Large Scale Stream Restoration after Two 500 Year Flood Events on Stillman Creek

Abstract:

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.