ALBANY PARK — Tuesday’s demolition of a 100-year-old, four-foot dam on the Chicago River may have been short on drama, but it was long on potential for the waterway’s future.
There was no quick demise by dynamite for the dam — often playfully referred to as Chicago’s only “waterfall.” Instead the structure, situated in River Park where the North Branch meets the North Shore Channel, is destined for death by a thousand cuts, or more accurately a thousand blows from a hydraulic excavator.
The low-key ending somehow seems fitting for a piece of infrastructure that played a minor, if key role in the feat of engineering that reversed the flow of the river, sending Chicago’s sewage to St. Louis instead of Lake Michigan.
Having been constructed to solve one problem, the dam, built in 1910, is now being torn down as the answer to a new challenge, Col. Aaron Reisinger, commander of the U.S. Army Corps of Engineers-Chicago District, told those gathered for Tuesday’s ceremonial kickoff to a months-long demolition project.
Thanks to innovations in waste treatment processes, a healthier river is home today to a growing ecosystem of vegetation and wildlife — and the dam is impeding progress, Reisinger said.
An Army Corps survey revealed that while dozens of species of fish can be found in the North Shore Channel, only one has been able to vault the dam and swim upstream into the North Branch.
“It’s now an unnecessary wall,” Reisinger said of the dam.
In spring 2017, the Army Corps, in partnership with the Chicago Park District and the Metropolitan Water Reclamation District, unveiled a plan to remove the dam and replace it with a series of manmade “riffle” pools — sections where the river will stream over rocks and create movement that mimics rapids.
Instead of the dam’s single four-foot drop, the riffle sections will provide three one-foot drops, giving the fish a chance to rest and feed in each pool before moving up to the next riffle.
A concrete channel that extends upstream from the dam will be removed as well to make way for the riffle pools.
The project is being funded with nearly $5 million from the EPA’s Great Lakes Restoration Initiative.
“As this dam goes down, those fish will now have the ability to move upstream,” said John Quail, director of watershed planning for Friends of the Chicago River.
“There’s eight dams on the river, almost all of those are coming down,” Quail said. “And when that’s done, this river will be free flowing all the way to the head waters, roughly Six Flags or Abbott Labs, so this is a really exciting day for the river, for the fish in the river and for the recreators of the river.”
Indeed, human paddlers should benefit as much as fish from the dam’s removal.
Low-head dams like Chicago’s often create deceptively dangerous currents, according to civil engineers.
Water flowing over the drop forms what’s called a “scour hole,” which traps and re-circulates anything that floats near it, including people and their watercraft.
Though the North Branch appeared quite tame on Tuesday as it poured over the dam — more like a faucet than a waterfall — a substantial rain increases its force substantially. Debris swirling around the scour hole often winds up choking a nearby canoe/kayak launch.
Once the dam is removed, some of its concrete will be salvaged and used to fill in the scour hole, according to Frank Veraldi, an Army Corps restoration ecologist.
These boulders, in addition to the riffle pools, should break up big flows from the North Branch, Veraldi said.
The more approachable riffle pools, and their novelty, will ideally raise the profile of River Park’s boathouse. Completed in 2014, the boathouse has struggled to attract a steady enough volume of paddlers to lure a consistent canoe/kayak rental vendor (or vice versa, in a chicken-egg scenario).
“We hope this [dam removal] project will help get more programming … whether it’s the Park District or a vendor,” said Cathy Breitenbach, director of cultural and natural resources for the Chicago Park District.
The Army Corps has a five-year contract to establish new plantings in the dam’s footprint. A second phase of the project, as yet unfunded, would create a gentler slope on the riverbank opposite the dam as well as restore native vegetation along the water in River Park, Legion Park and Ronan Park.
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