Resilient Coastal Roads
California's Key Insights on Protecting Transportation Infrastructure from Sea-level Rise and Flooding
You could wrap earth 2.5 times with the length of coastal roads at risk of flooding in the U.S.
Initial estimates indicate that approximately 60,000 miles of coastal roads are at risk from storm surge, flooding, and inundation, in the United States. Corresponding coastal erosion processes will further impact many additional miles of road.
Rising seas already flood and erode our transportation systems around the country. Future impacts will be worse, further disrupting the daily lives of Americans, upsetting coastal economies, risking public safety, impeding recreational area access, and degrading critical habitat for rare and endangered species.
In California, the California Department of Transportation (Caltrans) and other asset owners in the coastal zone are repairing and adapting many sections of transportation systems to address flooding and erosion while ensuring the vitality of coastal resources along transportation corridors now and into the future. This approach represents an important paradigm shift away from reactive individual asset maintenance actions to more holistic and collaborative transportation system planning and management.
Current scientific information makes it clear that we must take action now to have a resilient transportation system
It is known with complete certainty that sea levels are going to continue to rise in California and it is cheaper to act now. For projections of how much it will rise in the next 5-30 years, there is a narrow range of expectations and there are reliable strategies for planning to pursue long term adaptation strategies with less certain SLR projections between 2050 and 2100. This means we have both the SLR information and financial impetus needed to take action now as part of a long term strategy.
Projected increase in relative sea level change in Los Angeles for five different sea level rise scenarios. The low and high scenarios represent the minimum and maximum of plausible future sea level rise.
The challenges are immense but there are solutions.
Continue reading to learn how California is protecting its infrastructure and coastal resources, what informational resources are available, and what kinds of additional investment are needed.
Cardiff State Park Living Shoreline Project highlights a more holistic planning strategy than temporary shoreline armoring
Overview
A unique 20 year partnership between the California Coastal Commission and California Department of Transportation (Caltrans) has provided an important foundation for the state to more holistically approach the threats that climate change, especially SLR, present to critical infrastructure along the 1,200 mile California coast. Specifically, the partnership is improving the department's response to SLR with alternative approaches such as: applying a corridor perspective, avoiding loss of coastal resources, pursuing phasing strategies, and incorporating nature-based measures.
Focusing on integrating coastal resource policies into transportation project planning, design, and environmental review, the Coastal Commission and Caltrans continue to expand their work with other stakeholders to address the threats and uncertainties that climate change poses to shoreline communities, industries and economically- and environmentally- valuable coastal resources.
Try This: Scroll down the page to explore the four key insights of resilient transportation resulting from this partnership or choose a link to an insight of interest from the banner above.
Key Insight 1: Corridor Approach is Essential
The challenge of sea-level rise cannot be solved on a project-by-project basis. The standard approach of focusing improvements on one isolated asset at a time, such as a bridge or culvert, does not ensure a fully functional corridor. The corridor approach to planning includes examining all interconnected assets and making planning and investment decisions that will ensure travelers reach their destinations now and in the future.
The map below highlights case studies where Caltrans and the Coastal Commission are working together to apply a corridor planning perspective.
Corridor Approach Overview
We must shift transportation infrastructure planning and programming to the whole corridor perspective. This requires an understanding of how different transportation assets like roadway segments, bridges, and culverts will operate in concert together over the short-, medium-, and long-term to provide continual corridor-level service. For example, individual assets, like bridges, must be considered in connection with the adjoining roadway sections when evaluating exposure and scoping potential adaptation strategies, including elevation and relocation, which could make the entire corridor more resilient to sea-level rise. Corridor planning could include phased reconfiguration of all or some of the assets that make up the corridor over the longer term.
Eureka Arcata Hwy. 101 Corridor
Connecting the two cities of Eureka and Arcata, this highly vulnerable six-mile stretch of Highway 101 runs along Humboldt Bay. Some areas of the highway will become inundated with as little as one foot of sea-level rise. Recognizing that certain locations will be threatened by SLR effects at different times, Caltrans is working with the Coastal Commission, local municipalities, the Department of Fish and Wildlife and the engineering department at CalPoly Humboldt on a phased adaptation plan that will address vulnerabilities of state and local assets, ensuring long-term transportation resiliency of the corridor while protecting coastal resources.
Pacific Coast Highway Oxnard - Santa Monica Corridor
State Route 1 between Oxnard and Santa Monica primarily hugs the shoreline along this extremely constrained corridor. Many roadway segments and adjacent coastal resources are already exposed to erosion and undermining wave action.
Devil's Slide Tunnel Highway 1
The Devil’s Slide, a vital segment of Highway 1 in San Mateo County connecting the towns of Montara and Pacifica, was increasingly threatened by erosion and landslides exacerbated by climate change. It became subject to road closures in the mid-1990s from numerous rockslides, prompting difficult decades-long conversations surrounding how to best adapt the roadway for long-term resilience. The Devil's Slide Tunnel Highway 1 Project, completed in 2014, rerouted this segment of Highway 1 away from the vulnerable coastline by creating climate-resilient tunnels. The old highway was repurposed for the California Coastal Trail, providing additional coastline access for bicyclists and pedestrians.
Corridor Approach Overview
We must shift transportation infrastructure planning and programming to the whole corridor perspective. This requires an understanding of how different transportation assets like roadway segments, bridges, and culverts will operate in concert together over the short-, medium-, and long-term to provide continual corridor-level service. For example, individual assets, like bridges, must be considered in connection with the adjoining roadway sections when evaluating exposure and scoping potential adaptation strategies, including elevation and relocation, which could make the entire corridor more resilient to sea-level rise. Corridor planning could include phased reconfiguration of all or some of the assets that make up the corridor over the longer term.
Eureka Arcata Hwy. 101 Corridor
Connecting the two cities of Eureka and Arcata, this highly vulnerable six-mile stretch of Highway 101 runs along Humboldt Bay. Some areas of the highway will become inundated with as little as one foot of sea-level rise. Recognizing that certain locations will be threatened by SLR effects at different times, Caltrans is working with the Coastal Commission, local municipalities, the Department of Fish and Wildlife and the engineering department at CalPoly Humboldt on a phased adaptation plan that will address vulnerabilities of state and local assets, ensuring long-term transportation resiliency of the corridor while protecting coastal resources.
Essential for this approach are the scientific studies, such as this one , that have developed data on the flooding vulnerabilities of the corridor as it intersects with different topography and historic development such as aging bayside dikes. Additional scientific research is now providing valuable insights into the role that groundwater also will contribute to flooding in the future. These continuing studies importantly improve our understanding of potential solutions such as nature-based infrastructure, causeways, elevated roadway berms and other protection strategies.
Scroll through the images above or read this news article to find out more (North Coast Journal, Nov. 11, 2021).
Pacific Coast Highway Oxnard - Santa Monica Corridor
State Route 1 between Oxnard and Santa Monica primarily hugs the shoreline along this extremely constrained corridor. Many roadway segments and adjacent coastal resources are already exposed to erosion and undermining wave action.
