Sea Level Rise

Natural Shoreline Infrastructure in Humboldt Bay for Intertidal Coastal Marsh Restoration and Transportation Corridor Protection (2020-2022)

Humboldt County received funding from the National Fish and Wildlife Federation and the Ocean Protection Council of the California Natural Resources Agency to perform site characterization and prepare preliminary design (50%) for a project utilizing natural shoreline infrastructure techniques to help protect a portion of the Eureka-Arcata transportation corridor along Humboldt Bay from flood hazards.  The project will lay the groundwork for implementation of an innovative approach to restore and perpetuate intertidal coastal marsh, increase community resilience to flooding, and demonstrate the use of natural ecological systems for sea level rise adaptation.


Final Report, September 2, 2022 (report only, no appendices) (PDF, 17 Mb)

Appendix A - Compiled Exhibits (PDF, 52 Mb)

Appendix B - Habitat Mapping (PDF, 20 Mb)

Appendix C - Wildlife Species List (PDF, 0.6 Mb)

Appendix D - Extreme Wind Analysis (PDF, 0.6 Mb)

Appendix E - SWAN1D Wave Run-Up Analysis (PDF, 1 Mb)

Appendix F - SEDflume Study (PDF, 2 Mb)

Appendix G - Sediment Sampling (PDF, 7 Mb)

Appendix H - NSI 50% Plans (PDF, 34 Mb)

Appendix I - Sediment Mobility Plots (PDF, 3 Mb)

Appendix J - NSI 50% Design Construction Cost (PDF, 0.1 Mb)

Final Report, September 2, 2022 (report and appendices) (PDF, 136 Mb)

Technical Working Group

NSI Technical Working Group Meeting No. 1 Slides (PDF 24 MB)

NSI Technical Working Group Meeting No. 2 Slides (PDF 7.6 MB)

NSI Technical Working Group Meeting No. 3 Slides (PDF 3.5 MB)

NSI Technical Working Group Meeting No. 4 Slides (PDF 8.3 MB)

NSI Technical Working Group Meeting No. 5 Slides (PDF 6.5 MB)

NSI Technical Working Group Meeting No. 6 Slides (PDF 4.9MB)

Project Documents

NSI Grant Proposal (July 22, 2019) (PDF 5 MB)

NSI Reference List (July 16, 2020) (PDF 1.1 MB)

Sea Level Rise Adaptation Plan for Humboldt Bay/Eureka Slough Area (2018-2021)

Humboldt County received funding from the Caltrans Adaptation Planning Grant program to support the preparation of a sea level rise adaptation plan for the Eureka Slough hydrologic sub-unit of Humboldt Bay. This area includes segments of Highway 101, county and city roads, railroad, and the future Humboldt Bay Trail, along with Murray Field airport, utility transmission lines (gas, electrical, water), wastewater pump stations, and a mix of industrial, commercial, residential, agricultural and wildlife land use. Due to ground surface elevations, exposure to wind waves, and the condition of levees and embankments, this area is especially vulnerable to flooding hazards, with vulnerability expected to increase due to the progressive rise of sea levels.

The Eureka Slough area spans multiple municipal jurisdictions, and a variety of stakeholders including City of Eureka, HCAOG, Caltrans, North Coast Railroad Authority, California Department of Fish & Wildlife, the Humboldt Bay Harbor, Recreation and Conservation District, Humboldt County Farm Bureau and Pacific Gas & Electric Company desire to participate in regional collaboration for adapting to sea level rise. The City of Eureka and the Humboldt County Association of Governments were subapplicants for the grant, which is funded through Senate Bill 1, the Road Repair and Accountability Act of 2017.

Final Report (March 31, 2021)

Sea Level Rise Adaptation Plan Executive Summary (PDF 171 KB)

Narrative Report

Appendix A - Exhibits (PDF 139 MB)

Appendix B - Observation Protocol (PDF 26.6 MB)

Appendix C - Hydraulic Analyses Technical Memo (PDF 3.5 MB)

Appendix D - Hazard Scenarios (PDF 61.5 MB)

Appendix E - Qualitative Risk Assessment (PDF 1.4 MB)

Appendix F - Project #2 NSI Technical Memo (PDF 1.4 MB)

Appendix G - Jacobs Avenue Levee Needs Assessment FINAL (PDF 3.0 MB)

Appendix H -  Benefit Cost Analysis (PDF 622 KB)

Appendix I - Stakeholder Outreach Notes (PDF 1.3 MB)

Cultural Landscape Investigation (June 2020)

Situated at the interface between land and sea, the Humboldt Bay shoreline is a dynamic landscape subject to natural processes and human alterations. The lands along the shoreline between Eureka and Arcata were transformed in the late 19th and early 20th century from a complex network of sloughs and intertidal habitats to an interconnected system of hardened, linear features protecting infrastructure, agriculture, commercial businesses, and residences situated on low-lying land that would otherwise be subject to tidal flooding. The railroad, highways, and levees were built for the sea levels at the time when these levels were assumed to be non-changing (stationary). However, with sea level rise, this area represents one of the most vulnerable areas around Humboldt Bay to flooding impacts.

Humboldt County retained Jerry Rohde to perform a cultural landscape investigation of the Humboldt Bay shoreline between Eureka and Arcata. The purpose of this study was to document the human influence on the landforms and features along the shoreline to help understand the geomorphic setting and to inform considerations for (1) how human alterations may have changed natural processes, and (2) how the existing landscape may evolve with sea level rise. A primary focus of the work was to utilize historical maps and photos to help identify the specific locations of created landforms and their original intended use. The report documents the timeline and scope of the significant changes that have occurred within the study area between pre-development and today and tells the compelling backstories of remnant features observable today.

Humboldt Bay Shoreline Cultural Landscape Investigation (Rohde 2020) (PDF 26.3 MB)

March 2021 Workshop

Sea Level Rise Adaptation Plan March 2021 Workshop Presentation Slides (PDF 19 MB)

March 2020 Workshop

Sea Level Rise Adaptation Plan March 2020 Agenda (PDF 151 KB)

Sea Level Rise Adaptation Plan March 2020 Presentation Slides (PDF 54 MB)

Sea Level Rise Adaptation Plan March 2020 Planning Framework Summary (PDF 258 KB)

Project Documents

Project Scope of Work

Project Area Map

Project Existing Conditions Map Set (92 MB)

Humboldt Bay/Eureka Slough Sea Level Rise Presentation – Humboldt Bay Symposium (April 2019) (12 MB)

Jacobs Avenue Levee Informational Meeting Presentation (May 2019) (5.5 MB)

Humboldt Bay Sea Level Rise Adaptation Planning Project (2010-2015)

The Humboldt Bay Sea Level Rise Adaptation Planning Project was active from 2010 through 2015 and conducted two phases of regional collaborative planning with funding from the California State Coastal Conservancy.


Caltrans District 1 Climate Change Vulnerability Assessment – Main Document (December 2014) (PDF 3 MB)

Caltrans District 1 Climate Change Vulnerability Assessment – Appendices (December 2014) (PDF 22 MB)

Humboldt Bay Area Plan Update