1. BY ROY KROLL & COLIN KARK DIVISION of FLOOD MANAGEMENT FLOOD MAINTENANCE OFFICE

2. Vicinity Map: SBP East Levee

3. Construction Background Corps levee construction in SBP started in 1917 and completed in 1941 Levee widened & raised in 1951 in Nelson Slough Area USACE seepage interceptor trench installed off land side levee toe circa 1958

4. Argyle Dredger circa 1918

5. Flooding History Levee break at Nelson Slough during 1942 flood Sand boils, ground heaving, and cracks during 1958 flood Heavy seepage, boils, and heaving during 1997 flood Sand boils, ground heaving, and cracks during 2006 flood

6. Project Area Studies DFM/FMO Preliminary Geotechnical Evaluation Report 2006-05 DWR/DOE Project Geology Branch Report (draft) 2006-06 WLA Geomorphology Report (draft) 2007-08 URS/ENGEO Report (draft) 2008-03

7. USACE Probable Seepage Trench

8. Conceptual Cross Section

9. Seeps & Corps Seepage Trench Locations

10. East Levee: CPT & DH Locations Circa 2005 Sutter Bypass Wadsworth Canal Tisdale Bypass

11. Project Geology CPT & DH (draft) Findings Significant paleochannels under levee prism at LM 4.4, 6.0, 8.0 Smaller paleochannels under levee prism at LM 5.4, 6.8, 8.5, 10.0

12. Cenozoic Geology Map of SBP Tisdale Bypass Sutter Bypass Wadsworth Canal

13. WLA Geomorphology Map Tisdale Bypass Sutter Bypass Wadsworth Canal

14. Example of 1937 Photos Used for Paleochannel Delineation

15. URS Exploration – SBP East Levee Reach C Circa 2005 Wadsworth Canal

16. URS Exploration – SBP East Levee Reach D

17. WLA Conceptual Cross Section: East Levee at Tisdale Weir

18. URS & WLA Draft Findings Holocene & recent channel deposits are inset into the fine-grained basin deposits 27 paleochannels identified between Wadsworth Canal and Tisdale Bypass Channels are 6 to 8 feet deep with silt/clay cap Additional exploration of channels recommended Toe drain of Reach D may be clogged and need remediation

19. Closing Thoughts Geomorphology detailed mapping a vital step in developing an engineering strategy for repairs Old aerial photos and topo maps are a valuable resource that should be managed and preserved Old channels are bi-directional in water transmission in basin environments Toe Drains and interceptor trenches should be designed with engineering geologic input

20. Questions ?