconnected. “Now we kind have like all or nothing: superconnected or underconnected or no connection at all. So we’re trying to think of ways in the future we can get back to a more diverse set of viable options that are good for how we deal with wastewater by essentially using it to create wildlife habitat and other ecological values.”

2-Design complexity and connectivity in the Baylands landscape.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_22This again gets at the idea that wildlife are going to need more options to survive in the more variable future,” Dr. Grenier said. As an example, in some restored marshes and even some older marshes, a lot of vegetative complexity has been lost, and there isn’t a lot of vegetative structure; this is a problem especially during high tide and other high water events for wildlife to get out of the water. “So the idea is to build some artificial islands that provide that topographic complexity that used to be there, and you actually just get out there and get muddy and build it, and the ones they’ve done so far have revegetated really well and seem to be working.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_24We also really need to think about connectivity,” she said. “I think for the terrestrial and wetlands side of the world which is where I come from, we often think that things are underconnected, things are fragmented, and we have to reconnect them, and that’s what this graph shows. These are different patches of tidal marsh all around the bay, and if you’re doing any kind of project, you could look at this how your project relates to the connectivity that’s already out there, and hopefully improves it.”

In some aquatic environments, we’ve probably created too much connectivity, Dr. Grenier said. “A good example is in the Delta where there have been a lot of channels added, so when we talk about designing connectivity, we have to think about what’s the appropriate level and what’s the appropriate way to create that functional connectivity.”

3-Restore and conserve complete tidal wetland systems.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_26We have to stop thinking tidal marsh; we need to start thinking full tidal wetland system,” she said. “What are all the different elements of a tidal wetland system? Here’s the marsh, but it’s also has a mudflat next to it and a subtidal area, and it has a transition zone to the upland – all of this is part of what makes this system function. We have to start thinking that way to create systems that are resilient into the future and we need to start restoring all elements of the system.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_27In addition to that, we need to think even at a larger scale, what are the processes that maintain that complete tidal wetland system? What are we doing in the watershed with how we manage sediment and freshwater that affects this system? What are we doing in the bay that affects the tidal marsh system?


4-Restore Baylands to full tidal action prior to 2030.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_29The earlier that you get the marshes restored, the sooner the former marsh restored to tidal action, the sooner you’re going to get it vegetated in providing habitat for wildlife and other ecosystem services,” she said. “It takes time for this transition to happen from here to here, and ideally you would actually have this marsh accrete and get up higher in the tidal frame so you have that elevation capital that’s going to help that marsh persist for longer.”


5-Plan for the Baylands to migrate.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_31There are many elements to this in terms of thinking about where habitats are going to go, how things are going to shift, how are you going to have the genetic material you need to colonize a new habitat,” said Dr. Grenier. “One of the ideas that’s out there is creating these horizontal levees or platforms for the Baylands to move up as sea level rises, and there are places where this is going to be more appropriate than others.”


6-Actively recover, conserve, and monitor wildlife populations to avoid bottlenecks and buffer population sizes.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_34We need to think about all of our species – our endangered species, our not endangered species, and even things that aren’t birds and mammals, she said. “We’d like to keep everything as much as we can,” she said. “Unfortunately we’re going to have to actually to do the monitoring that we’ve never found the funding to do. We’re going to have to actually know what’s happening with these populations on a finer time scale … In the absence of monitoring, we’re not going to know and we’re not going to be able to act, so we’re really mostly talking about being much more active and that probably means investing more and knowing what’s up with wildlife and then responding to the situations that arise.”

7-Develop and implement a comprehensive regional sediment management plan.

We’re all aware of how critical sediment is; it’s an important resource that we need to use wherever we can,” she said. “That means places that we’ve thought about a lot, like dredge sediment; it also means excavated sediment from the upland, we’ll take it where we can get it as long as it’s clean.”