Ongoing erosion has required Caltrans to request emergency permits for roadway repairs at more than 20 sites over the years. For example, two secant (retaining) walls were installed in Point Mugu State Park after severe surf erosion and cracks in the roadway shoulder occurred. The secant walls, constructed in 2021, are authorized to stabilize the Pacific Coast Highway until 2051 at which point a longer-term plan, a comprehensive Multimodal Corridor Management Plan which is anticipated to be set by early 2025, will be the first of its kind to more broadly consider the long-term resiliency of this entire Pacific Coast Highway corridor. In conjunction, the County of Ventura is in the process of completing an update to the Local Coastal Program which will include adding sea level rise policies and provisions from the Ventura County Resilient Coastal Adaptation Project .
Devil's Slide Tunnel Highway 1
The Devil’s Slide, a vital segment of Highway 1 in San Mateo County connecting the towns of Montara and Pacifica, was increasingly threatened by erosion and landslides exacerbated by climate change. It became subject to road closures in the mid-1990s from numerous rockslides, prompting difficult decades-long conversations surrounding how to best adapt the roadway for long-term resilience. The Devil's Slide Tunnel Highway 1 Project , completed in 2014, rerouted this segment of Highway 1 away from the vulnerable coastline by creating climate-resilient tunnels. The old highway was repurposed for the California Coastal Trail, providing additional coastline access for bicyclists and pedestrians.
Key Insight 2: Phased Adaptation
A phased adaptation approach includes pursuing short- and medium-term, incremental measures to maintain transportation services in the face of coastal hazards in ways that do not prejudice future opportunities and that also buy additional time to design longer-term and more resilient adaptation strategies.
Phased Adaptation Overview
Phased adaptation approaches are essential to maintain the functioning of healthy ecosystems and critical infrastructure over time. Phasing adaptation activities is needed given the complexity of adapting structures like highway systems, the accelerating and uncertain pace of sea level rise, and the significant vulnerabilities that are expected to emerge over time within the built and natural environment. A phased adaptation approach can also include necessary initial actions to stabilize infrastructure in emergency situations, such as armoring, sand replenishment or other short-term living shoreline accommodation strategies, or temporary floodproofing and elevation. These interim measures are followed by further analysis and planning to develop longer term adaptation strategies like relocation that will result in more resilient longer-term protection. Overall, phased adaptation planning recognizes that these planning and design undertakings are complex in many ways, including adequate evaluation of climate change risk over the full asset life cycle, engaging local communities in the visioning of their climate change future, and securing the funding resources to realize the chosen adaptation strategies ahead of damaging and irreversible impacts.
Piedras Blancas, San Luis Obispo County
Piedras Blancas is a 3-mile-long section of Highway 1 in northern San Luis Obispo County, near Big Sur, that was relocated inland in response to chronic shoreline erosion. Initially, temporary rock slope protections were permitted for installation along sections of the highway while devising long-term alternatives. This allowed for consideration of a full range of infrastructure adaptation options that also protected natural resources, ultimately resulting in relocation of the highway inland with a 100-year design life. When bridges were constructed to daylight previously constrained streams and the new inland highway was completed, the old highway area was restored and the temporary rock protections were removed. These actions allowed the natural beach and bluff processes to return in conjunction with the mitigation of project impacts through various restoration activities.
Pleasure Point Coastal Access
Pleasure Point is a famed surfing spot in central Santa Cruz County. For years, ocean waves eroding the bluffs threatened adjacent trails, a county road, public utilities, and other development.
San Jose Creek Bridge Replacement Project
The San Jose Creek Bridge Replacement Project at State Route 217 in Santa Barbara County adapts infrastructure for threats associated with long-term sea level rise. The four-lane freeway bridge, constructed in 1963, is susceptible to flooding in the event of extreme sea level rise, according to high-end climate model estimates. To prepare for a range of future SLR, Caltrans proposed a new bridge to be engineered with features that will allow for the bridge to be elevated up to 3.5 feet higher by jacking without replacing major infrastructure components. Specifically, this adaptive design includes additional rebar with couplers and pins that can extend the bridge columns. The proposed bridge will also feature wider shoulder widths and a bicycle and pedestrian path on the northbound side to fit standards and accommodate multimodal transportation. Construction of the new bridge is anticipated to be completed by July 2026 and the site will be continuously monitored and formally evaluated by 2065 to determine whether to raise the bridge by 3.5 feet.
Phased Adaptation Overview
Phased adaptation approaches are essential to maintain the functioning of healthy ecosystems and critical infrastructure over time. Phasing adaptation activities is needed given the complexity of adapting structures like highway systems, the accelerating and uncertain pace of sea level rise, and the significant vulnerabilities that are expected to emerge over time within the built and natural environment. A phased adaptation approach can also include necessary initial actions to stabilize infrastructure in emergency situations, such as armoring, sand replenishment or other short-term living shoreline accommodation strategies, or temporary floodproofing and elevation. These interim measures are followed by further analysis and planning to develop longer term adaptation strategies like relocation that will result in more resilient longer-term protection. Overall, phased adaptation planning recognizes that these planning and design undertakings are complex in many ways, including adequate evaluation of climate change risk over the full asset life cycle, engaging local communities in the visioning of their climate change future, and securing the funding resources to realize the chosen adaptation strategies ahead of damaging and irreversible impacts.
Note the concept of time horizons is important to all transportation planning and investment but especially phased adaptation. From a coastal SLR planning perspective, the short-term generally refers to approximately 0- to 20 years, medium-term 20 to- 50 years, and long-term 50 to 100 years. Similarly, from a transportation project-level perspective, the design life—or expected service lifetime—of transportation assets generally are from 0 to 20 years (e.g. pavement), 20 to 50 years (e.g. concrete barriers), and 50 to 100 years (e.g. bridges). Complimenting these time horizons, many SLR projections and policies use the years 2030, 2050, and 2100 as benchmarks to evaluate SLR risk and inform development and resource management decisions along the coast.
It is also important to highlight the relationship between critical transportation infrastructure facilities—like bridges or a collection of assets along an exposed roadway in a corridor—have design lives of 75-100 years and provide essential services supporting the movement of people and goods which, if disrupted by SLR hazards, can prevent vital evacuation and emergency response services in the short term, as well as cause widespread supply chain disruptions which can result in major economic impacts at the local, regional, and even international levels. Accordingly, many policies in California’s coastal management program expect critical infrastructure projects to demonstrate that they are properly designed to avoid coastal hazards over the full asset lifecycle in order to qualify for coastal development permits. In a complimentary fashion, FHWA per 23 CFR § 515.5 also defines asset life-cycle planning as “a process to estimate the cost of managing an asset class, or asset sub-group over its whole life with consideration for minimizing cost while preserving or improving the condition.” As these critical infrastructure assets can be very costly to replace or adapt to SLR, it is important to consider these longer time horizons in today’s decisions about investing public funds. Finally, another important aspect of timing for large capital investment projects is that the programming, funding and planning to initiate projects, complete design and environmental review, and obtain necessary permits can take 10 years or more before construction begins; therefore, that time period is also a significant consideration in adaptation planning. Visit this guide for more for more information on California Coastal Act policy direction for planning and designing critical infrastructure .
