Sea Level Rise and the Transportation System in the Coastal Zone

June 2023

California relies on a multi-modal transportation network that supports nearly all aspects of our coastal economies—including tourism, agriculture, and coastal dependent industries—as well as the quality of life enjoyed by our citizens. As climate change and rising seas affect our transportation system, these events will disrupt the daily lives of Californians, upset coastal economies, risk public safety, contribute to losses of ecosystems that provide habitat for rare and endangered species, and impede public access and recreation in these coastal areas. Therefore, incorporating sea level rise (SLR) considerations during all phases of Caltrans project delivery is necessary to arrive at more resilient projects and safe and reliable transportation outcomes.

The California Coastal Commission (Coastal Commission) and local agencies with certified Local Coastal Programs (LCPs) will evaluate how SLR was analyzed throughout the Caltrans project development process when Coastal Development Permits (CDPs) are required for Caltrans projects. The Coastal Commission bases its standard of review for CDPs on the Chapter 3 policies of the California Coastal Act; Sections 30235, 30236, and 30253 focus on coastal hazards and shoreline development, and provide the primary basis for how the Coastal Commission considers SLR impacts on proposed Caltrans projects. These policies requiring protection of life, property, and coastal resources are complimented by other statutes such as AB 2800, SB1 2030(e), and SB 743 directing the transportation system to mitigate, minimize, and adapt to climate change.

This webpage is intended to provide a SLR orientation and resources for Caltrans Transportation Planners, Project Managers, Environmental Planners, Engineers, and other staff working on projects and plans in the Coastal Zone. This includes identifying project level permitting needs and the overall regulatory framework to support decision-making throughout transportation planning and programming, project initiation, design, environmental document preparation, CDP applications, and permit condition compliance.

In addition, this webpage provides information on current Coastal Zone permitting requirements for SLR in relationship to the Caltrans project delivery process; updates across companion Caltrans resources including the Standard Environmental Reference (SER) Forms and Templates, and additional technical guidance within appropriate Annotated Outlines, will occur on an on-going basis.

California Coastal Commission Sea Level Rise Policy, Guidance, and Resources

California Coastal Act – Public Resources Code, Division 20

The Coastal Commission bases its standard of review for CDPs on the Chapter 3 policies of the California Coastal Act. Coastal Act policies regarding coastal hazards (Sections 30235, 30236, and 30253) provide the primary basis for how the Coastal Commission considers SLR impacts on proposed development. Furthermore, the other Coastal Act Chapter 3 policies related to coastal resource protection are relevant in the context of SLR given the combined impacts that proposed projects could have on coastal resources as conditions change over time. Additionally, local governments with jurisdiction over a project and certified LCPs likely have Chapter 3 policies incorporated directly into their LCPs or by reference, as well as their own policies and provisions. It is important to carefully review all applicable policies and provisions to understand how they may apply to a specific project.

During the recent 2021 legislative cycle, SB 1 Coastal resources: sea level rise was signed into law by Governor Newson which added several provisions to the Coastal Act which mandates a more explicit consideration of sea level rise (Sections 30270 and 30001.5 (f)) which is of direct relevance for the transportation system. 

  • Coastal Act Section 30270 states: The commission shall take into account the effects of sea level rise in coastal resources planning and management policies and activities in order to identify, assess, and, to the extent feasible, avoid and mitigate the adverse effects of sea level rise.
  • Coastal Act Section 30001.5 (f) states: the basic goals of the state for the coastal zone are to […] Anticipate, assess, plan for, and, to the extent feasible, avoid, minimize, and mitigate the adverse environmental and economic effects of sea level rise within the coastal zone.
  • Coastal Act Section 30235 states: Revetments, breakwaters, groins, harbor channels, seawalls, cliff retaining walls, and other such construction that alters natural shoreline processes shall be permitted when required to serve coastal-dependent uses or to protect existing structures or public beaches in danger from erosion, and when designed to eliminate or mitigate adverse impacts on local shoreline sand supply. Existing marine structures causing water stagnation contributing to pollution problems and fish kills should be phased out or upgraded where feasible.
  • Coastal Act Section 30236 states: Channelizations, dams, or other substantial alterations of rivers and streams shall incorporate the best mitigation measures feasible, and be limited to (1) necessary water supply projects, (2) flood control projects where no other method for protecting existing structures in the floodplain is feasible and where such protection is necessary for public safety or to protect existing development, or (3) developments where the primary function is the improvement of fish and wildlife habitat.
  • Coastal Act Section 30253 states: New development [defined in Section 30106] shall: (a) Minimize risks to life and property in areas of high geologic, flood, and fire hazard. (b) Assure stability and structural integrity, and neither create nor contribute significantly to erosion, geologic instability, or destruction of the site or surrounding area or in any way require the construction of protective devices that would substantially alter natural landforms along bluffs and cliffs. (c) Be consistent with requirements imposed by an air pollution control district or the State Air Resources Board as to each particular development. (d) Minimize energy consumption and vehicle miles traveled. (e) Where appropriate, protect special communities and neighborhoods that, because of their unique characteristics, are popular visitor destination points for recreational uses.

