Arlington County Banks on Conservation District’s Bioengineering Skills for Stream Restoration on Four Mile Run

(Conservation Currents, Northern Virginia Soil and Water Conservation District, May-June 2003)

	The Northern Virginia Soil and Water Conservation District’s urban conservation engineer Asad Rouhi works with Arlington County’s Environmental Services and Parks departments to stabilize 120 feet of Four Mile Run in Benjamin Banneker Park. Rouhi designed the restoration plan for the highly eroded stream segment under a contract with Arlington County. Here he directs the backhoe operator to regrade the highly eroded stream bank. On the opposite bank, not visible in the photo, is an active floodplain. During a storm, when the channel receives a large volume of fast flowing water, the water can spread out over the floodplain to lessen the erosive energy of the flow.
	A double row of biologs will protect the toe of the newly graded bank from the erosiveness of the stream flow. These tightly bound cylinders of coconut (coir) fiber are held together with coir fiber netting. The material is tough, flexible, and absorbent. Once installed, the biolog becomes saturated with water, and vegetation can be planted directly in it. By the time the log degrades in seven or eight years, a root network of plants will have been established through and behind it. Biodegradable matting on the sloped bank will hold the soil and grass seed in place. The grass will grow through the mat and prevent erosion of the soil.
	With the biodegradable logs and matting in place, Arlington County staff planted about 60 riparian species including willows, dogwoods, and alders. In time, the banks will provide a lush wildlife habitat and shade for the stream critters.