1. 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

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

3. Why develop a CMZ?
Utahfloodrelief.com

5. Original Objective:
Hazard Mapping

6. Ecological Sustainability
Process Assessment
Outreach
Economics

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

8. Rappe and Abbe (2003) provides basic framework

9. 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.

10. 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

11. Basic Mapping Steps Define reaches
Map 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

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

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

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

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

16. 1955

17. 1977

18. 2005

19. HMZ

20. HMZ

21. 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?

22. 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

23. HMZ

25. Summarize migration rates by reach

27. 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

28. “ 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, Methodology for Predicting Channel Migration
Modeling capabilities will continue to improve

29. Avulsion Hazards Evidence from 1997 flood photos
Indicators are commonly subtle

30. 1997

31. 1997

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

34. Inundation Modeling: LiDAR (Yellowstone River)

35. Soup to Nuts

36. 1955

37. 1977

38. 2005

39. HMZ

40. HMZ

44. 1997

46. 1870

47. 1955

48. 1955

49. 1977

50. 2005

51. 1997

52. CMZ

53. May 22, 2009

54. Is our approach typical? Is there a typical approach?

55. 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

56. 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

57. 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

58. 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

59. “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

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

61. 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
Utahfloodrelief.com

62. 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

63. Discussion?

64. 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

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