Richardson Bay Resilience
What is the County of Marin doing to plan for the impacts of climate-induced sea level rise and flooding?
WHAT'S HAPPENING NOW?
Richardson Bay in Marin County is known for its dramatic landscape from the iconic views of Mt. Tam to the dynamic conditions along the Bayshore.
Climate change poses serious challenges to many of the public agencies and private landowners that are responsible for maintaining and ensuring the safe use of roads, trails, open spaces, buildings, and critical infrastructure. But the impacts go beyond the immediate shoreline to affect the entire community.
As you scroll through the site, we’ll discuss “WHAT'S HAPPENING NOW?” with regards to flooding today and anticipated sea level rise (SLR) projections. “HOW WILL SLR IMPACT US?” dives into various impacts beyond the shoreline and we ask you to show us where you've experienced flooding impacts on a map. “WHAT'S BEEN STUDIED?” summarizes recent and ongoing studies led by various county agencies. “WHAT'S POSSIBLE?” looks at a few of the well-known problem areas and collects potential adaptation strategies for each location. Finally, “WHAT DO YOU THINK?” provides an opportunity for additional community feedback and resources related to SLR impacts.
Flooding Today
Residents and visitors to Richardson Bay know all too well about many of the ongoing flooding issues that affect the shoreline. Large rain events and high tide conditions cause disruptive flooding multiple times a year. Winter King Tide events also give some insights as to how different areas will permanently flood as sea levels rise throughout the century. Check out the California King Tides Project for more great photos.
As a comparison to the video above, watch the computer model that shows how water moves through this area to flood the road, parking areas, and trail. The solutions are complicated because water is coming from so many different parts of the shoreline. Anticipated climate changes like sea level rise and increased storm events will worsen many of these present-day flooding challenges over the next decades.
Sea Level Rise Projections
The County of Marin completed a Vulnerability Assessment in 2017 to understand the anticipated impacts of sea level rise along the Bayshore known as BayWAVE. BayWAVE documented three different inundation scenarios at 10, 20, and 60 inches of permanent tidal inundation (plus each with the surge effects of a 100-year storm) corresponding with near-term (scenario 1&2), mid-term (scenario 3&4) and long-term (scenario 5&6) planning horizons. Since that publication, state guidance has been updated with higher potential water levels in the future. The range of projections based on human intervention to the process makes planning efforts more difficult, but what’s certain is that all projects must be adaptable, not only to mid-century conditions, but ought to be capable of adaption as sea levels continue to rise.
Throughout this story, we’ll focus on the near-term projections shown in BayWAVE Scenario 2 which is defined as 10 inches of sea level rise plus a 100-year storm event. The goal is to show that while long-term sea level rise is difficult to predict and plan around, near-term levels will have serious impacts that are imminent.
Want to explore projected sea level rise scenarios around the Bay? Visit the Adapting to Rising Tides webmap.
HOW WILL SLR IMPACT US?
How will these risks impact all of us if we don't address them?
The following series of maps explores the regional impacts based on BayWAVE Scenario 2, 10 inches of sea level rise and a 100-year storm event. Scroll through the maps to explore the impacts to commutes (bikeways, private vehicles, and public transit), access to emergency services, and access to parks, trails, and open space areas.
Click the icon on the bottom left of the maps in order to open the legend to know more.
COMMUTE
Bikeways and Private Vehicle Trips
Thousands of private vehicle trips per day (30,000 at Manzanita alone) could be affected by sea level rise inundation, creating large scale traffic congestion and rerouting.
Zoom into key areas:
Sources: Our Coast, Our Future (2016); County of Marin Dept. of Public Works (2020).
COMMUTE
Public Transit
As with private vehicles, transit riders will also experience similar degrees of disruption, with fewer options to shift routes.
Zoom into key areas:
Sources: Our Coast, Our Future (2016); Marin Transit (2019); Golden Gate Transit (2019).
COMMUTE
Traffic Rerouting due to Inundation
Because of this inundation, travellers will look to other routes that are not necessarily designed for the number of trips.
Sources: U.S. Census Bureau (2016); County of Marin Dept. of Public Works (2019).
EMERGENCY SERVICES
Regional Hospital Access
Due to inundation, access to hospitals will be compromised in certain locations. Explore this map to understand impacts to hospital access by neighborhood.
Sources: U.S. Census Bureau (2016); County of Marin Dept. of Public Works (2020).