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_38It also means rethinking watershed management to develop ways to safely bring sediment down creeks and other waterways and back into the Baylands. “There’s lots of examples of how there are marshes that are higher and more persistent near the mouth of these creeks because of the sediment loads that the creeks carry. It essentially forms a delta, and those are probably places that are going to persist a lot longer into the future for marshes.”

8-Invest in planning, policy, research and monitoring as critical to successful implementation.

This one is hard because there’s some really important work that needs to be done here particularly around policy and around figuring out how we can have a real adaptive management system going on for the Baylands,” she acknowledged. “It’s a big chunk to bite off and it’s not exciting. It’s sitting in meetings and making things happen … it’s an important aspect of what we need to do.”

9-Develop a regional transition zone assessment program.

6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_41 6-Grenier BEHGU Davis CC symposium 150606_woanim_v3_Page_43

The transition between the Baylands and the adjacent terrestrial areas was the subject of quite a bit of science in the update to the Baylands goals project, she said. “They came up with subzones of the transition zone, and these subzones are related to ecosystem services that they provide and they each do different things that are good,” she said. “There are markers that you can see in the field to identify where the transition zone is.”

10-Improve carbon management to prevent further subsidence, increase organic matter accumulation, reduce greenhouse gas emissions and sequester more carbon.

There are land management approaches that can do this, including restoring marshes and other wetlands,” she noted.

Visions and recommendations on various scales

In addition to regional recommendations, there is a vision for each subregion: north bay, south bay, central bay, Suisun bay, as well as segment level recommendations, so there are a lot of different scales at which we provide real details on what we think needs to be done, she said.

The report also identified recommendation highlights; Dr. Grenier noted that she had already discussed the first two, but the other three are also important. “We need to increase our coordination among stakeholder organizations,” she said. “We also need to create plans that factor in ecological outcomes after extreme events and other disasters. There are ways that the Baylands can get a double whammy after an extreme event; the event itself will harm wildlife populations and the habitats themselves just as they will harm human populations and our habitats, but in addition, our responses to those extreme events can be just as harmful. If there’s a big flood and we harden up a lot of the shoreline, we could have amplified effects from the tides and then those could cause further problems. So we need to really get out ahead of that and start working with the agencies that are responsible for making those kinds of choices, and making those kinds of response plans, and think about how can we talk to each other and come up with some outcomes that might be better ecologically for the long-term.”

And lastly, we need to engage the citizenry in advocating for the Baylands. “It’s not the core mission of a lot of our organizations, but in the long-term, if we want people to care about this resource, understand it and pay for it, they are going to need to have some level of engagement and so we’ve got to keep working on who do we partner with to make that happen, and how do we get those messages out there,” she said.

And with that …

JEREMY LOWE, Nature based adaptation to increase resiliency

Jeremy Lowe, senior environmental scientist with the San Francisco Estuary Institute, began by noting that sea level rise currently is projected to be between 12” and 36” by the year 2100.  He then used a series of pictures to illustrate what this means.

We need to think of a shoreline and landscape that can accommodate not just an amount of change but continuous change,” he said. “That’s partly is going to be us, partly the marshes, but it’s also it’s going to be how we as a society deal with it, how we protect ourselves, but eventually start to think about moving because we are seeing those issues already.”

8- v4 Lowe UC Davis 050615_Page_07He presented a picture from Marin County at the Sausalito on-ramp to the 101 showing flooding during king tides and noted that by 2030, you ‘d likely be able to take photos of similar flooding on a biweekly basis.

It’s not a large amount of flooding; it’s inconvenient, and that’s the problem,” he said. “Small amounts of flooding can be inconvenient. It’s going to interrupt business and it’s going to start having an effect because when it floods as it also leaves mud behind, so there’s a cleanup issue. So we need to start thinking about these sea level rise issues sooner rather than later.”

