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The west coast of the United States is extremely complex and changeable because of tectonic activity, mountain building, and land subsidence. These active environments pose a major challenge for accurately assessing climate change impacts, since models were historically developed for more passive sandy coasts.
In 2002, when USGS geologist Patrick Barnard was living in San Francisco, California, he saw an opportunity to provide more science to assist the city’s management decisions to protect a multimillion-dollar sewage treatment plant built along the coast in 1993. Inspired to conduct research on chronic erosion in this region, he carried out surveys along the southern end of Ocean Beach for well over a decade, during which this man-made beach rapidly narrowed and nearby parking lot asphalt fell away. Barnard’s scientific contributions are now incorporated into the Ocean Beach Master Plan, where they are helping the city deal with past infrastructure decisions, since erosion threatens not only the sewage plant, but also the Great Highway, which may potentially cost the city hundreds of millions of dollars.
Compared with the U.S. west coast, the sandy stretches of the east coast are a much easier place to predict future sea-level scenarios. No major seismic activity occurs along the east coast, and the topography is relatively flat. This “passive” environment is unlike the “active” west coast, where large faults are commonly adjacent to the coast such as the Cascadia subduction zone off the Pacific Northwest. Also, much of the coastline consists of steep, rocky cliffs and terrain that shifts up and down during tectonic activity and that wash out and collapse onto coastal highways as illustrated in Big Sur, California. Rivers here deliver more sediment to the coast from younger mountains, and the Pacific Ocean generally brings in bigger waves.
In areas of complex coastal geography like the west coast, traditional models used to predict sea-level rise aren’t adequate. Simple “bathtub” models developed in the 1950s show how much sea levels will rise based just on land elevation; they ignore other oceanographic factors, such as seasonal effects (El Niño), increased wave action, and storm surge. Though sea level is expected to rise as much as 1.7 meters along the California coast by 2100, large waves and storm surge can elevate those levels an additional 5 meters during extreme winter storms. Without incorporating this storm component into climate projections, an important aspect of future vulnerability would be missed. The joint impacts of cliff erosion, beach erosion, and flooding are also unknown.
Existing Global Climate Models (GCMs) are the basis for the well-known, policy-influencing reports that the Intergovernmental Panel on Climate Change issues. But the scale of the GCMs is low-resolution, providing, for example, only a single wind estimate every 200 kilometers. Narrowing that scale down to 10 kilometers for wind estimates allows researchers to resolve hydrodynamic features, such as currents, down to tens of meters. This downscaling makes the projections more relevant for coastal managers of specific stretches of a coastline. Cities need to prioritize funds for hazard mitigation and for adapting to state policies on climate change, so an accurate, consistent, and cost-effective method of modeling is needed, which works across many city coastlines.
In 2011 a pilot project in Southern California combined a 2010 El Nino-fueled storm with projected values of sea-level rise to improve future forecasts of coastal flooding through the year 2100. The USGS collaborated with Netherlands-based research institute Deltares to model coastal flooding from Point Conception to Mexico. This model, the Coastal Storm Modeling System (CoSMoS), has now been applied to many other parts of California. It can project coastal flooding hazards for a range of storm conditions and sea-level rise.
In 2013, the USGS Coastal Marine and Geology Program in partnership with academic institutions, non-profit organizations, and other U.S. government agencies, helped to adapt the CoSMoS model into a Google Earth-based public outreach tool that visually demonstrates the flooding that could happen from Bodega Bay to Half Moon Bay. Our Coast, Our Future (OCOF) created a flood-map interface where users can view future coastal scenarios by choosing choosing a magnitude of a storm, or a king tide combined with varying sea-level rise. Scientists then fine-tuned this interactive web tool with a much higher resolution scale of coastal flooding within 2 meters. This higher resolution model is more relevant for coastal inhabitants, because conditions at the Golden Gate Bridge, for example, can be very different from those in South San Francisco Bay.
In 2014, the flood maps used by OCOF have been further refined to take into account the complex bathymetry of San Francisco Bay, such as the reclaimed region around the airport and the South Bay Salt Pond Restoration Project. City planners and state officials can now use the OCOF flood maps to help formulate infrastructure projects.
In 2015, USGS scientists extended the CoSMoS model up the coast to Point Arena, California, incorporating socioeconomic factors for San Francisco Bay, such as real dollar values of how many schools and other significant real estate could be impacted. An additional collaboration with the National Weather Service added the combined effect from rivers and oceans flooding simultaneously in the San Francisco Bay area, formerly a poorly understood phenomenon. When floodwater from a low-gradient river collides with ocean flooding, the river water has nowhere to go. So it “builds” up-river and floods land upstream.