Piedras Blancas, San Luis Obispo County
Piedras Blancas is a 3-mile-long section of Highway 1 in northern San Luis Obispo County, near Big Sur, that was relocated inland in response to chronic shoreline erosion. Initially, temporary rock slope protections were permitted for installation along sections of the highway while devising long-term alternatives. This allowed for consideration of a full range of infrastructure adaptation options that also protected natural resources, ultimately resulting in relocation of the highway inland with a 100-year design life. When bridges were constructed to daylight previously constrained streams and the new inland highway was completed, the old highway area was restored and the temporary rock protections were removed. These actions allowed the natural beach and bluff processes to return in conjunction with the mitigation of project impacts through various restoration activities.
The project thus improved a number of natural, scenic, and recreational resources. Wetland and lagoon systems were restored, creating habitat for many important coastal species, including the elephant seal, which is a major draw for the local tourism economy.
Learn more: Scroll through the images above to see multi-modal access and resilience improvements to this roadway.
Pleasure Point Coastal Access
Pleasure Point is a famed surfing spot in central Santa Cruz County. For years, ocean waves eroding the bluffs threatened adjacent trails, a county road, public utilities, and other development.
Emergency rock slope protections were used numerous times in attempts to contend with coastal erosion hazards, but vulnerabilities remained and much of the beach and access were being lost to the growing footprint and erosional effects of multi-ton rocks. After considering detailed studies and stakeholder engagement, it was determined that a full-bluff concrete seawall was the most advantageous approach to protect infrastructure and recreation at this urban location at this point in time as a medium-term adaptation strategy, until longer-term strategies can be developed.
San Jose Creek Bridge Replacement Project
The San Jose Creek Bridge Replacement Project at State Route 217 in Santa Barbara County adapts infrastructure for threats associated with long-term sea level rise. The four-lane freeway bridge, constructed in 1963, is susceptible to flooding in the event of extreme sea level rise, according to high-end climate model estimates. To prepare for a range of future SLR, Caltrans proposed a new bridge to be engineered with features that will allow for the bridge to be elevated up to 3.5 feet higher by jacking without replacing major infrastructure components. Specifically, this adaptive design includes additional rebar with couplers and pins that can extend the bridge columns. The proposed bridge will also feature wider shoulder widths and a bicycle and pedestrian path on the northbound side to fit standards and accommodate multimodal transportation. Construction of the new bridge is anticipated to be completed by July 2026 and the site will be continuously monitored and formally evaluated by 2065 to determine whether to raise the bridge by 3.5 feet.
Key Insight 3: Nature Based Strategies
Nature-based adaptation strategies increasingly appear to hold promise as a more resilient approach to sea level rise adaptation. Incorporating ecological principles into nature-based shore protection strategies supports multiple benefits, including hazard adaptation and mitigation, natural resource enhancement, as well as recreation and scenic resource preservation. We also highlight that one of the most effective nature based strategies is referred to as “avoiding coastal squeeze.” When rigid infrastructure or hard armoring, such as seawalls or revetments are used on the coast our beaches, wetlands and public recreation areas, can be lost to inundation as they are squeezed between the hard shoreline and rising seas. When we realign our coastal infrastructure to allow for the coastal features like marshes or beaches to naturally migrate inland, we avoid coastal squeeze and keep the best parts of our coast and the ability to access them. Depending on the geologic setting and adjacent urban or rural development, critical infrastructure can be adapted in different ways to avoid the loss of valuable coastal areas by using strategies such as realigning, elevating, or tunneling structures, however this is more difficult in urban areas.
Nature Based Strategy Overview
When circumstances allow, the Coastal Commission encourages nature-based solutions, composed of natural or mostly natural elements, as a preferred alternative to traditional hardened shoreline protective devices that can have serious deleterious impacts on coastal resources. Nature based adaptation strategies also can form an important component of phased adaptation while potentially offering shorter- and medium-term protection of highway corridor segments.
Cardiff State Beach Living Shoreline Project
Located along a stretch of Highway 101 in San Diego County that is subject to ongoing flooding and erosion, the Cardiff State Beach Living Shoreline Project was completed in the spring of 2019 and consisted of an engineered dune system with a cobble toe on top of a buried revetment. The project was designed to accrete and erode with the seasons until approximately 2050, providing a natural buffer for the adjacent highway, a critical component of the region’s transportation network.
Surfer’s Point Shoreline Management Project
This project combines a realignment of paved infrastructure with beach nourishment and balances the need for public access and recreation with restoration of natural coastal conditions. This is an example of how nature-based adaptation strategies can use local conditions to inform successful design, function, and performance. The use of a cobble berm with an associated dune system, in this case, mimics natural cobble berm/platform nearby and has remained intact over a decade of winter storms. The beach, located near the mouth of the Ventura River was shrinking due to coastal erosion, and this project has proven itself as a successful example of possible shorter- to medium-term nature-based adaptation strategies. A second phase of the project funded by a $16.2 million grant from the Coastal Conservancy is currently underway to incorporate a new multi-use path and construction is set for fall 2024 to relocate damaged bike path and parking lot back to shoreline drive.
Gleason Beach Highway Realignment
In Sonoma County in northern California, between Jenner and Bodega Bay, sections of Highway 1 and adjacent homes were being undermined due to chronic erosion along the bluffs, which is accelerating with SLR. Seawalls failed to protect homes west of the highway and erosion continued, while much of the historic Gleason Beach at this location eroded away. Eventually portions of the highway also were threatened and repeated repairs became necessary to prevent significant travel disruptions along this sole transportation corridor servicing local coastal communities and businesses.
Scott Creek Bridge
In rural northern Santa Cruz County, Caltrans, the Commission, and a host of local, state and federal entities are pursuing habitat protection and climate change adaptation options for Highway 1 in the Scott Creek Lagoon area. This includes bridge and roadway reconfigurations that accommodate lagoon restoration in anticipation of projected SLR and its associated erosion and flooding.
Nature Based Strategy Overview
When circumstances allow, the Coastal Commission encourages nature-based solutions, composed of natural or mostly natural elements, as a preferred alternative to traditional hardened shoreline protective devices that can have serious deleterious impacts on coastal resources. Nature based adaptation strategies also can form an important component of phased adaptation while potentially offering shorter- and medium-term protection of highway corridor segments.
In California, coastal wetlands and beaches often represent the primary focus of nature based strategies. Using nature based strategies, in addition to other approaches that avoid “coastal squeeze,” helps to guard against losing the beautiful and valuable natural ecosystems and beaches along the California coast. These approaches can also provide increased buffering from the impacts of coastal flooding. A growing number of guides and analyses are available for informing opportunities to incorporate nature based strategies into traditional engineering alternatives analyses, such as FHWA's Nature-based Resilience for Coastal Highways Guide ; check out the resources section below for additional resources on this topic.
Nature based solutions, like all adaptation measures, require substantial technical studies and scientific research to implement and monitor in the context of their specific location, which may involve sensitive ecological habitats, significant public recreation areas, complex ocean wave and current regimes, or critical infrastructure and development.
The following projects exemplify some of the challenges of pursuing nature-based solutions in high-energy wave environments like the West Coast. Other concerns include that nature-based approaches may require large footprints and more upfront costs than traditional armoring in the short term. These issues need to be further addressed, but signs are that their long-term effectiveness and reduction of impacts are likely more environmentally sensitive and even more cost effective.
Cardiff State Beach Living Shoreline Project
Located along a stretch of Highway 101 in San Diego County that is subject to ongoing flooding and erosion, the Cardiff State Beach Living Shoreline Project was completed in the spring of 2019 and consisted of an engineered dune system with a cobble toe on top of a buried revetment. The project was designed to accrete and erode with the seasons until approximately 2050, providing a natural buffer for the adjacent highway, a critical component of the region’s transportation network.
