Applying Natural Restoration Techniques to Slope Restoration
Grand Maris Lake Superior Shoreline Area,
Minnesota Erosion Control Association
Basin Program Funds:
Sedimentation into Lake Superior is of particular concern along the north shore of the lake. Erosion from road construction is a particular challenge for state and local governments because of steep topography, shallow soils and a limited construction season. Soil exposure may exist for several months to years before traditional permanent erosion control measures are applied. This area is also a high environmental risk for damaging a state-listed outstanding water resource, i.e., Lake Superior. Replacement of bridges, culverts and drainage flows next to this resource will always require having no buffer for a period of time. This project examined novel deployment of finished compost to solve water control problems and achieve slope stabilization and topsoil enhancement for rapid plant establishment.
The transportation corridor along the north shore of Lake Superior is vital to commerce in Minnesota and the adjacent province of Ontario. Continual road safety upgrading exposes soil and causes aesthetics departures from established ecotourism ideals during the construction process. The soils in the area are very thin and consist of hydraulic soil group D. Typically, too little topsoil exists or remains after construction to fully restore the vegetation over the whole project limits. While rill erosion occurs frequently in channels, little is observed on slopes that are properly graded. Sheet erosion does occur on slopes and washes seed and mulch covers to the slope toe. Based on the Universal Soil Loss Equation, 1:6 slopes with these soil types have the potential to lose five to 61 tons/ac when left as is, 0.5 to 6.7 tons/ac when blanketed, and 0.3 to 3 tons/ac when compost blanketed. On 1:2 slopes, the numbers are 95, 19, and 4, respectively.
The goal for this project is to incorporate ecotype landscape architecture design elements to soften and even mask erosion control projects constructed on Minnesota’s North Shore, a highly visible transportation corridor. The Minnesota Department of Transportation supervised planning and construction of the “erosion control landscape context sensitive design”. The University of Minnesota School of Landscape Architecture consulted for planning and design techniques.
Almost no known effective sediment and erosion control BMPs exist for work on shallow
topsoils with high rock content due to construction activities. Revegetating these topsoils has proven difficult due to tied-up nutrients in the clay fraction, low organic carbon
content, poor water infiltration, a short growing season and cool temperatures. After construction, context-sensitive design considerations require landscaping for aesthetics.
This test program examined the potential to direct-seed woody shrubs in order to repair the aesthetics of the affected areas, from the perspectives of both vehicular travelers and users of DNR recreational trails. Eroding areas along the North Shore were identified and targeted for inclusion in the project. Landscape architects, project engineers, project inspectors were consulted regarding final design. Landscape architectural techniques were applied in constructing the project. Soil savings and natural amenities from the projects were documented.
This project consisted of applying leaf and grass clipping feedstock compost to clay and
rock outcrop soils typical of the North Shore road construction along Lake Superior. The test project was located along a 3-mile road reconstruction project in Grand Marais.
Test applications were performed along certain stretches, focusing on Fall River and
an unnamed creek. The process could not begin until the contractor completed the northbound lane. Test plots were identified based on field observation and wetland and hydraulic flow maps. The work began Oct. 21,2003 and finished Oct. 23. Two different fertilizers were used, at two different rates. A new seed mix designed with the assistance of the Department of Natural Resources, along with organic based, slow-release fertilizers, was injected into the compost at time of application.
The project was completed Oct. 24, 2003, after the contractor completed the final grading on slopes facing Lake Superior, Fall River,the unnamed creek and above the ditch rock cuts. Enough compost was back-hauled to the site to cover just under an acre of soil with a two-inch compost blanket, and about one-half acre with compost dressing.
In addition, 3,000 linear feet of filter berms were installed in the ditches and slopes, around culvert ends, along with perimeter controls above wetlands and storm water ponds. To date, no observable movement of compost due to heavy rains or snow has occurred.
Contact: Dwane Stenlund, 651-284-3787