Ocean lifeguard and Tam Valley resident talks about flooding
Be aware of your surroundings and adjust accordingly. Everyone has a responsibility to play a part. We live here in Marin together. Flooding is happening and we need to keep the conversation going and be open minded about how we’re going to deal with it.
RECREATION
Paths and Parks Access
Inundation will have an impact on access to local and regional recreation spaces. Parks, open spaces, and access points, have the potential to become submerged. Regular inundation will also threaten the health of tidal wetlands including Bothin Marsh.
Zoom into key areas:
Sources: Our Coast, Our Future (2016); County of Marin Dept. of Public Works (2020); Metropolitan Transportation Commission (2021); Marin Transit (2021)
Tell Us What You've Seen
What We've Heard
WHAT'S BEEN STUDIED?
The following series gives an overview of some of the past and ongoing efforts that various agencies and community groups have and are undertaking to document and plan for anticipated sea level rise impacts around Richardson Bay.
Past and Ongoing Efforts
WHAT'S POSSIBLE?
Communities around Richardson Bay are already having conversations about how to prepare for our changing environment. In this section, we'll share the youth perspective, discuss adaptation tools and walk through site-specific examples for adaptation.
Youth voices at the 2020 One Tam Virtual Summit on Climate: Change and Resilience
The younger generation will be the most impacted by climate change and their voices are an important part of planning for the future. One Tam's virtual series on Climate Change and Resilience included some student voices from the LINC (Linking Individuals to their Natural Community) program. Check out the link to the video below to hear students discussing topics concerning sea level rise, environmental justice, and the potential impacts on their neighborhoods.
ADAPTATION TOOLS
Sea level rise is a critical hazard whose effects will unfold over time. Responding to it and adapting our environment will require ingenuity, resources, and collaboration. This section describes some of the strategies we can use, alone or in combination, to adapt our vulnerable landscape, from infrastructure to sensitive habitat. We present these strategies in four categories: Nature-Based Strategies, Shoreline Hardening, Adapting Transportation, and Adapting Development.
Nature-Based Strategies
Coarse beach at Aramburu Island, Marin County Image: FWS Pacific Southwest
These approaches are “green infrastructure” designed to respond to natural processes, or mimic natural processes, in ways that provide protection to vulnerable coastal communities. Strategies may create landforms or vegetation communities that are found naturally along our shorelines but may have been lost or degraded, and which naturally counteract sea level rise impacts. Strategies may also address “upstream” processes, by creating or restoring natural drainage patterns, slowing stormwater and allowing sediment to settle in nearshore areas.
Shoreline Hardening
Sea wall at Embarcadero, San Francisco Image: San Francisco Chronicle
This set of strategies refers to more traditional “gray” infrastructure used to provide coastal protection. Shoreline hardening toolbox includes flood walls and bulkheads, riprap-armored shorelines, levees and dikes, breakwaters, jetties and groins. These are often constructed with concrete, rock and steel. They provide well-tested protection, while also tending to displace some of the hazardous dynamics of sea level rise to other coastal areas.
Adapting Transportation
Elevated levee at Hamilton Wetland, Novato Image: Stephanie A. Miller
In many places, our shorelines include transportation corridors—roads, highways, trails and rail lines. Some adaptation strategies are transportation specific. These include redesigning roadways with green infrastructure to detain and clean stormwater runoff, elevating roadways and trails on levee embankments, realigning highways, building long-span causeways, and even floating trails.
Adapting Development
The adapting development category includes a variety of means to adapt our buildings to sea level rise. Strategies include adapting existing structures to a changing landscape by elevating buildings; enabling new structures to be designed to accommodate sea level rise with “floodable” design elements or as floating buildings; and incentivizing a transition from existing building areas to sites where development will be less vulnerable.
Site-Specific Approaches
Site-Specific Approaches
We've highlighted a few key areas along the Richardson Bay shoreline that are impacted most in the near-term: Miller Avenue, Tam Junction, Manzanita, and Marin City. The site-specific approaches presented below are ideas and intended to inform a community conversation about how we can work together towards solutions.
Miller Avenue
Present Day
The Miller Avenue corridor is a critical multi-modal transportation link to and from Mill Valley.