8- v4 Lowe UC Davis 050615_Page_09He then presented a graph of the Golden Gate tidal range with extreme water levels projected, and noted that in the future, the number of 1 in 10-year and 1 in 20-year events will be increasing as well. “If we place a levee that we design today to accommodate the 100 year water level with a bit of freeboard on top of that, it works for now, but by 2060 or so, could well be down to 1 in 2 years, so we’re going to have to do some things soon to maintain the levels of protection that we’re expecting to see around the bay.”

Levees are big and difficult to move because rebuilding in another place is expensive and we’ve tended to build right up against them, he said. “Our levee tends to separate between the urban landscape and the natural landscape, and in doing that, we’re going to have difficulty moving the places. We talk about moving things around quite glibly, but it’s going to be extremely difficult and it’s not going to be a short conversation. What we need to think about in the next four decades are ideas that allow the marshes to evolve and be dynamic and that can accommodate amounts of sea level rise change, but can do that within the constraints of the existing levee line that we’ve drawn for the areas that we’re protecting.”

That hopefully will buy us some time,” said Mr. Lowe. “We shouldn’t be wasting that time, we should be spending that time discussing how as a society, we can start to think about moving – the larger scale changes.”

8- v4 Lowe UC Davis 050615_Page_11We need to think about how to make our Baylands more resilient as we don’t have a very resilient system now, he said. “We’ve tended to manage it for all sorts of different reasons – for salt farm production, for flood risk management, but we haven’t thought of in a joined-up sort of way,” he said. “In the past, we’ve built projects for one purpose and we’ve optimized them and we’ve done that pretty well. We’ve optimized our salt farm production, we’ve optimized levees, but at the expense of other parts of the system.”

Mr. Lowe noted that there were a number of long-term projects going on around the bay, such as in the South Bay salt ponds and the Palo Alto area, that are designed to achieve specific goals and objectives and accommodate some changes. “They are starting to think about much larger scale, and they are starting to think about joined up ways of thinking, but in the future, we’re going to want to do even more.”

8- v4 Lowe UC Davis 050615_Page_13The Baylands project is just one part of many efforts going on in the bay to create more resilient communities; there are others, he said. “We’re not talking about restoration on its own, but restoration as part of an adaptation of an urban estuary to accommodate the changes that we see in the future, not just climate change, but changes like reduction of sediment supply and others, so we’re trying to make a more resilient system.”

Of course, the one thing that governs all is finance, Mr. Lowe pointed out. “We have to think about how we can make these acceptable strategies and options that we have, but also make them affordable and actually buildable.”

8- v4 Lowe UC Davis 050615_Page_15The goal is to restore the complete tidal marsh. “We’re trying to make a better bay by incorporating upland areas and by incorporating the subtidal areas,” he said. He noted that the transition area is usually dominated by the levees, so in many cases, the marsh, the marsh doesn’t have freedom to transgress with sea level rise, so we’re relying on its vertical accretion to maintain it with sea level rise. “So what we’re thinking about are other ways in which we can restore upland areas, but also provide a way in which the marshes can transgress by providing more upland transition zones, but also maintaining the levee in place.”

Mr. Lowe said they have done some projects moving back levees and incorporating wetlands into those. “Look at a lot of the work on the south bay salt ponds and the work in the Napa,” he said. “We’re taking an outward levee and we’re moving it inland and recreating the marsh, We call that restoration, but what we’re really doing is we’re providing a wider marsh and we’re gaining the benefits that we have from that for flood risk management.”

8- v4 Lowe UC Davis 050615_Page_18There are a lot of opportunities in the bay, he noted. “We do have a lot of sediment but it tends to be in the wrong place … and we’ve tended to put our water into pipes and so on,” he said. “We used to have sediment coming into the back of the marshes, we used to have freshwater coming into the backs of the marshes, but we’ve put those in canals and pipes and we’ve separated them out from the marshes, so just at the time when our marshes need the most help to accrete and keep up with sea level rise, we actually have a system which is really designed to make them unresilient, so what we’re looking for is how can we put those back … how can we incorporate these ideas to make a more resilient shoreline.”

