Channel Migration Zones: What? Why? Where?

1. Channel Migration Zones:What? Why? Where? Shorelands and Environmental Assistance Program Washington Department of Ecology Patricia L. Olson

2. What is a channel migration zone? • WAC 173-26-020(6): "Channel migration zone (CMZ)" means the area along a river within which the channel(s) can be reasonably predicted to migrate over time as a result of natural and normally occurring hydrological and related processes when considered with the characteristics of the river and its surroundings

3. Wandering Meandered Anastomosed Braided Channel Patterns Channels with CMZ’s Alluvial Channel Morphology

4. Meandered channels Cohesive banks Lateral & downstream migration Not cohesive banks

5. Meandered channels Incised Entrenched erosive Entrenched Less erosive

6. Anastomosed channels

7. Braided channels

8. Wandering channels

9. Why identify channel migration zones?

10. Rivers migrate, depositing and eroding as they go • Impact to property in migration and avulsion areas • Geo and flood hazards

11. Provide habitat biodiversity and beneficial floodplain services Tied to no-net-loss of ecological functions • Highest concentration of Spring Chinook redds • 45% of total for Twisp River • Reach with the most area, length and diversity of side channels and wetlands per river mile

12. Update of Shoreline management regulations • Required channel migration zones (CMZ) be identified in Shoreline Management Program (SMP) updates • WAC 173-26-186: Shoreline Master Programs must include standards to implement a number of actions including CMZ delineation • WAC 173-26-201(3)(c)(vii): a required inventory item in the Shoreline Master Program watershed characterization and critical areas • WAC 173-26-221(2)(c)(iv)(B): development in the CMZ should be limited to that which does not interfere with migration and cause adverse impacts to property or public improvements and “net loss of ecological functions” • WAC 173-26-221(2)(c)(iv)(A): identified as critical freshwater and riparian habitat • WAC 173-26-221(3)(b-c): Applicable shoreline master programs should include provisions to limit development and shoreline modifications and reduce flood hazards in the CMZ

13. WAC 173-26-221(3)(b) is fairly specific on what should be considered in identifying channel migration areas: • The channel migration zone should be established to identify those areas subject to channel movement based on the historic record, geologic character and evidence of past migration. Human and natural changes may alter migration patterns. Consideration should be given to changes from human and natural alterations and their effect on future migration patterns. • For management purposes, the extent of likely migration along a stream reach can be identified using evidence of active stream channel movement over the past one hundred years. Evidence of active movement can be provided from historic and current aerial photos and maps and may require field analysis

14. Ecology’s Role • Review and approve SMP update documents • Provide technical assistance to local governments by developing tools to: • Make decisions on need for CMZ assessment • Determine approach, level of analysis and appropriate methods • Outline minimal acceptable standards of analysis • Provide technical assistance for implementing shoreland regulations where there are CMZs • Provide technical assistance for managing CMZs

15. Background—existing Ecology technical framework • 2002—A directed retreat of scientists was convened in anticipation of inclusion of CMZ delineation in Shoreline Master Programs and flood hazard reduction • Topics • Controls to channel migration • Effects of natural and human-induced disturbance • Develop definitions for the CMZ • Discuss methods to delineate a CMZ

16. Product • A Washington Department of Ecology technical document • Cygnia Rapp, R.G.; Timothy Abbe, Ph.D., R.G, 2003 http://www.ecy.wa.gov/biblio/0306027.html

17. Role of existing framework • The framework provides: • Information on the scientific basis for delineating channel migration zones • A resource intensive approach with a general discussion of methods • Sources of relevant data • Field data collection methods • It is not : • The only approach • Mandated to be used by local government • Replacement for other approaches used outside shoreline or floodplain jurisdictions (e.g., forest practices methods) • A compendium of other possible approaches

18. The framework does not provide information to assist local governments to: • Make decisions on need for CMZ assessment • Determine approach, level of analysis and appropriate methods • Outline minimal standards of practice for the assessment • Provide information to develop consistent criteria for identifying level of hazard

