Channel Migration Assessment

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Basic Introduction.

What is Channel Migration?

Why do we need to identify Channel Migration.

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Outlines Assessment Steps 1-5 with interactive Flow Chart for each step.

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Step 1: Determine if or where Channel Migration Assessment is needed.

Task 1: Use existing data to identify constraints to channel migration.

Task 2: Do a simple field survey.

Task 3: Map Disconnected Migration Area (DMA).

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Step 1b: Identify streams for channel migration assessment.

Step 1 Chart: Determining whether a Channel Migration Assessment if needed.

Table 1: Some sources of free information.

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Task 1: Map the channel gradient

Task 2: Is the channel confined?

Figure 2: Confinement can be determined from topographic maps.

Figure 3: Channel confinement and gradient can be an indicator of migration potential.

Table 2: Relationship between gradient, confinement, channel type and patterns.

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Task 3: Identify channel patterns.

Figure 4: Channel narrowing and decrease in migration or bar building indicates possible channel incision.

Figure 5: The Okanogan River near Oroville illustrates meandering pattern and migration associated with one type of meandering stream.

Figure 6: This wandering stream has three channel patterns within a single reach: (1) meandering with scroll bars; (2) braiding with multiple low flow channels; and, (3) Island braided with forested floodplain islands.

Looking for evidence of channel change.

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Optional task: Identify channel geomorphic processes.

Figure 8: (a) A clearing along the left bank of Buttermilk Creek indicates a potential bank failure as verified by field observation.

Figure 9: Bank erosion on the Elwha River provides an example of identifying potential erosion and avulsion hazards from topographic maps and aerial photos.

Table 3: Erosion potential of common rocks found in Washington.

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Step 2: Determine the Minimum Standards of Practice and Level of Effort

Step 2a: Channel migration assessment applicable methods for SMP update characterization and inventory

Figure 11: The numbers identify the linked summary of approaches and methods.

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Step 2b: Determine level of effort based on environmental values and existing infrastructure.

Figure 12: This chart provides criteria besides resources to determine the minimal level of effort on channel migration assessment for shoreline environmental and infrastructure values and potential channel movement occurring in terms of time (e.g, < 50 years, and 50-75 years).

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Step 2c: Choose appropriate approach and method based on planning and management objectives and level of effort.

Figure 13: Matrix cross-references channel migration assessments by scale (basin, reach, site), management objectives, level of effort, and channel pattern.

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Table 4: Summaries of minimum standards of practice are organized by scale and level of effort. Methods are numbered to correspond to watershed characterization and management objective matrices.

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What resources are needed for an Assessment?

Table 5: Lists some potential sources of funding available to do channel migration zone analysis.

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Step 3: Determine channel reach breaks for channel migration analyses

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Step 4: Analyze migration, erosion, and avulsion components and map CMZ, erosion and avulsion hazards

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Step 4: (continued).

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Step 5: Develop hazard rating zones (recommended but optional). This step is still under construction.

Page 17 - Appendix A: Glossary

Includes Glossary of Channel Migration Components.