8- v4 Lowe UC Davis 050615_Page_20He presented a general layout, saying that one idea they have been thinking about is behind the existing tidal marsh and the mudflat, what about building some upland areas behind it? “Low slopes, 1:30, 1:50, directly in front of the levee,” he said. “Not the steep slope, but emulating the upland areas that we’ve lost in the bay and allowing transgression of these marshes over time and providing an area of upland habitat refugia.”

Mr. Lowe acknowledged that in some places where this has been done, they tend to be weedy messes. “Just recreating the topography isn’t sufficient; it’s the hydrology as well,” he said. “We need to allow a salinity gradient to develop in these areas by introducing water at the back of the marsh and seeping them through … Allowing water to seep through the backs of marshes might be a way to sustain upland vegetation on these areas.”

One idea is to use treated wastewater effluent. “We have that at the moment going under the marshes in big pipes,” he said. “Maybe we can treat it and put some of the final polishing in through slopes, but supporting the wet meadow upland riparian type of vegetation we could have on these slopes, and then water coming down into the back of the marshes, creating the brackish marshes that we’ve lost and then coming up into the tidal salt marsh, so a more historic ecotone that we have lost in the bay.”

There are a lot of immediate co-benefits to this project besides sea level rise adaptation, such as flood management benefits, habitat benefits, and even wastewater benefits, he said. “The advantage of the wastewater is that they generate their own revenue streams, so not only more resilient in terms of the landscape, but it could be more resilient in financial ways.”

8- v4 Lowe UC Davis 050615_Page_23He then presented a diagram of the Oro Loma Horizontal Levee Project, a proof-of-concept project being built at the back of the Oro Loma Wastewater Treatment Facility. “The reason why its built there is because everything I’ve described is unpermittable, illegal, unfeasible, and unfundable so you have to build it in a place where that doesn’t matter so much, and that is in dry land in this area over here. It’s separate from the bay and any water we use comes out of the water treatment facility and goes straight back in again, so we can play around with it. It’s not part of a flood risk management project so if it doesn’t keep the water out, it doesn’t matter so much. To pay for it, this also doubles up as wet weather equalization facility to assist the wastewater people.”

8- v4 Lowe UC Davis 050615_Page_25The study focuses on the upland areas, so UC Berkeley students are testing various hypotheses. “Our goals are to have native species, so we have native species going to be planted on the slope and we’re using local analogs to drive the planting schemes … because we have a short time scale, we have to do the science, we have to do the engineering, we have to do the politics and the financing simultaneously. It’s not how we used to do things.

8- v4 Lowe UC Davis 050615_Page_26It’s very complex, but the process is important because it’s starting the conversation between a large number of people. “In the longer term, we’ve got to start deconstructing, decentralizing some of our large infrastructure in place,” he said. “SFEI is also looking at what used to be large landscape scales to see if we can start emulating some of those historic systems around the bay so we can take advantage of the natural resiliency of these systems, but emulate them to fit the modern urban estuary.”

The very last piece is the adaptation strategy,” he said. “It’s not measured in years because we have an uncertain future; it’s measured in feet. Our existing marshes can accommodate a certain amount of sea level rise, but then they could start falling behind, so we need to start thinking of new ways of managing and new ways of thinking about our systems. We have to think about that soon because it takes a long lead time to permit and raise money, so we need to start making decisions now.

Jeremy Lowe
Jeremy Lowe

If sea level rise is going to accelerate, then things are going to change more rapidly in the later part of the century, so we’ve got to start thinking about those even now because those are bigger changes,” he said. “If we get to the end of the century and it’s a high as four or five feet, we’re going to have to think about realigning, moving people, and changing things. Otherwise our adaptation might be slightly different than that and it might not be the most acceptable way to live our lives in the future.”

Thank you.”


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