Several unanticipated challenges arose following installation with sand eroding and washing into unfilled air voids in the buried rip rap, requiring an adaptive management approach and regular dredging of the adjacent lagoon to obtain additional sand for nourishment. In addition, a storm in April of 2021 caused erosion of the dune toe, requiring repairs and additional beach replenishment. Over 63,000 cubic yards of sand were added to Cardiff State Beach from the adjacent San Elijo Lagoon restoration site over four months -- equivalent to filling 19 Olympic-sized swimming pools. Still, the dunes have worked as hoped in protecting Highway 101 from damage and provide more time to plan a long-term solution for the corridor. The evolving project area also seeks to enable natural processes to continue at the site by planting native coastal vegetation that not only strengthens the dune structure but provides habitat for endangered species such as the Western Snowy Plover.
Surfer’s Point Shoreline Management Project
This project combines a realignment of paved infrastructure with beach nourishment and balances the need for public access and recreation with restoration of natural coastal conditions. This is an example of how nature-based adaptation strategies can use local conditions to inform successful design, function, and performance. The use of a cobble berm with an associated dune system, in this case, mimics natural cobble berm/platform nearby and has remained intact over a decade of winter storms. The beach, located near the mouth of the Ventura River was shrinking due to coastal erosion, and this project has proven itself as a successful example of possible shorter- to medium-term nature-based adaptation strategies. A second phase of the project funded by a $16.2 million grant from the Coastal Conservancy is currently underway to incorporate a new multi-use path and construction is set for fall 2024 to relocate damaged bike path and parking lot back to shoreline drive.
Gleason Beach Highway Realignment
In Sonoma County in northern California, between Jenner and Bodega Bay, sections of Highway 1 and adjacent homes were being undermined due to chronic erosion along the bluffs, which is accelerating with SLR. Seawalls failed to protect homes west of the highway and erosion continued, while much of the historic Gleason Beach at this location eroded away. Eventually portions of the highway also were threatened and repeated repairs became necessary to prevent significant travel disruptions along this sole transportation corridor servicing local coastal communities and businesses.
Caltrans, the Coastal Commission, and Sonoma County worked with stakeholders for a number of years and used SLR bluff retreat projections for 2100 to plan for resiliently adapting this section of highway to SLR. A realignment of the highway 400 ft inland was determined to be the best approach to ensure access while avoiding a hardened shoreline that would exacerbate the ongoing coastal squeeze on natural resources and its costly maintenance. Importantly, the approach also created opportunities for additional habitat restoration of Scotty Creek and adjacent wetlands and improved coastal public access by converting the old highway into a new segment of the California Coastal Trail.
Learn more: explore the series of images or the linked article above.
Scott Creek Bridge
In rural northern Santa Cruz County, Caltrans, the Commission, and a host of local, state and federal entities are pursuing habitat protection and climate change adaptation options for Highway 1 in the Scott Creek Lagoon area. This includes bridge and roadway reconfigurations that accommodate lagoon restoration in anticipation of projected SLR and its associated erosion and flooding.
In less developed areas like this, there may be a wider array of infrastructure adaptation options, including more expansive elevation and realignment. Such approaches protect natural processes while at the same time continue to meet the transportation needs of a region. A sound basis of scientific studies is proving vital for developing this extensive resiliency project so that it can holistically address highway infrastructure climate change vulnerabilities, reduce flooding hazards in the watershed, support significant creek and lagoon restoration, , dramatically reduce lengthy detour times, and improve public recreation opportunities.
Notably, the ecological needs of the Scott Creek Lagoon ecosystem were determined prior to the design and planning of the new bridge in order to successfully aid the restoration of important habitat for endemic species such as endangered Coho salmon. This experience underscores the need to retool traditional infrastructure development processes so that environmental features are characterized in much earlier phases and can be incorporated into infrastructure designs that will facilitate not only the resiliency of highways, but also the restoration and protection of coastal resources.
Key Insight 4: Early Project Engagement
Early Project Engagement Overview
Resilience projects can take many years to plan and develop before construction, in some cases up to a decade or more. Therefore, engagement at the very beginning of project development is critical so that collectively the fundamental needs have been identified and scoped early on to avoid costly surprises later in development. Early project engagement involves outreach to local stakeholders—as well as federal, state, or local agencies—to receive valuable input on opportunities for projects to achieve resilience in a manner that is collaborative, equitable, and achieves multiple benefits where feasible. A core benefit of early coordination, especially with permitting agencies, is that early feedback on opportunities for incorporating environmental requirements into the project can reduce time delays and costly redesign needs later in project development.
Eureka Arcata Corridor
The Eureka Arcata Corridor is a 6-mile stretch of U.S. Highway 101 along the east of Humboldt Bay that serves as a primary transportation hub in Humboldt County and contains essential utility lines, residential areas, and business. This Corridor has experienced flooding already and is extremely vulnerable to sea level rise going forward. Caltrans District 1 is developing a Comprehensive Adaptation and Implementation Plan (CAIP) for the Corridor that will be completed in December 2025 and will utilize best available science and monitoring reports to identify accommodation, protection, and relocation adaptation options. Coordination with local government, stakeholders, and public interest groups are aiding the project development process. This project will consider a combination of approaches such as raised roadways, viaducts, and ecotone levees to prevent or accommodate inundation from sea level rise and to mitigate damages from future flooding, storm surge, and erosion (Project 23856, HUM 101 PM 79.9 / 85.0).
Russian Gulch Bridge Replacement
The Russian Gulch bridge is on State Route 1 north of Jenner in Sonoma County. Currently, the bridge rail is in need of replacement—and given projected exposure to sea level rise—consideration of long-term resilience to climate stressors is a core objective of this bridge replacement project. Passing over the Russian Gulch Creek within the Sonoma Coast State Park, the adjacent parking lot provides public access to the Russian Gulch Trail to Russian Gulch State Beach. The creek is habitat for Federally-listed threatened steelhead trout, as well as other coastal California species. Long-term climate resilience for this bridge will consider both tidal and fluvial hazards, as well as opportunities to achieve multiple benefits for safety, ecological, public access, and multimodal improvement outcomes (Project 25027, SON 1 PM 24.5).
37 East Novato Causeway
State Route 37 is a vital highway along the San Pablo Bay connecting Sonoma, Marin, and Solano counties. Commuters and visitors already experience delays from intermittent storm-related flooding, and going forward the San Pablo Bay is expected to experience significant sea level rise by 2050 which will increase flooding events along the 21-mile corridor. This project will address these flooding hazards by advancing a long-term resilience solution including a causeway/viaduct on SR-37 between Novato Creek Bridge and Atherton Avenue, as recommended in the 2023 Caltrans District 4 SR-37 Planning & Environmental Linkages Study (PEL). Phase 1 of the project will see a replacement of the Novato Creek Bridge, and Phase 2 will include a portion of the causeway from US 101 to Atherton Avenue (Project 25079, MRN 37 PM 12.1 / 13.1).