Miller Avenue
No Action with BayWAVE Scenario 2
Without adaptation actions, we see that the roads and pathways will routinely flood and cause infrastructure to degrade with regular tidal inundation. The sensitive tidal marsh habitat and adjacent low-lying neighborhoods will be threatened. (BayWAVE Scenario 2: 10 inches of SLR and 100-yr storm)
Miller Avenue
Multi-Benefit Approaches
The county and city could collaborate with the community to engineer a levee that elevates the road and pathway. With engineering to address road safety and stormwater drainage, this levee could provide protection from the tides for this part of the shoreline through the mid-century.
The Evolving Shorelines Project at Bothin Marsh is exploring how to integrate a new elevated pathway with an ecotone slope that could maintain this important habitat into the mid-century. This approach would temporarily impact protected wetland habitat, however, the Bay Conservation Development Commission and other regulatory authorities are developing new policies to allow for beneficial fill placement that makes these novel sea level rise adaptation strategies feasible.
The Evolving Shorelines Project is also considering the potential for creation of beaches along the marsh edges at Bothin Marsh. This would replicate conditions once common throughout the San Francisco Bay and could provide the short-term benefits of reducing shoreline erosion and dampening the impact of storm surges. This approach would require an appropriate cobble sediment source and regulatory approval for placing beneficial fill in the Bay.
The majority of development in low-lying areas surrounding Arroyo Corte Madera del Presidio is built on former tidal marsh land and when storm events coincide with high tides, there is not much room for the water to go. Residents and businesses can work with cities and counties to update land use policies to allow for elevation of structures above flood levels.
Tam Junction
Present Day
The Tam Valley businesses and residents near Shoreline Highway are located in a low-lying area that was formerly part of Bothin Marsh.
Tam Junction
No Action with BayWAVE Scenario 2
Without adaptation actions, the Shoreline Highway, Bay Trail, adjacent properties and marsh habitats will be inundated. (BayWAVE Scenario 2: 10 inches of SLR and 100-yr storm).
Tan Junction
Multi-benefit Approaches
A 'complete green street' approach along Shoreline Highway could provide improved transportation benefits, accommodate for flooding protection, and offer safer modes of travel for pedestrians and bicyclists. This effort would require significant coordination between public and private sectors.
The Evolving Shorelines Project is considering the potential for the creation of coarse beaches to protect the marsh edges from eroding at Bothin Marsh. As mentioned in the Miller Avenue example, this would replicate conditions once common throughout the San Francisco Bay. This approach would require an appropriate cobble sediment source and regulatory approval for placing beneficial fill in the Bay.
The Evolving Shorelines Project at Bothin Marsh is exploring how to integrate a new elevated pathway and ecotone slope that could maintain this important habitat into the mid-century and beyond. Similar to the approach mentioned above in the Miller Avenue example, novel beneficial fill placement strategies are being explored here. New alignments for the pathway that minimize the impacts to the marsh are also being considered. Follow the project to stay involved as this planning effort progresses with your input.
A 'Super Levee' approach for the property owners along Shoreline Highway and Coyote Creek would require coordination to elevate existing and new structures as part of a flood protection project. This would require significant public and private property coordination and regulatory compliance across a larger community area which could benefit from these improvements.
Manzanita
Present Day
The convergence of Highway 101 and Shoreline Highway along the Bay is one of the areas most notorious for flooding today.
Manzanita
No Action with BayWAVE Scenario 2
Without adaptation actions, segments of Shoreline Highway, adjacent freeway ramps, Park-and-Ride lots, and pathways are inundated. Some parts of the commercial district are also impacted in the near-term. (BayWAVE Scenario 2: 10 inches of SLR and 100-yr storm).
Manzanita
Multi-Benefit Approach
The Mill Valley-Sausalito Multi-use Pathway, which is also part of the Bay Trail network in this area, could be re-designed as part of an elevated levee structure in this area. Multiple alignments are possible and could be coordinated with the Bothin Marsh adaptation approach mentioned above. Coordination with nearby businesses would be required to ensure private access is maintained.
Floating structures along the Bay are already a common approach in this area. These structures and their utilities would need to be updated to accommodate higher and higher tide levels throughout the century, which may become cost prohibitive.
In some locations along the Bay, the property ownership extents or ecological conditions may not make it possible for nature-based approaches to work in isolation. Sea walls may be needed to limit the extent of high tides in the area. In this case, a series of sea walls could work in collaboration with pumps to protect the area.
In the long-term planning scenarios, it's possible that retreat plans may be appropriate for these areas. Especially if other options mentioned above, like floating structures, or sea walls are not adequate or financially feasible to maintain.
