Projects > Big Hole River Bank Stabilization & Habitat Restoration

bighole

Confluence was contracted by the Arctic Grayling Recovery Program to complete two bank stabilization and floodplain revegetation projects along the Big Hole River between Wisdom and Jackson Montana.The bank stabilization projects were completed to slow the rate of channel migration and reduce the recruitment of transportable bed material to the river. The toe of each bioengineered bank was stabilized by excavating a key trench in the riverbed and installing a blanket of round cobbles.The upper banks were regraded to a 3:1 slope and completely covered with sod mats.A row of willow cuttings were placed on top of the cobble toe material and extended slightly beyond the waters edge at low flow.The upper banks were stabilized with approximately 50 transplanted mature willows from a nearby borrow source.Each bank was approximately 500 feet long, for a total stabilized bank length of 1000 feet.

The purpose of initiating a revegetation project along the Big Hole River was to increase willow density on river banks to ultimately enhance bank stability, increase channel roughness, and provide shading to improve fish habitat. Initial field surveys along the upper Big Hole River indicated reaches with dense woody vegetation exhibited narrower and deeper channels with sharper meanders and abundant pool habitat. In contrast, reaches with little or no woody vegetation displayed channels with a very high width/depth ratio, low radius of curvature, extensive gravel bar deposits, and very low pool density. These observations lead to the conclusion that a long-term, phased approach would be required to restore the form and function of the river channel and floodplain, with the initial phases to include revegetation and riparian fencing.

Conventional planting methods such as hand planted willow stakes or installing container-grown nursery stock proved too labor intensive and not cost effective. Confluence chose to harvest mature willows and clippings of willow canopies onsite as planting materials. Material stocks of mature willows and canopy clippings came from areas generally well away from the active channel. Mature willows were harvested with an excavator, placed in a rock truck, and transported to the river’s edge for replanting. Clippings were approximately 5 to 7 feet in length. Approximately 7 clippings were bound together in a bundle and placed in an excavated hole. Each hole was excavated to an average depth of 3 feet or until ground seepage into the hole was evident. Planting patterns were arranged accordingly to mimic successional growing patterns of existing willows onsite. After planting was complete, numerous willow clippings were trimmed further for the purpose of conducting a study on plant survival and propagation of transplanted willows. These revegetation efforts were completed with the assistance of Montana Conservation Corps crews. At the conclusion of ten weeks of field work, 22,461 willow clippings were planted and approximately 824 mature willows were transplanted along the floodplain and banks of 2.75 miles of the Big Hole River.

 

Taken in 2008

Taken in 2008

Taken in 2015

Taken in 2015