Array of Measures and Screening

Measures for this study were screened by reach using professional judgement, effectiveness, efficiency, and acceptability. Table 1 - Table 4 summarize the screening of measures to develop the final array of measures for alternative formulation. Measures highlighted in red were screened from consideration. Integrate bank treatment was initially carried forward but was later screened because the frequent flooding and high velocities would make it difficult/infeasible to establish vegetation and utilize established vegetation as a reliable erosion resistance feature. Based on historical imagery and data analyzed during the evaluation of the existing conditions, the team concluded that there was no observable erosive threat in Reach 4. Table 4 summarizes measures that were considered for Reach 4 but were screened after determining that there was no observable erosive threat. River Access was considered to address improved access to the Minnesota River to support culturally significant activities such as fishing. This measure is further described in Section 2.5.2.

Table 1: Preliminary Measures considered for Reach 1 REACH 1

Measure Pros Cons

Screening Criteria

Screening Justification Effective

ness Efficiency Acceptability Plus - Neutral - Negative

Longitudinal Peak Stone Toe

Allows for riparian buffer plantings Banks will stabilize in short term Launchable toe stone provides protection from additional channel scour/thalweg migration

Expensive

Launchable toe stone can reduce habitat diversity

Measure may solve the problem;

other measures are likely more robust for the problem. Retained until further H&H information is available.

Slope Banks with Ground Cover

Allows for riparian buffer plantings Banks will stabilize in short term

Material must be stockpiled Will not prevent erosion for long if thalweg is shifting or velocities increase

Slopes may be 1:3 or shallower (pending soil types in the area this may be an issue)

Neutral Neutral Negative

While this measure may be cost-effective, it is not an effective long-term and robust solution for the problem.

Riprap Slopes:

Steeper slopes = less removal of material

Does not increase aquatic habitat

Plus Plus Neutral

Retained, measure will likely solve the problem, while it may not be the most environmentally friendly.

Root wad / Boulders

Creates aquatic habitat Tolerates high velocity if well anchored effective long-term solution for the problem.

Measure is relatively expensive and may not be an effective long-term solution for the problem.

Bendway Weirs Diverts channel thalweg Creates aquatic habitat

Material must be trucked in Will not prevent erosion for all stages

Stockpiling and construction will increase disturbance

Plus Plus Plus

Retained, will likely help with the overall problem, likely need to be combined with other measures.

Integrated Bank Treatment

Rock on lower part of bank would provide stabilization

Plantings on the higher section would provide habitat

Rock can be expensive Need stockpiling location

Neutral/

Negative Plus Plus

Measure is a slight variation from rip rap and would be more

environmentally friendly, but would likely not solve the problem, less erosion resistance

Toe Wood -

Sod Mats Provides habitat Scour at the toe Neutral/

Negative Neutral Neutral

Measure may be environmentally friendly, but not likely a robust solution for the problem.

Table 2: Preliminary Measures considered for Reach 2

ness Efficiency Acceptability Plus - Neutral - Negative

Neutral Neutral Neutral

Riprap Slopes:

Steeper slopes = less removal of material

Does not increase aquatic habitat

Plus Plus Neutral

Retained, measure will likely solve the problem, while it may not be the most environmentally friendly.

Can be used on steeper slopes (1:1)

Must be built during low flows Labor intensive

Rock fill potentially needed if bedrock doesn't extend under slope (need boring information) Ice jams / impacts could unravel geotextile if flooding occurs soon after install

Neutral Neutral Neutral Relatively expensive measure, and not an effective long-term solution.

Bendway Weirs Diverts channel thalweg Creates aquatic habitat

Material must be trucked in Will not prevent erosion for all stages

Must be keyed into bank Stockpiling and construction will increase disturbance

Plus Plus Plus

Retained, will likely help with the overall problem, likely need to be combined with other measures.

*Integrated Bank Treatment

Rock on lower part of bank would provide stabilization

Plantings on the higher section would provide habitat

Rock can be expensive Need stockpiling location

Neutral/

Negative Neutral Plus

Measure is a slight variation from rip rap and would be more

environmentally friendly, but would likely not solve the problem, less erosion resistance

Toe Wood -

Sod Mats Provides habitat Scour at the toe Neutral/

Negative Neutral Neutral

Measure may be environmentally friendly, but not likely a robust solution for the problem.

Vegetation - incorporate where possible

Vegetation can stabilize the bank

Increase or improve habitat None Neutral Neutral Plus

Retained - vegetation should be considered where possible, it is a cost-effective action to improve habitat.

Table 3: Preliminary Measures considered for Reach 3

ness Efficiency Acceptability Plus - Neutral - Negative

Does not increase aquatic habitat

Plus Neutral Neutral

Measure may solve the problem;

other measures are likely more robust for the problem. Retained until further H&H information is available. Can be used on steeper slopes (1:1)

Must be built during low flows Labor intensive

Rock fill potentially needed if bedrock doesn't extend under slope (need boring information)

Ice jams / impacts could unravel geotextile if flooding occurs soon after install

Plus Neutral/

Negative Neutral

While this measure may be cost-effective, it is not an effective long-term and robust solution for the problem.

*Integrated Bank Treatment

Rock on lower part of bank would provide stabilization Plantings on the higher section would provide habitat

Rock can be expensive

Need stockpiling location Neutral/

Negative Plus Plus

Measure is a slight variation from rip rap and would be more environmentally friendly, but would likely not solve the problem, less erosion resistance

Table 4: Preliminary Measures considered for Reach 4

ness Efficiency Acceptability Plus - Neutral - Negative

Stocking piling & construction access

may be limited Based on historic images and

flows it was determined that there was no erosion problem in this reach. It is not recommended that any action is taken in this reach and any further changes on this reach would not negatively impact reaches 1-3.

Erosion Control Barriers

Light weight, easier to install (synthetics)

Possibly able to use natural materials nearby (fallen trees) arranged and staked Prevents some soil erosion

Lifespan is limited unless more expensive products are used Unnatural appearance for some syntenic products