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Channel Migration Zones

December 5th, 2024

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Today’s Speakers:

Heather Rogers is a Hydrogeologist IV with the Department of Ecology’s Flood Unit, where she leads the statewide effort to map channel migration zones. Heather also provides technical expertise in fluvial geomorphology to local governments, tribes, state agencies, and the Floodplains by Design grant program. With more than 12 years of experience in geomorphology, remote sensing, and geologic mapping, Heather brings a wealth of expertise to her work in flood hazard management.

Jessica Hamill worked for the Department of Ecology in the early days of Floodplains by Design and helped build the grant program. Jessica is currently a Project Specialist IV with Snohomish County Surface Water Management and manages the Community Floodplain Solutions (CFS) program, which is working collaboratively to implement multi-benefit actions in the Snohomish basin. Jessica has over 11 years of experience working on integrated floodplain project/program development and implementation.

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Agenda:

12:00 - 12:05 - Welcome and Context

12:05-12:25 - Heather Rogers, Ecology

12:25 - 12:45 - Jessica Hamill, Snohomish County

12:45-12:55 - Discussion

12:55-1:00- Closing

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Stream Channel Migration

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Adapted from Applied Geomorphology Inc., 2017

Channel Migration Zone

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Why do CMZs matter?

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Loss of property

Potential loss of life

Pollution of waterways

Equity Issue

This Photo by Unknown Author is licensed under CC BY

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Salmon

Riparian Management

Restoration

Ecological Protection

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Why Does Ecology have two CMZ mapping methodologies?

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2003

Shoreline Management Act requires the location of CMZ

WAC 173-26-221

2008

Puget Sound Biological Opinion

2014

Planning Level CMZ Methodology or

100-year floodplain

2020

Riparian Ecosystems, Volume 2:�Management Recommendations

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Adapted from Applied Geomorphology Inc., 2017

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2003

Shoreline Master Plans required to locate the CMZ

2008

Puget Sound Biological Opinion

2014

Planning Level CMZ Methodology

2020

Riparian Ecosystems, Volume 2:�Management Recommendations

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2003

Shoreline Master Plans required to locate the CMZ

2008

Puget Sound Biological Opinion

2014

Planning Level CMZ Methodology

2020

Riparian Ecosystems, Volume 2:�Management Recommendations

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Detailed vs. Planning CMZ

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Detailed CMZ	Planning CMZ
Field-checked	Desktop Only
Can be used for parcel-scale development regulation	Can be used to identify the need for a detailed level CMZ study
Last ~30-100 years of channel migration	Last ~1000 years of channel migration
Expensive	Relatively cheap

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2003

Shoreline Master Plans required to locate the CMZ

2008

Puget Sound Biological Opinion

2014

Planning Level CMZ Methodology

2020

Riparian Ecosystems Vol 2:�Management Recommendations

2021 CFHMP

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What do CMZs look like in Washington today?

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This Photo by Unknown Author is licensed under CC BY-SA-NC

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Spokane pCMZ Circa 2007

DNR lidar

Circa 2019 - 2020

This Photo by Unknown Author is licensed under CC BY-SA

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Key Takeaways

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Few detailed CMZ Studies are available due to cost

Updated mapping is needed in certain areas

Current and future management needs require more detailed information than is currently available in planning level CMZs

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Washington State Hydrography Dataset (WASHD)

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Washington State Hydrography Dataset (WASHD)

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Mapping the Historical Migration Zone Statewide 2024 - 2031

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Prioritize mapping the historical channel locations of streams where the probability of channel migration is moderate to high

Currently in pilot phase in the Stillaguamish Basin

Seeking ongoing funding

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Heather Rogers, LG

Washington Department of Ecology

Fluvial Geomorphologist

heather.rogers@ecy.wa.gov

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Snohomish County - Community �Floodplain Solutions (CFS)

CFS Program – Skykomish CMZ Study Utility

FbD Lunch & Learn

December 5, 2024

Jessica Hamill – CFS Program Manager & Integrated Project Coordinator – jessica.hamill@snoco.org

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Meet the Challenges Together

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Partners

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- County completed a geomorphic assessment of the Lower Sky (up to Gold Bar) in 2020. Study included 3 key elements including: Hydraulic and hydrologic modeling, channel migration zone study, and an infrastructure assessment.

