Protecting the South Coast from Sea Level Rise
Learn about the impacts of sea level rise to the South Coast of San Mateo County and explore the many ways to protect our communities.
The South Coast
South Coast Region
The South Coast of San Mateo County spans more than 30 miles of rural coastline from the southern end of Half Moon Bay down to Año Nuevo State Park. The coast has miles of public beaches where locals and visitors alike enjoy walking and hiking, fishing and oyster harvesting, and water recreation, and enjoy historic landmarks like the Pigeon Point Lighthouse.
Farms and ranches dot the South Coast and surround the small town of Pescadero, providing the region with Brussels sprouts, pumpkins, and other cool weather crops. Agriculture is the backbone of the local economy here.
The region is home to many small businesses, such as the Highway 1 Brewing Company as well as many local farm stands. One of the most remarkable parts of the region is the natural beauty and vitality of the coastal blufftops and cliffs, the intertidal zone, beach and dunes, estuaries and creek habitats, and the species they support. Through it all, Highway 1 winds along the South County coast, providing the primary transportation connection and offering spectacular coastal views that draw visitors from around the world. The ocean has shaped the South Coast’s past and present - physically, biologically, culturally, and economically. As the ocean changes, it also reshapes our life by the sea.
What is Sea Level Rise?
Our planet is getting warmer due in large part to human actions, like burning fossil fuels. As Earth gets warmer, the water in our oceans expands, and glaciers and ice sheets near the earth's poles begin to melt, releasing more water into the oceans. As a result, sea levels are rising, and we are already feeling the effects.
More Natural Hazards, More Often
Sea level rise means more frequent and severe floods and coastal landslides, and more rapid coastal erosion (the process of gradually losing land to the ocean). Many South Coast communities already live with natural hazards like flooding and erosion, but this risk will rise over time. It is important to understand that flood or other hazard events can happen at any time, and we need to be prepared for those impacts.
Why Should We Care?
Sea level rise is already happening. Though we can make educated guesses about how sea level rise will affect us in the future, it is uncertain exactly when increasingly frequent impacts like floods or landslides will occur, or how extreme they will be. That is why we need to start preparing for sea level rise now. Together, we have the knowledge and resources to prepare ourselves for future conditions and reduce the impacts that sea level rise has on our communities.
Governments, stakeholders, and communities should also consider that the South Coast is the ancestral home of the Ramaytush Ohlone and is rich in cultural areas, cultural materials, and natural resources that are of high importance to them. Many of the cultural areas in the region have helped archaeologists better understand past ecological and climatic conditions that Ohlone People lived with before European colonization. Some of these cultural resources are at risk to sea level rise impacts, though these assets may not be as visible or measurable to non-Native landowners or land managers and therefore don’t often appear in typical sea level rise vulnerability assessments. To identify and reduce potential sea level rise impacts to cultural resource like these, it is important for government and other landowners to collaborate, coordinate, and share information with Tribes (in the case of the South Coast, the Ramaytush Ohlone, via the Association of Ramaytush Ohlone [ARO]) so that these cultural resources can continue to be identified and protected as much as possible.
SMC South Coast Sea Level Rise Vulnerability Assessment 2021
Vulnerability Study
The first step in preparing for sea level rise is understanding our risk. From 2019-2021, the County of San Mateo Office of Sustainability (OOS) collaborated with the U.S. Geological Survey and Integral Consulting, Inc. to map the areas of the South Coast that will be impacted by erosion and flooding as a result of sea level rise.
The study shows what places along the South Coast will most likely be affected by coastal flooding and erosion with different sea level rise amounts projected to happen over time. The scenarios indicate the projected extent of flooding and erosion should the area experience a 1% chance annual storm plus sea level rise. The baseline scenario shows the possible extent of flooding and erosion with a 1% annual chance storm. The near-term scenario shows the possible extent of flooding and erosion during a 1% chance annual storm plus 0.8 feet of sea level rise. The mid-term scenario shows the possible extent of flooding and erosion during a 1% chance annual storm plus 1.6 feet of sea level rise. The long-term scenario shows the possible extent of flooding and erosion during a 1% chance annual storm plus 4.9 feet of sea level rise.
