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Intricate pump system helps exhibit function as a balanced ecosystem
Visitors to the Northwest Stream Center near Everett, Wash, will soon have a close-up view inside the world of cutthroat trout. A unique exhibit will show how the fish progress from fresh spawn to hatched fingerlings and eventually into 8- to 10-in.-long mature fish within a carefully created artificial stream. Adopt-A-Stream-Foundation (AASF), an environmental education and restoration group, is nearing completion of their new Trout Exhibit, expected to become a key attraction at the organization’s environmental learning center.
“We wanted it to function like it was created by Mother Nature,” Tom Murdoch, AASF director, explained. “Our goal is for visitors to take lessons learned at the Northwest Stream Center back to their home watersheds where they will work to protect and enhance streams throughout the Pacific Northwest.”
The headwaters of the Trout Exhibit is between concrete retaining walls; however, the channel will replicate a natural stream with a gravel and cobble bottom and stream banks covered with native vegetation to shade the stream and keep the water cool and oxygen levels high. An intricate pumping system will control the flow rates, which will vary with the seasons.
The native creek and the Trout Exhibit extend along either side of a path from the entrance to the Visitor Center. The closed-loop water flow of the Trout Exhibit originates at a two-level, L-shaped headworks with a below-grade mechanical room housing sand filters beneath a 14,000-gal vault situated eight feet above it. Two pumps are installed within a wet-well manhole located between the source water pond and the headworks structure.
From the cascade at the headworks structure, the water flows between 10-ft U-shaped concrete retaining walls and in a downward gradient at a current rate that maintains different habitat types before reaching the 6-ft.-deep pond recovered from the former parking lot. Along the way are riffles and pools created by simulated debris.
The Seattle office of Gray & Osborne, Inc., Consulting Engineers donated civil engineering services and designs for the exhibit and more than 40 construction-related companies participated in the project, led by Everett-based Wilder Construction as the general contractor. Whitney Equipment Co. donated ITT Flygt 7 ½- and 15-hp submersible pumps as the heart of life-giving waters through the channel’s recirculation system from the pond back to the headwaters. The Model NP3153 1,700-gal per minute (gpm) and CP3127 340-gpm submersible pumps recirculate the water from within a common manhole. A supplemental well will have another pump capable of adding 5 to 10 gpm.
The challenge for the AASF and the design engineers resides in creating healthy stretches of stream habitat as close to natural as possible within manmade construction. The channel is more than just an aquarium—it functions as a balanced ecosystem. Regulations prohibited merely diverting some flow from the adjacent wild stream into the channel and discharging back into it because endangered Coho Salmon spawn there. Therefore, a closed-loop flow of recirculating water was necessary.
The smaller Flygt pump draws approximately one-third of the return flow from the pond and passes it through sand filters while the larger pump feeds the headwaters cascade with enough direct return off the pond to maintain the variable current within the channel’s different habitat zones. The new resident trout require water temperatures within a critical range of 50° to 55° F and oxygenated to a ratio of 9 to 11 parts per million per liter. The supplemental well and shading plants along the channel will help maintain this balance of the channel’s lifeblood, as will an air-induction system dovetailed into the well’s water line. The pond’s recirculation line and the filtration system should also contribute to the desired water quality.
The Trout Exhibit should eventually represent a $1.5-million project that will encourage residents to help restore and preserve their local watersheds.