Please use this identifier to cite or link to this item:
Title: Final Environmental Assessment : Kenmore Federal Navigation Channel Maintenance Dredged and Disposal FY2020, King County, Washington
Authors: United States. Army. Corps of Engineers. Seattle District
Keywords: Washington, Lake (Wash.)
Dredging spoil
Dredged material
Environmental management
Environmental protection
Publisher: United States. Army. Corps of Engineers. Seattle District.
Abstract: In accordance with the National Environmental Policy Act, this Environmental Assessment evaluates the impacts of the proposed maintenance of the Kenmore Federal Navigation Channel. The authorized navigation channel is approximately 2,900 feet (ft) long and 100 to 120 ft wide. The channel is adjacent to the Sammamish River at the north end of Lake Washington. The U.S. Army Corps of Engineers (USACE) completed construction of the Kenmore Federal Navigation Channel in March 1981 and performed maintenance dredging in the channel once in 1998. Maintenance need is determined by hydrographic condition surveys, indicating that shoaling (settling of suspended sediments) has altered the channel from the authorized dimensions. The authorized channel depth is 15 ft below low lake level in Lake Washington (equivalent to +20 feet MLLW). The Hiram M. Chittenden Locks at the Lake Washington Ship Canal (“Locks”) connects the salt water of Puget Sound to the freshwater of Lake Union and Lake Washington. The Locks provide for transport of commercial cargo vessels as well as recreational vessels. Additionally, the Locks provides for passage of anadromous fish and maintains the level of Lake Washington between +20 and +22 feet MLLW. The authorized navigation channel dimensions allow safe navigation during all lake levels. The purpose for channel maintenance is to support the navigation activities and regular shipping traffic for regional economic development. The channel provides access to the Kenmore Industrial Park, which occupies 97 acres of industrially zoned land. Businesses within the industrial park rely upon the waterway for shipping. Barges are towed between Kenmore and Puget Sound through the Lake Washington Ship Canal. The primary activity is transportation of sand and gravel, as well as materials to produce concrete. Other activities include the operation of seaplanes associated with Kenmore Air, which operates the largest international seaplane facility in the country. To maintain the navigation channel, the USACE proposes to remove up to about 45,000 cubic yards (cy) of accumulated sediment from the navigation channel. Dredging would occur within the inwater work window of 16 November 2020 through 1 February 2021. The dredging will be accomplished using a mechanical clamshell dredge designed to minimize the potential for impacts to the surrounding environment (e.g. excessive turbidity or re-sedimentation). Dredged material will be placed in sealed barges for dewatering and transportation to a transloading site (location to be defined by the Contractor). Dewatering of material will occur in open water near the navigation channel. All dredging and dewatering will be performed in accordance with the water quality monitoring plan (Appendix B) developed for this project. Transfer to the disposal location will use sealed, non-leaking containers or trucks, in order to meet standards of the water quality monitoring plan or other regulated conditions. Dredging may take up to the 77 days of the in-water work window, depending on total quantity of material removed, mechanical breakdowns, and weather conditions.
Description: Environmental Assessment and Finding of No Significant Impact
Rights: Approved for Public Release; Distribution is Unlimited
Appears in Collections:Environmental Documents

Files in This Item:
File Description SizeFormat 
Kenmore Federal Navigation Channel Maintenance Dredging FONSI and EA_2020.pdf15.51 MBAdobe PDFThumbnail