Soil Testing / Phreatic investigation: Lake Superior Shoreline Stabilization
Lake, Cook and St. Louis Counties, MN

Grantee: Minnesota Board of Water and Soil Resources
Basin Program Funds: $9,700
Non-federal Funds: $4,600
Project Duration: 06/1998 - 05/1999
Status: complete

Problem Statement
There is very little applicable soil testing and phreatic, or groundwater, surface information available for the red clays and silts that compose a significant portion of the non-rock Lake Superior shoreline in Lake, Cook and St. Louis Counties, Minnesota. Without this information, conservative assumptions must be made for slope stability analyses which, in turn, lead to relatively uncertain and conservative slope stabilization designs. The goal of this project is to create a base of information to address these situations, reduce the costs of shoreline stabilization designs and stretch cost-share funds to more projects.

Installing a piezometer.

The North Shore of Lake Superior is often perceived as being entirely rocky. There are however, approximately 60 miles of Minnesota shoreline on the lake where the bedrock dips to or below the lake level and red clay and silt deposits up to 70 feet high. Over geologic time, cobbles and sand veins in the clay eroded into bolder-strewn and cobbled bays which provide excellent habitat for fish and other aquatic life.

Nonpoint source pollution is one of the major threats affecting water quality in Lake Superior. These threats are due to the erosion and sedimentation of the area's red clay soils. Tourism and development is increasing at a rapid rate along the north shore of Lake Superior in Minnesota and is imposing increasing pressures on the resource. Approximately 36 miles of Minnesota's Lake Superior shoreline have been identified as high erosion hazard areas.

Many of the eroding shoreline areas are landslide prone and must be stabilized in order to control erosion and maintain water quality. Engineering solutions to these problems are restricted by a lack of readily or directly applicable information on soil composition, stability and other relevant characteristics. This situation makes it more difficult for North Shore landowners to compete for state-wide cost-share funding for conservation practices. This project is intended to develop a database of information to help in these situations.

The project team reviewed potential project sites and selected three demonstration sites with high, eroding clay banks. They installed 18 piezometers at the project sties. The team reviewed several designs and installation methods and chose the most effective, low-cost design. During installation, approximately 62 soil samples were collected. The team reviewed soil logs and initial piezometer performance in order to determine which samples to send to the lab for plasticity index, sieve analysis, direct shear and water content. At the same time, the team took weekly piezometer readings during the project period.

Finished project.

The team held an informal project workshop discussing the results with Dr. Peter Bosscher, University of Wisconsin. Site design has been revised given the results of the slope stability analysis. If projects on the three demonstration sites are implemented, project personnel estimate a total of 16,420 tons of soil saved over the projects' estimated 20 year life-span. An additional 164,200 pounds of phosphorus and 32,840 pounds of nitrogen will also be saved. The project team has met with seven landowners during four site visits during the project period. They estimate contacting at least an additional 20 landowners whose property will benefit from the knowledge gained here in the future.

Contact: Gene R. Clark, (218) 723-4752


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