Chehalis Basin Strategy Studies & Publications

The Chehalis River Basin Flood Warning System is a public website with forecasts, inundation maps, and real-time river level data and alarms that could save your life. Tune in for a training from the Chehalis River Basin Flood Authority.

Watch the November 2, 2022 webinar recording.

Flooding is a fact of life in the Chehalis Basin, and we know that its danger and urgency is intensifying. That’s why the Chehalis Basin Strategy is putting solutions in place to protect people, fish, and wildlife now, while also planning for a more resilient future. Learn how the Office of Chehalis Basin is taking new climate change projections into account, and what it means for you in the Basin.

Watch the October 25, 2022 webinar recording.

As part of the Local Actions Non-Dam Alternative (LAND) effort to develop and evaluate a comprehensive, Basin-wide flood damage reduction approach, the LAND Steering Group met with public officials and community members with interest, expertise, and direct experience with flooding damage. This Values Planning Process kicked off the discussion about flood protection needs and opportunities throughout the Basin.

• View Values Planning Process presentation slides
• View project timeline

To better understand Chehalis Basin ecosystems, the Aquatic Species Restoration Plan Steering Committee hosts symposium events to share the scientific knowledge that has come from Chehalis Basin Strategy investments and to provide a venue for feedback and ideas about aquatic habitat restoration.

View all Symposium materials.

On March 9, 2022, the Office of Chehalis Basin hosted an informational webinar so the public could learn more about its work to study ways in which the Skookumchuck Dam might be improved for flood damage reduction and/or fish passage.

• Watch the Skookumchuck Dam Webinar recording
• Skookumchuck Dam FAQ

In fall 2020 and spring 2021, the Office of Chehalis Basin hosted a series of public meetings to connect with and hear directly from Chehalis Basin residents and others about choices related to reducing flood damage and restoring aquatic species habitat that will impact the future of the Basin.

Learn more by viewing the meeting recordings and presentations from the public meetings:

• Public Meeting #1: Nov. 10, 2020: View the meeting recording
• Public Meeting #2: Feb. 17, 2021: View the meeting recording | View the meeting presentation
• Public Meeting #3: March 9, 2021: View the meeting recording | View the meeting presentation
• Frequently Asked Questions (FAQ): View the FAQ summary from the meetings

Large parts of the Chehalis Basin are natural floodplains. While portions of the floodplains have been developed, flooding remains a normal—but often dangerous—part of life in the region. Read the below studies to learn more about flooding in the Basin:

• Delineation of Late-Century 100-Year Floodplains for the Chehalis Basin (Watershed Science and Engineering, July 2021)
• Chehalis River Basin Climate Change Flows and Flooding Results (Anchor QEA, May 2019)
• Status of Improved Regulatory Standards (French & Associates, 2017)
• Floodplain Management Assessment Master Report (French & Associates, 2015)
• Repetitive Flood Loss Strategy (French & Associates, 2014)
• Community Rating System Program Review (French & Associates, 2014)
• Chehalis River Basin Basin-Wide Floodplain Management Assessment (French & Associates, 2014)
• Structures in Floodplain Survey Report (Watershed Science and Engineering, 2014)
• Hydraulic Model Report (Watershed Science and Engineering, 2014)

The Chehalis River and its tributaries are home to some of the most culturally- and ecologically-important species in the Pacific Northwest, including seven types of salmonids (including steelhead, Chinook, coho, and chum salmon). The Basin also supports the highest diversity of amphibian species anywhere in the state. Read the following studies to learn more about aquatic species and other wildlife in the region:

Salmon

• Chehalis River Smolt Production Report 2018 (Washington Department of Fish and Wildlife, January 2019)
• Chehalis River Smolt Production, 2018 (Washington Department of Fish and Wildlife, 2019)
• Grays Harbor Fall Chum Abundance and Distribution, 2017 (Washington Department of Fish and Wildlife, 2018)
• Movement and Home Range Study of Select Native Fishes in the Chehalis River, Washington State (Washington Department of Fish and Wildlife, 2018)
• Summer Riverscape Patterns of Fish, Habitat, and Temperature in Sub Basins of the Chehalis River, 2013-2016 (Washington Department of Fish and Wildlife, 2018)
• Investigating Juvenile Life History and Maternal Run Timing of Chehalis River Spring and Fall Chinook Salmon using Otolith Chemistry (Washington Department of Fish and Wildlife, 2017)
• Intensive Off-channel Survey (Washington Department of Fish and Wildlife, 2016)
• 2015 Upper Chehalis Instream Fish Study (Washington Department of Fish and Wildlife, 2016)
• 2016 Chehalis ASRP Intensive Surveys in Off-Channel Habitat: 2nd Progress Report (Washington Department of Fish and Wildlife, 2016)
• Behavior and Movement of Adult Spring Chinook Salmon in the Chehalis River Basin (Liedtke, USGS, 2016)
• 2015 Draft Riverscape Study Report (Washington Department of Fish and Wildlife, 2016)
• 2015 Chehalis ASRP Off-Channel Habitat Summary Based on Egg Mass Surveys: 2nd Progress Report (Washington Department of Fish and Wildlife, 2015)
• 2015 Chehalis ASRP Off-Channel Habitat Summary Based on Off-Channel Extensive Surveys: 2nd Progress Report (Washington Department of Fish and Wildlife, 2015)