The Coastal Commission’s 2018 Sea Level Rise Policy Guidance is a resource for Caltrans staff and interested stakeholders to review for direction on applying the Coastal Act to address SLR in Coastal Commission planning and regulatory actions.

Within the 2018 Sea Level Rise Policy Guidance, several relevant chapters and appendices for Caltrans include Chapter 6, Addressing Sea Level Rise in Coastal Development Permits; Chapter 7, Adaptation Strategies; Chapter 8, Legal Context of Adaptation Planning; Appendix F, Primary Coastal Act Policies Related to Sea Level Rise and Coastal Hazards, includes a synthesis of Coastal Act policies relevant to SLR, coastal hazards, and coastal resources; and Appendix G, Sea Level Rise Projections for 12 California Tide Gauges, includes local SLR projections for the 12 California tide gauges. The other appendices contain valuable technical information on how to determine local hazard conditions, mapping tools and data, resources for adaptation measures, and more.

When developing segments of transportation infrastructure that are vulnerable or that are expected to become vulnerable to coastal hazards, including those associated with SLR, decision-makers implementing Coastal Act and LCP policies will likely require Caltrans to identify adaptation strategies to avoid or minimize risks to development and to avoid or minimize and mitigate impacts on coastal resources. A full suite of potential adaptation strategy alternatives should be considered and documented for inclusion in the CDP application, including nature-based solutions, active management strategies, relocation, elevation, and short- or potentially longer-term armoring. Long-term adaptation solutions may take years of planning and coordination with local governments and other public entities, and the process for long-term planning and collaboration may need to become an element of the overall proposed project and its funding.

In general, the Coastal Commission requires strategies be prioritized that avoid hazards related to SLR, such as relocation or elevation, and nature-based adaptation strategies be employed as feasible to protect existing infrastructure while implementing phased long-term adaptation. In all cases, the selected strategy or strategies must avoid or minimize and mitigate impacts on coastal resources, including public access, recreation, marine and terrestrial resources, and visual resources; ensure safety and stability of infrastructure; and maintain transportation services to communities that are responsive to shifting community needs over time. For Caltrans, adaptation plans—which could include project-level plans, Corridor Plans, or District System Management Plans addressing specified vulnerable segments over near- and longer-term time frames—should address the impacts of SLR on transportation infrastructure and coastal resources before they occur and should incorporate appropriate periods of lead time that allow for planning, funding, and implementation.

When an existing Caltrans facility—such as a segment of roadway or bridge—is at risk from coastal hazards including SLR and a shoreline protective device is being considered for protection of the facility, it is important to consider applicable Coastal Act and LCP policies and permitting requirements.  Although shoreline protective devices may cause adverse impacts on coastal resources, the Coastal Act recognizes that shoreline protection may be potentially allowable in certain limited circumstances, often for limited time periods.

Caltrans has received permits from the Coastal Commission for projects that protect, repair, or restore sections of roadway that are at risk of failure from coastal erosion. Some of the adverse impacts on coastal resources from the use of hard shoreline protective devices can include loss of shoreline habitat, decreased sand supply, and reduction of public access and recreational opportunities. Coastal Act Section 30235 lists types of development that may allow shoreline protection, including coastal-dependent uses, existing structures, and public beaches in danger from erosion, and specifies that such protection is only approvable “when designed to eliminate or mitigate adverse impacts on local shoreline sand supply.” Armoring may be lawfully allowed in these circumstances and may represent a reasonable short- to mid-term SLR adaptation strategy. This may be especially true where critical infrastructure exists, and where the armoring is the least environmentally damaging alternative within the context of phased adaptation responses. However, any such short-term design feature that relies on armoring will often be permitted for a limited time period, and permit approval would likely be subject to conditions, which would include requirements for long-term SLR adaptation planning that protects public safety and coastal resources in a manner that does not require the long-term retention of the protective device.

Local governments with jurisdiction over a project may have Coastal Act Section 30235 incorporated directly in their LCPs, or by reference, and may also have additional shoreline protective devices/coastal armoring policies and provisions that are similar to or different from Section 30235. It is important to carefully review all applicable policies and provisions to understand how they may apply to a project.

