Twenty-First Century Levee Overtopping Projections from InSAR-derived subsidence rates in the Sacramento-San Joaquin Delta: 2006–2010

To provide an updated synoptic assessment of vertical land motion rates in the Sacramento-San Joaquin Delta, the research team performed synthetic aperture radar interferometry (InSAR) on 35 radar scenes from the Envisat platform acquired from 2006–2010.

The study used contemporaneously collected continuous global positioning system data to tie the InSAR results to an absolute reference frame. In accord with the researchers’ previous study from 1995–2000 (VLM00), the new results (VLM10) demonstrate general subsidence of the Delta with respect to its margins. The average rates of ~1-2 millimeters per year (mm/yr) are slightly lower than the ~3-5mm/yr rates from 1995–2000. An unexpected finding is the uplift associated with Roberts Island, in the Delta’s southeastern sector.  The time- and space-varying differences between the two solutions (VLM00 and VLM10) highlights the need to develop a physical model for the Delta.

The study used the updated ground-motion rate map and the most current twenty-first century sea-level rise predictions to project when Delta levees will subside below high-water design thresholds. The study showed that the time period between 2050–2075 is a critical time period, when levees will start to fall below design thresholds, and by 2100 most Delta levees will probably do so.