Streambank stabilization techniques can have excellent environmental benefits when live poles are incorporated into construction. Pole plantings provide cover and increased habitat when used with such stabilization techniques as riprap, gabions, rootwad revetments, deflectors, and longitudinal peaked stone toe protection.The poles have tremendous tensile strength, which can enhance the strength and shear resistance of the soil. When incorporated into structural practices, the poles can increase the strength and longevity of the structures. The cuttings are intended to sprout and take root, stabilizing the surface with a dense matrix of roots. Pole plantings need to be planted deep, usually requiring heavy equipment-assisted construction techniques.When established, pole plantings can protect from scour and the deep roots provide remarkable pullout resistance, which can greatly reduce future collapse of the structures. Planting poles is a valuable way to provide habitat enhancement to standard structural engineering practices. Pole planting was used to enhance rock riprap repairs to San Vacinte Creek in Santa Cruz County, CA, as a part of an emergency watershed protection project in 1998. The Natural Resources Conservation Service and the County of Santa Cruz collaborated on this project to repair approximately 300 ft. of flood-damaged streambank to protect three homes and a commercial establishment. The live pole plantings were intended to reinforce the structural components while enhancing critical riparian and wildlife habitat diversity along San Vacinte Creek.Pole planting is also a useful standalone revegetation technique for replacing and/or reestablishing riparian vegetation and cover. A riparian mitigation forest was planted in Sulfur Creek, a tributary to the Sacramento River in Redding, CA. A second-year progress report gave survival rates of irrigated, pole-planted Salix spp. at 90% and for Populus fremontii at 80%.Construction Specifications
A power auger excavates deep holes.
Poles planted into a longitudinal peaked stone toe protection keyway.Pole planting areas might need to be accessible to heavy equipment, as the poles should be planted into deep holes. Pole planting techniques might require the use of a power auger, a large metal punch bar mounted on a backhoe or hydraulic excavator, or some other method to excavate deep holes. The location of the water table (saturated zone) and vadose zone (moist soil zone including the capillary fringe, located above the saturated zone) should be approximately identified so the pole plantings can access sufficient moisture. Pole planting techniques implemented after construction is complete – for instance, after riprap placement – is very difficult. Pole plantings should ideally be installed during the construction of any large structures. MaterialsWhen planting poles, use relatively long, large-diameter cuttings, about 5-10 ft. long, taken from willow (Salix spp.) or cottonwood (Populus spp.). Larger-diameter cuttings have a greater supply of stored energy. The technique works well with nonirrigated projects because the deep planting can ensure contact of the basal ends of the poles with the vadose zone during hot, dry summer months. A pond or storage area for soaking the cuttings will be necessary. The harvested cuttings (ideally during the dormant season) need to be soaked for five to 10 days. Poles have been successfully established after 30 days of soaking. Plant poles into an augered, “punched,” or excavated hole. The holes should extend to approximately 1 ft. above the water table and through the vadose zone. In the case of widely fluctuating season water levels, ensure that the ends of the poles reach the low water line at the time of plantings. Plant the poles during riprap placement such that the poles extend through the riprap and backfill and into contact with the “native” bank. Poles can be planted into trenches excavated for keyways or scour trenches. The backfill can be placed over and around the poles rather than having to punch holes through the riprap. The pole plantings, especially the basal ends, must have good contact with the soil. “Mudding” (filling the hole with water and then adding soil to make a mud slurry) can remove air pockets.
