Students from West Linn’s Environmental Sciences classes came out to our site on good old Abernethy Creek this week to get some exciting work done. Since they last came to the site in December, a lot has happened there, most notably the flooding Abernethy experienced in January. The most obvious change was a very large 2-3 foot deep trench that the extreme precipitation carved out of the hillside above the creek. Uphill from our site a parking lot was recently constructed, and this impermeable surface has been channeling all of the water falling on it to one location. Rather than percolating into the ground, this runoff water flows downhill all together, which has quickly caused this erosion. In order to preserve the hillside and prevent further sediment from making its way into Abernethy creek, the biggest task this week was to do something about the trench. It was a good thing we called in the already masters of bioengineering: the West Linn High School Green Team students.
The parking lot causing the damage is built, there is nothing anybody could do about that to prevent more runoff from flowing down the hill in future high precipitation situations. Therefore we had to figure out a way to deal with this newly formed intermittent stream. The solution was to simply create a mini riparian zone at this site! If we planted willow and created dams of organic material such as dead brush, this will not only slow down the water (taking away its energy to erode) but it will also create a matrix of tree and plant roots that will hold in the soil and prevent it from washing downhill. They created 6 brush dams.
The first task was to dig out a trench:
This trench will then be used to fill with fascine bundles of freshly harvest willow and dogwood twigs. These branches will take root and leaf out into trees:
Once the bundles were in place, large live willow stakes were placed downhill from the bundles to prevent bundles from washing downhill as well as provide more opportunity for trees to grow. Large wooden stakes were also placed behind the bundles to provide further stability in this living fence. Straw and large dead branches of willow were then placed right uphill of this fence and tied down. This will really slow down the water in the meantime before the willow and dogwoods grow:
The completed brush dams all look great and I am sure will be very successful at preventing further erosion from this site.
While all of this was going on, students also managed to get a lot of the plants they planted earlier in the season mulched, and got the last handful of plants for the site in the ground.
Thanks for all of your hard work on this complicated project! It will be exciting to see these brush dams in action!
**Special thanks to Krista for taking some of the photos***