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.  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.    The District acknowledges that given the urbanized nature of much of the watershed, success of District programs and projects is dependent on the participation and dedication of public and private partners towards achieving mutual goals.

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 Minnehaha Creek Stream Assessment identified numerous localized areas of erosion on Minnehaha Creek.  Strategies in the Minnehaha Creek subwatershed will focus on identifying erosion problems on a continuing basis, working with LGUs to correct them, and implementation of stream restoration programs to improve streambank stability.

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 the lakes in the subwatershed
  • Nutrient loading goals (lbs) for Minnehaha Creek and the lakes of the subwatershed
  • Macroinvertebrate Index of Biotic Integrity (M-IBI) in Minnehaha Creek
  • Stream Visual Assessment Protocol (SVAP) in Minnehaha Creek

Goal 15.1 - Minnehaha Creek

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 and the Minnehaha Creek Stream Assessment.
  2. In collaboration with riparian cities and property owners, other agencies and infrastructure owners, restore degraded streambanks on Minnehaha Creek to achieve a Stream Visual Assessment Protocol mean score above 5.0   and other streams to stabilize streambanks; reduce pollutant loading, erosion and sediment transport; and increase habitat.  Figure 20 illustrates areas identified in the Stream Assessment as high priorities for restoration.
    1. Periodically update the Minnehaha Creek stream assessment to assess current stream condition and ecological integrity.
  3. Work in partnership with creek riparian communities and other agencies and utilities to spot repair streambank erosion.
  4. Work cooperatively with the National Park Service and Minneapolis Park Board to identify necessary streambank restoration and structure improvements in the Mississippi River gorge from Minnehaha Falls to the Mississippi River.
  5. The HHPLS modeled higher than desirable velocities at several outfalls that could lead to erosion.  Work cooperatively with the riparian cities to evaluate the need to provide erosion control or energy dissipation measures or reconstruct these outfalls to prevent erosion and downstream sediment transport. 
  6. Inspect erosion-prone areas of Minnehaha Creek at least annually to assess their condition and inspect the entire creek at least every five years.
  7. Implement the regulatory and management goals identified in this plan.
  8. Regulate new development and redevelopment and ensure compliance with erosion control standards.

Goal 15.2 - Minnehaha Creek

 Manage streamside infrastructure to enhance stream stability.

Actions

  1. Promote replacement of deteriorated streambank protection with bioengineered protections where practical and effective.  Enhance existing boulder riprap protection with deep-rooted vegetation.  Where improvements are made preserve only selected retaining walls and other streamside structures that are of historical significance. 
  2. Protect other beneficial uses (infrastructure) of the streamside corridor from damage by streambank erosion.
  3. Promote other riparian zone uses such as streamside trails, with appropriate erosion protection and riparian vegetation enhancements.
  4. Work cooperatively with the adjacent property owners to prevent erosion and sediment transport and stabilize streambanks as necessary.