Willow weavings allow for inexpensive custom-made structures made from locally harvested willows to fit specific sites without using fence posts, cable, entire trees, concrete, car bodies and riprap. A huge advantage of using willows is that if they wash out they will decompose or perhaps take root elsewhere like beaver cuttings often do ? not leaving unsightly and hazardous debris in and along the water.
Even a relatively small willow weaving utilizes hundreds of willow poles - full length and untrimmed. The poles are laid horizontally and packed tightly on the stream bank and held together by willow poles jammed into the bank from the top and bottom of the structure. The willow weaving method allows for just about every willow pole to root in the mud whether "planted" vertically or horizontally. Roots from willows and other native riparian woody plants grow deeply and branch out to hold together and stabilize stream banks.
There is no exact science to restoring native riparian areas - each river and creek is unique and responds in its own way to restoration methods. We used basic knowledge about willow cuttings and found that dormant cuttings respond well with future root growth, but cuttings that are beginning to go dormant in the fall or have already broken bud in the spring also have worked well for us.
The design concept is simple: willow poles held in place in mud are likely to root out and grow. We use water jet stingers in hard substrates to make deep holes in which to plant willow poles to securely hold other willows - horizontally placed, weaved and packed tightly - in place to prevent them from washing out during spring run-off and other high water events.
We have also found that in softer substrates or even in sandy gravel we can plant large "stake" willow poles with sledgehammers which is effective to hold horizontal poles. Often we will create a staked structure of poles hammered in vertically and horizontally to begin our willow weaving, and then begin to weave poles up and down through the structure. As willows are added each are woven differently which tightens up the structure as the process continues. We will stake at the end if there are loose areas in our structure. Lastly, when the structure looks finished we will go back and slide poles behind the whole mass if there is room to make use of the mud behind the structure that is not touching a willow pole!
Darin Zarbnisky, who initiated our willow weaving projects in April 2005 along Round Valley Creek, took advantage of a slightly overhanging bank and a chunk of the bank that had fallen into the creek to use to anchor the willow poles. This structure still remains in 2013! We watched the stream narrow, deepen and undercut the willow weaving providing excellent fish habitat. The downstream half of the willow weaving eventually washed out in 2011 but not to a complete loss - there were willow clumps alive just downstream as the rooted into new areas of the creek. The structure was repaired in the fall of 2012 and large containerized plants were planted deep in the bank behind.
Perhaps no revetment-type structure will remain forever, but we have found that willow weavings will hold actively eroding banks for a long period of time and allow for stabilization to take place. Often the willow weaving holds as the bank above slowly stabilizes and reaches an angle of repose. Other plantings behind those banks can have a chance to root out and help stabilize the area and we have seen sedges "plant" themselves in front of willow weavings as the structure catches sediment and allows the plants enough soil stability to establish. As native woody plants return to the system we see erosion slowing and riparian areas well on their way to functioning the way they were intended.
Also see the Interactive Panorama of this willow weaving on Round Valley Creek, 4/05.