Protecting wetlands during construction
In addition to enhancing the natural beauty of Minnetonka, wetlands collect storm water, filter runoff, and recharge groundwater. They also provide habitat for wildlife, fish, beneficial insects, and rare plants. Damaging wetlands during construction may increase flooding, cause water to turn brown with sediment, and encourage algal blooms. The residents of Minnetonka value the quality of their open waters and wetlands. In addition, wetlands are protected by federal, state, and local laws. You can help protect these valuable local resources by following the guidelines below.
The city of Minnetonka Public Nuisance Ordinance forbids the erosion or stockpiling of any material onto a public street that is not part of a public improvement; or erosion or drainage from a property when it is causing, or has the likelihood of causing, serious harm to neighboring property or to natural resources such as significant trees, water bodies, wetlands, and wetland buffers. Serious harm includes actual damage as well as interference with reasonable use of the property (Minnetonka City Code Section 845.010 subdivision 16).
Silt Fence
Double-row of silt fence
upslope of wetland
Before construction activity begins, install silt fence upslope of the wetland or adjacent to any drainage ways that lead to the wetland. It is important to provide or maintain a buffer of native vegetation adjacent to the wetland. A buffer width of 16 to 25 feet comprised of upland vegetation will help filter fine particles and pollutants, providing a long-term benefit to the wetland.
Immediately replace or repair damaged silt fence adjacent to a wetland and remove any sediment that has collected down slope of the fence. On steep slopes, use heavy, wire-backed silt fence or install two parallel rows of silt fence spaced 5 to 8 feet apart. In addition to controlling sediment, the silt fence will serve as a construction limit to prevent damage to existing vegetation.
Construction Equipment and Materials Storage
Silt fence and dumpster
for house demolition
Avoid stockpiling materials adjacent to a wetland if an alternative location is available. If it is necessary to stockpile near a wetland, use two layers of silt fence (spaced 5 to 8 feet apart) for large piles on slopes; one layer is sufficient for small, temporary piles. Place the silt fence at least 8 feet down slope from the pile edge to avoid overtopping the fencing during rainfall. Seeding or covering piles with tarps or mulch will reduce erosion problems. Do not allow construction materials or debris to spread or blow into the wetland. Parking vehicles and equipment near a wetland damages vegetation and increases erosion.
Soil stockpiles and slopes equal to or greater than 3:1 that will not be worked for over 14 days must be stabilized with vegetation, mulch, tarps or other means unless no run-off from them is directed toward a watercourse, tree protection area, or the site perimeter when working under an approved grading and erosion control plan (Minnetonka City Code Section 300.28 subdivision 17).
Storm Drain Protection
Geotextile used to
filter fine sediment
Sediment that collects in city streets passes into storm drains causing the water in neighborhood creeks, wetlands, lakes, and ponds to turn brown. When working near a wetland you should use devices that remove fine particles such as geotextile, biolog, and devices with sediment filters. Stone is less effective at filtering fine sediment, but may be necessary in areas with high flow volumes.
Silt fence fabric
and biolog
To prevent sediment from passing through culverts and channels into wetlands, install a horseshoe-shaped ring of riprap or silt fence 6 feet from the culvert end. Create dam checks using biolog, rock, or equivalent structures to slow sediment-laden runoff.
Wetland Buffers
Existing buffer of
upland vegetation
between wetland
and heavy silt fence
Upland vegetation adjacent to the wetland serves as a buffer that slows water and filters sediment. Protecting existing buffers of vegetation will help preserve wetlands. If it is necessary to disturb the soil adjacent to a wetland, restore vegetation as quickly as possible.
Wetland buffer
with native planting
For more information about wetlands and construction please contact the Minnetonka natural resources division at 952.988.8422.
References
- Storm-Water and Wetlands (PDF)
Planning and Evaluation Guidelines for Addressing Potential Impacts of Urban Storm-Water and Snow-Melt Runoff on Wetlands
