Dynamic coastlines along the western U.S.

Science Center Objects

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.

Woman stands on beach below eroded parking area, where some men are standing and looking down at beach.

Secretary Sally Jewell faces a field trip entourage on Ocean Beach in San Francisco, where a major part of the road as eroded. Behind USGS research geologist Patrick Barnard (arms crossed), Phil Ginsburg, General Manager of the San Francisco Recreation and Parks Dep't, chats with the mayor of SF Ed Lee (red cap). In the foreground is Ben Grant, Public Realm and Urban Design Program Manager at SPUR.

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

Issue

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 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.

Big ocean wave crashes against house and beachfront properties.

Waves crashing against a house at Stinson Beach near Bolinas, California.

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.

 

 

 

 

Man in foul-weather gear and hard hat sits in a parking lot on all-terrain vehicle equipped with GPS, ocean in background.

Jeff Hansen on an all-terrain vehicle (ATV) at Ocean Beach, San Francisco, in 2006. The ATV is equipped with instrumentation which records beach topography.

What the USGS is doing

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.

First map shows aerial view of beach area, next with 50-centimeter sea-level rise, last with added annual storm.

Flood maps from Our Coast, Our Future showing Stinson Beach today (slide 1); with a 50-centimeter sea-level rise (slide 2); and when an annual storm strikes in addition to 50-centimeter sea-level rise (slide 3). Green patches are low-lying areas prone to flooding.

Man with a backpack on holds a special camera flat on the wet sandy beach to capture a digital photograph of sand grains.

Student Andrew Schwartz positions a camera to measure beach-sand grain size. The grain size parameters can be extracted from a digital image by an analysis of the variation and offset of the pixel intensities. This allowed us to process over 300 sediment samples in less than a day, whereas traditional sieving could take several months of work. A standard digital camera is housed in a custom waterproof casing for use in the coastal environment.

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, the CoSMoS model will be extended up the coast to Point Arena, California, and will incorporate 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 aims to model the combined effect from rivers and oceans flooding simultaneously in the San Francisco Bay area, 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. Further modeling work in Southern California will look at how cliff and beach erosion will contribute to flooding, and also integrate the effects of flooding rivers.

Man wears a backpack and holds a small device in one hand, a pole in the other, on a beach with coastal mountains far off.

USGS Ocean Engineer Gerry Hatcher walks along South Jetty Beach, south of Ventura Harbor in southern California, to record beach elevations using a handheld computer and mobile GPS equipment.

 

 

 

 

 

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.

Parking spots and benches near a short seawall at the beach are inundated by winter waves.

The waterfront in Capitola, California, underwent severe flooding from a large storm in March 2014.

What the USGS has learned

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. [For more information, see: San Francisco Bay Coastal System Study]

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. [For more information, see: Santa Barbara Littoral Cell Coastal Processes Study]

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)]

Photograph shows eroding cliff in Isla Vista, California, with parts of houses hanging over edge.

Homes along the edge of the coast in Isla Vista, California, Santa Barbara County, face a short lifespan because of eroding bluffs that support them.

house perched at the top of cliff edge above beach.

Exposed bedrock on the beach during very low (negative) tide at Isla Vista, California

News

“A Growing Threat on the Shoreline” - NY Times, August 17, 2017

“Local Research with Global Effects: Coastal Scientists Study El Niño in Northern California” - USGS Sound Waves Newsletter, March 2016

“Ocean Beach’s Sand Supply Dries Up, Leaving Plovers Squeezed” - Bay Nature, September 2014

“Travels with Sediment in the San Francisco Bay, Delta, and Coastal System” - USGS Sound Waves Newsletter, January 2014

 

“Interactive Tool for Assessing Climate-Change Impacts Along the North-Central California Coast Supported by USGS Modeling System” - USGS Sound Waves Newsletter, April 2013

“SF Bay mining alarms conservationists” - SFGate.com, December 2012

“Environmental group sues state over San Francisco Bay sand mining report” - San Francisco Examiner, November 2012

Release of Geophysical Research Letters article in 2011 resulted in significant media attention:

  • “Battered West Coast a lesson on warming, study finds”: MSNBC, July 2011
  • “Violent Pacific storms of 2010 worst on record”: San Francisco Chronicle, July 2011
  • “Heavy coastal erosion in 2009-2010 winter linked to climate change”: Contra Costa Times
  • “Climate scientists evaluate impact of El Nino Modoki on the Pacific coast”: Oregon Live/The Oregonian, July 2011
  • “Forces of Nature Are Working to Destroy Ocean Beach”: Bay Citizen.org, January 2011
People with backs to the camera on hill above beach, man on right holds an electronic tablet and the woman on the left looks on.

While overlooking Pacifica State Beach (a.k.a. Linda Mar Beach), USGS geologist Patrick Barnard shows Secretary of the Interior Sally Jewell the predicted extent of flooding that could occur in the city of Pacifica during future large storms.

“Climate Change and Coastal Processes” - National Park Service podcast, July 2010

“USGS Scientists Investigate Coastal Processes Affecting a Restored Tidal Wetland in the San Francisco Presidio” - USGS Sound Waves Newsletter, February 2008

“Mystery of vanishing sand may be solved” - San Francisco Chronicle, January 2007

“City’s beautiful but hidden sand dunes” - San Francisco Chronicle, July 2006

“Beach study hopes to unlock mystery of erosion” - Richmond Review, March 200