Turning Basin no. 3 Restoration Project

Location: Duwamish River, Seattle, Washington

Funding Source: City of Seattle/Metro Settlement

Design Objectives:

• "Daylight" intertidal and subtidal areas by removing vessels.
• Reduce pollution potential by curtailing commercial activity.
• Remove existing commercial upland and in-water structures.
• Recontour bank to create three intertidal and supratidal habitat benches.
• Reestablish native intertidal and riparian vegetation.
• Increase food sources for trust resources.
• Protect the site in perpetuity for natural resources.

Site Summary

The project site is located on the former Kenco Marine Services property at the western upstream boundary of the maintained navigation channel (Turning Basin No. 3) where the Duwamish Waterway is formed from the Duwamish River. The upland portion of the site was composed of fill material and is covered with asphalt and concrete pads, in addition to an office/warehouse structure, small storage sheds and a house. A commercial pier extended 125 feet into the Turning Basin. Barges and other vessels moored in the intertidal and subtidal area.

Portions of the area had already been restored to natural wetlands by federal agencies, including the National Oceanic and Atmospheric Administration (NOAA), the U.S. Fish and Wildlife Service (FWS), and the Port of Seattle, under a Coastal America Partnership. The Panel funded the purchase of additional land to increase estuarine habitat in this area, to be held under the trusteeship of the Muckleshoot Tribe. Over one acre of mudflat has been day-lighted by the removal of derelict vessels at the site. The commercial pier and shoreside structures were removed and the area was recontoured and revegetated to provide an enhanced intertidal wetland area.

Restoration Activities

Project implementation includes:

• Removal and prohibition against moorage of barges and other vessels at the site allowed 18,000 square feet of intertidal and subtidal mudflats to become permanently exposed (1998). See design map.
• Demolition and removal of former commercial structures, concrete foundations, paved areas, including the dock structure and creosoted wooden supporting piles (2005).
• Recontouring and revegetating the area created an enhanced intertidal wetland area consisting of three habitat benches at various elevations:
  • A "lower bench” at +2 to +6 feet at a 10:1 slope of sand over 3/4” gravel substrate created 6,500 square feet of intertidal habitat. Bank stabilization was accomplished by using "soft” substrates (wood) in lieu of riprap at the transition to the emergent zone bench.
  • An "emergent zone bench” at +9.5 to +11 feet at 20:1 slope was planted with native intertidal vegetation and random rock placement to create 6,050 square feet of marsh habitat.
  • A "groundcover and shrub zone bench” at elevation +14 to +17 feet at a 3:1 slope planted with native riparian vegetation created 1,850 square feet of riparian habitat.
• Monitoring for intertidal habitat success is being conducted under the Elliott Bay/Duwamish Restoration Program's monitoring plan through 2015.
• Project start/completion: Project construction began in September 2005 and was completed in April 2006. Additional planning was conducted in 2007 to replace plants that had died.

The Common Names of Plants Established at the Turning Basin No. 3 Restoration Project Site

Lyngby’s Sedge, Hardstem Bulrush, Three-square Bulrush, Seaside Arrowgrass, Red-Osier Dogwood, Sweet Gale, Pacific Ninebark, Hooker's Willow, Douglas Aster, Tufted Hairgrass, Saltgrass, Meadow Barley, Pacific Silverweed, Red Alder, Indian Plum, Black Cottonwood, Pacific Willow, Snowberry.