Amphibians

• Stream-associated Amphibian Survey (4th progress report) (Washington Department of Fish and Wildlife, 2017)
• Stream-associated Amphibian Survey (3rd progress report) (Washington Department of Fish and Wildlife, 2016)
• Amphibian Egg Mass Off-channel Survey (Washington Department of Fish and Wildlife, 2016)
• 2016 Chehalis ASRP Instream Amphibian Surveys: 3rd Progress Report (Washington Department of Fish and Wildlife, July 2016)
• Stream-associated Amphibian Survey (2nd progress report) (Washington Department of Fish and Wildlife, 2015)
• Terrestrial Amphibian Survey (Washington Department of Fish and Wildlife, 2014)

Waterfowl

• Waterfowl and Waterbird Abundance (Washington Department of Fish and Wildlife, 2017)

Climate change is already impacting the Chehalis Basin environment and communities and is predicted to continue to influence the region through more frequent, intense flooding, warming water temperatures, and degrading habitat for salmon and other aquatic species. Read the below studies to learn more about climate change in the Basin:

• Chehalis Basin: Extreme Precipitation Projections (UW Climate Impacts Group, Feb. 2021)
• Modeling climate change conditions for the Chehalis Basin Strategy (Watershed Science and Engineering, June 2021)
• Delineation of Late-Century 100-Year Floodplains for the Chehalis Basin (Watershed Science and Engineering, July 2021)
• Chehalis River Basin Climate Change Flows and Flooding Results (Anchor QEA, May 2019)
• Effects of Climate Change on the Hydrology of the Chehalis River Basin (Mauger et al, July 2016)

The Chehalis Basin has a rich and complex geologic history that shapes its hydrology to this day. Learn more about the region’s hydrology through the following studies:

• Chehalis River Existing Conditions RiverFlow2D Model Development and Calibration (Watershed Science and Engineering, Feb. 2019)
• Chehalis River Basin Hydrologic Modeling (Watershed Science and Engineering, Feb. 2019)
• Chehalis River Off-Channel Habitat Hydrologic Monitoring Project (Anchor QEA, Oct. 2018)
  • Appendices A-C
  • Appendices D-F
• Effects of Climate Change on the Hydrology of the Chehalis River Basin (Mauger et al, 2016)

A flood retention facility, which would include a dam and fish passage facilities on the Chehalis River as well as airport levee improvements, has been proposed by the Chehalis River Basin Flood Control Zone District as a potential project to protect some Basin communities from large-scale, catastrophic flooding. The below links include environmental reviews, studies, and technical reports which are being used to inform a final decision about whether the facility is constructed:

Environmental Impact Statement reviews

• State environmental review
• Federal environmental review

Planning and evaluation analyses

• Resource Library of Planning and Evaluation Analyses (Chehalis River Basin Flood Control Zone District)
• Chehalis-Centralia Airport Levee Wetland Delineation Report (Anchor QEA, May 2019)
• Chehalis Basin Strategy Phase 3 Landslide Evaluation (Shannon & Wilson, May 2019)
• Rock Quarry Characterization Potential RCC Aggregate Sources for Chehalis Dam (Shannon & Wilson, March 2019)
• Phase 3 Chehalis Dam Geotechnical Data Report (Shannon & Wilson, March 2019)
• Wetland, Water, and Ordinary High Water Mark Delineation Report (Anchor QEA, Dec. 2018)
• Chehalis River Off-Channel Habitat Hydrologic Monitoring Project (Anchor QEA, Oct. 2018)
  • Appendices A-C
  • Appendices D-F
• Flood Retention Facility – Expandable (FRE) Supplemental Design Report (Sept. 2018)
• Fish Passage: Collect, Handle, Transfer, and Release (CHTR) Preliminary Design Report (Feb. 2018)
• Literature Review of the Potential Changes in Aquatic and Terrestrial Systems Associated with a Seasonal Flood Retention Only Reservoir in the Upper Chehalis Basin (Anchor QEA and WDFW, 2017)
• Geomorphology, Sediment Transport, and Large Woody Debris Report (Watershed Geodynamics and Anchor QEA, 2017)
• Combined Dam and Fish Passage Design Conceptual Report (2017)
• Reservoir Water Quality Model (Anchor QEA, 2017)
  • Appendix A
  • Appendix B
  • Appendix C
  • Appendix D
  • Appendix E
• Summary of Water Quality Data Collected on February 9, 2017 and March 29, 2017 (2017)
• Operations Plan for Flood Retention Facilities (Anchor QEA, 2017)
• Upper Chehalis Basin HEC-HMS Model Development (Watershed Science & Engineering, 2017)
• Chehalis Basin Strategy: Reducing Flood Damage and Enhancing Aquatic Species, Phase 2 Site Characterization, Technical Memorandum (2017)
  • Appendices A-D
  • Appendices E-I
• Chehalis Basin Strategy: Reducing Flood Damage and Enhancing Aquatic Species, Phase 2 Site Characterization, Technical Memorandum — Draft (HDR and S&W, 2016)
• Site Characterization and Dam Conceptual Design Presentation (HDR and S&W, 2016)
• Chehalis Basin Strategy: Flood Retention Dam Summary of Costs and Life of Dam (HDR and Anchor QEA, 2016)
• Chehalis Basin Strategy: Reducing Flood Damage and Enhancing Aquatic Species, Phase 1 Site Characterization, Technical Memorandum (HDR and S&W, 2015)
• Landslide Reconnaissance Evaluation of the Chehalis Dam Reservoir (S&W, 2015)
• Comparison of Alternatives Report (EES and HDR, 2014)
• Water Retention and Fish Passage Report (HDR Engineering, 2014)
• Aquatic Species Restoration Program Effects Report (2014)

