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