NASA in cooperation with the U.S. Geological Survey is helping emergency planners in Southern California get a more complete picture of the increasing risk of coastal flooding by looking at the highest of tides -"king tides."

"King tide" is the informal term generally used to describe an exceptionally high tide, which most often occurs when the Moon and the Sun are aligned and their gravitational pull on the Earth is at its strongest. King tides can be just a few inches higher than normal, but when combined with other factors, they can have damaging effects.

That's what happened in the winter of 2018-19 when a king tide occurred as a series of coastal storms hit California, resulting in a surge of water and waves breaching a seawall in San Diego and causing significant damage to the city's Ocean Beach Pier. King tides also regularly cause flooding in the low-lying communities of Newport Beach and Imperial Beach, San Diego.

"These extreme high tides are an example of potential everyday impacts with sea level rise," said Andrea O'Neill, an oceanographer with the USGS. "With rising sea levels, the extreme water levels experienced today with king tides will become more frequent and will become a challenge for our coastal communities and infrastructure."

To plan for higher waters, coastal engineers like Lesley Ewing of the California Coastal Commission use results from a USGS-based flood-simulation model for Southern California called the Coastal Storm Modeling System (CoSMoS). This online tool simulates flooding potential from sea level rise and coastal storms along the central and southern California coastline.

"It provides powerful visualizations," Ewing said. "We use CoSMoS as a screening and analysis tool to help determine safe sites for development."

Until recently CoSMoS got much of its sea level data from tidal gauges scattered along the California coastline, according to O'Neill with the USGS' Pacific Coastal and Marine Science Center. "These observations offer great insight at one particular location, but don't show how flood levels may vary across our complex shoreline."

To fill the gaps between the gauges, CoSMoS' developers at the USGS and NASA are adding data from NASA's satellite and airborne missions. NASA's Jet Propulsion Laboratory's Neda Kasraee worked on the project as part of the NASA Earth Science DEVELOP team. The DEVELOP program is a national training and development program for individuals to gain experience applying Earth observations to environmental issues facing local areas.

"We use both radar imagery and optical imagery," Kasraee said. The optical imagery, supplied by the Landsat mission, let the team update the baseline for impacts of future king tides along the southern California coastline. The team used radar data from a NASA airborne mission that used a modified Gulfstream airplane with the Uninhabited Aerial Vehicle Synthetic Aperture Radar to map water excursion limits and coastal flooding from Santa Barbara to San Diego during a 2016 king tide.

With the addition of the Earth-observing data, O'Neill said USGS will validate and update CoSMoS' flood simulations, providing better flood hazard forecasts for California communities. "This project provides a uniquely invaluable dataset for any end-users of CoSMoS, as well as other coastal researchers."

Due to continuing sea level rise, scientists predict a future with more frequent flooding for many coastal communities. O'Neill says the USGS is looking to expand the program beyond central and southern California to other areas of the United States, with the northern California coast coming online in the near future.

Related Links
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