Slope Stabilization Work Plan For Poplar River Management Board

Slope Stabilization Work Plan
North American Wetland Engineering, LLC.
January 18, 2007 4444 Centerville Rd, Suite 140
Poplar River Management Board White Bear Lake, MN 55127
Phone: 651-255-5050
Fax: 651-255-5060
Section 4 - Existing Site Conditions
4.1 Megaslump Watershed Investigation
On September 26, 2006, North American Wetland Engineering made a site visit to assess the
characteristics of the megaslump area. The purpose of the site visit was to inspect the face of the
slump and gather information relating to potential causes of the slump. At the time of the
investigation, the river was at a very low stage and the weather was overcast and drizzling.
Photographs were taken of the entire slump area and are included in Appendix A.
On the face of the slump, rill erosion was prevalent as were a number of large gullies. The
effluent pipe from the Caribou Highlands wastewater treatment lagoons was located at the top of
the largest gully,. There was water leaking out of this pipe into the gully and the soil was
saturated at this location. There were grasses growing on the face of the slump in some areas
and certain areas had well established tree growth. At the top of the slump, undercutting of the
bank was taking place and roots from trees were exposed.
There were three main portions of the slump that were identified. The first was the upstream
third of the slump. This area had numerous gullies and the most prevalent rill erosion. There
were well established trees at the base of the slump adjacent to the river. The second area was
the middle third of the slump. This area had exposed soils throughout the entire height of the
slump. This area also had the steepest slope from the river to the top of the slump. The
downstream third of the slump had exposed soils on the top portion of the slump and well
established tree growth on the bottom two thirds of the slump. The slope in this area was not as
steep as the middle third of the slump area. It was determined that three different approaches to
stabilize the slope may be necessary in these different areas.
On November 30, 2006, North American Wetland Engineering investigated potential watershed
issues within the megaslump area. Specifically, the investigation was to determine possible
surface water runoff contributions to the area on the upland portion of the megaslump. The
Poplar River itself was also re-examined to identify peak flow levels, existing armoring,
potential physiographic disruptions, and potential diversion routes.
River investigation – The Poplar River channel takes two sharp bends near the megaslump. One
upstream near where Lutsen Mountains removes river water for snow making and one that
effectively defines the boundaries of the megaslump. The snow making withdrawal and storage
is located just after a bend in the river upstream from the megaslump. The surrounding land is
only a few feet higher than the river.