- The purpose of flood hazard mapping studies funded through CFS is to model, assess and map river conditions to inform future projects. Flood hazard mapping typically looks at water depth -- how much water is in the river channel or on the floodplain.

- The intent with looking at 2D modeling in combination with a CMZ study is to look at the river's changing shape and location, not just water depth, across a broader reach scale. Want to note that the CMZ study looked at erosion (estimated rates of erosion) and avulsion (rapid and often dramatic shift in the location of the channel – typically during a single flood event and often into a prior channel location) as well as lateral channel migration processes (occurs as a more gradual and progressive combination of bank erosion along one riverbank coupled with sediment deposition and revegetation of the opposite bank).

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Web Map – Decision Support Tool

JESSICA

We overlayed spatial data on fish priorities (from Tulalip Tribes acquisition strategy), data on farmland preservation priorities (from WFT), actively farmed areas (USDA), 2D H&H model to see velocity and depth, and avulsion & CM layers so we understand the potential flood risks. We also came up with a set of integrated criteria that would help us identify where farm, fish, flood priorities overlap and where there are collaborative opportunities.

High Priority to Remain Farmland (light blue)

High Priority for Salmon Recovery (cream color)

High Priority for Flood Risk Reduction (dark blue)

High Priority for Salmon Recovery and Flood Risk Reduction (pink)

High Priority for Multi-Benefit Acquisition Project (orange)

High Priority for Multi-Benefit Acquisition Project – Not Actively Farmed (yellow)

Based on WSDA Agricultural Land Use data, 2019

High Priority for Multi-Benefit Acquisition Project – Substantial Flood Risk to Agricultural Productivity (green)

Based on depth/velocity in a 2-year flood, avulsion areas, and erosion/migration

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30 Acres - Floodway Secured for Integrated Actions

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Agreement with local farmer on 20 acres

Agreement provides credits for site management and stewardship like site clean-up, cover-crop and mowing

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RELOCATION - URA

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Roth Family Farm Preservation & Fern Bluff Project Area

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Current and Future Studies

From confluence in Arlington to the Bridge to Nowhere ( ̴35miles)

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Questions �and Feedback

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Upcoming Events

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Upcoming FbD Events

December 17: Funding and Policy Action Group Quarterly Summit. 11am-1pm. (email Allan Warren <awarren@b-e-f.org> for invite)

January 9th L&L: Status of the Habitat Recovery Pilot Program

February 6th L&L: Topic TBD

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Thoughts for future programming? Ideas to share?

Please share any ideas you may have here. If you’d like to be included in follow-up or have specific speaker ideas, please leave your name and contact information or reach out to Matt (matt.gerlach@ecy.wa.gov ), Allan (awarren@b-e-f.org) or Carol (cmacilroy@gmail.com) directly.

MARS - now Montana Freshwater Partners

FbD circulate the white paper Jessica/Snoho county did on easements. Links about the referenced Montana easement efforts (note Snoho white paper builds on the Montana work)

Example of kind of work being done by NHC nhcweb.com/wp-content/uploads/2019/11/Naches-River-Geomorphic-Atlas.pdf

Identify what the root issue issue is behind Channel Migration Easement long term funding issues

Challenges of NRCS older easements with CME

Promote floodplain friendly farming (sediment settling, woody debris inundation) could partner with an easement progrm - Judi Radloff KC idea - could FbD help with this?

www.freshwaterpartners.org

The Salish Sea Restoration Platform is always available for product sharing and archiving case studies and linking evidence across agency firewalls... ;-) https://salishsearestoration.org