Caltrans state and system transportation planning activities—including statewide transportation plans, District System Management Plans, and Corridor Plans to name a few—should address the unique SLR adaptation planning needs in the Coastal Zone. Relevant Coastal Commission SLR recommendations for planning activities can be found in Chapter 5 of the 2018 Sea Level Policy Guidance (PDF).  In general, identification of long-term adaptation strategies that avoid or minimize risks to Caltrans’ transportation system and avoids or minimizes and mitigates impacts on coastal resources may take years of planning and coordination with local governments and other public entities. 

Coordination on SLR adaptation across Caltrans divisions including Transportation Planning, Project Delivery, and Asset Management/Maintenance will become increasingly important as sections of roadways and Caltrans assets that are vulnerable to coastal erosion increase as sea levels rise. Regional and corridor-level transportation planning is necessary to address both incomplete and unforeseen project permitting requirements for SLR in a manner that identifies programmatic needs and funding. For example, Caltrans is currently developing Adaptation Priorities Reports for each district, and as various system plans are updated—including Corridor Plans and District System Management Plans—there is an opportunity going forward to identify longer-term transportation system adaptation strategies that avoid impacts on coastal resources, resolve outstanding and potential permit requirements, and ultimately deliver a resilient coastal transportation system. At the same time, projects that are moving forward in the Coastal Zone will likely need SLR analysis and planning, regardless of the status of the statewide Caltrans SLR planning efforts.

Utilizing existing Caltrans Transportation Planning and Asset Management procedures that could integrate these long-term SLR adaptation needs for a more streamlined and efficient permitting process aligns with the goals identified by the Assembly Bill 1282 Transportation Permitting Taskforce. For example, as Project Nomination Teams assess project needs that are in the Coastal Zone there is an opportunity going forward to identify within the Transportation Planning Scoping Information Sheet (TPSIS) whether the project could be vulnerable to SLR and the resources needed to adequately design for adaptation.

Multiple emergency follow-up CDPs and regular CDPs granted by the Coastal Commission for roadway segments that are vulnerable to coastal erosion have included special permit conditions that require long-term SLR adaptation solutions to coastal hazards. These emergency projects have included use of shoreline armoring solutions—such as seawalls, rock slope protection, or revetments—which the Coastal Commission has considered to be the least environmentally damaging short-term, or temporary, project alternative while a longer-term, more permanent solution, for the coastal transportation system is developed. These special conditions have included monitoring, mitigation, and/or submission of a future CDP application within a designated time period to retain or replace the device that includes analysis of coastal hazards—including SLR—as well as an explanation of how the project fits within a longer-term transportation adaptation plan or strategy that addresses vulnerabilities in a way that eventually removes the shoreline protective device and avoids negative impacts on California’s coastal resources.

A priority emphasized by California’s 2022 Climate Adaptation Strategy, the State’s commitment to advancing multi-benefit, nature-based solutions seeks to ensure that California’s communities and natural systems continue to thrive together in the face of climate change—and also reflects the opportunity to avoid maladaptation—or the concept that constructing protective infrastructure like seawalls in some of our most hazard-prone areas can “lock-in” and increase vulnerabilities while providing a false sense of security (IPCC AR6 (PDF), 2022). Natural or nature-based solutions should be prioritized wherever feasible, particularly in areas that could be flooded or eroded from tidal or fluvial processes like riverine or coastal areas.  The Federal Highway Administration has released implementation guidance for nature-based solutions, which indicate that these measures can enhance the resilience of coastal highways to SLR under conditions ranging from typical to extreme weather events. The Coastal Commission has also identified nature-based adaptation solutions as one of the preferred alternatives for addressing SLR and the vulnerability of existing endangered structures, including transportation infrastructure, to coastal hazards. Nature-based solutions rely on natural ecological and physical processes to offer protection services to the built coastal environment. More generally, Executive Order B-30-15 and EO N-82-20 (PDF) obligates state agencies to prioritize and accelerate use of natural infrastructure solutions, and various state policy resources identify nature-based solutions as a priority adaptation strategy, including the OPC’s 2018 SLR Guidance (PDF), the Climate Action Plan for Transportation Infrastructure (CAPTI), and the California Climate Adaptation Strategy. Below are some resources on natural infrastructure, as well as a permitted project that utilizes natural infrastructure to protect a section of Highway 101 in Cardiff.