Surfers Beach
Surfers Beach in San Mateo County is a popular beach north of Half Moon Bay known for its ideal sheltered surfing conditions. For several decades since the construction of the Pillar Point Harbor breakwater north of the beach, it has experienced significant storm surge, flooding, and bluff erosion, leading to a loss of beach area as well as erosion and flooding of Highway 1. Coordinating with a local nature-based sand berm project[SS1] led by the San Mateo County Harbor District, this project will consider interim adaptation strategies including a sand berm and micro-realignments associated mid-century sea level rise exposure. Opportunities to achieve additional benefits for safety, as well as ecological, public access, and multimodal improvement outcomes will also be considered (Project 25080, SM 1 PM 31.8 / 32.349).
Gleason 2.0
Located along State Route 1 north of Jenner in Sonoma Coast State Park, this project will complete a micro-realignment inland to address bluff erosion that undermines the roadway. The project delivers on the Department’s commitment to address long-term adaptation needs for the northern roadway tie-in to the recently constructed Gleason Beach Highway Realignment Project (CDP 2-20-0282, 2020). This transportation corridor servicing local coastal communities and businesses, if disrupted, is associated with a 29.3-mile detour. As feasible and appropriate, opportunities to achieve additional benefits for safety, as well as ecological, public access, and multimodal improvement outcomes will also be incorporated (Project 25081, SON 1 PM 15.6 / 16.1).
Manzanita
In the Richardson Bay area of Marin County, this proposed project will address recurring flooding and sea level rise at the Manzanita Park and Ride lot, State Route 1 (SR 1) at the SR 1/ US 101 Separation, and US 101 from the US 101/Donahue Street on/offramps to the SR 1/US 101 Separation. Adaptation strategies that will be considered include a combination of accommodation, retreat, and nature-based solutions. As feasible, multimodal, safety, and environmental benefits will be incorporated into the project (Project 25083, MRN 101 PM 3.3 / 4.2).
Santa Clara Living Levee
Along Santa Clara County’s South bay shoreline, a 3.5 mile stretch of Highway 101 between Palo Alto and Mountain View is adjacent to the San Francisco Bay. At a regional level for this location, partners including the U.S. Army Corps of Engineers (USACE), the California State Coastal Conservancy, and regional stakeholders are exploring though the San Francisco Bay Shoreline Protection Project opportunities to provide tidal flood protection, restore and enhance tidal marsh and related habitats, and provide recreational and public access opportunities along Santa Clara County’s shoreline. The project will provide coastal flood protection from a rising sea level, and will restore and enhance tidal marsh by using a combination of flood protection levees, wetlands and transitional zone habitats also known as ecotones. Ecotones will provide an additional protective buffer for the levee and allow marsh habitat to migrate upslope as the sea level rises (Project 24716, SCL 101 PM 49.0 / 52.55).
Tomales Bay
In Marin county, State Route 1 follows along the eastern shoreline of Tomales Bay. The shoreline has evolved significantly over the last several centuries, both in response to natural processes and human interventions. Today, both its ecological resources and human infrastructure including State Route 1 along the shoreline are under threat of flooding and erosion from projected sea-level rise. Several permits have been issued over time for various locations on Highway 1 along Tomales Bay including for rock slope protection (RSP) along Reynold’s Cove. Annual storm flooding occurs near Lagunitas Bridge and will become more drastic along Tomales bay as sea-level rise advances. This project will consider nature-based solutions such as those envisioned by the Tomales Bay Living Shoreline Feasibility Project including include creek-to-bay reconnection, placement of rocky intertidal habitat features, native oyster restoration, submerged aquatic vegetation management, tidal flat restoration, tidal marsh restoration, and construction of beaches, dunes and rocky habitat appropriate to the Tomales Bay setting. Specifically, Caltrans will replace the Millerton Gulch Bridge with a long-term adaptation solution such as a causeway/viaduct that spans the historic wetland ensuring both long-term resilience as well as providing important habitat accommodation space. Broader planning coordination opportunities will leverage reports like the Transportation Concept Report: State Route 1 North as well as collaborative working group outcomes from the Marin County Coastal Communities Working Group (Project 18737, MRN 1 PM 31.2 / 46.1).
Marin 101 Corridor
In Marin County, the US 101 is the primary highway corridor providing transportation needs at multiple scales: locally, regionally, as well as interstate north/south connectivity for the movement of both people and goods. There are several locations along US 101 from Marin City to San Rafael that already flood during large storms and high tides, which will worsen as sea levels rise. This portion of the corridor connects travelers to schools, regional parks, and hospitals, with few alternative routes. Areas that are safe from flooding may be cut off from essential services such as transportation, water, electricity, and emergency response. Low-lying areas subject to flooding now or in the future include economically or socially disadvantaged communities. This project will incorporate adaptation strategies from Caltrans’ Marin 101 Adaptation Planning Study which is just getting underway that will consider several local and regional planning efforts to address sea level rise adaptation needs and vulnerabilities—such as the BayWAVE program, the Transportation Authority of Marin (TAM) planning study on sea level rise and flooding—among others (Project 24696, MRN 101 PM 7.0 / 11.0).
Doolittle Drive Ecotone Levee
Doolittle Drive/State Route 61 along the northeastern edge of Oakland International Airport on Bay Farm Island in Alameda County is considered part of the California Freeway and Expressway System, a network of highways that are essential to the country’s economy, defense, and mobility by the Federal Highway Administration. A new trail has been recently completed along the southern end of Doolittle Drive that flanks Martin Luther King Jr. Regional Shoreline and provides better access to the water where people fish, boat, and swim. Across the Airport Channel in San Leandro Bay from Doolittle Drive, Arrowhead Marsh can be viewed to the west which is home to endangered Ridgway’s rails, salt marsh harvest mice, and many species of resident and migrant birds. This project will restore eroded slopes with nature-based adaptation measures like an ecotone levee and replace the metal beam guardrail (MBGR) with the Midwest Guardrail System (MGS) (Project 23365, ALA 61 PM 17.53 / 17.9).
Bolinas Lagoon
A 5 mile stretch of Highway 1 in Marin County runs along Bolinas Lagoon, a 1,100-acre world-renowned tidal estuary with unique habitats and ecosystem services that support wildlife and people. The Lagoon forms part of the National Oceanic and Atmospheric Administration (NOAA) Greater Farallones National Marine Sanctuary, and is within the Golden Gate Biosphere, an Audubon Important Bird Area, and one of the only seven Ramsar Wetlands of International Importance in the western United States. As changing climate conditions increase vulnerabilities to the area—such as extreme weather events and sea level rise—the region needs long-term climate adaptation solutions to ensure the resiliency of infrastructure and natural lands. Several collaborative Bolinas Coastal Resilience Projects are underway including the Bolinas Lagoon Wye Wetlands Resiliency project, the Stinson Adaptation & Resilience Collaboration, and the Caltrans-led MRN 1/Bolinas Lagoon Sea Level Rise Adaptation Planning Study which will conduct lagoon modeling, sediment conveyance modeling, and high tide studies to develop site-specific technical climate change adaptation strategies. In collaboration with the San Jose State University Research Foundation (SJSURF) and in early inter-organizational communication with key stakeholders and the local community, this two-year study will begin in August 2024 and conclude in 2026. Caltrans will utilize this study in the project development process to create treatment plans and project alternatives that prioritize nature-based solutions for sustained resilience on the Highway 1 Bolinas Lagoon causeway (Project 24650, MRN 1 PM 12.5 / 17.109).
