1. An Overview of the Statistical Reliability of Levee Design Data SAME 2009 Water Conference Sacramento, California Chris Groves, P.E. Shannon & Wilson, Inc.

2. Early levees were constructed by farmers.

3. Standard practice for levee design is EM 1110-2-1913

4. EM recommends boring explorations on 200- to 1000- foot centers.

5. Explorations could easily miss a critical subsurface feature.

6. For an agriculture levee the risk may be acceptable.

7. Some agricultural levees later become urban levees.

8. Hydrology and Hydraulics have been expressed as a frequency or probability of exceedance

9. Geotechnical issues are deterministic. The public believes we are dealing with certainty. What is the probability of a geotechnical failure when the factor of safety is 1.4?

10. Alluvial deposits are sorted by water and as a result can vary significantly in a short distance.

11. Geomorphology can help

12. Geophysics can help

13. The variability of soil properties has been addressed with the Taylor method of analysis.

15. The method looks at an entire levee reach not a single location.

16. The method assumes that the soil profile can be accurately determined at each CPT or boring

17. Levee geometry is also required for each section

18. The method assumes the analysis parameters can be determined at each section CPT data reduction

19. Seepage Analysis

20. Stability Analysis

21. Plot of Factor of Safety Versus Cumulative Probability Distribution

22. A seepage and stability berm may be added

23. Reanalyze with levee improvements

24. This method may give an estimate of the hazard due to high variability along a reach Less Site Variability