Geotechnical Risk and Reliability Evaluation of the Levees Protecting the City of Sacramento, California

The paper provides information on the geotechnical risk and reliability (R&U) evaluation of the levee system protecting the City of Sacramento, California and surrounding area. The analyzed levee system is located on the east bank of the Sacramento River, north and south bank of American River, south bank of the Natomas Cross Canal, east and west banks of the Natomas East Main Drainage Canal and tributaries, and Pleasant Grove Creek Canal. The geotechnical R&U was based on available geotechnical data, geomorphology of the area, and past performance. The reliability of the levee systems was determined by evaluating foundation and embankment materials and assigning values for the probability moments of the random variables considered in the analyses of the critical reaches identified by deterministic analyses. The performance functions considered were slope stability, underseepage gradients, and past performance of the levee based on the erosion history, existing encroachments, and vegetation covering the levees. A set of conditional-probability-of-failure versus floodwater-elevation graphs were developed as related to underseepage piping stability, slope stability, and judgmental conditions. An expert elicitation panel with highly recognized professional specialists, representing the levee districts managing and operating the levee system and specialists in erosion and in geotechnical issues determined the judgment part of the geotechnical reliability curves for the flood control structures, considering the existing conditions on the analyzed levee system. Reliability analysis was performed using Taylor's Series Method.