IMA was contracted by the Lemhi Regional Land Trust to design a plan to stabilize a 450 ft section of eroding bank on the Salmon River.  The Salmon River experiences very high spring flows which have been eroding this bank at a rate of 5-10 ft per year.  Both the client’s goals and the permitting climate required a bioengineered solution.  A full topographic survey of the project reach and the adjacent river was performed to provide data for engineering analysis.  Hydraulic modeling, HEC-RAS, and reference reach comparisons drove the design process.  The design utilized bank re-sloping, willow transplants, and coir wrapped soil lifts for short term bank stability. Long term bank stability and riparian function was addressed with a variety of containerized native woody plant species. A full construction bid package was generated with comprehensive installation specifications and material quantities.

After completing the design of the Lemhi River– Cole project for the Lemhi Regional Land Trust, IMA was chosen through a competitive bid process as the installation contractor.  IMA partnered with a local excavation firm and procured local labor to complete the project.  450 linear feet of streambank were stabilized using a variety of bioengineering techniques.  75 willow clumps were transplanted at the toe of the slope, followed by the elevated soil lifts wrapped with erosion control fabric.  600 native container plants were planted into the soil wraps and planting clusters at the top of the bank, with an additional 35 willow clusters transplanted at the top of the bank.  The entire project area was fenced to exclude livestock. 

Before - the river was easily eroding the bank and the landowner was rapidly losing his pasture

Before - the river was easily eroding the bank and the landowner was rapidly losing his pasture

After - the bank is stabilized with many rows of willows, and fenced to protect the new plants from the cattle grazing in the meadow

After - the bank is stabilized with many rows of willows, and fenced to protect the new plants from the cattle grazing in the meadow

During construction - transplanted willows are installed at the toe of the slope, the first soil lift is installed, and the first row of containerized willows has been placed by the volunteers

During construction - transplanted willows are installed at the toe of the slope, the first soil lift is installed, and the first row of containerized willows has been placed by the volunteers

Local volunteers help with planting

Local volunteers help with planting