River Restoration in Minnesota Repairs Stream Banks, Reduces Sediment Load

Project Summary: Erosive stream banks on the Knife River were restored by reducing the stress from water flowing into the bank, decreasing sedimentation in the Knife River.

Project name: Knife River Restoration

 

Location: Lake County, Minnesota

  

Eroded stream banks cause excessive sedimentation, inundating crucial spawning grounds for fish. Photo courtesy of Lake County Soil and Water Conservation District.

Eroded stream banks cause excessive sedimentation, inundating crucial spawning grounds for fish. Photo courtesy of Lake County Soil and Water Conservation District.

Description: The Knife River is one of the premier cold-water fisheries in Minnesota. With approximately 50 percent of the available migratory fish habitat in the entire Lake Superior system, the river is an extremely valuable fishery for trout and other game fish. Unfortunately, changes to the Knife River watershed have drastically altered its natural hydrology. Extensive logging in the early 20th Century removed many of the area’s coniferous trees. Without conifers to collect and store rainfall and snowmelt, water runoff into the river intensified, increasing water flow through the river’s channel by as much as 25 to 33 percent. The excess water crashes into stream banks with tremendous speed and energy, destabilizing the river’s channels. The heavily eroded river banks results in excessive sedimentation that blankets the streambed, covering up crucial spawning grounds for trout and other fish. The sediment also makes the water murkier, decreasing sunlight penetration and reducing the system’s productivity. The river eventually carries this sediment into Lake Superior, a significant source of drinking water for many people; this increases the amount of public funds that must be spent on water filtration processing.

 

Workers created floodplain benches at the base of the stream banks by installing logs and covering them with woody debris and soil. Photo courtesy of Lake County Soil and Water Conservation District.

Workers created floodplain benches at the base of the stream banks by installing logs and covering them with woody debris and soil. Photo courtesy of Lake County Soil and Water Conservation District.

Thanks to grants from the Great Lakes Restoration Initiative and Minnesota’s Clean Water Fund, the Lake County SWCD is reducing sedimentation in the Knife River. The SWCD identified stream banks significantly contributing to sedimentation, and then stabilized high priority banks by shifting water flow to reduce the stress applied to the banks. Workers created stream vanes by installing large boulders or logs in a “V” shape pointed upstream; this formation directs water flow away from the destabilized banks and towards the center of the river. Workers also created floodplain benches at the base of stream banks by installing logs that stick out into the river, covered with woody debris and soil. The benches create a floodplain, allowing water to escape the river channel during peak flows and spread out on to the land next to the river. This dissipates the energy of the water flow, reducing the stress caused by water hitting the eroding stream bank. A variety of native trees, sedges, shrubs, grasses, and wildflowers are planted to hold everything together.

 

Floodplain benches allow water to escape the river channel during peak flows, reducing the stress on eroding stream banks. Photo courtesy of Lake County Soil and Water Conservation District.

Floodplain benches allow water to escape the river channel during peak flows, reducing the stress on eroding stream banks. Photo courtesy of Lake County Soil and Water Conservation District.

The SWCD has already stabilized two high priority stream banks, reducing the Knife River’s total sediment load by an estimated 17 percent. This sediment reduction will enhance habitat quality for trout and other aquatic species, and may reduce filtration costs for drinking water suppliers utilizing Lake Superior’s water. This project enhances the watershed’s ecological health in a variety of other ways. The woody materials of the floodplain benches are submerged underwater, providing habitat shelter for fish. The shoreline vegetation planted along the benches creates shade that reduces water temperatures, and enhances the travel corridors along the river for mammals, reptiles, and amphibians. Shoreline vegetation also provides a variety of leaf litter that increases both the complexity of underwater habitats and the nutrient availability at the base of the river’s food web. The Lake County SWCD plans to seek additional funding and collaborate with other groups to continue restoring the Knife River’s stream banks. They are working with partner organizations on public outreach to improve the stormwater management practices within the watershed. The SWCD hopes this project will promote a stewardship mentality and become a model for river restoration throughout the region.

 

Approximate cost of project: $500,000, with most funds coming from the Great Lakes Restoration Initiative or Minnesota Clean Water Fund grants.

 

Resource challenges addressed: Erosion, sedimentation, aquatic habitat loss, and drinking water degradation.

 

Key partners (public and private): U.S. Geological Survey, South St. Louis SWCD, Minnesota DNR Section of Fisheries, Minnesota Pollution Control Agency, and Technical Service Area 3 Group

 

Types of jobs created: Stream restoration specialist, engineers, contractors, natural resource professionals, and general labor.

 

Results and accomplishments: Two of the highest priority stream banks, which contribute significant sedimentation, have been stabilized, reducing the Knife River’s total sediment load by 17 percent. This significantly enhances habitat quality for aquatic species and reduces filtration costs for Lake Superior’s drinking water. Reducing sedimentation also reduces river the turbidity of the Knife River, which is currently listed as impaired for turbidity under the Clean Water Act. Submerged woody materials from the installed floodplain benches provide habitat shelter for aquatic wildlife. Shoreline vegetation planted along the shore reduces thermal pollution, enhances the travel corridors along the river for wildlife, and provides leaf litter that increases both the complexity of underwater habitats and the nutrient availability at the base of the river’s food web. The Lake County SWCD is working with partner organizations on public outreach to improve the stormwater management practices of both urban and rural landowners.

 

Website: http://www.co.lake.mn.us/departments/soil_and_water_conservation_district/knife_river_watershed_projects.php

 

Originally published March 22, 2016

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