Baseline (Present Conditions): 0 feet Near-term (2030): 0.8 feet Mid-term (2030-2060): 1.6 feet Long-term (2060-2100): 4.9 feet
The study looks at impacts to and potential solutions for: - Land use and structures (Houses, buildings and privately and publicly owned land) - Agriculture (Land used for growing crops and ranching) - Transportation and parking (Highway 1 and other public roads and parking lots) - Parks, recreation and coastal access (Beaches, trails, parks)
In the sections below, you will read about some of the South Coast's resources that are at risk to sea level rise impacts, including Highway 1, coastal communities, and our access to the beach. If you are interested in learning about sea level rise vulnerability in greater San Mateo County, click here .
Highway 1
Highway 1 is the primary transportation connection along the entire South Coast of San Mateo County. It is a lifeline for the residents and small communities, farms, ranches, businesses, and visitors of the South Coast. Erosion is already threatening parts of the highway, and impacts are projected to worsen in the future with higher sea levels. This could affect the integrity of the roadway, leading to the need to stabilize or relocate stretches of the Highway 1.
When a part of Highway 1 is lost or buried by an erosion event, expensive cleanup and repairs can last for months – even years –disrupting access for communities, businesses and visitors.
Detours shift the Highway 1 traffic onto small, winding roads not meant for so much traffic, which can cause accidents and even more delays. In the South Coast, these disruptions are much more than an inconvenience. Without Highway 1, emergency responders cannot get to emergencies, and farmers cannot get their products to market.
The South Coast Sea Level Rise Study identified some areas on Highway 1 that are especially vulnerable to sea level rise:
Highway 1 at Bean Hollow State Beach When: Near-Term (Now to 2030) Problem: High tides cause sand to plug the highway drainage pipe, preventing the creek from draining under the highway. With sea level rise, higher high tides are making this happen more often.
What Can We Do? Currently, Caltrans cleans out the pipe to prevent water from backing up and blowing out the road. Carrying on with as-needed repairs will soon lead to unreasonable access disruptions and costs. Other approaches that adapt this area to the “new normal” could range from an upgraded drainage pipe to a new crossing over the creek.
Highway 1 Near Pomponio State Beach When: Near-Term (Now to 2030) Problem: At this spot, Highway 1 dips down as it it cuts across the outlet of Pomponio Creek. Currently, it is protected from coastal wave flooding by dunes that back Pomponio State Beach. With high sea level, these dunes will rapidly erode, leaving the highway unprotected and vulnerable to storm waves and flooding.
What Can We Do? Protecting and restoring dune habitat (e.g. revegetation) will help prolong the buffering benefits. This would provide time to plan and implement a more “permanent” solution such as elevating the highway with a bridge crossing at the creek.
Highway 1 near Pescadero When: Mid-Term (2030-2050) Problem: Bluff erosion is undermining the highway.
What Can We Do? In the near-term, Caltrans can continue to use rock to “armor” this and similar spots on Highway 1, but this comes at a price in terms of increased repair costs, access disruptions and harm to adjacent beach and bluff habitats.
When we have built environments like the highway that interrupt natural environments, like dune and marsh habitat, we tend to see negative consequences for both the roadway and surrounding habitats. Eventually, relocating and realigning portions of Highway 1 will likely be necessary. This is a process that will take decades. To have solutions in place when we need them, we need to start planning now.
Coastal Communities
Many coastal communities dot San Mateo County's South Coast, each with their own unique identities. Two of these communities are particularly vulnerable to sea level rise: Martin's Beach, which sits directly on the coast, and Pescadero, an inland town that will be affected by sea level rise through coastal impacts to the two creeks that flow through it.
Martin's Beach
Martin's Beach is both a residential community and a popular recreation spot for surfers, birdwatchers, and beachgoers. The secluded cove is flanked by high bluffs of farmland and accessible only by a single private road.
A postcard of Martin's Beach, estimated to date to the 1960s.
Impacts to Martin's Beach
Because of its natural topography, Martin's Beach and its surrounding bluffs are already vulnerable to damage from flooding and erosion during winter storms. Despite the temporary seawall and rip-rap pilings already in place, the roadway and some structures still flood. As sea levels rise, storm wave flooding and coastal erosion are projected to increase, threatening the natural habitat along this shoreline as well as possibly damaging existing structures and the access road.
