How to Take Down a (nearly) Century-Old Dam
TRAVERSE CITY – Remote computer commands and old fashioned, hand-operated cranes will likely open the gates of Brown Bridge Dam toward the end of the summer, draining the 170-acre pond it created.
State and private engineers are preparing to remove the 90-year-old dam using a mix of early 20th and 21st century technologies. They call it the largest dam-removal in Michigan's history.
"This is such a unique project. In my entire 30 years, this is one of the coolest projects I've ever worked on," says Sandra Sroonian, project director and an engineer for the TC office of Mac Tec, which devised the removal plan.
In May, Traverse City and Grand Traverse County officials applied for state permission to gradually lower the waters behind the city-owned Brown Bridge Dam and the county-owned Sabin Dam to natural levels.
While those involved expect the application to be granted, partly because local and state officials are on board, the process does include opportunities for public input.
During the 90-day approval process, any citizen may request a public hearing on the project. In June, the federal government held a hearing for its part in the lengthy approval process.
Whether Sabin is included in the first year depends on how many public and private dollars are available. If all goes as planned, it will be done within six years and cost between $5 million and $8 million.
Intentions for next year are to disassemble Sabin and Brown Bridge dams and begin drawing down Boardman Dam and modifying Union Street Dam.
Project members prefer the word "deconstruction" to "demolition."
"They're not going to be blown up," says Todd Kalish, a fisheries expert for the Department of Natural Resources.
How will it happen? First, crews will check the dams for hazardous materials and remove any asbestos, lead paint or oil. Next, they'll dismantle turbines and other machinery and deterine if any markets exist for it. Finally, they'll take apart the building; not quite brick-by-brick but in a way that will salvage materials that others may want to reuse.
Because total draw-down will be 13 feet, with a maximum reduction of six inches per day, people who live downstream are not expected to see large fluctuations in river levels during that time, Kalish says.
"We draw it down extremely slowly, so that the vast majority of sediment that has accumulated since 1921 in this impoundment settles out in the impoundment and isn't transported downstream."
And, as the surface of the man-made Brown Bridge Pond steadily drops, biologists will monitor loons that currently nest there. Hopefully, the notoriously reclusive birds will relocate to one of the 97 other lakes in the watershed, Kalish says.
The draw-down will uncover almost 100 acres of bottomlands, which will then be allowed to revert back to nature.
"[The soil] will be extremely fertile," Kalish says, adding that seeds deposited and buried there for almost a century will re-vegetate the newly revealed banks, drastically altering the ecosystem that has grown around the dam.
Still, the end result will be a plus for the environment, supporters promise.
For one thing, the ecosystem of the pond is not ecologically unusual within the Boardman River Watershed, Kalish says.
"What is unique, is what's underneath this impoundment," he says, standing on the man-made berm that serves as a bank to the pond.
Kalish says the rocky rapids now sitting below the dam will be reconstructed, so the river will once again tumble over for an overall drop of 32 vertical feet. That unfettered flow should allow for the return of many cold-water aquatic species that thrived in these waters before Traverse City harnessed the water to turn on its lights.
"Those particular areas within the Boardman River provide some of the most significant aquatic habitat for species throughout the watershed," Kalish says, adding that the existence of the pond actually raises the temperature of the river by an average of 6 degrees between spring and fall.
"That's significant," Kalish says. A Michigan State University study in the 1990s found 2/3 more aquatic species upstream of the pond than downstream and attributed that to the temperature differences.
The only dam slated to remain on the Boardman River, Union Street, is also the oldest. It was built in 1867 and is the farthest downstream before the river empties into West Grand Traverse Bay.
A popular fishing spot near downtown, Kalish says it will be modified to capture upstream-bound fish. The catch will then be sorted so lake trout, bass and other sport fish can be released to continue their journey. Undesirables, invaders and parasites like sea lamprey will be weeded out. BN