Levee/Bank Stabilization along Montana, Yellowstone River

A broad view of the slope (top) and a close-up of the riverbank (below) one year after restoration reveal the stabilization of the bank and slope with a combination of deep creek stones consistent with the size of native materials, plant materials and the use of ?EUR??,,????'??soft?EUR??,,????'?? technology?EUR??,,????'??+erosion control blankets (ECBs) and permanent turf reinforcement mats (TRMs). THI disdained the more expensive ?EUR??,,????'??hard armor?EUR??,,????'?? solution of rock riprap, which is less appealing visually, can alter the flow of the waters and create more erosion for downriver banks and slopes.

Riprap along the banks of the Yellowstone River in Montana is commonly used to protect properties, but when waters rise, water propelling off these ?EUR??,,????'??armored?EUR??,,????'?? banks can create damage to downriver banks and levees. In February 2002, the multidisciplinary team from Trout Headwaters, Inc., in Livingston, Mont., heeded the urgent call of a property owner by the Yellowstone River to stabilize a levee and manage the eroding river bank just upstream from the levee.

Phase I of the project involved stabilizing a 1,200-foot levee face. Along with dormant plant material THI workers put down 53 rolls of permanent turf reinforcement mat. Here they are anchoring the mats with live willow stakes, willow wattle and fascines. The mats are manufactured with a colored thread stitched along the outer edges as an overlap guide for adjacent mats. Schindler Excavation, Manhattan, Mont., handled the heavy equipment for phase I; Stream Works, Inc., Lincoln, Mont., was the primary heavy equipment contractor for phase II.

The toe of the slope was secured with deep creek stones, consistent with the size of native materials and C350 permanent turf reinforcement mats, 6.5 ft. wide by 55.5 ft. long, covering 40 sq. yards. Coir fiber is evenly distributed across the width of the matting and stitch bonded between three layers of heavy-duty netting, based on one esitmate for protecting a 16 ft. x 1,000 ft. drainage channel, 30 inches of rock riprap would cost $32,000 and $21,300 in labor, while use of a permanent mat would cost $7,800-9,900 with labor costs of $6,400-7,900.

With the toe of the slope secured with stone and permanent turf reinforcement mats, the 46,410 lb. Komatsu PC200LC-7 goes to work to prepare the upper slope for erosion control blanketing by backsloping (lowering) and smoothing the grade. Application of lime, fertilizer and seed, if required, are applied before the biodegradable blankets are rolled out.

Phase I of the project involved stabilizing a levee. THI decided that vegetation along the 1,200-foot levee face would best reduce erosion and not threaten other river properties. Along with dormant plant material THI put down 53 rools of permanent turf reinforcement mat (North American Green?EUR??,,????'???s C350), anchored with live willow stakes, willow wattle and fascines. The mats and vegetation treatments worked. However, THI kept an eye out for bank erosion on the property just upriver from the levee.

C125 double-net,100% coconut fiber blankets were installed on the upper slope. These slow-degrading fiber and stabilized nettings blankets provide up to 36 months of protection for slopes exceeding 1:1.

The bank held in 2002, but later that year, as Phase I was completed, an upriver bank stabilization project (riprap) directed more water to the monitored bank, which began losing many feet of slope and threatened the owner?EUR??,,????'???s home. Phase II kicked in: stabilizing 570 feet of eroding streambank with a combination of rock, blankets and vegetation. Deep creek stones, consistent with the size of native materials, were placed at the toe of the slope. Double-net temporary erosion control blankets of coir fiber and permanent turf reinforcement mats were anchored with live willow stakes, willow wattle and fascines.

Installation for Phase II was completed during February 2004. Peak flows on the Yellowstone lasy year reached 12,200 cubic feet per sec., but THI reports the Phase I and Phase II bank stabilization and restoration treatments have remained intact as the vegetation continues to mature.