Bank Stabilization Using Bankform Roughness--Johns Demonstration Project
Barry Duff, ARCO Environmental Remediation, LLC

A meander bend in the Upper Clark Fork River, just upstream of the confluence with Dempsey Creek, actively eroded in recent years.  The outer bank had no deep-rooted vegetation.  Bank soils consist of an upper cohesive layer of silts and clays and a lower cohesionless layer of sand and gravel. The bank was undermined as the cohesionless layer was eroded, and the overlying cohesive layer would eventually collapse into the river. 

The purpose of the demonstration project was to stabilize the streambank by increasing bankform roughness using natural materials (large willows, small shrubs, and willow cuttings). The bankform was intermittently  cutback at a 25-foot interval to create a “scalloped” shape.  Additional shade was provided with large willows, reducing water temperature and improving aquatic habitat.  The design draws from research of Dr. J. Duncan Smith of the U.S. Geological Survey (USGS).  This voluntary demonstration project was undertaken by ARCO Environmental Remediation, LLC with the cooperation and assistance of the local landowner (Allen Johns), the U.S. Environmental Protection Agency, USGS, the Montana Department of Fish Wildlife and Parks, and other agencies. 

Construction began on December 15, 1999 and was completed on January 24, 2000. Approximately 664-lineal feet of streambank were stabilized.  A total of 20 “scallops”, on approximately 25-foot centers, were constructed.   One hundred twenty-five large willows and 100 containerized shrubs were installed. Sod was cut prior to excavation and re-installed afterwards, and disturbed areas were seeded with a native riparian grasses seed mix.  Willow stakes will be cut and planted in spring, 2000.  Coconut fabric and geo-coir fabric were installed to provide short-term erosion protection until vegetation is established.  Riprap was installed at the toe of the bank to anchor the geo-coir fabric and provide additional erosion protection.  Riprap was installed below the water surface to preserve a natural look.  Less riprap was used than typically associated with a “hardened toe” approach. Fencing was installed to prevent disturbance from livestock until vegetation is established. Work was completed at a unit cost of $127 per lineal foot, including design, oversight, and construction.  To evaluate effectiveness of the technique, monitoring will quantify erosion rates, based on surveys after ice-flow and spring runoff 2000.