With sea levels rising and storms increasingly threatening their shorelines and cliffs, officials in Southern California face some difficult decisions.
Do they focus on saving public beaches now disappearing beneath rising seas? Or should they close off those beaches with boulders and concrete walls to protect the neighboring communities and cliffside homes? What about the seaside highways where wave erosion is gobbling up the ground beneath them? And when do you declare homes uninhabitable as bluffs supporting them start to crumble away?
Patrick Barnard, a research geologist with the U.S. Geological Survey’s (USGS) Pacific Coastal and Marine Science Center (PCMSC) in Santa Cruz, CA, thinks his office can help in that conversation.
Barnard, Li Erikson, and their PCMSC colleagues have created the Coastal Storm Modeling System (CoSMoS)—an innovative scientific vision that enables detailed flood projections useful in assessing California’s coastal vulnerability to sea level rise and storms. The USGS thinks so much of CoSMoS that it awarded Barnard and Erikson its 2017 Excellence in Leadership Award.
Unlike the East Coast, where long, sandy stretches of beach prevail, the California coastline is marked by steep, rocky cliffs and terrain resulting partially from tectonic forces at work, and in other areas by narrow strips of sand bordering beach-front communities. CoSMoS’ value lies in its ability to model the impacts of sea level rise and storms on that dynamic landscape, especially as it continues to change under the unrelenting forces of large pounding waves, storm surges, and periodic El Niños.
To project the impacts of long-term coastal change from flooding at high resolution across vast extents of California’s coasts, CoSMoS relies on topobathymetric digital elevation models (TBDEMs) created by the Coastal National Elevation Database (CoNED) project. Headquartered out of the Earth Resources Observation and Science (EROS) Center near Sioux Falls, SD, CoNED’s accurate, three-dimensional merged renderings of both topography (land elevation) and bathymetry (water depth) serve up a seamless, integrated elevation look at California’s complex coastal geography.
Barnard calls the TBDEMs a backbone of CoSMoS.
“In all the modeling we do (with CoSMoS), the elevation data are absolutely critical to the accuracy of our projections,” he said. “This collaboration we have with EROS has been absolutely critical to our success.”
Informed in part by the CoSMoS effort, the USGS is predicting that cliff erosion in Southern California could double by the end of this century from the rates observed between 1930 and 2010. As sea levels rise and waves pound cliffs more frequently, homes in the San Francisco area have already been removed from the edge of rapidly eroding cliffs and flood-prone areas. San Francisco officials are taking steps to move the Great Highway away from Ocean Beach because erosion is eating away at the ground beneath it.
Given all that, vulnerability maps produced through projects like CoSMoS are essential to planners and managers tasked with mitigating the associated risks and costs to both human communities and ecosystems. With CoSMoS’ analysis and forecasting of multiple storm conditions under a suite of sea-level rise scenarios, communities are now better able to manage and meet their own planning horizons, and to specify degrees of risk tolerance.
Though he and his colleagues pieced together some of the elevation data for CoSMoS early on, Barnard said the expertise of the staff at CoNED and EROS “have been a huge addition to our team, especially in adding in the expertise of these seamless elevation products that these guys are experts at creating.”
The CoNED TBDEMs rely on many data sources, including topographic and bathymetric light detection and ranging (lidar) point clouds, hydrographic surveys, and sonar surveys obtained from multiple agencies. Jeff Danielson, the CoNED Applications Project Chief at EROS, said they also use Landsat 8 and WorldView satellite data as part of their bathymetry calculations in the Pacific.
CoNED’s value to the work of Barnard and his colleagues in California is the same as it is to many nongovernmental organizations and governmental agencies trying to project the impacts of climate change and sea level rise along coastal shorelines. They all need elevation estimates that are accurate both vertically and horizontally. That’s true whether they’re working with sediment-starved wetlands, looking to site a waste treatment facility, or like CoSMoS, projecting how storms and sea level rise will impact bluffs, beaches, and seaside communities.
Like CoSMoS, the National Oceanic and Atmospheric Administration’s (NOAA) Sea Level Rise Viewer projects inundation scenarios. In fact, the Sea Level Rise Viewer uses much of the same elevation data as CoSMoS, and similarly incorporates hydraulic connectivity—areas only flooded if they are directly connected to the ocean—as well as other features, including mapping nuisance flooding areas.
But the Sea Level Rise Viewer focus is on inundation starting at high tide—or the average highest tide each day—combined with sea level as it rises in 1-foot increments, up to an additional 6 feet. That’s useful in effectively mapping the everyday impacts of future sea levels on high tides. The primary difference then with CoSMoS is that it also considers the regional dynamic physical processes that affect the coast during a storm, such as waves, storm surge, tides, river discharge, and sea level anomalies, as well as long-term, climate-driven changes in storm patterns and shoreline evolution.
“When you talk about anything in a coastal environment, it’s all elevation related. That sounds simplistic, but it’s really true,” Danielson said. “And the reality is, building topobathy is not rocket science per se. But it takes some careful hand-holding on how you convert the datums, how you blend all the data together. A lot of folks could do it, but no one was really doing it. That’s why CoNED was founded.”
Again, his staff could do that elevation work, Barnard acknowledged. But why not rely on Danielson and the CoNED team, who “are really the best in the world in creating these integrated, seamless topobathy products,” he said.
“In terms of how to blend all these different products together to make these seamless elevation maps, they are the experts,” Barnard said of CoNED. “They have all the contacts. They know where to get the latest and greatest data. They really have allowed us to achieve the kind of success we’ve had with our modeling system.”
Of course, creating powerful modeling results was only the first step for CoSMoS. Displaying and communicating these complex and highly detailed flooding projections in a clear and usable way was equally crucial. So Barnard and his colleagues partnered with Point Blue Conservation Science and Our Coast, Our Future to design and deliver a web-based viewer for CoSMoS products.
Now that easy access to the projections is supporting a lot of climate adaptation efforts going on in California, Barnard said. The siting of power plants is one example. Evaluating the siting of public and private infrastructure is another. Caltrans (the California Department of Transportation) is using CoSMoS data throughout the state to identify bridges and roads that are going to be at risk in the future and will need to be raised or moved.
None of that would be possible without the partnership with CoNED, Barnard said.
“(CoNED) allows us to move more rapidly, and with a lot more confidence, to other geographies because we can hand that task off to the (EROS) experts,” Barnard said. “So that’s been a great collaboration. We certainly hope to keep that going.”
For more information:
Our Coast - Our Future tool: www.ourcoastourfuture.org
HERA Tool: www.usgs.gov/apps/hera