Martin's Beach: What Can Be Done?
Coastal armoring strategies such as seawalls and revetments currently in place, have limited effectiveness in the present and will become significantly less effective over time. Notably, coastal armoring often has negative impacts on the coastline over the long-term and can exacerbate erosion down the coast. As such, it is important to consider strategies that are structure-specific, such as:
- Elevate structures, utilities, and roadways where possible and floodproof assets that cannot be raised
- Explore the future possibility of relocating repetitively damaged and at-risk structures and utilities out of the high-hazard zone
Pescadero
Pescadero is an unincorporated community known for its historic downtown, pristine coastal recreation areas, and family-owned farms and ranches covering hundreds of acres in the Pescadero-Butano watershed. Visitors enjoy its miles of beaches and hiking trails spread throughout acres of county and state parks and open space preserves.
The town dates to the 1850s and serves as a community center for people living and working from Highway 84 south to the Santa Cruz County border, providing vital services such as the region’s post office, fire station, health and welfare resources, schools, places of worship, meeting halls, and a public radio station, as well as markets, restaurants, and shops which serve both residents and visitors alike.
Just northwest of town, the Pescadero Marsh is a critical habitat for both migratory and native wildlife, and connects the freshwater Pescadero and Butano Creeks with the tidal basin of the Pacific Ocean. The largest ecological preserve between San Francisco and Santa Cruz, the marsh is breeding ground for several endangered and threatened species, and offers priceless views for wildlife observation from its many hiking trails.
From Highway 1, Pescadero Creek Road is a vital thoroughfare to the residential enclaves of Butano Canyon and Loma Mar, as well as the main access route for emergency responders and visitors to the region’s many parks and farm stands.
Pescadero's town sign at the intersection of Highway 1 and Pescadero Creek Rd.
What's at risk?
Sea level rise has the potential to reshape the Pescadero community, economy, and environment in two significant ways. Beach and cliff erosion could displace homes, farm fields, and other types of land use on the western side of Highway 1. Higher sea levels could also increase the frequency and severity of flooding in low-lying areas adjacent to Pescadero Marsh, as tidal waters spread further inland. Sea level impacts on potable water supply are an ongoing concern for many residents; it is still uncertain exactly how saltwater intrusion to groundwater may occur with rising seas. Though sea level rise impacts to groundwater were not part of this study, the County is aware that this issue needs to be examined and mitigated.
The map to the right shows sea level rise hazard zones over time. As sea levels rise, areas at risk to flood and erosion expand inland. These areas are represented by shades of blue. Darker blue represents hazard areas right now and the lighter blue represents where hazard areas are projected to expand to in the future.
The areas with blue crisscross lines represent the current FEMA flood zone, added to the map to give readers a fuller picture of local flood risk. Some of the FEMA flood area extends beyond the flood area that will be affected by sea level rise. This just means that sea level rise and coastal processes are unlikely to change flood patterns here, though higher precipitation and other natural processes could still impact frequency and severity of flooding in this area.
Impacts to Homes, Businesses, and Roads
The homes and businesses along Pescadero Creek Road, particularly structures along Water Lane, are most likely to need protection from creek flooding exacerbated by sea level rise. Chronic flooding may make homes unsafe to occupy, leaving families without shelter in a region with few housing alternatives. Businesses may require expensive modifications or risk damage to inventory and equipment, as well as face rising insurance costs.
West of Highway 1, erosion may threaten clifftop homes and other structures. While engineered solutions like sea walls and rip-rap can provide temporary protection to an individual property, these options may also unintentionally harm adjacent parcels and shoreline habitats
The intersection of Pescadero Creek Rd. and Stage Rd. during a 2017 flood.
What has been done or is in progress?
State, county, and local partners are already taking steps to reduce risks to people, habitats, and the built environment in the Pescadero region. To reduce severity and frequency of flooding in the short- to medium-term, San Mateo Resource Conservation District (RCD) and California State Parks successfully restored the Butano Creek channel in 2019 to alleviate sediment build-up and storm-induced flooding across Pescadero Creek Road (read more about this project here ). The photo swipe to the right shows the restoration of the water channels through the marsh, meant to reduce the frequency, severity, and duration of flood events in town.
