The San Joaquin Valley is located in the southern half of the Central Valley of California. Agriculture in an essential part of the economy but in terms of annual rainfall, the area is classified as a desert. There is thus a high level of dependence on deliveries of surface water or, in times of drought, the pumping of groundwater.
a) The famous image of Joseph Poland illustrating 9m of subsidence between 1925 and 1977; b) Different telegraph pole, different era, same problem: The Stanford team visits Tulare where several meters of subsidence has occurred in recent decades.
In the San Joaquin Valley, groundwater extraction has caused “the single largest human alteration of the Earth’s surface topography”, with over 8 m of subsidence occurring in some locations between 1943 and 1969. Despite a pause in subsidence between the 70s and early 2000s, major subsidence has returned in the past two decades, with observed rates matching historic levels. This subsidence causes substantial infrastructural damage and permanent loss of groundwater storage, yet many details of the link between pumping and subsidence remain unclear. Two such details are the relative contribution of the various levels in an aquifer system to the subsidence, and the time lag between groundwater pumping and subsidence.
We are using measurements of subsidence, derived from interferometric synthetic aperture radar (InSAR) data in conjunction with high-quality head data and lithology information to develop hydromechanical models. These models accurately simulate the link between groundwater pumping and subsidence, allowing us to develop and improved explore various scenarios that can inform groundwater management Understanding of the way in which groundwater pumping is linked to subsidence is essential for the development of plans for sustainable groundwater management.