Spring is a time when many are excited to spruce up their outdoor spaces. As you make your landscaping plans, don't forget about your shoreline! The Lake Leelanau Lake Association is a proponent of natural shorelines. Native plants with deep roots can stabilize the shoreline to resist erosion, while adding beauty and habitat for fauna, and attracting pollinators at the same time. Simple techniques like creating a "no-mow" zone at the water's edge can accomplish many goals.
However, there are situations when these interventions will not be enough. Some shorelines are subject to intense wave action, whether because of wind coming across a long fetch, or wakes from recreational boats, especially wake boats. Others have a steep slope or are composed of intrinsically loose materials, which can predispose them to erosion. Removing an old seawall is a worthy goal, but over the years, that seawall has artificially altered the shoreline in ways that will make it susceptible to erosion if there is no intervention. In cases like these, there needs to be a strategy to protect the shoreline.
Many of these strategies go under the heading "bioengineering."
Bioengineering 101
Also called "soft armoring", this is the practice of using biodegradable materials and native vegetation as an alternative to hard structures like riprap and seawalls. The purpose is to stabilize the shoreline, controlling erosion by absorbing wave energy. At the same time, it will enhance water quality by filtering runoff to remove pollutants and enhance the habitat for both aquatic and terrestrial inhabitants. Bioengineered structures are self-repairing and become stronger as plants grow, while hard armor materials weaken over time.
Bioengineering Techniques
The following are bioengineering techniques. While in some cases these individual techniques can suffice, bioengineering usually involves a combination of multiple techniques.
Buffer Zone:
The simplest version of a natural shoreline is a buffer zone, ideally about 35’ wide, comprised of native plants. A buffer zone is an alternative to a grassy lawn extending to the edge of the water, as the root length of native plants is significantly longer than that of grass, and better bolsters the shoreline.
Coir Logs:
One commonly used technique employs biodegradable coconut fiber rolls called coir logs to stabilize new soil and plantings until they are established. They are placed at the "toe" of the slope at the water’s edge, right where the water hits the shoreline. Since they face the lake, they are the first line of defense against wave energy. They are made of soft material, so, unlike a seawall, they absorb wave energy rather than refracting it and causing further erosion.
Erosion control blankets:
A biodegradable erosion control blanket may be used on the slope. Layers of biodegradable fabric placed between soil and mulch can help prevent the organic material from being washed away. It can be pierced, or holes can be cut or burned into it where needed, to install plants. Similarly, brush mattresses are a layer of live branches placed in a crisscross pattern over the soil surface, acting as a living blanket that protects against high-velocity flows, traps sediment, and creates instant habitat.
Woody Vegetation:
Woody vegetation, such as wattles or live stakes, can be employed. Wattles are bundles of branches, placed horizontally in strategic areas to buffer wave energy. They reduce water velocity, trap sediment, and hold the soil in place. Live stakes are shrub cuttings installed vertically into a bank. They are cut from shrubs like willow or red osier dogwood and staked into the shoreline or to help hold erosion control blankets in place. When done correctly, they may sprout and grow, further bolstering the shoreline.
Encapsulated Soil Lifts:
Another method uses encapsulated soil lifts, which are layers of soil that are encased in biodegradable fabric, much thicker versions of the blankets described above. On a foundation of rocks, these are stacked like steps, each set back from the one below it to create the desired slope of the shoreline. Coir logs can be used in conjunction with these lifts. The soil is planted with seedlings, and the fabric holds everything together until roots are established, which can take 2-3 years. Typically, live stakes, as referenced above, are placed between the layers where they will eventually root. This technique is sometimes termed a vegetative geogrid and may, in some cases, replace a seawall.
Fieldstone Revetment:
Fieldstone revetment is an environmentally conscious use of stone. This uses rounded fieldstone on a 1:4 slope (1 foot vertical to 4 feet horizontal), in conjunction with a coir log at the water’s edge and native plantings. This is in contrast to riprap, where improperly sized and placed rock can create barriers for wildlife, and may be difficult on which to grow plants, which are a requirement for bioengineering. In time, a properly designed fieldstone revetment can become hidden by vegetation.
