River Restoration in Minnesota Repairs Stream Banks

Reduces Sediment Load

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.

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, 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. This increased flow led to increased riverbank erosion, harming fish and wildlife habitat and increasing sediment in Lake Superior. Thanks to grants from the Great Lakes Restoration Initiative and Minnesota’s Clean Water Fund, the Lake County Soil and Water Conservation District is reducing sedimentation in the Knife River. Streambanks significantly contributing to sedimentation were identified and then high priority banks were stabilized 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 streambanks 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 streambank. A variety of native trees, sedges, shrubs, grasses, and wildflowers are planted to hold everything together.

Resource Challenges Addressed

  • Erosion
  • Sediment build up
  • Aquatic habitat loss
  • Drinking water degradation

KNIFE RIVER RESTORATION

Streambank with tree saplings

To prevent streambank erosion native plants are often used. Similar to the method shown here, the Knife River has had its streambanks reinforced with plants. Credit: Jefferson County Soil and Water Conservation District.

Results and Accomplishments

Two of the highest priority streambanks, 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 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 Soil and Water Conservation District is working with partner organiza­tions on public outreach to improve the stormwater management practices of both urban and rural landowners.