Contemporaneous Subsidence and Levee Overtopping Potential, Sacramento-San Joaquin Delta, California

Benjamin Brooks,Charles Werner,Gerald Bawden,Joel Dudas,James Foster,Daniel Cayan,Noah Knowles,Deepak Manjunath

doi:10.15447/sfews.2012v10iss1art4

Abstract

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.

Highlights

The largest estuary in the Western United States, the Sacramento–San Joaquin Delta provides fresh water to ~1 million cultivated hectares and more than twothirds of California’s human population (Figure 1)
The elevated average subsidence rates occur within a broad area defined by the Delta islands (Figure 4)
The InSAR-derived rates from 1995–2000 in the Delta are significantly less than the ~ 40 to 70 mm yr-1 measured in island interiors (Deverel and Rojstaczer 1996; Deverel and others 1998; Rojstaczer and Deverel 1995) and estimated by assuming that the islands were at sea level at the start of the 19th century

Summary

Introduction

The largest estuary in the Western United States, the Sacramento–San Joaquin Delta provides fresh water to ~1 million cultivated hectares and more than twothirds of California’s human population (Figure 1). Because there are a number of gas and oil fields in the Delta (Figure 6), it is critical to assess whether the InSAR ground-motion data are contaminated by the anthropogenic signals.

Results

Conclusion