Stabilizing shoreland property to prevent erosion
With more shoreline than California, Florida and Hawaii combined, Minnesota is bound to have areas where shoreland erosion is a problem. It's obvious that wave-pounded properties lose soil and ultimately their value. What isn't as obvious is that your practices can accelerate or slow erosion. Slow erosion by diverting water runoff away from hills and bluffs. Use drain pipes or French drains to create a safe route for water that can't be diverted. Leave natural shoreland vegetation and beach rocks undisturbed. The shore edge can be further protected by installing rip-rap (big rocks).
Bluffs and erosion
Shoreland properties often slope toward the water. Some hills are gradual, but some are extreme, like bluffs. Erosion is a big problem for bluffs. Increased runoff is especially damaging to high bluffs.
Slumping of bluffs can be caused by:
- Unstable soil caused by surface or ground water reaching the bluff.
- On lakes, waves can erode supporting soil at the bottom of the bluff.
- Along river bluffs, river currents can erode the supporting soil.
Preventing bluff erosion
Prevent erosion of higher shoreline bluffs by:
- Retaining moisture-absorbing vegetation on the bluff.
- Diverting surface runoff away from the bluff (including rain gutter outlets).
- Reducing runoff rate toward the bluff.
- Minimizing paved areas that increase runoff.
- Limiting ground water flow toward the bluff.
- Installing septic systems and drainfields away from the bluff.
- Avoiding additional weight on the bluff edge, such as pools, buildings or storage sheds.
Create safe routes for water you can't divert
On property with steep slopes or bluffs, reducing the amount of water reaching the bluff will help with stabilization. Sometimes, diverting water away from the bluff is impractical. In these cases, create a safe route for the water to travel.
1. Use a drain pipe that reaches the very bottom of the bluff.
Use a non-perforated plastic drain pipe that outlets at the very bottom of the bluff. Rock should be placed around the outlet to prevent erosion at the bottom of the drain.
2. Install a "French drain" to catch surface water.
Surface water and some ground water can be drained before it reaches the bluff by installing a "French drain". A French drain is a narrow trench set back from, but parallel to, the top of the bluff and filled with free-draining sand or gravel.
A perforated, corrugated plastic pipe at the bottom collects water and should drain away from the bluff. The entire perforated length of pipe must be wrapped with fabric or a filter sock. Installing deeper drains will intercept more ground water and provide better protection for the bluff.
Keep extra weight off of the top of the bluff
No additional weight should be placed near the top of the bluff.
- NO buildings.
- NO garage slabs.
- NO vehicles.
These are especially inappropriate near the top of a bluff because they add weight and water:
- NO septic systems.
- NO swimming pools.
Shoreland and erosion
Leave the shore undisturbed
For most property that slopes toward water, leaving the natural shoreland undisturbed is often the best and least expensive protection against erosion. A filter strip of thriving vegetation should be left on and near the shore. This binds the soil and minimizes soil loss from surface runoff and waves, and from use by people (Figure 3). Existing vegetation can be enhanced by planting woody or aquatic plants.
Natural shoreline features provide natural protection. While swimmers may not enjoy walking on cobblestones, and an ice-pushed ridge may block some of the view from your lawn chair, these features help "nourish" your beach by reducing erosion and trapping sand. Even driftwood absorbs a certain amount of wave energy that otherwise erodes soil.
Additional shore protection
Regardless of the natural protection on your shore, the right combination of conditions (such as high lake level and wind direction) can result in a severe wave pounding, and shoreland soil may need additional protection.
Placement of large rock, usually referred to as rip-rap, is the preferred and most common form of shore protection. There are technical methods available to determine rock size, placement geometry and elevations to ensure the best protection. Your county Soil and Water Conservation District (SWCD), the MN Board of Water and Soil Resources (BWSR) and the federal Natural Resources Conservation Service (NRCS) can provide technical assistance.
The above agencies will also have information on other types or remedies that may be appropriate for your particular situation. Potential shore protection alternatives include:
- Bulkheads (retaining walls).
- Gabions (rock-filled wire baskets).
- Articulating blocks (cable-connected concrete blocks).
- Geoweb matrix (thick, open-cell plastic grid).
A few of the alternatives can be placed by hand. Some other alternatives, such as railroad ties, are often tried but rarely work. If you have your own idea for a solution, you should seek technical advice first.
Rip-rap (large rocks)
If rip-rap is used, crushed or blasted rock locks together better than rounded boulders, but can be very expensive unless it is readily available.
Use geotextile fabric
Geotextile fabric is usually placed beneath the rock rip-rap to prevent soil loss through the rock openings. It's easy to place and provides an excellent filter barrier.
- Prevent punctures: In order to prevent punctures, plenty of slack should be provided over protruding objects that cannot be removed. A layer of sand or fine gravel can be placed on the fabric for extra protection against puncture.
- Wrap together as one unit: Enough fabric should be laid out so that the rip-rap periphery can be "wrapped" by bringing the fabric up and back down into the rip-rap. This will help hold the rip-rap together as one structural unit. Keep in mind that sunlight will degrade exposed fabric.
- Graded filter layer: As an alternative to the fabric, a graded filter layer can be used beneath rip-rap to prevent soil loss through the rip-rap openings.
Sufficient rock must be placed at the base of the rip-rap for toe protection. Excavated toe material must be removed from the lakebed and placed in a non-wetland area.
The price of rip-rap placement depends on local contractors, distance to the nearest rock source and access to the project site. It also depends on how much other work, such as clearing or earthwork, is required.
Protection for Lake Superior shoreline typically costs more than for inland lake shoreline. Inquire at the county SWCD office about cost-share assistance.
A project cost can also be estimated by calling earthwork contractors in your area. A big savings can be realized if you can install these items yourself.
Stabilizing a slumping bluff
Find out about soil types and ground water level
If you want to stabilize a slumping bluff, find out about soil types and ground water level. The record from when your well was drilled may be a good information source. You can obtain this record from the state or county health department or from your well driller. Contact your county SWCD for information on soils.
Get technical assistance
Effective bluff stabilization will require technical assistance.
- Request an engineer from the BWSR, SWCD or NRCS to inspect your site.
- Consider hiring a geotechnical engineering firm. They can take soil borings, analyze soil properties and recommend a remedy.
Regulations often apply
All erosion protection projects that alter the lakebed or riverbed require a protected waters permit from the Department of Natural Resources (DNR).
Contact the DNR Area Hydrologist for:
- Permit guidelines.
- Other agencies that might require a permit.
- For assistance in planning your erosion prevention project.
Some rip-rap projects may not need a permit.
For more information
Local country offices:
- Soil and Water Conservation District (SWCD).
- Planning and zoning department.
Minnesota state agency regional offices:
- Minnesota Board of Water and Soil Resources (BWSR).
- Minnesota Department of Natural Resources (DNR) Area Hydrologist.
Reviewed in 2018