1. De-Confounding of Relations Between Land-level and Sea-level Change in Northern California Tom Leroy Pacific Watershed Associates Also featuring: Jason Patton, Todd Williams, Jeff Anderson, Ray Weldon, & Whelan Gilkerson

2. Variables that determine locally observed sea level Eustatic (global water volume changes) Tectonic (land-level changes) Sediment Accretion (local sediment deposition)

3. Variables that determine locally observed sea level Eustatic (global water volume changes) Tectonic (land-level changes) Sediment Accretion (local sediment deposition)

4. Tectonic forces in Northern California are primarily driven by the Cascadia subduction zone

5. Bathymetry,topography, and primary faults of the Cascadia subduction zone 52Ê52Ê50Ê50Ê48Ê48Ê46Ê46Ê44Ê44Ê42Ê42Ê40 Ê40Ê240Ê238Ê236Ê236Ê234Ê234Ê232Ê232Ê

6. Cross-section of a subduction zone

7. Atwater & Satake, 2009 Interseismic (between earthquakes) Coseismic (during earthquake)

10. Flück, et al., 1997 Wang, et al., 2003 other deformation estimates for Cascadia

12. So how can we figure out which areas of our coastline are undergoing tectonic deformation and which areas are going up and which ones are going down? Analysis of historic leveling surveys Tide gage analysis

13. Preliminary analysis of northern California leveling data (Weldon)

14. Both NOAA’s calculated absolute sea level trend estimates and the more precise difference between the two sites suggest that North Spit subsides relative to Crescent City at about ~5.4 mm/yr. Given eustatic sea level rise of ~2.3 mm/yr for 1977 to 2010, Crescent City rises, absolutely, at ~3 mm/yr and North Spit sinks at about ~2.5 mm/yr. Northcoast Sea Level Ray Weldon, Oct. 2010

15. Mad River Slough Relative to Crescent City Mad River Slough subsides relative to Crescent City at 4.2 mm/yr. This indicates that Mad River Slough is sinking at a rate 1.2 mm/yr less than North Spit (5.4 mm/yr). Mad River Slough Relative to North Spit Mad River Slough subsides 0.9 mm/yr less than North Spit. This estimate is close to above rate of 1.2 mm/yr. The Crescent City estimate is probably more accurate due to length of record. Jeff Anderson, Northern Hydrology Engineering, Jan. 28 2010, HBI Meeting

16. Humboldt Bay Vertical Reference Group – US. Fish and Wildlife Service – Northern Hydrology – Pacific Watershed Associates – Humboldt State University – University of Oregon – Many others

17. 1931: San Jose – Eureka 1931: Eureka – Grants Pass 1944: Arcata – North Spit 1967: Longvale – Crescent City 1988: Eureka – Redding 1988: Westport – Arcata – North Spit 1992: Garberville – Loleta 2004: State Hwy – Countywide GPS Source: NGS Integrated Database; compiled by Don Campbell, CalTrans Dist. 1, 2010. ~ 70 control points surveyed from 1931-1992 ~ 40 observed either 1944-1967 or 1967-1988 ~ 20 observed 1944-1988 Historic Leveling, Humboldt Bay

18. Historic Temporary Tide Gage Locations, Humboldt Bay 1977-1980

19. Historic Temporary Tide Gage Locations, Humboldt Bay 1977-1980 Plan to observe 3-6 of the historic gage locations: 2012 Mad River Slough Eureka South Bay/Hookton Slough

20. Historic Temporary Tide Gage Locations, Humboldt Bay 1977-1980 Plan to observe 3-6 of the historic gage locations: 2012 Mad River Slough Eureka area South Bay/Hookton Slough 2010 US Army Corps of Engineers -Fields Landing -Samoa

21. Coastal subsidence, Japan 2011