Seismic Vulnerability Evaluation of Levees in California’s Central Valley

The California Department of Water Resources (DWR) is currently implementing the Urban Levee Evaluations (ULE) Project for about 400 miles of urban project and non-project levees protecting populations of about 10,000 or more. The ULE Project evaluates steady-state seepage, stability, rapid drawdown, erosion, and freeboard conditions using established USACE procedures and the ULE Project specific considerations based on recent improved understanding of levee evaluations. For the evaluations of earthquake-induced vulnerability, a screening level approach has been developed for the ULE Project based on region-specific probabilistic seismic hazard analyses (PSHA), site specific 2-dimensional seismic response analyses, empirical relationships for liquefaction and slope deformation, and limit equilibrium static and pseudo-static slope stability analyses. A simplified seismic vulnerability assessment classification system has been developed for the ULE levees considering estimated remaining freeboard and conditions of internal structures (such as cutoff walls). This screening level seismic vulnerability classification is assigned to seismic segments of each urban levee system, which are developed considering results of a comprehensive liquefaction assessment, levee geometry, and topography. The main contributors to the seismic vulnerability of a levee system are earthquake intensity (Magnitude and Peak Horizontal Acceleration [PHA] for a 200-year return period earthquake scenario), depth and thickness of liquefiable layers, post-earthquake strengths of liquefiable layers, and levee geometry (such as landside and waterside slopes and presence or absence of waterside natural berms, etc.). This paper presents an overview of the step by step approach of seismic vulnerability assessment of the ULE levees, and an example of its application.