Scientists working on reducing sediment from the Poplar River in Lutsen hope to get a lot of bang for the buck out of a grant from the Great Lakes Restoration Initiative (GLRI). The ULLR Tightline project, one of several interventions funded by this grant, is scheduled to be completed this summer. This is the only project on the North Shore to receive funding from this round of GLRI funding.
At the February 2012 meeting of the Poplar River Management Board, engineer Keith Anderson outlined potential methods that could be implemented on the next project, the Caribou Highlands Flowpath. This will likely involve work on one or two gravel roadways running parallel to the Lutsen Ski Hill Road (County Road 5) as well as the areas around parking lots and buildings. “We have a pretty good feel for where the flow is coming from,” he said, and the goal is “to intercept the water and transfer it down the hill in a safe and non-erosive way” in the cheapest way possible.
Anderson said he also thinks they should be looking at treating the first half-to-oneinch of runoff from impervious surfaces in the area and “knocking off peak flows.” This could involve natural means such as rain gardens.
Anderson said he would like the result to be close to what would be put in place if the developments were being constructed now rather than years ago before these types of intervention were expected. “I’d say we’re about midway through the analysis,” he said.
Discerning how much sediment entered the river before logging, ski hills, roads, and buildings is difficult, although they make estimates within a range of confidence. “We don’t know,” Anderson said. Engineer Keith
“We’re tryingAnderson ” to pick the projects that will bring the greatest benefit for the money spent,” said Anderson. Interventions could include grading, crowning, and ditching service roads; replacing culverts; building rock-lined channels; and creating storm water ponds.
A road running between the river and the Lutsen Ski Hill Road, the “Bus Road,” is likely to be part of the Poplar River project as well as the pathway for a pipeline that will deliver water to the ski hill for snowmaking, to the Superior National at Lutsen golf course for irrigation, and to housing developments all the way up the hill. Lutsen Mountains coowner Tom Rider said, “We’re pretty far into the process of designing the pipeline….”
TMDL study
The Minnesota Pollution Control Agency (MPCA) continues to gather data in a process that will result in a standard (“Total Maximum Daily Load” or TMDL) regarding how much sediment in the Poplar River will be considered acceptable. Results of two large studies came up with very different data, however, and researcher John Nieber found that one of the studies did not account for the variability of absorbent material between the surface and the bedrock in the land around the river. “It’s so variable up here,” said Keith Anderson. More research is being done to determine how this “effective hydraulic conductivity” affects sediment in the river.
Regarding what is under the surface, Marland Hansen said, “The trees tell you what it is. It’s an indication.”
He said, for example, that maple and ash grow in clay, pine grows in gravel and sand, and birches grow in burnedover areas. Aerial photos in the fall “color code the entire county,” he said.
The data so far show that grasslands soak up water much differently from wooded areas. The depth of the drainage material above the bedrock has a greater affect on runoff in grassy areas.
Data from other past and present work in the area, such as the water pipeline, geothermal infrastructure at Caribou Highlands, construction of the golf course, and a nationwide soil survey coming soon to Lutsen, will help add the necessary data to do this analysis.
Karen Evens of the MPCA indicated that the further they get into this study, the more detail they are asking their researchers to investigate. Results of the Poplar River TMDL will be used to evaluate other rivers along the North Shore, she said.
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