4.15 Erosion Control

Goal 15 - Erosion Control

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) in 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. 

The Upper Watershed Stream Assessment identified several localized areas of erosion on Gleason 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.   In addition, the Gleason Lake Management Plan identified some locations of lake shoreline and channel erosion.   Strategies in the Gleason Lake 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 Gleason Lake
  • Clarity by satellite-estimated Secchi depth for Hadley, Kreatz, and Snyder Lakes
  • Nutrient loading goals for Gleason Lake
  • Stream Visual Assessment Protocol (SVAP) in Gleason Lake Creek

Goal 15.1 - Gleason Lake

Identify and address erosion problems in the subwatershed.

Actions

  1. Identify, inventory, and prioritize channel, shoreline and other erosion problems in addition to those already identified in the HHPLS, Gleason Lake Management Plan, and Upper Watershed Stream Assessment.
  2. Restore degraded streambanks on Gleason Lake Creek to achieve a Stream Visual Assessment Protocol mean score above 5.0. and on other streams to stabilize streambanks; reduce pollutant loading, erosion and sediment transport; and increase habitat.  
    1. Periodically update the Gleason Lake Creek stream assessment to assess current stream condition and ecological integrity.
  3. The HHPLS modeled higher than desirable velocities at the TH 101 culvert at Snyder Lake, and the CR 6 culvert conveying Ditch #15 that could lead to inlet or outlet erosion.  Work cooperatively with the City of Plymouth, Hennepin County, and MnDOT to evaluate the need to provide erosion control or take energy dissipation measures at these crossing to prevent erosion and downstream sediment transport.
  4. Work cooperatively with LGUs to spot repair identified erosion problems.
  5. Regulate new development and redevelopment and ensure compliance with erosion control standards.

Goal 15.2 - Gleason Lake

Manage water volumes to Gleason Creek and Ditch #15 to prevent further erosion.

Actions

  1. Implement the regulatory and management activities identified in this plan.
  2. Inspect erosion-prone areas of Gleason Creek and Ditch #15 at least annually to assess their condition.
  3. Work cooperatively with the Cities of Plymouth and Wayzata to reduce volumes as necessary.