Below are some resources with specific engineering design guidance and California case-studies:

Caltrans Sea Level Rise Resources for Project Delivery

Caltrans projects in the Coastal Zone that will need CDPs from the Coastal Commission or local agency with a certified LCP should consider SLR in all phases of project delivery, especially early in project nomination and scoping activities (such as within the Preliminary Environmental Assessment Report/ Project Initiation Document) and in preparation of environmental documentation. Projects should consider coastal hazards including SLR and how these impacts change over time in conjunction with flooding, 100-year storms, and wave impacts, erosion, and geologic instability.

Key conditions for whether a project or project site should consider SLR include if it:

  • Is projected to be exposed or affected by future SLR and coastal hazards
  • Has been or could be within or adjacent to an identified floodplain
  • Has been or could be exposed to flooding or erosion from waves, tides, or rivers/creeks/streams
  • Is currently in a location protected by constructed dikes, levees, bulkheads or other flood-control or shoreline protective structures
  • Is on or close to a beach, estuary, lagoon or wetland
  • Is on a coastal bluff susceptible to erosion
  • Is reliant upon shallow wells for water supply

If a project meets any of these conditions, coordination early and often throughout the project delivery process should occur with the Coastal Commission and/or local agency staff in order to adequately address SLR in the project, avoid delays in processing the CDP application, and meet Ready to List (RTL) deadlines.

The following resources, project examples, and other information provided here are available for review and consideration when preparing a SLR analysis for an environmental document or CDP application for a project and may also be relevant for Caltrans system plans and other planning activities.

Early coordination during the Project Initiation Document (PID) / Preliminary Environmental Assessment Report (PEAR) Phase—or sooner in district or corridor planning activities—is essential. It is advised that discussions occur between the Project Development Team (PDT) and the Coastal Commission and/or local agency staff to appropriately address SLR for the project. Early coordination will help determine the technical SLR studies that will need to be conducted, ensure a full range of project alternatives will be evaluated that consider resiliency over time within the project corridor, and allocate adequate resources (time and funding) for those assessments. This coordination will improve project outcomes and minimize delays in processing the CDP application.

A technical SLR study should be completed no later than the Project Approval and Environmental Document (PA&ED) Phase, and potentially earlier depending on the project. Caltrans’ Coastal Program recommends that environmental staff utilize the 5 Steps identified within Chapter 6: Addressing Sea Level Rise in Coastal Development Permits (PDF) of the Coastal Commission’s 2018 Sea Level Rise Policy Guidance for receiving permits. This could include conducting a coastal policy consistency analysis (PDF)—and addressing relevant policies and provisions of certified LCPs where applicable—within environmental documents and CDP applications. If the SLR analysis within the informational materials assembled to request a CDP is found inadequate, the application will likely be deemed incomplete and may create serious project delays.

For projects that are vulnerable—or are expected to become vulnerable—to coastal hazards including SLR, a full suite of potential adaptation strategy alternatives should be considered and documented for inclusion in the CDP application. This analysis should include nature-based solutions, active management strategies, relocation, elevation, and short-term or potentially longer-term armoring. The Coastal Act recognizes that shoreline protection—such as rock slope protection or seawalls—may be allowed in certain limited circumstances. Harmful impacts on coastal resources from shoreline armoring can include disruption of sand supply, increased erosion along the adjacent shoreline, diminished public access and recreational space, and result in the loss of beaches and other coastal habitats and resources as sea levels rise. Coastal Act Section 30235 lists types of development that may be allowable shoreline protection, including coastal-dependent uses, existing structures, and public beaches in danger from erosion. Section 30235 also specifies that such protection is only approvable “when designed to eliminate or mitigate adverse impacts on local shoreline sand supply.” Armoring may be lawfully allowed in these circumstances and may represent a reasonable short to mid-term SLR adaptation strategy.

Examples of Caltrans projects that have successfully received CDPs are provided here:

Long-term adaptation of California’s transportation system—including roadway corridors, bridges, railways, culverts, and bicycle and pedestrian paths—to SLR will require an extraordinary and unprecedented level of coordination that navigates complex regulatory requirements and inspires a shared vision that motivates collective innovation in how Caltrans plans, designs, and finances transportation adaptation. Caltrans and the Coastal Commission have a long history of working together effectively to protect coastal resources and to provide safe roadway networks and access to California’s coastline; within the 2016 Caltrans & California Coastal Commission: Plan for Improved Agency Partnering (PDF), SLR was identified as a key focus area for both agencies and going forward, the Caltrans Coastal Program is focusing efforts to provide useful information to Caltrans staff and other interested stakeholders about opportunities to address SLR and respond to the challenges it poses. These efforts include:

