In 2010, IMA was contracted by the Idaho Department of Transportation to assist with a severely eroding bank on the Salmon River at Ellis, ID. The eroding bank was degrading the recreational use of the area and threatening to erode around a highway bridge abutment. The first phase of work involved surveying cross sections of the river with sufficient detail to run a hydraulic model and understand the magnitude of forces acting on the bank. IMA overcame the inherent challenges of surveying the large river by conducting the survey during the low flow season and using a jet boat to access areas too deep to safely wade across. After generating a map of the area, IMA used the cross sections and hydraulic calculations of peak flow events for HEC-RAS modeling to perform a hydraulic analysis. Results from HEC-RAS analysis showed that hydraulic forces were in a range appropriate for a bioengineered bank restoration including large woody debris with rootwads, soil wraps with erosion control material, and planting and seeding native woody shrubs, trees, and understory plants.  Deep-rooted willows were custom grown for the project to ensure groundwater would be reached at planting time to improve plant survival. The presence of four endangered fish species in this section of the Salmon River posed some permitting challenges, but the project was constructed in summer 2014 and is performing as designed two years out.

Before - upstream - eroding bank undermining the parking area

Before - upstream - eroding bank undermining the parking area

After - upstream - bank is stabilized with rootwads, erosion control fabric, willows, other tree species, and has been seeded.

After - upstream - bank is stabilized with rootwads, erosion control fabric, willows, other tree species, and has been seeded.


Before - downstream - unstable eroding bank, destroying established river access and threatening highway bridge

Before - downstream - unstable eroding bank, destroying established river access and threatening highway bridge

During construction - downstream - installing erosion control fabric between layers of plantings

During construction - downstream - installing erosion control fabric between layers of plantings

After - downstream - bank is re-sloped, stabilized, and re-vegetated.

After - downstream - bank is re-sloped, stabilized, and re-vegetated.

October, 2016. Willows are well established, seeding has been successful, and the bank stabilized.

October, 2016. Willows are well established, seeding has been successful, and the bank stabilized.