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Riprap and Geotextile Use – 7 Lakes Alliance Policy and Background

General Principles of Shoreline Stabilization:

  • Wave and ice action cause shoreline erosion from the lake side

  • Stormwater runoff & human activity cause shoreline erosion from the land side

  • Use as many native plants as possible, including a buffer

  • Use riprap only when necessary (Buffers are better both ecologically and economically)

Riprap and Shoreline Stabilization:

  • All riprap projects must submit a Permit-by-Rule (PBR) application to the Maine Department of Environmental Protection (DEP).

  • Riprap can only be used when a shoreline bank slope is greater than 3:1 (3 horizontal feet to 1 vertical foot) [1]

  • A filter layer should be placed under the riprap, either:

    1. A 6” thick layer of crushed stone ranging from ¾” to 3”, or

    2. Filter fabric (geotextile) followed by a 3” thick layer of clean ¾” crushed stone

The Maine DEP wrote the PBR shoreline stabilization standards in 2008 and is currently in the process of reviewing and updating the PBR standards.


Geotextiles and Shorelines:

Geotextiles (filter fabrics) are synthetic materials that can be used in construction or erosion control projects. They are not biodegradable and most geotextiles are susceptible to photodegradation: they break down from the UV in sunlight and release micro-plastics into the environment [2].


Maine DEP staff (John Maclaine, June 2023) told 7 Lakes staff that geotextiles are considered problematic for several reasons:

  • Geotextiles inhibit the growth of shoreline vegetation

  • They inhibit ecosystem functions and naturalizing of shorelines

  • Geotextiles add hydrocarbons and chemical pollutants to natural areas

  • They prevent riprap from sinking into the shoreline sediment and becoming stable

  • They can cause riprap to slump into lake

  • As material settles, underlying fabric becomes visible over time and is unsightly; biodegradable shoreline stabilization products are available at similar cost

Because of these limitations, the 7 Lakes Alliance is deliberate on when and where we use geotextiles in our shoreline stabilization projects. Keeping the lakes healthy is our main priority.


 

[1] Maine DEP Factsheet, Conservation Practices for Homeowners: Lake Shoreline Riprap (maine.gov), Document Number: DEPLW-0922 June 2008. [2] EPA Factsheet, Stormwater Management Practices: Geotextiles, Matting and Netting (epa.gov), Document Number: EPA-832-F-21-028T Dec 2021.

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