De-Confounding of Relations Between Land-level and Sea-level Change in Northern California Cal-Trans Briefing 2014 Tom Leroy, Jason Patton, & Todd Williams Cascadia GeoSciences, Northern Hydrology, HSU Geology, U of O Geology, & HBI members Jeff Anderson, Ray Weldon, Reed Burgette Mark Hemphill-Haley Whelan Gilkerson

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

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

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

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

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

Cross-section of a subduction zone

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

Why is this important? (1)This demonstrates the elastic nature of the crust. (2) The sense of motion for interseismic and coseismic land level changes are inverted. Why is this important? (1)This demonstrates the elastic nature of the crust. (2) The sense of motion for interseismic and coseismic land level changes are inverted.

Coastal subsidence, Japan 2011

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

How can we determine the spatial distribution of vertical land level change? Tide gage analysis Historic level survey analysis

Historic Tide Gage Locations Humboldt Bay

HBV Tide Gage Deployment Locations Mad River Slough Eureka (Chevron Dock) Hookton Slough

Additional Records NOAA North Spit 2010 US ACOE Fields Landing Samoa

Mad River Slough Relative to CC Mad River Slough subsides relative to Crescent City at 4.2 mm/yr. Hookton Slough Relative to CC Hookton Slough subsides relative to Crescent City at 6.8 mm/yr. North Spit Relative to CC North Spit subsides relative to Crescent City at 5.4 mm/yr. Monthly Mean Sea Level (Station Datum, mm) plotted vs. Time * assumes 2.28 mm/yr SLR

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, ~ 70 control points surveyed from ~ 40 observed either or ~ 20 observed Historic Leveling, Humboldt Bay

Land level – Tide Gage Misfit Site(mm/yr) CC0.69 ± 0.38 MRS0.40 ± 0.20 NS0.31 ± 0.36 HS0.10 ± 0.51 Land level Change (mm/yr) * assumes 2.28 mm/yr SLR

Future Projects and Objectives: Campaign Tide Gage Campaign Tide Gage – densify network of tide gages in Humboldt Bay to better understand the spatial variation in vertical deformation. Continuous GPS collocated with tide gages Continuous GPS collocated with tide gages – to continuously tie the tide gage water surface elevation data to the tide gage station datum; to provide independent measure of vertical land level change Permanent Tide Gage at Hookton Slough Permanent Tide Gage at Hookton Slough – to better model higher order controls on sea level (meteorological, storms, ENSO, etc.) Repeated Level Surveys Around Humboldt Bay – Repeated Level Surveys Around Humboldt Bay – to better understand the spatial variation in vertical deformation Geodetic Modeling Geodetic Modeling – build a predictive model for estimates of vertical motion between benchmarks and tide gages Sediment Coring Sediment Coring – to characterize the prehistoric record of Paleodeformation