Waddell Creek Bridge
The Waddell Creek Bridge is located in Santa Cruz County on State Route 1 north of Davenport within the Big Basin Redwood State Park. The bridge and adjoining roadways cross through the Waddell Creek watershed, beach, and lagoon system as the creek discharges into the Pacific Ocean. Waddell Beach attracts surfers, kite and windsurfers, tide pool explorers and families—and it also provides important habitat for Federally-listed endangered coho salmon, threatened steelhead trout, threatened western snowy plover, endangered California red-legged frogs, endangered tidewater goby, and numerous other species native to the Santa Cruz Mountains. Opportunities to utilize information coming from the Planning for Coastal Resilience along the Highway 1 Corridor at Waddell and San Vincente Creeks that is being developed by the Santa Cruz County Regional Transportation Commission will help inform the adaptation options to replace the bridge in a manner that provides resilience for the transportation system as well as improved ecological outcomes for the beach and lagoon system (Project 23851, SCR 1 PM 36.3).
Moss Landing / Elkhorn Slough Highway 1 Project
An 8-mile stretch of Highway 1 through Moss Landing and Elkhorn Slough is in the planning phase for adapting to climate vulnerabilities such as flooding associated with sea level rise and storm surge. Ensuring the resiliency of this segment of Highway 1 is important, as it is an essential transportation route connecting Santa Cruz and Monterey Counties. Improving the ecological health of Elkhorn Slough—which is a National Estuary providing important habitat to a variety of endangered and threatened species—is a high priority for this project. As this highway resilience project continues to develop, it will be important to leverage and integrate information from several companion planning efforts that are just beginning to get underway that can support a collective, shared understanding of long-term resilience for the estuary and transportation system. Specifically, the Transportation Agency for Monterey County (TAMC) recently received $2.2 million to produce the Highway 1 Elkhorn Slough Corridor Climate Resiliency Project. This effort is also complemented by a recent award of $71.1 million to the California Marine Sanctuary Foundation by NOAA for Regional Adaptation for Climate Resilience of Monterey Bay Coastal Communities (Project 24886, MON 1 PM 95.2 / 97.6).
Mugu Lagoon
In Ventura county, the Pacific Coast Highway follows along the eastern shoreline of Mugu Lagoon south of the city of Oxnard. Mugu Lagoon is the largest and most intact saltmarsh in Southern California containing coastal beach, dune, estuary, marsh, and upland habitat for a diversity of rare and imperiled species within the Point Mugu Naval Station area. The Naval Base Ventura County (NBVC) supports a population of 19,000 personnel supporting around $2 billion annually for the regional economy. In recognition that the hazards already experienced in terms of flooding, erosion, and storm damage will worsen in terms of intensity, frequency, and duration as sea levels rise—NBVC has partnered with The Nature Conservancy on Restoring Coastal Wetlands for Climate Resilience with the understanding that robust evidence indicates natural systems are often more effective and more resilient against storms and flooding than traditional hardening responses like seawalls. Going forward, in collaboration with NBVC and the Ventura County Resilient Coastal Adaptation Project, Caltrans will replace the bridges at Calleguas Creek and Revolon Slough to adapt to flooding associated with both projected tidal and fluvial flooding (Project 25129, VEN 1 PM 9.6 / 10.1).
Crystal Cove
In Orange County, the Pacific Coast Highway crosses El Moro Canyon within Crystal Cove State Park. Winter storms continue to cause high surf, flooding, and beach erosion at Crystal Cove State Park, reflecting the need for long-term adaptation solutions for the area. After a particularly harsh storm in January 2023, sand was washed away at Moro Beach and lifeguard facilities were cut off, requiring 15,000 cubic yards of sand to be moved from the Talbert Channel at Huntington Beach to repair the damage. In coordination with state agency partners including California Department of Parks and Recreation, the California Coastal Commission and others—Caltrans will conduct the PCH Bolsa Chica and Crystal Cove Climate Adaptation Planning Study to consider long-term hazards to the roadway as sea-level rise and storm events worsen and identify adaptation strategies for long-term resilience that provides public access to one of Orange County’s largest remaining open spaces and natural seashore—as well as opportunities for improvements for roadway safety, wildlife connectivity, and multimodal benefits (Project 24922, ORA 1 PM 11.6 / 12.2).
State Route 75
State Route 75 in San Diego County connects Coronado City to Imperial Beach City along a thin strip of land behind Silver Strand State Beach to the west and San Diego Bay to the east. This scenic highway is an important route for locals as well as tourists, and is considered part of the National Highway System providing essential services for the economy, defense, and mobility. In addition, there are many environmental resources in the area; Silver Strand State Beach is home to endangered species such as the California Grunion and Western Snowy Plover—and at the southern end of SR 75, the San Diego Bay National Wildlife Refuge offers one of the last expanses of open space in coastal southern California with exceptional biological, social, and economic values—protecting a rich diversity of endangered, threatened, migratory, and native species. SR 75 is especially vulnerable to sea-level rise and climate change as identified in the City of Coronado’s Sea Level Rise Vulnerability Assessment and Adaptation Plan. Caltrans will identify adaptation measures through the SR-75 Sea Level Rise Adaptation Planning Study in order to plan for resiliency on this highway in manner that considers the surrounding land-uses and opportunities to improve safety, mobility, and provide environmental benefits (Project 24402, SD 75 PM 11.2 / 18.51).
Early Project Engagement Overview
Resilience projects can take many years to plan and develop before construction, in some cases up to a decade or more. Therefore, engagement at the very beginning of project development is critical so that collectively the fundamental needs have been identified and scoped early on to avoid costly surprises later in development. Early project engagement involves outreach to local stakeholders—as well as federal, state, or local agencies—to receive valuable input on opportunities for projects to achieve resilience in a manner that is collaborative, equitable, and achieves multiple benefits where feasible. A core benefit of early coordination, especially with permitting agencies, is that early feedback on opportunities for incorporating environmental requirements into the project can reduce time delays and costly redesign needs later in project development.
Through the State Highway Operation & Protection Program (SHOPP), Caltrans has made an investment of approximately $2.3 billion in Climate Adaptation and Resilience within the 2024 Q3 10-Year SHOPP Project Book for a cohort of projects directly focused on sea-level rise adaptation. Going forward, as these projects are now at the very beginning stages of development—they are a set of ideal candidates for early engagement and productive collaboration as support from federal, state, and local partners will be necessary for successful delivery.
Eureka Arcata Corridor
The Eureka Arcata Corridor is a 6-mile stretch of U.S. Highway 101 along the east of Humboldt Bay that serves as a primary transportation hub in Humboldt County and contains essential utility lines, residential areas, and business. This Corridor has experienced flooding already and is extremely vulnerable to sea level rise going forward. Caltrans District 1 is developing a Comprehensive Adaptation and Implementation Plan (CAIP) for the Corridor that will be completed in December 2025 and will utilize best available science and monitoring reports to identify accommodation, protection, and relocation adaptation options. Coordination with local government, stakeholders, and public interest groups are aiding the project development process. This project will consider a combination of approaches such as raised roadways, viaducts, and ecotone levees to prevent or accommodate inundation from sea level rise and to mitigate damages from future flooding, storm surge, and erosion (Project 23856, HUM 101 PM 79.9 / 85.0).
