Lake Leelanau shorelines exhibit a variety of appearances. Our watershed and shoreline have everything from natural woodlands, aquatic vegetation, and beaches to man-made control structures (i.e., riprap) to combat soil erosion. Questions commonly arise from riparians as to the functionality and drawbacks of riprap on our lake shorelines. The Lake Leelanau Lake Association would like to shed some light on this important topic.
What is Riprap?
Riprap is a general term and typically refers to stone placed and fitted to the shoreline slope to create a barrier against high wave energy. Riprap protects soft shorelines and soil surfaces to lessen sedimentation where significant erosion and scour may occur. The rough rock surfaces serve to deflect the wave energy and absorb further energy in the cracks, crevasses, and channels.
Riprap stone varies in size, with larger stones specified for higher water velocity areas. Loose stones may be set by hand to produce a dense, uniform configuration, placed in a brick-like formation, or grouted as a wall. Large individual riprap stones (say, up to two cubic feet, weighing 50 lbs. or more) or large volumes may require machinery for placement depending on field conditions. The stone is commonly irregularly-shaped, angular, and of granite or limestone. Considered a permanent-type construction, riprap removal after installation is difficult. This long-term durability is useful for high-energy (strong or fast waves, or both) situations with greater wave intensity and winds.
Riprap installations often include the placement of the stone materials atop filter fabrics, meshes or geotextile products. Then, this is followed by continuous gravel underlayment or other stone bedding. In some situations, anchors may also be used. These are not do-it-yourself projects. Due to the project size, mass of materials, heavy-duty equipment, and expertise, professional contractors are typically required for the design, permitting, and construction of riprap.
Common Uses & Drawbacks
Riprap has been used commonly for shoreline erosion control due to its relative ease of installation, protection in areas with high wave energy, and the short amount of time it takes to install. However, there are several drawbacks when considering the use of it on your shoreline:
- These hard structures modify the shoreline permanently—this means that shoreline habitat may be destroyed or drastically altered. Rock and installed inert materials are not helpful to vegetative growth nor the presence of small aquatic animals.
- Since riprap is made of hard rock, it does not absorb wave energy but deflects it. Diverted wave energy from one property’s riprap shifts the energy to neighboring properties, often causing new erosion problems.
- The State of Michigan requires a permit with shoreline energy calculations is required for such installations, and approvals of riprap projects are often exceptions at best. Local or township requirements sometimes do not allow riprap installations at all.
- New riprap projects on Lake Leelanau should only be considered for unique energy and erosion situations. Much of the Lake’s shorelines exhibit a low-to-moderate risk for significant erosion. And usually, you can employ other shoreline protection measures (e.g., native vegetative plantings, mulching, etc.).
- Riprap projects typically have higher overall costs for installation when compared to installing a native shoreline. Although, maintenance costs are estimated to be low.
- The science of shoreline restoration projects (non-riprap) has improved considerably in recent years, and its use is encouraged by EGLE for permitting. New designs and products (e.g., coir logs, biodegradable fabric meshes, and “turtle” logs) can address most shoreline sites that might have greater wind and wave energy circumstances.
- Riprap does not benefit the lake’s water quality or aquatic life. In fact, the use of it instead of natural shorelines can take habitat away from critters such as turtles, shallow-water fish, otters, and other shoreline-reliant animals.
For these reasons, we discourage the use of riprap in most cases. Instead, we promote the development of natural shorelines. For more information, please click here to learn about natural shorelines and other ways to protect Lake Leelanau’s watershed.
Considering the time it takes to grant permits for shoreline projects, we advise you to look into options for any projects planned for next summer now. If you have any questions or want to schedule a consultation, please, contact our Shoreline Ambassador, Nancy Popa, at [email protected] or 231-944-9509.
This blog was written by Greg Vogt, LLLA Board Member and Lake Stewards Subcommittee Member.