What can I do to keep my shoreline from washing away?
If your shoreline is eroding, any of the following events may be destabilizing your soil, resulting in erosion: fluctuating water levels, increased wave or wake action, ice pushes, loss of natural vegetation, and human activity.
Protecting your shoreline from erosion may not require you to replace natural shoreline with a high-cost, highly engineered retaining wall or riprap. There are affordable, low-impact methods to stabilize your shoreline and still protect property values, water quality, and habitat. The Minnesota Department of Natural Resources (DNR) strongly encourages you to consider planting native vegetation to control shoreline erosion, enhance aesthetic values, and contribute to better water quality in your lake (see Maintaining and restoring natural shorelines).
Both riprap and retaining walls can reduce erosion, but can be expensive and negatively affect lakes by creating a barrier between upland areas and the shoreline environment. Riprap should only be used where necessary and never to replace a stable, naturally vegetated shoreline. Additionally, installing riprap on a stream or river bank is a special condition that may require professional advice to ensure that the structure will stand up to the fluctuations in water levels and flowing conditions.
Natural rock riprap consists of coarse stones randomly and loosely placed along the shoreline. You should consult your local DNR Area Hydrologist to determine whether your shoreline needs riprap to stop erosion. If there is a demonstrated need, such as on steep slopes, you may want to consider placing riprap or a combination of riprap and vegetation. In most cases, vegetation planted in the rocks will stabilize the riprap and improve the appearance of your shoreline. Naturalizing your shoreline is the most important contribution you can make to enhance water quality, maintain fishery resources, and provide wildlife habitat.
Is a permit required to install riprap?
Installation of natural rock riprap is allowed only where there is a demonstrated need to stop existing erosion or to restore an eroded shoreline. Using riprap as a method of landscaping is not allowed. Placement of riprap may only include areas of the shoreline where erosion is present. For most projects constructed below the ordinary high water level (OHWL) of public waters, an individual Public Waters Work Permit is required by the DNR.
However, an individual permit from the DNR is not required for riprap placement if the installation meets all of the following conditions:
The riprap must not cover emergent aquatic vegetation, unless authorized by a DNR aquatic plant management permit.
The rock is sized appropriately, based on the erosion potential of the wave or current action of the water body.
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.
A filter of crushed rock, gravel, or filter fabric material must be placed underneath the rock. The riprap must be no more than 6 feet waterward of the ordinary high-water level.
The riprap must conform to the natural alignment of shore and must not obstruct navigation or the flow of water.
The finished slope, as measured on top of the rocks waterward of the ordinary high water level (OHWL), must be no steeper than 3 to 1 (horizontal to vertical).
The riprapped area must be no more than 200 linear feet of shoreline along public water lakes and wetlands or, along shorelines of streams, must be less than five times the average width of the affected watercourse.
The site must not be a posted fish spawning area, designated trout stream, or along the shore of Lake Superior.
Agents and contractors are required to submit a Landowner Statement and Contractor Responsibility form whether or not a permit is required (MN Stat. 103G.241). Apply using the MNDNR Permitting and Reporting System.
What are some other issues to consider?
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 damage the near-shore environment. They cause wave action that scours the lakebed, displacing bottom sediment and create a 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. Consider planting within the riprap to add color, interest, and diversity. Live cuttings and plant plugs can be planted within riprap to provide additional slope stability and give your shoreline a more natural appearance.
What local government requirements apply?
The DNR has jurisdiction for riprap installed below the OHWL and local units of government have jurisdiction above the OHWL and may require a permit for the project, especially if more than 10 cubic yards of materials are moved, removed, or added to the property (including riprap). Always check with your zoning authority for local erosion control regulations.
If you have questions concerning this information, contact your local DNR Area Hydrologist.