The Chehalis Basin Strategy is addressing flooding at all scales across the Chehalis Basin, from small, local flood projects to large-scale planning. Read the below studies to learn more about some of the flood damage reduction strategies that have been analyzed to-date:

• Local Actions Program Advisory Group Reports and Materials (2020-2021)
• Restorative Flood Protection Feasibility Assessment (Natural Systems Design, Jan. 2020)
  • Appendix 1: Existing Conditions Summary (part 1)
  • Appendix 1: Existing Conditions Summary (part 2)
  • Appendix 2: Cost Assessment for Property and Transportation Impacts
  • Appendix 3: Hydraulic Modeling Part 1 Report
  • Appendix 3: Mapbook A – 100-year Flood Maps
  • Appendix 3: Mapbook B – Highly Engineered RFP 100-year Flood Maps
  • Appendix 3: Mapbook C – Climate Change 100-year Flood Maps
  • Appendix 3: Mapbook D – Landcover – Existing
  • Appendix 3: Mapbook E – Landcover – RFP
  • Appendix 3: Mapbook F – Landcover – HE – RFP
  • Appendix 4: Analysis of Agriculture
  • Appendix 5: Landowner Interview Project Summary
  • Appendix 6: Plant Communities
• Restorative Flood Protection Technical Report – Draft (NSD, Sept. 2016)
• WSDOT I-5 Chehalis Flood Report (2014)
• Small Flood Damage Reduction Projects Report (HDR and Watershed Science & Engineering, 2014)

The Aquatic Species Restoration Plan (ASRP) prioritizes habitat protection and restoration for the species that will benefit the most, particularly salmon and steelhead.

• Chehalis Basin Aquatic Species Restoration Plan (ASRP Steering Committee, 2019)

Below are some of the studies that have informed the plan’s creation and implementation. See also the Aquatic Species & Wildlife Studies section above.

• Science Review Team Guidance: 2017-2021 (ASRP Steering Committee, 2021)
• Changes in the Chehalis Floodplain: 1938-2013 (WDFW, 2017)
• Upper Chehalis Basin Large Wood Loading Inventory (Anchor QEA, September 2016)
• Aquatic Species Restoration Program Effects Report (Aquatic Species Enhancement Plan Technical Committee, 2014)
• Aquatic Species Restoration Program Report (Aquatic Species Enhancement Plan Technical Committee, 2014)
• Aquatic Species Enhancement Plan Data Gaps Report (Aquatic Species Enhancement Plan Technical Committee, 2014)

Erosion in the Chehalis Basin is made worse by frequent flooding. In some situations, it poses serious risks to property and structures, and can diminish habitat for salmon and other aquatic species. Learn more about erosion management analysis through the studies below:

• Initial Historical Channel Mapping and Floodplain Topography in Priority Erosion Hazard Areas (Anchor QEA, May 2021)
• Erosion Management Strategy in Priority Erosion Hazard Areas (Anchor QEA, March 2021)

The Chehalis Basin Strategy uses a number of different types and sizes of actions to tackle both flood damage reduction and aquatic species habitat restoration. This integrated approach has been informed by extensive research and scientific analysis, some of which is captured in the below reports:

• Programmatic Environmental Impact Statement
• Analysis of Salmonid Habitat Potential to Support the Chehalis Basin Programmatic Environmental Impact Statement (July 2017)
• Development and Calibration of the Chehalis River CE-QUAL-W2 Water Quality Model (PSU, April 2017)
• Chehalis Basin Strategy 2015-2017 Biennium Scope and Budget (2014)
• Chehalis Basin Work Group Recommendations Report (2014)
• Ruckelshaus Center Alternatives Report (William D. Ruckelshaus Center, 2012)
• Executive Summary of the Ruckelshaus Center Alternatives Report (William D. Ruckelshaus Center, 2012)
• Comments on the Draft Ruckelshaus Center Alternatives Report (2012)