Performed large scale stream restoration on Stillman Creek, located in Boistfort, Washington after two 500 year storm events hit the area within 13 months of each other. After the first 500 year storm event in December of 2007 (listed as an actual hurricane), approximately 450,000 cubic yards of sediment were deposited over 50 acres. During second 500 storm event in January of 2009, a new 1000 foot long channel was cut into the sediment deposited from the 2007 storm event. The new channel threatened to take out the driveway access to a single family residence. Unfortunately, the landowner did not wait to obtain the required permits and filled the newly cut channel back in with the deposited sediment and received a Hydraulic Project Approval (HPA) Violation from the Washington Department of Fish and Wildlife (WDFW).
For mitigation, Key Environmental Solutions designed 2 Large Woody Debris (LWD) structures, a 450 foot long side–channel with 2 small LWD structures and to replant 31,400 square feet of riparian area.
The upper LWD jam is 140 feet long by 30 feet wide and has 140 pieces of LWD. The second LWD structure is 200 feet long by 40 feet wide and has 300 pieces of LWD. The 1st LWD structure in the new side–channel is 100 feet long by 30 feet wide and has 120 pieces of LWD and the 2 nd LWD structure in the side–channel is 75 feet long by 30 feet wide and as 90 pieces of LWD Several different techniques were utilized in anchoring the LWD structures; pile technique, large rock, digging down below the streambed and cabling.
The created side–channel habitat area that was created is 450 linear feet long and is approximately 18,000 square feet. LWD debris was placed in all meander bends and throughout the side–channel habitat area.
The riparian area was planted in the spring of 2010. Total square feet of riparian area to be replanted is approximately 31,400 square feet,Â this includes the area from the start of the upper LWD placement to the edge of the existing outlet of the side–channel area and both sides of the newly created side–channel habitat. The riparian area will be 20 feet wide. All riparian vegetation will be planted 3 feet on center and will include native conifer and shrubs. Suggested riparian plants were: cedar, willow, dogwood, and snowberry.Â Â All riparian vegetation was planted in the spring of 2010.
Key Environmental Solutions, obtained all required permits, designed entire project, designed riparian replanting plan and provided construction oversight for all LWD structures. Ross Hojem with RNC Clearing LLC. was the contractor and did excellent work.
Construction of side–channel and 4 LWD jams took 2 months and was completed on September 30, 2009. The riparian replanting will take place in the spring of 2010. Riparian monitoring for 80% plant survival will take place over the next 3 years. Monitoring on the LWD structures will take place 5–10 times a year for the next 5 years.