From 2015-2018, we expanded the southern California model to include storm-hazard information for the coast from the Mexican Border to Pt. Conception in CoSMoS v3.0 for Southern California.
From 2018-2019, data developed for CoSMoS v3.1 for Central California covers the coastline from Pt. Conception to Golden Gate Bridge.
With just 4 percent of California’s coastline monitored for seasonal changes, more than 800 miles of open coast remains to be surveyed. A monitoring program began in 2004 at Ocean Beach near San Francisco, which experiences some of the highest erosion rates along California’s coast. Another ongoing monitoring program in Santa Barbara started a year later. Both provide a long-term perspective of coastal change.
For this monitoring, a team surveys bathymetry from personal watercraft, measures the grain size of the beach sand, and collects elevation data on foot and from all-terrain vehicles to create three-dimensional maps of the beach topography. They also deploy web cameras and instruments to measure water levels, currents, waves, and shoreline positions.
Ultimately, this team would like to know how California’s entire coastline will change over time. Adding more variables to the models, such as impacts to groundwater, will help provide a tangible picture of change, and what it will cost to relocate, or to preserve California’s coastal infrastructure and habitats.
The USGS found that the amount of sediment coming into San Francisco Bay from the Sacramento-San Joaquin River Delta has decreased. This sediment normally feeds many of the beaches south of the Golden Gate Bridge. Human activities such as damming, dredging, and sand mining affect the amount of sand that makes it to the open coast, which is insufficient to replace what is being washed away. In addition, erosion around a sewage outfall pipe 4.5 miles offshore from Ocean Beach has carved out a 200-meter-long trench spanning both sides of the pipe, which changes wave patterns in that area. USGS surveys also help to inform San Francisco city planners about the swiftly disappearing southern part of Ocean Beach¬– built out to accommodate the scenic highway alongside it– which is also at risk. The city’s challenge is to decide whether to invest in costly barriers and sand replacement, or let nature take its course.
The coast near Santa Barbara is part of a smaller watershed that brings much less sand to the ocean. Dams trap a large quantity of sand, further limiting the amount of sand contributed to beaches, which are fairly narrow in this area. The Santa Clara River, farther south in Ventura County, has no dam and is a main source of sand, as evidenced by the much wider beaches south of the river mouth.
In southern California, the team identified places particularly vulnerable to climate change, such as Venice, Marina Del Ray, Huntington Beach, Newport Beach, and many areas around San Diego. In March 2015, Barnard gave an invited presentation to San Diego area government officials and coastal managers on climate-change impacts and how the CoSMoS model could assist their planning for the region. [For more information, see: Coastal Storm Modeling System (CoSMoS)]
This research is part of the USGS project titled, “Coastal Climate Impacts.”Explore other research topics associated with this project, below.
Below are data or web applications associated with this project.
Below are publications associated with this project.
USGS Coastal Change Hazards research provides scientific tools to protect lives, property, and the economic well being of the Nation. The mission of the USGS Coastal Change Hazards Program is to provide research and tools to protect lives, property, and the economic well-being of the Nation. This is a story map that introduces the value of our coasts and the threats they face with global change.
Below are news stories associated with this project.
A new multidisciplinary case study from USGS and collaborators looks at how even modest sea-level rise threatens coastal communities, infrastructure...
USGS researcher quoted in major news stories about the August 2 coastal cliff collapse that killed three people on a beach in Encinitas, California
From October 9–15, USGS personnel surveyed beaches and the adjacent ocean floor along Monterey Bay’s northern coast.
From September 12–14, scientists from the USGS Pacific Coastal and Marine Science Center used all-terrain vehicles and small watercraft to map the...
USGS scientists combined a series of computer models to forecast cliff erosion along the Southern California coast.
Coastal cliffs from Santa Barbara to San Diego might crumble at more than twice the historical rate by the year 2100 as sea levels rise.
Research geologist Patrick Barnard and research oceanographer Li Erikson have been recognized for leading efforts to better assess coastal...
Pacific Coastal and Marine Science Center researchers plan to survey selected beaches and parts of the shallow seafloor in Santa Barbara and Ventura...
USGS geologist Patrick Barnard spoke to the public at a “Coffee and King Tides” gathering held in Half Moon Bay, California, on December 4.
Using a newly-developed computer model called “CoSMoS-COAST” (Coastal Storm Modeling System – Coastal One-line Assimilated Simulation Tool) scientists...
SANTA CRUZ, Calif. — The projected upsurge of severe El Niño and La Niña events will cause an increase in storm events leading to extreme coastal...
Secretary of the Interior Sally Jewell, Acting USGS Director Suzette Kimball, and San Francisco Mayor Ed Lee took part in a coastal climate change...