Projected responses of the coastal water table for California using present-day and future sea-level rise scenarios
Dates
Publication Date
2020-08-11
Citation
Befus, K.M., Hoover, D.J., Barnard, P.L., and Erikson, L.H., 2020, Projected responses of the coastal water table for California using present-day and future sea-level rise scenarios: U.S. Geological Survey data release, https://doi.org/10.5066/P9H5PBXP.
Summary
Coastal groundwater levels (heads) can increase with sea level rise (SLR) where shallow groundwater floats on underlying seawater. In some areas coastal groundwater could rise almost as much as SLR, but where rising groundwater intersects surface drainage features, the increase will be less. Numerical modeling can provide insight into coastal areas that may be more or less vulnerable to hazards associated with SLR-driven groundwater shoaling (moving closer to the ground surface) and emergence (flooding the ground surface), providing coastal planners with critical information that can be used to increase public safety, mitigate physical damages, and more effectively manage and allocate resources in complex coastal settings. Seamless [...]
Summary
Coastal groundwater levels (heads) can increase with sea level rise (SLR) where shallow groundwater floats on underlying seawater. In some areas coastal groundwater could rise almost as much as SLR, but where rising groundwater intersects surface drainage features, the increase will be less. Numerical modeling can provide insight into coastal areas that may be more or less vulnerable to hazards associated with SLR-driven groundwater shoaling (moving closer to the ground surface) and emergence (flooding the ground surface), providing coastal planners with critical information that can be used to increase public safety, mitigate physical damages, and more effectively manage and allocate resources in complex coastal settings.
Seamless unconfined groundwater heads for coastal California groundwater systems were modeled with homogeneous, steady-state MODFLOW simulations. The geographic extent examined was limited primarily to low-elevation (land surface less than approximately 10 m above mean sea level) areas. In areas where coastal elevations increase rapidly (e.g., bluff stretches), the model boundary was set approximately 1 kilometer inland of the present-day shoreline. Steady-state MODFLOW groundwater flow models were used to obtain detailed (10-meter-scale) predictions over large geographic scales (100s of kilometers) of groundwater heads for both current and future sea-level rise (SLR) scenarios (0 to 2 meters (m) in 0.25 m increments, 2.5 m, 3 m, and 5 m) using a range of horizontal hydraulic conductivity (Kh) scenarios (0.1, 1, and 10 m/day). For each SLR/Kh combination, results are provided for two marine boundary conditions; local mean sea level (LMSL) and mean higher-high water (MHHW), and for two model versions. In the first model version, groundwater reaching the land surface is removed from the model, simulating loss via natural drainage. In the second model version, SLR impacts are modeled by simply raising the present-day (SLR 0m) modeled groundwater head by the amount of sea-level rise, simulating the worst-case "linear" response to sea-level rise. Modeled groundwater heads were then subtracted from high-resolution topographic digital elevation model (DEM) data to obtain water table depths.
Groundwater head and water table depths are presented in raster GeoTIFF format. Polygon shapefiles also present water table depths by depth range (emergent, 0 to 1, 1 to 2, 2 to 5, and greater than 5 meters depth). All results are presented by County.
These data are intended for policy makers, resource managers, science researchers, students, and the general public. These data can be used with geographic information systems or other software to identify and assess possible areas of vulnerability. These data are not intended to be used for navigation. This work is part of on-going CoSMoS modeling efforts for California and the western United States. For more information on CoSMoS implementation, see https://www.usgs.gov/centers/pcmsc/science/coastal-storm-modeling-system-cosmos
Rights
Inundated or affected areas shown should not be used for navigation, regulatory, permitting, or other legal purposes. The U.S. Geological Survey provides these data as is for a quick reference, emergency planning tool but assumes no legal liability or responsibility resulting from the use of this information. The suggestions and illustrations included in these data are intended to improve coastal-flood awareness and preparedness; however, they do not guarantee the safety of an individual or structure. The contributors and sponsors of this product do not assume liability for any injury, death, property damage, or other effects of coastal flooding.