December 28, 2009 § 2 Comments
Down in Long Beach, streambank stabilization continues. The Friday before the Christmas holidays, Drew Goetting of Restoration Design Group (in other words, my boss) flew down from Berkeley to train folks working at the El Dorado Nature Center on the process. Following is a little photo essay on making a willow wattle, for example.
The running joke was how much it was like making sushi. You lay down your fabric (or seaweed) in a little trench, put in the willow and soil (or rice, fish, avocado…) and roll it up. Two big exceptions to the analogy: the wattle needs stakes (we used live willow posts that will sprout into trees) and the sushi roll tastes better.
Soil bioengineering techniques like this have been used for centuries, and have found a resurgence in rural areas of America, as well as in some urban restorations in Northern California. Willow has long been observed to have tenacious roots that provide natural armoring of streambanks. And while the roots are strong, the trees themselves are flexible: if they fall over in a large flood, they form a layer that also protects the banks. But it is important to understand the dynamic interplay between a stream’s structure and how it functions, or forms its channel, however, in order to place these treatments correctly.
Stream restoration projects installed a couple of years ago at the Mountains Restoration Trust (Dry Canyon Creek) and (to a lesser degree) on Las Virgenes Creek also used forms of streambank soil bioengineering – proving that it has applicability here in Southern California.