Shoreline Guide for Homeowners

FLARA encourages homeowners on Fish Lake to assess and restore their own
shoreline. On September 8, 2020 you received an email with resources and
website links for shoreline management and protection. FLARA would like to
provide Fish Lake homeowners with some additional detail.

How does shoreline erosion occur?

  • Excessive water, wind or lack of protection must exist. (1)

  • Soil becomes saturated and fluid. (1)

  • Wave action pulls suspended solids from the shoreline to lower levels. (1)

  • Areas where the water undercuts the shoreline erode faster than areas where water only flows over the shoreline. (1)

Most common options to mitigate shoreline erosion

  • Rock riprap (hard armor)

  • Native plant restoration (soft armor)

  • Combination of riprap and native plant restoration

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*Important:  When the slope of the shoreline achieves an 8:1 or 10:1 ratio (horizontal vs. vertical), very little erosion will occur no matter what the protective surface. (1)

*Sand beaches require a much flatter slope, such as 8:1 or 10:1, compared to rock riprap. 

Rock riprap

* Slope and fabric are the key components to a long-lasting riprap shoreline.

 

Bank Slope Preparation--3:1 or flatter back slope to minimize the force of the waves.  (1). Steeper slopes will cause rock to tumble down the slope during high water periods.   (1)

 

Fabric--A minimum of 6-8 oz. of Geotextile fabric is the protection barrier. All the other components of the design are to keep the fabric in place to do the work. Fabric allows water to move freely through it but not the solids, thus protecting the integrity of the shoreline.  (1)

 

Rock covering--the purpose of the rock is to hold the fabric in place and prevent ice damage.  (1)

Only natural rock (cannot average less than 6 inches or more than 30 inches in diameter) may be used that is free of debris that may cause pollution or siltation. Concrete is not allowed.  (2)


Height needed for protection--when evaluating the highest level to which protection should reach, determine the highest historical flood levels and then add the amount of wave run up.  (1)

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* A row of boulders at the water’s edge is not considered natural rock riprap. Rows of stacked boulders function as a retaining wall, and installation would require an individual permit from the DNR. Retaining walls are very damaging to the near-shore environment. Retaining walls cause wave action that scours the lakebed, displacing bottom sediment and creating an extremely sterile environment. The cumulative effect of numerous wall structures on a lake reduces critical habitat for fish and wildlife resources and much of the food chain they depend on. Retaining walls require structural maintenance and are frequently damaged by ice action and undermined by wave action. Riprap is not maintenance free and does not eliminate ice heaving, but it is easier to return the rocks to their original positions than to repair a wall.  (2)

 

Ice - Ice expansion alone can exert 10-12 tons per square foot on anything in its way. If flooding occurs while the ice is still thick, strong winds can slam the ice ashore with a tremendous force. If the lake levels are above normal during freeze-up, sand and rocks captured in the ice can be lost to the lake during the spring. Every effort must be made to allow the ice to slide up and over the revetment instead of plowing into it. (1)

Rock revetments require some annual maintenance replacing rocks moved by the waves or ice. (1)

Native Plant Restoration:  

 

You can restore your shoreline with plants that are water tolerant and act as native buffers.  Choosing the appropriate plants for your shoreline is an important aspect of the project.  The MN DNR provides materials for shoreland owners on implementing shoreland restoration and protection projects. The information includes shoreline assessment and design, as well as plant guides.

 

MN DNR Restore Your Shore

 

https://www.dnr.state.mn.us/rys/index.html

 

Lake Shore Videos

 

Great video from Anoka Conservation District

https://www.youtube.com/watch?v=dwjAoRwLrmM&feature=youtu.be

 

Another great resource for native plant restoration of your shoreline is this YouTube video from the Crow Wing Soil and Conservation District:  https://youtu.be/3Z1paPcIVeM

 

If you choose native plant restoration, please consider Hennepin County's Natural Resource Grant Program.  They will assist homeowners with projects for water quality improvement and natural area enhancement. Project examples include shoreline improvements, native vegetation restoration, vegetated filter strips, and rain gardens. Please contact Kirsten Barta at Kirsten.barta@hennepin.us or 612-543-3373 for further assistance.

 

Hennepin County Natural Resource Grants

 

https://www.hennepin.us/residents/environment/natural-resources-funding
 

Sources:
 

(1) Shoreline Stabilization Guidelines - SD Department of Environment and Natural Resources

(2) Shoreline Alterations: Riprap - MN DNR