What can I do to keep my shoreline from washing away?
Consider natural alternatives to riprap
If your shoreline is eroding, any of the following events may be destabilizing your soil, resulting in erosion: fluctuating water levels, increased wave action, ice pushes, loss of natural vegetation and human activity. There are many affordable, low-impact methods to stabilize shorelines while protecting property values, clean water and habitat.
Where appropriate, the Minnesota Department of Natural Resources (DNR), encourages you to consider natural alternatives to riprap to control shoreline erosion, enhance aesthetic values and contribute to better water quality in your lake (see Maintaining and restoring natural shorelines).
Riprap considerations
Natural rock riprap consists of coarse stones randomly and loosely placed along the shoreline. It can reduce erosion but is expensive and negatively affects lakes by creating a barrier between upland areas and the water. Riprap is not maintenance free and does not eliminate ice heaving. Vegetation planted within the rocks will stabilize the riprap and improve the appearance of your shoreline and habitat value. Naturalizing your shoreline is an important way to enhance water quality, maintain fishery resources and provide wildlife habitat.
Riprap requirements
Riprap is only allowed where there is a demonstrated need to stop existing erosion or to restore an eroded shoreline and not for landscaping or to replace a stable, naturally vegetated shoreline. Placement of riprap may only include areas of the shoreline where erosion is present. You should consult your local DNR Area Hydrologist to determine whether there is a demonstrated need for riprap to stop erosion. For most projects constructed below the ordinary high water level (OHWL) of public waters, a Public Waters Work Permit is required by the DNR.
However, a permit from the DNR is not required for riprap placement if the installation meets all of the following conditions:
The riprap must not cover aquatic emergent 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, 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 (DOC) whether or not a permit is required (Minn. Stat. 103G.241).
If the installation of riprap does not meet the above criteria, then a public waters permit is required. Apply using the MNDNR Permitting and Reporting System.
Other issues to consider
One or more rows of stacked boulders function as a retaining wall and are not considered riprap. Installation requires a permit from the DNR. Retaining walls damage the near-shore environment. They cause wave action that scours the lakebed, displacing bottom sediment and creating 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. Installing riprap on a stream or riverbank may require professional advice to ensure that the structure will stand up to the fluctuations in water levels and flowing conditions.
Local government requirements
The DNR has jurisdiction for riprap installed below the OHWL and local units of government have jurisdiction above the OHWL. A local permit may be required, especially if more than 10 cubic yards of materials are moved, removed, or added to the property (including riprap). For riprap installed below the OHWL and in a mapped floodplain, if a DNR permit is not required, a local permit is required. Always check with your zoning authority for local permit requirements and erosion control regulations.
If you have questions concerning this information, contact your local DNR Area Hydrologist.