The dredging of Butano Creek aimed to reduce the severity and duration of flood events along Pescadero Creek Road.
To protect critical infrastructure and ensure emergency personnel have the capacity to respond to emergencies, San Mateo County is planning to relocate and update Cal Fire Station 59 out of a high-risk flood zone. Its proposed location near Pescadero High School is significantly less prone to flooding, even with sea level rise. Read more about this project here .
The design for a relocated and updated Cal Fire Station 59.
What More Can We Do?
- Monitor and prevent silt build-up and allow a natural, gradual transition between Butano Creek and the marsh to reduce the frequency of road flooding.
- Elevate at-risk structures above the potential sea level to protect these buildings while allowing flooding to occur.
- Identify and relocate sources of potentially hazardous materials or contaminants, such as septic tanks, fuel tanks, agricultural chemicals, or household products to further reduce risks.
- Elevate or re-align Pescadero Creek Road or prepare other routes to the downtown district to protect access to vital services and homes.
- Consider areas for potential relocation. This may include changes to land use policy, zoning ordinances, and building and permitting processes as well as identifying funding mechanisms to assist property owners with financing relocation projects.
Impacts to Agriculture in the Pescadero Region
With even moderate rises in sea level, floods will move further inland, impacting more agricultural land. Land that is now profitably farmed may become less fertile as the soil salinity rises. Realignment of roads and trails could force relocation or loss of farmed areas, and as clifftop land erodes, some agricultural operators may lose access to arable land and structures along the coast. All of these impacts would reduce the economic stability of the Pescadero region, and weaken the community’s cultural identity.
This map demonstrates the agricultural parcels that are at risk to sea level rise-exacerbated flooding. Red parcels are at risk now, with orange and yellow parcels representing future hazard risk to the parcel.
Agriculture: What Can We Do?
Acknowledging the critical importance of agriculture to the South Coast's economy and the many farmworkers the sector employs, it is important to consider implementing multiple adaptive actions that can be carried out at the farm operator level, and the community and regional scales, including:
- Storm proof and elevate structures
- Further research impacts to water quality from sea level rise and potential impacts to irrigation
- Plan and develop projects to protect human health and the quality of drinking water
- Participate in creek and floodplain restoration projects
- Test and utilize agricultural practices that build soil health and stability and productivity to buffer against the deterioration and loss of farmland affected by flooding
- Begin long-term planning for transition to crops that are flood- and saltwater-resistant in zones projected to be highly affected by sea level rise
- For more information on long-term agricultural adaptation to saltwater intrusion, see the USDA's informational page here .
The Pescadero Marsh
As the gateway to the town, Pescadero Marsh Nature Preserve is a critical cultural and environmental resource. Its trails and observation points are a favorite destination of residents and tourists alike, with an estimated 63,000 visits per year.
Impacts to Pescadero Marsh
Beyond affecting recreational access to the marsh during increasingly frequent flood events, sea level rise will impact available habitat for native species over time. Though rising sea levels may at first expand habitat, over the long-term, available marsh habitat becomes limited.
In the Pescadero Marsh, sea level rise will cause inundation of wetlands habitats, creating a need for more sediment to allow habitats to “keep pace” with higher water levels.
What Can We Do?
Right now, a collaborative effort by the San Mateo Resource Conservation District, Integral Consulting, Inc., UC Davis, CSU Monterey Bay and California State Parks is modeling marsh conditions and designing a restoration project to help fix existing issues for habitat protection that are caused by past land use decisions. This work is also evaluating changes over time, including sea level rise, to consider future project options for redesigning water control structures in the marsh to manage sediment distribution and protect vulnerable marsh habitats for as long as possible.
Coastal Access
The San Mateo County South Coast is a natural treasure that visitors from near and far flock to every year.
From the elephant seals at Año Nuevo State Park, to the surfing and other water recreation opportunities, to the iconic Pigeon Point Light House, the South Coast is full of wonder.
Coastal access points, beaches, and trails, and parking and restrooms, are already impacted by flooding and erosion and sea level rise is projected to exacerbate these impacts.
