Mill Pond Dam Removal, Seattle City Light, Metaline Falls, WA

NSD is providing site assessment, design, permitting assistance, public outreach and construction supervision for the design-build effort to remove the fifty-foot tall concrete dam impounding over 1 million cubic yards of sediment in a 60 acre site. NSD staff will monitor sediment evacuation from the site and adapt the design to accommodate subsurface conditions to restore over a mile-long network of meandering stream channels and floodplain, restore a naturally-functioning channel through the dam site and supervise helicopter installation of several log jams upstream of the reservoir.

Project

Mill Pond Dam Removal, Metaline Falls, WA

Rocky led the stream and floodplain restoration designs over a 30-acre site in response to repeated flooding in downtown Silverdale, WA. To confirm that restoration alternatives would provide flood relief throughout the project area, NSD used HEC-RAS and sediment transport analysis to assess the preliminary design. In order to identify the preferred channel location, avoid impacts to existing high-quality wetlands, and enhance degraded wetland features, NSD delineated and mapped all wetlands.  Products included a wetland features map, including locations of vegetative communities and buffer zone and riparian and channel enhancement plans.  Project success required that NSD staff lead complex negotiations with multiple stakeholders including the County, project neighbors, trail users, the Suquamish Tribe, WDFW, and USACOE to address conflicting priorities.

Lloyd Dixon, Seattle City Light

Construction elements include a 5,000 ft. channel, installation of over 500 logs, excavation of 30,000 CY of material to restore the floodplain, removal of 1,500 LF roadway and installation of 3 bridges. Rocky led the restoration design, managed a team of five subconsultants, led the permitting efforts and supervised construction of the $2.3 million project which was constructed in 2016. The project was selected for the “Vision 2040” by the Puget Sound Regional Council in 2017 for its ability to ensure a sustainable future as the region grows.

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