Native Plants:
A key component of any of these techniques is the use of native plants. Native species can be chosen to adapt well to a particular environment. They will have deep roots, become established quickly, and be tolerant to flooding and ice. Examples include woody shrubs like willows and dogwood; emergent plants (at the water’s edge) like sedges, reeds, and rushes; and a wide variety of shoreline plant species. Many of these, such as milkweed species, also attract pollinators. Click here to download LLLA's specially curated native plant list, which also includes locations to buy them.
Choosing a Design
The graph below shows that the type of design, and techniques employed, depends largely on the amount of wave energy to which the shoreline is exposed.
Wave energy contributing to erosion is related to 3 factors:
- The maximum fetch distance is the longest unobstructed distance to the opposite side of the lake. The longer the fetch, the more energy that can be built up into waves when the wind is from that direction.
- The slope of the lakebed. An important measure is distance from shore where the water depth exceeds 2’, which is where waves will break if they are 2-3’ high. The farther out until the depth is 2’, the farther out waves will break, thus dissipating their energy.
- The level of boating activity is a factor, particularly near marinas or busy recreational areas. The wake of a ski boat 300’ away creates a 5” wave at the shoreline; for a wake boat, this is a 10” wave. (This is why it is recommended, and may become law, that wake boats need to stay 500’ from shore and operate in over 20' of water.)
EGLE has an energy assessment tool to estimate the erosive energy a particular shoreline is exposed to. This is customized to your exact location.
Use contour maps to help you understand the depth of the water in front of your property.
Permitting issues
EGLE requires permits for shoreline activity at or under the ordinary high water mark. Their website gives guidance on what may be allowed depending on the risk of erosion.
For low energy sites:
- Placement of biological erosion control structures, including fiber rolls, fiber mats, live stakes, brush mattresses, brush bundles, and plantings of native vegetation.
- Limited placement of natural stone or rock riprap, covering no more than 25% of the length of the project and allowing for the free growth of plants, if necessary, to stabilize biological materials.
- Temporary placement of fiber rolls or similar materials to serve as wave breaks or barriers placed in close proximity to the existing shoreline and in a manner that does not interfere with navigation, to facilitate the establishment of biological control structures or plantings.
For higher energy sites:
- Biological erosion control structures, including soil lifts or fiber blocks, fiber rolls, fiber mats, live stakes, brush mattresses, brush bundles, and plantings of native vegetation, are placed at or above the existing shoreline.
- Natural stone may be placed if it allows for the free growth of plants, does not extend more than 6 feet waterward of the ordinary high water mark, and is minimized based on site conditions. The stone shall be placed at a 1-on-4 slope (e.g., 1 foot vertical to 4 feet horizontal) or gentler.
- Vegetation, in the form of seed, plantings, or other potentially viable material such as live stakes, brush bundles, or other gathered woody material, shall be used along the length of the installation. Vegetation shall be comprised only of plant species that are considered native to Michigan.
- Excavation and backfill shall be permitted under this subcategory only to the extent necessary to stabilize slopes and to place bioengineering structures.
Designs incorporate shoreline stabilization while taking into account the needs of the property owner, such as swimming, lake access, relaxing, and maintaining an open view of the lake.
It is important to work with a qualified contractor, one who is a Certified Natural Shoreline Professional. Go to Michigan Natural Shoreline Partnership to see if your contractor is certified or contact the Lake Association for help.
For more information on bioengineering techniques, download EGLE's new Introductory Guide for Bioengineering Techniques.
Get Tailored Bioengineering Advice
If you're ready to remove your seawall or develop a strategy to protect your natural shoreline, the Lake Leelanau Lake Association is here to help. Schedule a complimentary shoreline consultation with our trained Shoreline Ambassadors.
Schedule a Shoreline Consultation
Learn more about the program here, or click below to schedule your own shoreline consultation.
Main photo from EGLE