4.15 Erosion Control

Goal 15 - Erosion Control

Control temporary sources of sediment resulting from land disturbance and identify, minimize and correct the effects of sedimentation from erosion-prone and sediment source areas.

Discussion

Erosion within the subwatershed can result in sediment being transported to lakes, wetlands, and streams, where it can degrade water quality and habitat.  Sediment accumulating in channels, culverts, and other facilities can reduce their ability to convey stormwater, while erosion can undermine their stability.

The key areas identified in this plan for conservation activities include buffer zones adjacent to streams and channels.  In some cases these buffer zones are riparian or flow-through wetlands, and those wetlands have been identified as key conservation areas (see Figure 19).  Where streams and channels flow through upland areas, conservation of native vegetation within these zones would also increase or maintain infiltration rates; decrease or maintain runoff rates and pollutant conveyance to water resources; and help minimize erosion.   Restoration of lakeshore would have the same benefits.  Identifying, addressing, and preventing erosion is necessary to meet District goals as well as to meet state and federal nondegradation, water quality and biological integrity requirements and to prevent the need for future TMDLs. 

Requiring new development and redevelopment to infiltrate some of the new stormwater generated would reduce post-development volumes downstream and help reduce future erosion in streams and channels; minimize new pollutant loading that would have been conveyed by that stormwater; and help maintain groundwater levels, preserving wetlands.  Limiting discharges from subwatersheds and basins that are currently landlocked is necessary to prevent further degradation of downstream water quality as well as to limit new volumes discharged to channels that are already experiencing erosion.

The Upper Watershed Stream Assessment identified several localized areas of erosion on Six Mile Creek.  Other streams and channels within the subwatershed may currently be experiencing erosion or may develop erosion problems as development in the upper subwatershed increases the amount of impervious surface and stormwater runoff.  Strategies in the Six Mile Marsh subwatershed will focus on identifying erosion problems on an ongoing basis and working with LGUs to correct them, as well as considering potential downstream impacts of new volumes discharged from development.

Desired Outcomes:  Reduction in pollutant loading of temporary and permanent nature from erosion to supplement other goals.

Metrics:

  • In-lake nutrient concentrations/Trophic State Index Scores (TSI) for Halsteds Bay and the lakes in the subwatershed
  • Nutrient loading goals (lbs) for Halsteds Bay and the lakes in the subwatershed
  • Macroinvertebrate Index of Biotic Integrity (M-IBI) in Six Mile Creek
  • Stream Visual Assessment Protocol (SVAP) in Six Mile Creek

Goal 15.1 - Six Mile Marsh

Identify and address erosion problems in the subwatershed.

Actions

  1. Identify, inventory, and prioritize gully, channel, shoreline and other erosion problems in addition to those already identified in the HHPLS and Upper Watershed Stream Assessment.
  2. The HHPLS modeled higher than desirable velocities at several culverts that could lead to inlet or outlet erosion.  Work cooperatively with the respective cities, Carver County, and Three Rivers Park District to evaluate the need to provide erosion control or take energy dissipation measures at these crossing to prevent erosion and downstream sediment transport.
  3. Restore degraded streambanks on Six Mile Creek to achieve a Stream Visual Assessment Protocol mean score above 5.0  and other on streams to stabilize streambanks; reduce pollutant loading, erosion and sediment transport; and increase habitat.  Figure 20 illustrates areas identified in the Stream Assessment and the lakes TMDLs as high priorities for restoration.
    1. Periodically update the Six Mile Creek stream assessment to assess current stream condition and ecological integrity.
  4. Spot repair identified erosion locations in Six Mile Creek and develop strategies to prevent future erosion and sediment transport.
  5. Regulate new development and redevelopment and ensure compliance with erosion control standards.

Goal 15.2 - Six Mile Marsh

Manage water volumes to Six Mile Creek to prevent further erosion.

Actions

  1. Implement the regulatory and management actions identified in this plan.
  2. Inspect erosion-prone areas of Six Mile Creek periodically to assess their condition.
  3. Work cooperatively with the adjacent property owners and LGUs to prevent erosion and sediment transport and stabilize streambanks as necessary.