| Summary: | The levee system in California’s Sacramento-San Joaquin Delta helps protect freshwater quality in a critical estuarine ecosystem that hosts substantial agricultural infrastructure and a large human population. We use space-based synthetic aperture radar interferometry (InSAR) to provide synoptic vertical land motion measurements of the Delta and levee system from 1995 to 2000. We find that Delta ground motion reflects seasonal hydrologic signals superimposed on average subsidence trends of 3-20 mm/yr. Because the measurements are insensitive to subsidence associated with peat thickness variations over Delta-island length scales, it is most likely that InSAR rates reflect underlying Quaternary sedimentary column compaction. We combine InSAR rates with sea-level rise scenarios to quantify 21st century levee overtopping potential. If left unmitigated, it is likely that 50 to 100 years from now much of the levee system will subside below design thresholds.
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