19. Now where do we go?

20. Bigger Picture—longer term goal • Develop a decision support system • Provides a framework for making decisions and answering questions, for example • Do I need to do a CMZ delineation? • What level of effort is needed? • What approach and methods are appropriate? • What resources will it take? • Purpose: • Provide a logic sequence that can be followed • Recommend appropriate methods based on geomorphic characteristics, land use management, and resources

21. Actions to date • A web survey for local government planning and/or shoreline staff was sent out August 2005 • To obtain information to improve our ability to provide technical assistance to local governments • To identify where CMZ assessments have been done • Desired outcome • Information that will direct us in providing appropriate technical information on CMZ assessments in relation to: • Shoreline Master Plans (SMP) updates • Critical area ordinance (CAO) adoptions • Integration of CMZ and on-going floodplain hazard mapping

22. Survey results • Sent to 38 counties • 18 responded • Primary resource concerns for conducting a CMZ assessment • Expertise—94% • Sufficient data—71% (particularly air photos and channel surveys) • Cost—75% • Adequate guidance—53% • Resources that would help • Examples of completed delineations—82% • Grant funding assistance—73% • Guidance document on CMZ—65% • Technical assistance—64% 7 • Time—62% • Hazard ratings—55%

23. Some counties have completed CMZ’s • Based on methods described in the CMZ technical report • Jefferson, Pierce, King, Yakima (Naches) • Some counties and municipalities have draft CMZ delineations • Whatcom, Snohomish, Yakima, Okanogan, Mason • Darrington • Most communities began before SMP update • CAO, Comprehensive Flood Hazard Management Plans

25. Desired elements on maps • Erosion hazards—90% • Meander belts—70% • Gradations of risk—70% • Avulsion potential—60% • Useful guidance for implementing & managing CMZs • Limitations on new subdivisions—60% • Limitations on new shoreline modifications—67% • Geotechnical analysis guidance—60% • Other concerns • Property owner concerns—88% • Implications to the regulations of my jurisdiction—75%

26. 1-day workshop of professionals who have done CMZ assessments for local governments • Provide a forum to: • Discuss a minimal standard of practice for CMZ assessments based on physical processes (consider past land use activity on physical processes) and local government needs • Appropriate and scientifically credible methods • Discuss criteria for consistent hazard ratings • Discuss consistency in methods and mapping/GIS products • Desired outcomes • Framework for minimal standard of practice • Criteria for developing consistent hazard ratings

27. Preliminary Questions • How much CMZ analysis is enough? What is the minimal standard of practice given • Physical processes • Local government needs/objectives e.g., planning, implementation, hazard assessment • Can a logical sequence/roadmap be developed for local governments? • Decision system: “if, when and to what extent”

28. Decision Tree—CMZ Assessment Migration analysis needed?

29. Is a channel migration assessment needed? • Are there migrating rivers and/or other geo-hazards such as eroding banks or avulsions? • Where?

31. Exemptions--WAC 173-26-221(3)(b): • Within incorporated municipalitiesand urban growth areas, areas separated from the active river channel by legally existing artificial channel constraints that limit channel movement should not be considered within the channel migration zone. • All areas separated from the active channel by a legally existing artificial structure(s) that is likely to restrain channel migration, including transportation facilities, built above or constructed to remain intact through the one hundred-year flood, should not be considered to be in the channel migration zone. • In areas outside incorporated municipalities and urban growth areas, channel constraints and flood control structures built below the one hundred-year flood elevation do not necessarily restrict channel migration and should not be considered to limit the channel migration zone unless demonstrated otherwise using scientific and technical information.

32. http://www.ecy.wa.gov/programs/sea/sma/st_guide/jurisdiction/CMZ.html • Channel migration site with WAC citations and links • http://www.ecy.wa.gov/biblio/0306027.html • Rapp and Abbe technical report