Marin City
Present Day
The Marin City and Sausalito areas are connected to the region via Highway 101.
Marin City
No Action with BayWAVE Scenario 2
Without adaptation actions in the near-term, private properties and local roads and pathways will experience permanent inundation. Areas that already flood during storm events today, like the areas along Donahue Street near Highway 101, would experience longer periods of inundation, while they wait for tides to recede before they could drain. (BayWAVE Scenario 2: 10 inches of SLR and 100-yr storm).
June Farmer, Marin City People's Plan speaks to flooding issues in the community.
Marin City
Multi-Benefit Approach
Similar to the Manzanita approach above, the Mill Valley-Sausalito Multi-use Pathway could be re-designed as part of an elevated levee structure in this area. Coordination with nearby property owners would be required to ensure private access is maintained. There is potential to include an ecotone slope in some areas here as well.
Sea walls may be needed to limit the extent of high tides in the area, especially along some of the local roads in the near-term. Longer-term scenarios will require bigger impact solutions to protect the highway. In this case, a series of sea walls could work in collaboration with elevated levees to protect the area in the near-term.
Tide gates may be necessary in multiple locations where existing stormwater drainages meet the Bay. In Marin City, it's especially important to design a robust stormwater system that connects to the detention pond under Highway 101, directly to the Bay. As sea levels rise, there may be a need to augment the tide gate to include pumps.
Floating structures along the Bay are already a common approach in this area. These structures and their utilities would need to be updated to accommodate higher and higher tide levels throughout the century, which may become cost prohibitive.
The detention pond in Marin City is currently being studied as part of a larger improvement and maintenance effort. There may be more detention ponds needed around the area to accommodate local storm flooding as sea level rise.
WHAT DO YOU THINK?
There’s more to do! These collections of strategies each present major trade offs that will need to be resolved within the community. The adaptation process will continue to evolve over the coming decades and will require major coordination and cooperation partnerships.
Tell Us What You Think
After looking at the potential adaption strategies above we would like to know your priorities and which strategies resonate with you. We will continue to engage with the community to discuss strategies to adapt in the future.
Community Call to Action
Supervisor Stephanie Moulton-Peters speaks to the importance of community collaboration and adaptation planning.
Want to Learn More?
- Adapting to Rising Tides Flood Explorer : This website helps Bay Area communities explore current and future flooding in their neighborhood due to sea level rise and storm surges.
- National Park Service Climate Change Subject Site: Sea Level Change : Explore what we know about how sea level rise will affect National Parks.
- State of California Sea-Level Rise Guidance : Summarizes available science to support and inform planning for sea-level rise in California.
- Marin Watershed Program : Provides insight into the projects taking place in Marin County.
- Tam Valley Neighborhood Response Group
Contact for More Information
Chris Choo , Principal Watershed Planner, County of Marin
Data Sources
Our Coast Our Future Sea Level Rise (Used throughout the Story Map for BayWAVE Scenario 2 )
- Ballard, G., Barnard, P.L., Erikson, L., Fitzgibbon, M., Moody, D., Higgason, K., Psaros, M., Veloz, S., Wood, J. 2016. Our Coast Our Future (OCOF). [web application]. Petaluma, California. www.ourcoastourfuture.org. (Accessed: February 8, 2021).
Roads (Used throughout the Story Map to show inundation of the transportation network)
- County of Marin Department of Public Works. San Rafael, C.A. Road on marinmap.org (Accessed: September 21, 2020).
Bikeways (Used for Recreation: Paths and Parks Access and Commute: Bikeways and Private Vehicle Trips maps)
- County of Marin Department of Public Works. San Rafael, C.A. Bikeway on marinmap.org (Accessed: November 18, 2020).
Census (Used for Emergency Services: Regional Hospital Access map)
- U.S. Bureau of the Census. TIGER/Line: American Community Survey, 2016 estimates. Washington, D.C.: Bureau of the Census. (Accessed June 11, 2019).
SF Bay Trail (Used for Recreation: Paths and Parks Access)
- Metropolitan Transportation Commission/Association of Bay Area Governments. San Francisco, California. opendata.mtc.ca.gov (Accessed: January 5, 2021).
Transit (Used for Commute: Public Transit map)
- Marin Transit. (2019). Transit routes, stops, and average daily trips.
- Golden Gate Transit. (2019). Transit routes, stops, and average boardings for October 2019.
