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New Model Shows Sea-level Rise Can Cause Increases in Groundwater Levels along California’s Coasts

A new model that combines sea-level rise scenarios and information about associated groundwater level responses shows that coastal water tables will rise as groundwater levels are pushed up by landward intrusions of seawater due to sea-level rise.

Two maps illustrate two states of computer modeling scenarios around a large bay and coastal area.
Examples of CoSMoS-GW mapping products that show (left) modeled current groundwater tables with red depicting sites of emergent groundwater and (right) groundwater tables with 6 feet of sea-level rise. Blue indicates coastal-driven flooding and inundation. Both figures are for a horizontal hydraulic conductivity of 1.0 m/d and LMSL tidal datum. Credits: Juliette Finzi-Hart, Patrick Barnard, Kevin Befus, USGS.

This article is part of the August-September 2020 issue of the Sound Waves newsletter.

A new paper, “Increasing threat of coastal groundwater hazards from sea-level rise in California,” published in Nature Climate Change on August 17, 2020, describes a numerical model that estimates the depth of the present-day coastal water table and the future response of these groundwater levels to a range of sea-level rise scenarios for the entire California coast. The new USGS publication uses projected sea-level rise scenarios to assess the potential threat these higher groundwater levels pose for related hazards along the California coastline. Projected sea-level rise and storms could result in coastal flooding causing severe threats to communities, infrastructure, the economy, and natural resources.

The USGS model MODFLOW was used in this study. A unique aspect of this work is that the model covers a huge spatial domain (the State of California) at high resolution by stitching together overlapping model domains. The extremely high resolution allows the model to capture the influences of topography and drainage networks on groundwater levels that could help pinpoint areas where ponding at land surface may occur, or where the water table intersects shallow, sub-surface infrastructure, such as basements, parking garages, buried utilities, road beds, and other infrastructure.

The work is the first to quantify the potential coastal flooding that could result from water table rise along the entire coast of California and serves as a possible model approach for building out an assessment across the entire United States coastline. Findings show that low-lying coastal communities and critical infrastructure are most at risk of future rising water tables, including areas in San Francisco Bay, Santa Barbara, Ventura, Port of L.A., Long Beach, Seal Beach, San Diego Bay and San Francisco and San Diego Airports.

The research supports fundamental goals for understanding natural hazards associated with sea-level rise and provides actionable science needed by other federal agencies such as Federal Emergency Management Agency (FEMA), The Environmental Protection Agency (EPA), Department of Defense (DOD) and others focused on mitigating natural hazards, reducing risk associated with disasters, protecting natural resources and preparing for and reducing impacts of climate and land-use change on coastal populations and infrastructure. The results presented here provide greater insights to help coastal communities and policy makers better understand potential coastal hazards from sea-level rise.

Learn more on the USGS CoSMoS-Groundwater project page.

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