  • Developing tools that enable Caltrans to meet Coastal Act requirements and related State Highway mandates, for development to minimize risks in areas of high geologic, flood, and fire hazard and to ensure project stability and structural integrity over its lifetime.
  • Identifying planned and/or programmed Caltrans projects located in areas that are vulnerable to climate change/SLR over their projected design lives and use them as case studies to improve our collective ability to address climate change and SLR into the future.
  • Reviewing the SLR-related studies and information that should be developed (during the course of transportation corridor evaluations; project purpose, need and scoping efforts; and project detailing throughout environmental evaluations/design engineering), particularly in anticipation of filing complete CDP applications.
  • Sharing information on SLR models and viewing tools and promoting a common understanding of their utility for plans and projects in the Coastal Zone.
  • Identifying Caltrans transportation facilities/infrastructure (including highways, railways, bike and pedestrian pathways, and other corridors) “hot spots” that are currently, or most likely to be, affected by SLR in the nearer term, and develop interagency strategies with other stakeholders to address those areas.

Local and Regional Plans

*Under Development* A comprehensive dataset of Local Coastal Program plans, regional transportation plans, local plans, and Caltrans plans is in the process of being developed that will allow for identification of plans or analysis that may be relevant for Caltrans project scoping or for planning engagement as they are updated or amended.

In the meantime, this section provides a list of local governments with certified LCPs that are in the process of updating plans and policies on SLR that may benefit from Caltrans transportation district coordination.

California Coast

Best Available Science

In recent years, there have been substantial advances in the scientific understanding of SLR and how it will affect California. Knowledge will continue to evolve, possibly significantly, in coming years. Coastal Act Section 30006.5 finds that “sound and timely scientific recommendations are necessary for many coastal planning, conservation, and development decisions […] especially with regard to issues such as coastal erosion and geology, marine biodiversity, wetland restoration, sea level rise, desalination plants, and the cumulative impact of coastal zone developments.”

For transportation projects in the Coastal Zone, it is important to recognize that the Coastal Commission considers the best available science in rendering its decision to approve or deny a Caltrans project. Therefore, it is critical that Caltrans engages Coastal Commission staff early and throughout the planning and project delivery process in order to utilize best available science.

Currently—in alignment with the OPC State of California Sea-Level Rise Guidance: 2018 Update (PDF)best available science for SLR analysis for critical infrastructure projects like transportation should assess the medium-high and extreme (H++) SLR projections for the anticipated life of the project in conjunction with the combined effects of the coastal hazards that have the potential to affect the site (i.e., wave run-up, flooding, erosion) and 100-year storm activity.

Understanding that scientific advances in observed phenomena, modeling data output, tools, plans, and policy will likely continue to evolve, the Resources section on this webpage will be continually updated with state guidance, data, plans, and tools.


5 Steps to Address SLR in CDPs

Chapter 6 (PDF) of the Coastal Commission’s 2018 Sea Level Rise Policy Guidance outlines information and specific recommendations for addressing SLR in CDP applications and outlines the following five-step process to address SLR in the project design and permitting process in cases where SLR may contribute to or exacerbate hazards or affect coastal resources: 

  1. Establish projected SLR range for the proposed project: define expected project life, select appropriate SLR scenario (i.e., medium-high and extreme (H++)).
  2. Determine how SLR impacts may constrain the project site: evaluate SLR impacts in conjunction with coastal hazards as appropriate (i.e., cliff erosion, 100-year storm, wave runup, etc.).
  3. Determine how the project may impact coastal resources, over time, considering SLR: coastal resources can include Public Access and Recreation, Coastal Habitats, Natural Landforms, Agricultural Resources, Water Quality and Groundwater, Scenic Resources.
  4. Identify project alternatives to both avoid resource impacts and minimize risks to the project.
  5. Finalize project design and submit permit application.

The National Oceanic and Atmospheric Administration (NOAA) and the Federal Highway Administration (FHWA) invited Caltrans along with the California Coastal Commission to jointly provide a presentation on their partnership for a briefing to the United States Congress on September 9th, 2021 entitled, Protecting coastal roads from sea level rise and storm surge flooding with the Federal Highway Administration. The following presentation materials are available:

Disclaimer: This collection of data and tools are provided for informational purposes only; Caltrans makes no evaluation or statement of their accuracy, completeness, or appropriateness for use in any particular purpose. The tools and data are based on a variety of methodologies and model simulations, and real-world outcomes will differ from the results of the tool and data.

The Caltrans Division of Environmental Analysis’ GIS Library contains all of the sea level rise data listed below, and allows for it to be viewed alongside other data like the coastal zone, habitat, and transportation information.  REST services available on this website.