1D Compaction Modeling of Subsidence in California’s San Joaquin Valley
The semi-arid San Joaquin Valley is a major agricultural production center in the southern two-thirds of California’s Central Valley. As such, it has substantial water needs, yet rainfall is insufficient. Water is obtained from surface water and groundwater, yet a series of extreme droughts in recent years have increased dependence on groundwater resources, causing numerous issues pertaining to overdraft.
The aquifer system in the San Joaquin Valley (SJV) is primarily unconsolidated alluvial sediments composed of coarse-grained sand and gravels interbedded with fine-grained clays and silts. The presence of so much clay means the aquifer system is susceptible to compaction when groundwater is extracted at unsustainable rates, which has resulted in large land subsidence. Subsidence in the SJV is amongst the most extreme in the World, exceeding 9 m since 1925 and threatening infrastructure and future storage capacity. New advances in satellite imaging, in particular InSAR, have allowed imaging of the subsidence at unprecedented spatial and temporal scales, leading to substantial improvements in our understanding of many aspects of land subsidence. However, there are many outstanding questions regarding the geomechanical processes driving this subsidence and time scales over which it occurs.
Our approach is to develop 1D compaction models, which take measurements of hydraulic head as inputs and simulate the gradual compaction of sands and clays, to explore the nature of the subsidence. We validate our models against surface deformation data from InSAR, leveling surveys and extensometers, and use the model results to assess the depths and timespans over which subsidence occurs.
We focus on the Kaweah and Tule subbasins, areas both impacted by severe subsidence and where we have strong local partnerships to provide data and expertise required for actionable modeling. First, we worked at a single site in the Kaweah subbasin to develop the workflow; now, we are expanding to multiple sites across the subbasins
Results to Date
We developed a 1D compaction model at one site in the Kaweah subbasin, simulating subsidence over a 65-year period from 1952-2017. We found timescales of deferred subsidence of order 10s-100s of years, and found that at least 80% of the subsidence originated as compaction in the deep, lower aquifer. As a consequence of the long timescales of subsidence, we found that head recovery is necessary to stop subsidence. This is contrary to the current best practices in groundwater management where it is assumed that head stabilization is sufficient. Our work has triggered discussions with managers and management agencies, and we are engaged in how we can take our science towards implementation.
Gordon and Betty Moore Foundation (Grant GBMF6189)
NASA Applied Sciences Water Resources Program in the Earth Science Division (Grant 80NSSC19K12480)
Stanford Graduate Fellowships
Project Publications and Presentations
Lees, M., Knight, R., Smith, R. (2022). Development and Application of a 1D Compaction Model to Understand 65 Years of Subsidence in the San Joaquin Valley. Water Resources Research. e2021WR031390. https://doi.org/10.1029/2021WR031390
Lees, M., Knight, R., Smith, R. (2021): Land Subsidence in California’s San Joaquin Valley Set to Continue for Decades. American Geophysical Union Fall Meeting, December 13-17, 2021, abstract #NS41A-03.
Lees, M., Knight, R., Smith, R. (2021): Linking Subsidence to Changes in Stored Water in California’s San Joaquin Valley. Association of Environmental & Engineering Geologists 65th Annual Meeting, September 20-26 2021.
Lees, M. and Knight, R. (2021): Understanding Land Subsidence: Insights from a Hydromechanical Model of Head-Driven Compaction and Expansion within a Multi-Layer Aquifer System. GRA Annual Groundwater Congress 2021, September 13-15, 2021.
Lees, M., Knight, R. J., Smith, R. (2020). Understanding the Link Between Changing Head Levels and Land Subsidence: A Field Experiment in California’s San Joaquin Valley. American Geophysical Union Fall Meeting, December 1-17, 2020, abstract #674984.
Knight, R. J., Smith, R., Lees, M., Lauknes, T., Goebel, M., Abraham, J. D., Asch, T., Cannia, J. (2019). Advancing the Use of InSAR Data through Integration with Geophysical Data. American Geophysical Union Fall Meeting, December 9-13, 2019, abstract #624725a.
Lauknes, T.R., Lees, M., Knight, R.J. (2019). The Use of Ground Motion Data from InSAR to Explore and Manage the Groundwater Systems in California’s Central Valley. GRA Annual Groundwater Congress, September 17-19. https://www.grac.org/media/files/files/8e6c3174/17-2-1-c-tom-lauknes.pdf