Channel Migration Assessment

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

Shoreline Master Programs should include provisions to limit shoreline development and modifications that may result in interference with channel migration WAC 173-26-221(3)(b).

Interference in channel migration can cause adverse impacts to property, public improvements, safety, and the aquatic and riparian ecosystems. The Master Program provisions should also include standards and regulations [WAC 173-26-221(2)(c)(iv)(C)(IV)] to assure no net loss of ecological functions associated with the river or stream corridors as a result of new development [WAC 173-26-221(2)(c)(iv)(B)].

The minimal level of effort is often defined by the availability of resources (e.g., money, time, trained staff, and data and environmental and infrastructure values). However, in general, the fewer resources used, the lower the confidence in the delineation.

Shoreline planning objectives, channel pattern, and the possibility of channel movement occurring in terms of time (e.g., < 50 years, 50-75 years) are more objective measures for determining level of effort (See Figure 12 below).
Environmental value high moderate low

Level of effort

Geomorphic
process possible:
Erosion, flooding, avulsion in years

+100 low low low
75-100 moderate moderate low
50-100 high moderate moderate
<50 high high moderate
 
Infrastructure value low moderate high

Level of effort

Geomorphic
process possible:
Erosion, flooding, avulsion in years

+100 low low low
75-100 low moderate moderate
50-100 moderate high high
<50 moderate high very high

 

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). The environmental value provides information for protecting existing ecological value or developing restoration strategies, whereas the infrastructure value emphasizes evaluating hazards to people or critical infrastructure. Depending on the jurisdiction’s objectives both matrices can be used or one of the other used for specific reaches. 

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