Factors and Processes Affecting Levee System Vulnerability

Abstract

We appraised factors and processes related to human activities and high water, subsidence, and seismicity. Farming and drainage of peat soils caused subsidence, which contributed to levee internal failures. Subsidence rates decreased with time, but still contributed to levee instability. Modeling changes in seepage and static slope instability suggests an increased probability of failure with decreasing peat thickness. Additional data is needed to assess the spatial and temporal effects of subsidence from peat thinning and deformation. Large-scale, state investment in levee upgrades (> $700 million since the mid-1970s) has increased conformance with applicable standards; however, accounts conflict about corresponding reductions in the number of failures.Modeling and history suggest that projected increases in high-flow frequency associated with climate change will increase the rate of levee failures. Quantifying this increased threat requires further research. A reappraisal of seismic threats resulted in updated ground motion estimates for multiple faults and earthquake-occurrence frequencies. Estimated ground motions are large enough to induce failure. The immediate seismic threat, liquefaction, is the sudden loss of strength from an increase in the pressure of the pore fluid and the corresponding loss of inter-particle contact forces. However, levees damaged during an earthquake that do not immediately fail may eventually breach. Key sources of uncertainty include occurrence frequencies and magnitudes, localized ground motions, and data for liquefaction potential.Estimates of the consequences of future levee failure range up to multiple billions of dollars. Analysis of future risks will benefit from improved description of levee upgrades and strength as well as consideration of subsidence, the effects of climate change, and earthquake threats. Levee habitat ecosystem benefits in this highly altered system are few. Better recognition and coordination is needed among the creation of high-value habitat, levee needs, and costs and benefits of levee improvements and breaches.

Implications for Greenhouse Gas Emission Reductions and Economics of a Changing Agricultural Mosaic in the Sacramento–San Joaquin Delta

“…Subsidence and associated seepage is a key factor that contributes to decreasing agricultural sustainability and levee vulnerability in the Delta (Deverel et al 2015;Deverel et al 2016b). Managed wetlands stop and reverse the effects of subsidence (Miller et al 2008).…”

Perspectives on Bay–Delta Science and Policy

“…All of these changes will challenge the capacity of the water and environmental management systems to sustain ecologically desirable conditions in the Delta while providing a reliable water supply to millions of Californians. In addition, rising sea level and higher flood flows will increase the risk of levee failure (Deverel et al 2016), with attendant dramatic effects on Delta agriculture and communities, on water exports from the Delta, and on the ecosystem.…”

“…10 These surveys indicated that 84% of the length of levees surveyed conformed to the minimal Hazard Mitigation Plan standard, whereas only 61% of the surveyed length conformed to the stricter PL84-99 standard. Most non-compliant levees were located in the central Delta (Deverel et al 2016). However, because of the variable material composition of the levees, borehole surveys are insufficient to fully characterize internal levee structure.…”

“…Over the past decade, remote sensing techniques have been more widely used to assess levee structure. Two techniques that have provided important information about levee deformation are synthetic aperture radar (SAR) and LiDAR (Deverel et al 2016). …”

“…InSAR measurements are taken in image swaths that can be up to hundreds of kilometers wide, while detecting surface deformations as small as 5 to 10 mm. Significantly higher accuracy of 1 to 2 mm deformation per year can be achieved from repeated measurements (Deverel et al 2016). InSAR also has the advantage that it can see through clouds, smoke, and haze, and can image surfaces without solar illumination.…”