Russian Gulch Bridge Replacement
The Russian Gulch bridge is on State Route 1 north of Jenner in Sonoma County. Currently, the bridge rail is in need of replacement—and given projected exposure to sea level rise—consideration of long-term resilience to climate stressors is a core objective of this bridge replacement project. Passing over the Russian Gulch Creek within the Sonoma Coast State Park, the adjacent parking lot provides public access to the Russian Gulch Trail to Russian Gulch State Beach. The creek is habitat for Federally-listed threatened steelhead trout, as well as other coastal California species. Long-term climate resilience for this bridge will consider both tidal and fluvial hazards, as well as opportunities to achieve multiple benefits for safety, ecological, public access, and multimodal improvement outcomes (Project 25027, SON 1 PM 24.5).
37 East Novato Causeway
State Route 37 is a vital highway along the San Pablo Bay connecting Sonoma, Marin, and Solano counties. Commuters and visitors already experience delays from intermittent storm-related flooding, and going forward the San Pablo Bay is expected to experience significant sea level rise by 2050 which will increase flooding events along the 21-mile corridor. This project will address these flooding hazards by advancing a long-term resilience solution including a causeway/viaduct on SR-37 between Novato Creek Bridge and Atherton Avenue, as recommended in the 2023 Caltrans District 4 SR-37 Planning & Environmental Linkages Study (PEL). Phase 1 of the project will see a replacement of the Novato Creek Bridge, and Phase 2 will include a portion of the causeway from US 101 to Atherton Avenue (Project 25079, MRN 37 PM 12.1 / 13.1).
For more information, see this Project Visualization developed by Caltrans D4.
Surfers Beach
Surfers Beach in San Mateo County is a popular beach north of Half Moon Bay known for its ideal sheltered surfing conditions. For several decades since the construction of the Pillar Point Harbor breakwater north of the beach, it has experienced significant storm surge, flooding, and bluff erosion, leading to a loss of beach area as well as erosion and flooding of Highway 1. Coordinating with a local nature-based sand berm project [SS1] led by the San Mateo County Harbor District, this project will consider interim adaptation strategies including a sand berm and micro-realignments associated mid-century sea level rise exposure. Opportunities to achieve additional benefits for safety, as well as ecological, public access, and multimodal improvement outcomes will also be considered (Project 25080, SM 1 PM 31.8 / 32.349).
Gleason 2.0
Located along State Route 1 north of Jenner in Sonoma Coast State Park, this project will complete a micro-realignment inland to address bluff erosion that undermines the roadway. The project delivers on the Department’s commitment to address long-term adaptation needs for the northern roadway tie-in to the recently constructed Gleason Beach Highway Realignment Project ( CDP 2-20-0282 , 2020). This transportation corridor servicing local coastal communities and businesses, if disrupted, is associated with a 29.3-mile detour. As feasible and appropriate, opportunities to achieve additional benefits for safety, as well as ecological, public access, and multimodal improvement outcomes will also be incorporated (Project 25081, SON 1 PM 15.6 / 16.1).
Manzanita
In the Richardson Bay area of Marin County, this proposed project will address recurring flooding and sea level rise at the Manzanita Park and Ride lot, State Route 1 (SR 1) at the SR 1/ US 101 Separation, and US 101 from the US 101/Donahue Street on/offramps to the SR 1/US 101 Separation. Adaptation strategies that will be considered include a combination of accommodation, retreat, and nature-based solutions. As feasible, multimodal, safety, and environmental benefits will be incorporated into the project (Project 25083, MRN 101 PM 3.3 / 4.2).
Santa Clara Living Levee
Along Santa Clara County’s South bay shoreline, a 3.5 mile stretch of Highway 101 between Palo Alto and Mountain View is adjacent to the San Francisco Bay. At a regional level for this location, partners including the U.S. Army Corps of Engineers (USACE), the California State Coastal Conservancy, and regional stakeholders are exploring though the San Francisco Bay Shoreline Protection Project opportunities to provide tidal flood protection, restore and enhance tidal marsh and related habitats, and provide recreational and public access opportunities along Santa Clara County’s shoreline. The project will provide coastal flood protection from a rising sea level, and will restore and enhance tidal marsh by using a combination of flood protection levees, wetlands and transitional zone habitats also known as ecotones. Ecotones will provide an additional protective buffer for the levee and allow marsh habitat to migrate upslope as the sea level rises (Project 24716, SCL 101 PM 49.0 / 52.55).
Tomales Bay
In Marin county, State Route 1 follows along the eastern shoreline of Tomales Bay. The shoreline has evolved significantly over the last several centuries, both in response to natural processes and human interventions. Today, both its ecological resources and human infrastructure including State Route 1 along the shoreline are under threat of flooding and erosion from projected sea-level rise. Several permits have been issued over time for various locations on Highway 1 along Tomales Bay including for rock slope protection (RSP) along Reynold’s Cove. Annual storm flooding occurs near Lagunitas Bridge and will become more drastic along Tomales bay as sea-level rise advances. This project will consider nature-based solutions such as those envisioned by the Tomales Bay Living Shoreline Feasibility Project including include creek-to-bay reconnection, placement of rocky intertidal habitat features, native oyster restoration, submerged aquatic vegetation management, tidal flat restoration, tidal marsh restoration, and construction of beaches, dunes and rocky habitat appropriate to the Tomales Bay setting. Specifically, Caltrans will replace the Millerton Gulch Bridge with a long-term adaptation solution such as a causeway/viaduct that spans the historic wetland ensuring both long-term resilience as well as providing important habitat accommodation space. Broader planning coordination opportunities will leverage reports like the Transportation Concept Report: State Route 1 North as well as collaborative working group outcomes from the Marin County Coastal Communities Working Group (Project 18737, MRN 1 PM 31.2 / 46.1).
Marin 101 Corridor
In Marin County, the US 101 is the primary highway corridor providing transportation needs at multiple scales: locally, regionally, as well as interstate north/south connectivity for the movement of both people and goods. There are several locations along US 101 from Marin City to San Rafael that already flood during large storms and high tides, which will worsen as sea levels rise. This portion of the corridor connects travelers to schools, regional parks, and hospitals, with few alternative routes. Areas that are safe from flooding may be cut off from essential services such as transportation, water, electricity, and emergency response. Low-lying areas subject to flooding now or in the future include economically or socially disadvantaged communities. This project will incorporate adaptation strategies from Caltrans’ Marin 101 Adaptation Planning Study which is just getting underway that will consider several local and regional planning efforts to address sea level rise adaptation needs and vulnerabilities—such as the BayWAVE program, the Transportation Authority of Marin (TAM) planning study on sea level rise and flooding—among others (Project 24696, MRN 101 PM 7.0 / 11.0).
Doolittle Drive Ecotone Levee
Doolittle Drive/State Route 61 along the northeastern edge of Oakland International Airport on Bay Farm Island in Alameda County is considered part of the California Freeway and Expressway System, a network of highways that are essential to the country’s economy, defense, and mobility by the Federal Highway Administration. A new trail has been recently completed along the southern end of Doolittle Drive that flanks Martin Luther King Jr. Regional Shoreline and provides better access to the water where people fish, boat, and swim. Across the Airport Channel in San Leandro Bay from Doolittle Drive, Arrowhead Marsh can be viewed to the west which is home to endangered Ridgway’s rails, salt marsh harvest mice, and many species of resident and migrant birds. This project will restore eroded slopes with nature-based adaptation measures like an ecotone levee and replace the metal beam guardrail (MBGR) with the Midwest Guardrail System (MGS) (Project 23365, ALA 61 PM 17.53 / 17.9).