The Our Coast Our Future tool is one model that demonstrates how flooding will affect coastlines with different levels of sea level rise.
Trails
In the northern part of the study area, approximately 5 miles of California Coastal Trail follow the bluff edge from the Ritz-Carlton Hotel in Half Moon Bay south to Seal Rock along the Cowell-Purisima Trail. 22% of this trail is projected to be impacted by erosion with near term (2030) sea level rise of 0.8’. With 1.6’ of sea level rise (projected in 2030-2060) the amount of projected affected trail is 47%.
Coastal trail sections in the southern part of the study area may similarly be affected, including:
- Arroyo de los Frijoles Trail (Bean Hollow State Park)
- Mel’s Lane & Pigeon Point Bluffs Trails (Pigeon Point County Park)
- Atkinson Bluff Trail (Año Nuevo State Park
- Año Nuevo Point Trail (Año Nuevo State Park)
Beaches, Parking, and Restrooms
Popular beaches throughout the South Coast are vulnerable to sea level rise impacts. At each of these beaches, coastal erosion and wave flooding may threaten the beach, access trails, and beach facilities.
At Pomponio, Pescadero and Bean Hollow State Beaches, dunes currently provide some protection against coastal erosion and wave flooding, but dune erosion caused by sea level rise will eliminate these natural buffers.
Visitors regularly park along the west side of Highway 1 near coastal access. These areas are not maintained or formally recognized, but they serve a critically important role for providing beach access on the South Coast. These areas are also at risk to coastal flooding and erosion.
What Has Been Done?
State Parks released a Sea Level Rise Adaptation Strategy in 2021 that provides a framework for how the department will incorporate sea level rise considerations into existing park operations. The Strategy is not park-specific, but rather provides a department-wide approach to sea level rise adaptation planning. State Parks' Sea Level Rise Strategy can be found here .
As outlined in the Sea Level Rise Strategy, State Parks recognizes the need to complete site-specific sea level rise vulnerability assessments, which will better inform coastal projects and long-term adaptation planning.
State Parks uses models from the United States Geological Survey (USGS) Coastal Storm Modeling System (CoSMoS) to evaluate projected exposure to future sea levels. The projections that are selected for analyses are based on the recommendations included in the State of California Sea Level Rise Guidance , which was released by the Ocean Protection Council in 2018.
What More Can We Do?
- Use nature-based systems to strengthen the shoreline
- Complete site-specific vulnerability assessments to inform project planning and long-term adaptation planning
- Research ecologically-friendly ways to protect historic and cultural resources
- Expand pedestrian access to coastal areas
Our ability to protect coastal access and recreation activities along the South Coast will depend on whether we give them space to move inland as the shoreline retreats.
Accomplishing this will take significant time, coordination, collaboration, and investment. To ensure solutions are in place when we need them, we need to start planning now.
What Can We Do?
With a better understanding of how sea level rise will affect the San Mateo County South Coast, we can identify what individuals, communities and government can and should do to prepare and develop a plan and timeline for taking actions.
At the government and community level
Solutions for long-term viability of communities, agriculture and other businesses, transportation access, coastal access and recreation, cultural and historic resources and coastal habitats require coordinated, comprehensive, and collaborative planning by the County, other local and state agencies, and local communities and businesses. Projects and policies can focus on protecting structures, infrastructure and resources from flooding, as well as modifying and moving them to better accommodate sea level rise and other climate impacts. Impacts won't happen all at once, so we'll need to think both near- and long-term to develop multi-part responses that we can implement over time, as conditions or impacts prompt us to begin the next phase of a project.
At the household and individual level
As individuals we can advocate for and engage as much as possible in these planning efforts and projects at the community and county level that increase our preparedness for sea level rise impacts and other hazards. In the near-term, residents and businesses may have opportunities - in partnership with local and state assistance programs - to make their homes, businesses and communities overall more resilient to flooding. These opportunities include:
- Floodproofing and elevating structures, utilities, and other assets where feasible
- Participating in creek and floodplain restoration projects
- Testing and utilizing agricultural practices that build soil health and stability and productivity to buffer against the deterioration and loss of farmland affected by flooding
For more information, email us at: sustainability@smcgov.org
