ScholarWorks at University of Montana

Evaluating the Effectiveness of Streambank Stabilization Techniques for Reducing Bank Erosion on the Upper Clark Fork River, Western Montana

Lateral channel movement on the upper Clark Fork River of western Montana has resulted in loss of valuable agricultural land and delivery of sediment and mine tailings into the river. In spring 1996, we initiated a study to evaluate the effectiveness of streambank stabilization treatments to reduce the potential for bank erosion. The treatments implemented in this study focus on the use of native riparian vegetation to stabilize banks instead of traditional "hard" treatments such as rip rap. This study examines the effectiveness of 21 different bank stabilization treatment combinations for reducing bank erosion on a large river system. The treatments incorporate coir (coconut husk) fabric, conifer revetments, log barbs, rock barbs, rock toe stabilization, coir fascines, willow (Salix spp.) and red-osier dogwood (Cornus stolonifera) fascines, willow cuttings, containerized seedlings, mature shrub transplants and rock rip rap. Treatments were installed in fall 1996, spring and summer 1997, and fall 1998 on 24 reaches totaling 1,740 m (5,708 ft) in length. Typical sites are on the actively-eroding, concave side of channel meanders and consist of 5-ft. tall, nearly-vertical banks. 140 permanently-monumented cross sections have been monitored before construction and after the construction for all treatments, after ice events in 1997 and 1998 for treatments established at that time, and after peak flow events in 1997 and 1998. A total of 100 bank surface profiles have been monitored by total station and changes in streambank surface volume have been calculated. Survival rates of various vegetative treatments were also monitored, and costs of construction for each individual treatment were calculated from detailed monitoring of construction activities.The 1996-97 and 1997-1998 bankfull discharge ice event caused little erosion. However, the 1997 flood event, rare in its volume and duration, caused substantial erosion of treatment and control banks. 1997 and 1998 flood-caused erosion rates varied between treatments. First year survival was high for mature transplants (100%), containerized seedlings (90%), and vertically-planted willow cuttings (88%). Second year survival was also high for mature transplants and constainerized seedlings, but survival rates dropped drammatically in the second year for vertical willow stakes. Cost of various treatment implementation ranged widely from a low of $5.58/ft to a high of $82.29/ft.