Bolinas Lagoon
A 5 mile stretch of Highway 1 in Marin County runs along Bolinas Lagoon, a 1,100-acre world-renowned tidal estuary with unique habitats and ecosystem services that support wildlife and people. The Lagoon forms part of the National Oceanic and Atmospheric Administration (NOAA) Greater Farallones National Marine Sanctuary, and is within the Golden Gate Biosphere, an Audubon Important Bird Area, and one of the only seven Ramsar Wetlands of International Importance in the western United States. As changing climate conditions increase vulnerabilities to the area—such as extreme weather events and sea level rise—the region needs long-term climate adaptation solutions to ensure the resiliency of infrastructure and natural lands. Several collaborative Bolinas Coastal Resilience Projects are underway including the Bolinas Lagoon Wye Wetlands Resiliency project, the Stinson Adaptation & Resilience Collaboration, and the Caltrans-led MRN 1/Bolinas Lagoon Sea Level Rise Adaptation Planning Study which will conduct lagoon modeling, sediment conveyance modeling, and high tide studies to develop site-specific technical climate change adaptation strategies. In collaboration with the San Jose State University Research Foundation (SJSURF) and in early inter-organizational communication with key stakeholders and the local community, this two-year study will begin in August 2024 and conclude in 2026. Caltrans will utilize this study in the project development process to create treatment plans and project alternatives that prioritize nature-based solutions for sustained resilience on the Highway 1 Bolinas Lagoon causeway (Project 24650, MRN 1 PM 12.5 / 17.109).
Waddell Creek Bridge
The Waddell Creek Bridge is located in Santa Cruz County on State Route 1 north of Davenport within the Big Basin Redwood State Park. The bridge and adjoining roadways cross through the Waddell Creek watershed, beach, and lagoon system as the creek discharges into the Pacific Ocean. Waddell Beach attracts surfers, kite and windsurfers, tide pool explorers and families—and it also provides important habitat for Federally-listed endangered coho salmon, threatened steelhead trout, threatened western snowy plover, endangered California red-legged frogs, endangered tidewater goby, and numerous other species native to the Santa Cruz Mountains. Opportunities to utilize information coming from the Planning for Coastal Resilience along the Highway 1 Corridor at Waddell and San Vincente Creeks that is being developed by the Santa Cruz County Regional Transportation Commission will help inform the adaptation options to replace the bridge in a manner that provides resilience for the transportation system as well as improved ecological outcomes for the beach and lagoon system (Project 23851, SCR 1 PM 36.3).
Moss Landing / Elkhorn Slough Highway 1 Project
An 8-mile stretch of Highway 1 through Moss Landing and Elkhorn Slough is in the planning phase for adapting to climate vulnerabilities such as flooding associated with sea level rise and storm surge. Ensuring the resiliency of this segment of Highway 1 is important, as it is an essential transportation route connecting Santa Cruz and Monterey Counties. Improving the ecological health of Elkhorn Slough—which is a National Estuary providing important habitat to a variety of endangered and threatened species—is a high priority for this project. As this highway resilience project continues to develop, it will be important to leverage and integrate information from several companion planning efforts that are just beginning to get underway that can support a collective, shared understanding of long-term resilience for the estuary and transportation system. Specifically, the Transportation Agency for Monterey County (TAMC) recently received $2.2 million to produce the Highway 1 Elkhorn Slough Corridor Climate Resiliency Project . This effort is also complemented by a recent award of $71.1 million to the California Marine Sanctuary Foundation by NOAA for Regional Adaptation for Climate Resilience of Monterey Bay Coastal Communities (Project 24886, MON 1 PM 95.2 / 97.6).
Mugu Lagoon
In Ventura county, the Pacific Coast Highway follows along the eastern shoreline of Mugu Lagoon south of the city of Oxnard. Mugu Lagoon is the largest and most intact saltmarsh in Southern California containing coastal beach, dune, estuary, marsh, and upland habitat for a diversity of rare and imperiled species within the Point Mugu Naval Station area. The Naval Base Ventura County (NBVC) supports a population of 19,000 personnel supporting around $2 billion annually for the regional economy. In recognition that the hazards already experienced in terms of flooding, erosion, and storm damage will worsen in terms of intensity, frequency, and duration as sea levels rise—NBVC has partnered with The Nature Conservancy on Restoring Coastal Wetlands for Climate Resilience with the understanding that robust evidence indicates natural systems are often more effective and more resilient against storms and flooding than traditional hardening responses like seawalls. Going forward, in collaboration with NBVC and the Ventura County Resilient Coastal Adaptation Project , Caltrans will replace the bridges at Calleguas Creek and Revolon Slough to adapt to flooding associated with both projected tidal and fluvial flooding (Project 25129, VEN 1 PM 9.6 / 10.1).
Crystal Cove
In Orange County, the Pacific Coast Highway crosses El Moro Canyon within Crystal Cove State Park. Winter storms continue to cause high surf, flooding, and beach erosion at Crystal Cove State Park, reflecting the need for long-term adaptation solutions for the area. After a particularly harsh storm in January 2023, sand was washed away at Moro Beach and lifeguard facilities were cut off, requiring 15,000 cubic yards of sand to be moved from the Talbert Channel at Huntington Beach to repair the damage. In coordination with state agency partners including California Department of Parks and Recreation, the California Coastal Commission and others—Caltrans will conduct the PCH Bolsa Chica and Crystal Cove Climate Adaptation Planning Study to consider long-term hazards to the roadway as sea-level rise and storm events worsen and identify adaptation strategies for long-term resilience that provides public access to one of Orange County’s largest remaining open spaces and natural seashore—as well as opportunities for improvements for roadway safety, wildlife connectivity, and multimodal benefits (Project 24922, ORA 1 PM 11.6 / 12.2).
State Route 75
State Route 75 in San Diego County connects Coronado City to Imperial Beach City along a thin strip of land behind Silver Strand State Beach to the west and San Diego Bay to the east. This scenic highway is an important route for locals as well as tourists, and is considered part of the National Highway System providing essential services for the economy, defense, and mobility. In addition, there are many environmental resources in the area; Silver Strand State Beach is home to endangered species such as the California Grunion and Western Snowy Plover—and at the southern end of SR 75, the San Diego Bay National Wildlife Refuge offers one of the last expanses of open space in coastal southern California with exceptional biological, social, and economic values—protecting a rich diversity of endangered, threatened, migratory, and native species. SR 75 is especially vulnerable to sea-level rise and climate change as identified in the City of Coronado’s Sea Level Rise Vulnerability Assessment and Adaptation Plan . Caltrans will identify adaptation measures through the SR-75 Sea Level Rise Adaptation Planning Study in order to plan for resiliency on this highway in manner that considers the surrounding land-uses and opportunities to improve safety, mobility, and provide environmental benefits (Project 24402, SD 75 PM 11.2 / 18.51).
Conclusions: Need for federal support and long-term strategies
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