Envirocon was recently awarded a competitively-bid, design-build contract by Seattle City Light (City Light) for the Mill Pond Dam Removal and Habitat Restoration Project located in Metaline Falls, Washington. The site is located on a small tributary of the Pend Oreille River in the remote northeast corner of Washington State. The dams, originally used for lumber milling operations and power generation, are being removed to restore the natural riverine ecosystem structure and function to Sullivan Creek. This project is part of long-term plan for watershed improvements and restoration of the original site while preserving and enhancing the recreation and cultural amenities of the area.
Leveraging its growing design-build experience, Envirocon assembled a uniquely qualified design team to prepare a superior technical and responsive proposal for City Light. Envirocon and its team used City Light’s project goals and objectives to develop an innovative preliminary design which received the client’s highest technical scoring. Envirocon’s team brings a variety of unique, specialized skills from past experience with complex dam removal, river reconstruction, and habitat restoration.
After completing the design and permitting phase, Envirocon will begin installing in-stream habitat and bank protection measures upstream of Mill Pond followed by the simultaneous removal of two dams, the concrete Mill Pond dam and a log crib dam immediately upstream of the Mill Pond dam. Envirocon will sequence the dam removal to optimize reservoir sediment transport via enhanced natural stream erosion as much as practical. Envirocon also anticipates using mechanical processes to facilitate reservoir sediments mobilization. Using natural and mechanical means, upwards of 400,000 cubic yards of sediment will be flushed downstream following dam removal.
After dam removal and reservoir drawdown, the former pond area will be graded to create an ecologically functioning landscape and the new stream channel stabilized. Over one mile of stream channel and floodplain restoration will occur through the dam impoundment area by installing over 70 engineered log jams. The log structures provide habitat diversity and a healthy stream channel for base flow conditions. Due to access constraints and the goal of minimizing environmental impacts, engineered log structures will also be placed using a helicopter in over 2,000 feet of steam channel upstream of the reservoir. .
Upon completion of the floodplain grading and stream channel construction, the former pond area will be seeded and planted with native plants using seed stock and cuttings collected from the surrounding area during the design phase and propagated in a nursery. The following spring, we will conduct an adaptive management evaluation of the restored areas to ensure revegetation efforts are successful.
The final phase includes construction of several recreational facilities including the installation of a new pedestrian bridge across Sullivan Creek. Additional recreation features may include USFS campground enhancements, new multi-use trails and historic interpretive signs.
Design and permitting activities are planned through the summer of 2017, with construction activities beginning in the fall of 2017 and extending through 2019. Another key element of this project is stakeholder involvement and community outreach. Throughout the project, Envirocon will maintain a project website, live camera feed and participate in informational meetings with the local community. Follow our progress at www.MillPondDam.com.
Envirocon has completed several other major dam removal projects in its 28-year history. The $75M Milltown Dam Removal design-build project in Milltown, Montana included the removal of a 100-year old dam, and excavation and transportation of 2 million cubic yards of impacted sediments. Envirocon completed another design-build project in 2011; the Woodside Dam Demolition Project included the removal of two historic concrete dams and the associated restoration of the impacted stream channels located on 12 Mile Creek in Western South Carolina.
The Mill Pond Dam Project is another important multi-year design-build project that holds to Envirocon’s vision; Inspired People Improving our World.