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Shallow Groundwater Response to Sea Level Rise


Bay Area Council’s California Resilience Challenge

Pathways Climate Institute and the San Francisco Estuary Institute collaborated to extend their groundwater research to better support regional adaptation planning. This work was funded by pro bono contributions from Pathways and a California Resilience Challenge Grant, submitted on behalf of four Bay Area counties: Alameda, San Mateo, San Francisco, and Marin County.

As sea levels rise and extreme storms become more frequent, communities are developing climate adaptation plans to protect housing, jobs, ecosystems, and infrastructure from flooding. However, vulnerability assessments and adaptation plans often neglect an important potential flood hazard – rising and emergent groundwater. In nearshore coastal areas, where shallow aquifers are unconfined, the groundwater table will rise as sea levels rise. This slow but chronic threat can flood communities from below, damaging buried infrastructure and roadway subgrades, increasing infiltration into sewer systems, flooding below grade structures, mobilizing contaminants, and emerging aboveground as an urban flood hazard, even before coastal flood waters overtop the shoreline due to sea level rise.

Pathways developed GIS layers of existing shallow groundwater surface that represents the water table at its highest elevation during wet winters, when emergent groundwater is first likely to occur (when the groundwater table rises above the surface of the ground and creates surface flooding). This represents a temporary or episodic condition that would occur sporadically in response to heavy precipitation. After validation with the local communities, the existing groundwater surface was modified in response to sea level rise scenarios to represent a range of future conditions. The sea level rise scenarios were selected to pair with sea level rise inundation mapping presented in the Adapting to Rising Tides Shoreline Flood Explorer.

This project included digitizing hundreds of soil borings to fill data gaps and improve the assessment, extensive coordination with city and county staff to ensure the end products meet their needs, and coordination with at-risk communities on messaging and outreach strategies. This project also included a Technical Advisory Committee, with academics (Dr. Kristina Hill, Professor at UC Berkeley and Dr. Kevin Befus, Assistant Professor at University of Arkansas) and scientists (Dr. Patrick Barnard, USGS) who are also pushing the science of the groundwater’s response to sea level rise forward. This collaboration allows cross-sharing of information and new techniques, as well as review at key milestones to keep the project grounded in the latest science.

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