Developing a Channel Migration Zone (“CMZ”) for the Clark Fork River Bitterroot River Confluence to Huson -A Pilot Study- Karin Boyd, Applied Geomorphology, Inc. Peter Nielsen, Missoula City-County Health Department Tony Thatcher, DTM Consulting, Inc. 1

How much area does the Clark Fork River occupy through time? “The CMZ Concept” Rapp and Abbe, 2003 2

Why develop a CMZ? Utahfloodrelief.com

Original Objective: Hazard Mapping

Ecological Sustainability Process Assessment Outreach Economics

Objective: Map a 100-year zone of occupation for the Clark Fork River from the Bitterroot confluence to Huson

Rappe and Abbe (2003) provides basic framework

CMZ Mapping is a multi-step process Each Step Creates Discussion Each Step Requires Decision Making Each Step Has Outreach Potential Applications can be considered in the process, but the PROCESS itself is critical.

The importance of PROCESS CMZ Mapping The importance of PROCESS Engage local staff and technical experts Capitalize on education/outreach opportunities Collaboratively consider management applications Pilot Study Approach

Basic Mapping Steps Define reaches Map 1955-2005 channel locations (Historic Migration Zone) Based on rates of change in a given reach, estimate area prone to erosion over next 100 years (Erosion Buffer) Identify areas prone to avulsion (Avulsion Hazard Zone) Compile composite CMZ

Reach Delineation Based on river pattern and observed rates of change Used to group migration rate measurements Used to develop reach-scale erosion buffers

Older Alluvium (lake, glacial, and stream deposits) Pre-Quaternary Geology 10-30 ft Quaternary Terrace

Reach Delineation: Discussion Points What scale are we targeting for this study? Do available resources support the desired level of effort? 14

Historic Migration Zone (HMZ) Map bankfull channel locations since 1955 Define the collective footprint of channels

1955

1977

2005

HMZ

HMZ

HMZ Discussion Points What are some potential sources of error? Accuracy of rectification Variations in flow at time of photography Accuracy of digitization (visibility of bankline) Resolution of air photos Should islands be included, regardless of active channel occupation? What occurred during this time frame? Floods? Ice jams?

Erosion Buffers Measure 50-year migration distances Summarize by reach Select statistic for buffer (avg, mean, 75th Percentile?) Apply 100-year migration buffer to modern banklines Place buffer layer under HMZ layer

HMZ

Summarize migration rates by reach

Creating a Buffer: Discussion Points Over a 100-year time frame, is reach averaging appropriate for the Clark Fork River? If so, what statistic should we use? Do data and resources support another strategy? Is predicting movement over a century possible at any scale? What about Milltown? What about the flood history? Should we be modeling migration to develop the buffer? “It’s tough to make predictions, especially about the future” – Yogi Berra

“ The only complete model of a river is the river itself “ The only complete model of a river is the river itself. While the past behavior of a meandering reach is not necessarily indicative of its future behavior, at least the historical record integrates the effects of all the relevant variables as they operate in that location.” ---Lagasse, et al, 2004. Methodology for Predicting Channel Migration Modeling capabilities will continue to improve

Avulsion Hazards Evidence from 1997 flood photos Indicators are commonly subtle

1997

1997

Mapping avulsion hazards using 1997 flood photos Are there better approaches?

Inundation Modeling: LiDAR (Yellowstone River)

Soup to Nuts

1955

1977

2005

HMZ

HMZ

1997

1870

1955

1955

1977

2005

1997

CMZ

May 22, 2009

Is our approach typical? Is there a typical approach?

Washington Department of Ecology CMZ Mapping: Minimum Standard of Practice Basin/Watershed Scale Low Level Moderate-high Level Reach Scale Moderate Level High Level Site Scale Minimum Level www.ecy.wa.gov

Reach Scale Low Level Moderate Level High Level www.ecy.wa.gov Data: Air Photos, DEM, LiDAR Hazard area is meander belt plus average amplitude distance or HCMZ plus half the width of average amplitude as a buffer or the FEMA 100-year floodplain, which ever is greater Confirm Assumptions and Findings with Sufficient Field Verification Moderate Level Calculate migration rates for each bend and composite for reach Define CMZ over 100 years (can use average maximum migration rate per year X 100 Hazard area = 100 year HMZ +EHZ +AHZ plus buffer that is equal to 1 meander amplitude, or the FEMA 100-year floodplain, whichever is greater High Level Develop Spaghetti Map showing historic channels Measure historic rates of migration and apply calculated distance to OHWM Map Potential avulsion channels Construct Meander Amplitude Map/Envelope www.ecy.wa.gov

Reach Scale: What We Ended up Doing Low Level Data: Air Photos, DEM, LiDAR Hazard area is meander belt plus average amplitude distance or HCMZ plus half the width of average amplitude as a buffer or the FEMA 100-year floodplain, which ever is greater Confirm Assumptions and Findings with Sufficient Field Verification Moderate Level Calculate migration rates for each bend and composite for reach Define CMZ over 100 years (can use average maximum migration rate per year X 100 Hazard area = 100 year HMZ +EHZ +AHZ plus buffer that is equal to 1 meander amplitude, or the FEMA 100-year floodplain, whichever is greater High Level Develop Spaghetti Map showing historic channels Measure historic rates of migration and apply calculated distance to OHWM Map Potential avulsion channels Construct Meander Amplitude Map/Envelope www.ecy.wa.gov

Reach Scale: Our Additional Steps Historic Context Review of flood events captured in historic timeframe Comparison of results with 1870 GLO Maps Data Analysis Grouped analysis based on geology Selection of statistic for buffer application Hazard Mapping Reviewed 1997 flood patterns

“Once a local government actually gets involved with a specific project in a specific reach of river, it is possible to really understand the process, the methodology, its limitations and how the information can be used for information and to inform regulatory processes. This has been a tremendous learning process for us. We understand so much more about the processes and the CMZ methods now than we did a year ago. We are able to move forward to assess doing this sort of thing on other streams in the county. We have begun to acquire the imagery necessary for some streams. We have found that simply acquiring the historic imagery and having it rectified allows visualization of the historic migration zone, which is in itself very informative and useful for our purposes. “ ---Peter Nielsen, Missoula County

Recommendations Engage local staff and technical experts Consider initial pilot-scale effort Leverage interim products

Regulatory Applications King County, WA: Reach Scale Ordinance in Place Jefferson County WA: No CMZ-based ordinance can be defended at any scale--- the inherent uncertainties in prediction are unacceptable No road map for regulatory application www.kingcounty.gov Utahfloodrelief.com

Potential CMZ Map Applications Outreach “Buyer Beware” Education and Awareness Irrigation Infrastructure Placement Planning Sanitarian Review Subdivision Review Building Permit Review River Conservation Development Standards Floodplain Permits Restoration Priority Incentive-Based Programs Voluntary Sloughing Easements BMPs Conservation Easements Management Leasing for Tax Reduction Regulatory Apply Setback to CMZ Boundary No Build Zones Mitigation Requirements Development Standards Additional Review or Analysis Standards

Discussion?

What’s to gain from the process? Developing an overall approach Compiling historic air photos Discovering graphic capabilities Discussing historic and anticipated future conditions Considering application opportunities and limitations Discovering interim product value

CMZ Map Variability Hazard severity-based map units Example of CMZ mapping along the middle Green River www.kingcounty.gov CMZ Map Variability Hazard severity-based map units Process-based map units