Tom G Farr, Cathleen Jones, Zhen Liu
Jet Propulsion Laboratory California Institute of Technology
Executive summary Subsidence caused by groundwater pumping in the Central Valley has been a problem for decades. Over the last few years, interferometric synthetic aperture radar (InSAR) has been used from satellites and aircraft to produce maps of subsidence with sensitivity of fractions of an inch. For this study, we have obtained and analyzed Japanese PALSAR data for 2006 -- 2010 and Canadian Radarsat--2 data for the period May 2014 – January 2015 and produced maps of the total subsidence for those periods. As multiple scenes were acquired during these periods, we can also produce time histories of subsidence at selected locations and transects showing how subsidence varies both spatially and temporally. Geographic Information System (GIS) files will be furnished to DWR for further analysis of the 4 dimensional subsidence time--series maps.
For both periods, two already known main subsidence bowls in the San Joaquin Valley have been mapped: The larger is centered on Corcoran and extends 60 miles to the NW, affecting the California Aqueduct. For the period 2006 -- 2010, maximum total subsidence was found to be about 37” near Corcoran. From May 2014 – January 2015, maximum subsidence of over 13” was found just SE of Corcoran. A second bowl is centered on El Nido and is approximately 25 miles in diameter, encompassing most of the East Side Bypass. From 2006 -- 2010 maximum subsidence totaled about 24” S of El Nido. From May 2014 – January 2015, maximum subsidence of about 10” occurred in the same area. In the Sacramento Valley, a single area N of Yolo subsided about 6” from 2006 -- 2010. From May to November 2014, an extended area W of Yolo showed small areas with a maximum subsidence of about 3”; another diffuse area N of Yolo had a maximum subsidence of about 2.5”; and an unusually small intense area of subsidence just W of Arbuckle showed a maximum subsidence of about 5”.