Detection and measurement of land subsidence and uplift using interferometric synthetic aperture radar, San Diego, California, USA, 2016–2018

Justin T Brandt,Wesley R Danskin,Michelle Sneed

doi:10.5194/piahs-382-45-2020

Abstract

Abstract. Land subsidence associated with groundwater-level declines is stipulated as an “undesirable effect” in California's Sustainable Groundwater Management Act (SGMA), and has been identified as a potential issue in San Diego, California, USA. The United States Geological Survey (USGS), the Sweetwater Authority, and the City of San Diego, undertook a cooperative study to better understand the hydromechanical response of the coastal aquifer system using Interferometric Synthetic Aperture Radar (InSAR) techniques. Three periods of interest were analyzed for this study that correspond to the periods before and after two substantial changes were made to the location and volume of pumpage: (1) April–August 2016 when groundwater levels and land surface elevation were relatively stable during normal pumping, (2) September 2016–May 2017 when groundwater levels recovered and the land surface uplifted during a period of substantially reduced pumping, (3) June 2017–October 2018 when groundwater levels declined and land subsidence occurred when pumpage resumed and expanded to new wells. Spatial and temporal characterization of the hydromechanical response to changes in pumpage is important for managing land subsidence. Further study using InSAR techniques, especially when combined with ground-based geodetic and monitoring-well networks, will provide water managers information to help effectively manage groundwater resources as stipulated in the SGMA.

Highlights

Introduction and backgroundGroundwater is an important source of water supply for the San Diego metropolitan areas serviced by the Sweetwater Authority (SWA)
Recent state-wide emphasis on developing alternative water supply has provided the SWA with grant funding to expand its desalination programs, in part by drilling new wells perforated in brackish groundwater that had previously been considered unusable for human consumption (Danskin, 2006)
Because land subsidence is described as an “undesirable result” in California’s Sustainable Groundwater Management Act (SGMA), the SWA and the City of San Diego began a cooperative study with the United States Geological Survey (USGS) to better understand the hydromechanical response of the coastal aquifer system under varying hydrologic conditions

Summary

Introduction and background

Groundwater is an important source of water supply for the San Diego metropolitan areas serviced by the Sweetwater Authority (SWA). Recent state-wide emphasis on developing alternative water supply has provided the SWA with grant funding to expand its desalination programs, in part by drilling new wells perforated in brackish groundwater that had previously been considered unusable for human consumption (Danskin, 2006). Pumpage from these new wells has the potential to cause groundwaterlevel declines, compaction of the aquifer system, and resultant land subsidence in densely populated areas. Brandt et al.: Detection and measurement of land subsidence and uplift using InSAR

Description of study area

Interferometric synthetic aperture radar methods

InSAR reveals deformation in the San Diego area

Findings

Conclusions