There are a variety of good reasons to build dams, and just as many to remove them. A true economic driver in the early to mid-1900s, dams helped to create new industries through harnessing the power of a river. Additionally, they were effective tools to divert water for irrigation and create lakes for recreational activity. As times and technologies changed, many dams no longer serve their original purposes, leaving behind structures that have proven to be dangerous to people and a detriment to the surrounding environment. Over the past two decades, municipalities and conservation organizations have relied on WBK Engineering’s experience and expertise to remove nearly a dozen such dams in the Midwest.
Dam removal is equal parts brain and brawn, as engineers conduct a thorough hydraulic assessment to understand the effects of removing the structure before work begins.
Danger in the Water
First and foremost, dams can create a too-often fatal safety risk, with more than four dozen deaths annually caused by dams. The Hammel Woods Dam on the DuPage River in Will County was no different – responsible for three deaths in just 8 years, it was clear it needed to go. Called a “low-head dam” or “run-of-the-river dam”, it ran the entire width of the river from bank to bank. Flow conditions at this dam, not unlike many low-head dams, can trap even the most experienced paddlers and swimmers. WBK was called in to assess the structure and create a plan for its removal.
“Removing a dam may seem fairly straightforward but understanding the changing hydraulics of the river before and after is paramount,” explains WBK Water & Environment Practice Manager Scott Randall. “Dams affect the flow of the river, and simply removing them can have unexpected results such as flooding or releasing pollutants downstream.”
Projects begin with an engineering and environmental analysis of the dam, observing both the hydraulics of the river, as well as the contents of the sediment that naturally build up on the upstream side of the dam. To do this, a water sample is taken and analyzed for contaminants. If the levels are too high, sediment must be managed prior to removal of the dam.
“Naturally, dams affect the flow of the river, and simply removing them can have unexpected results such as flooding or releasing pollutants downstream.”
Coffering a Dam
Coffering a dam is necessary to allow demolition equipment a dry foundation to remove the dam structure.
(Courtesy of Forest Preserve District of Will County.)
The first step of removal is to coffer the dam area, creating a barrier to divert all the water to one side of the structure, de-watering the coffered area so construction equipment, usually backhoes, can begin the demolition process. Once one side has been removed, water is released to the un-dammed side and the other side is then coffered and de-watered for removal.
Environmental Impact
Removing barriers creates a more free flowing river, leading to healthier water with more microinvertebrates for the larger ecosystem to once again thrive.
WBK Engineering’s dam removal experience began nearly 20 years ago with the Brewster Creek Dam near Elgin, Illinois. The 75-year-old, 11-foot-high dam was designed to create a canoeing and swimming lake for the neighboring YMCA, but sediment built up at the dam site over time, making navigability of the lake difficult. Unfettered growth of reed canary grass had decreased water quality and threatened the aquatic habitat of much of the river’s wildlife. Recognizing the environmental benefits of removing the dam, consensus was reached on an approach to the project that called for a gradual notching of the dam spillway over the course of nine months. The notching of the dam allowed a channel to form gradually and naturally through the impounded sediments.
As science has advanced and the ability to quantify the effects of dams on the surrounding environment has come along, dam removals have become a frequent discussion item among municipalities and county forest districts.
“Beyond simply eliminating barriers to fish passage, removing dams can be a benefit to all the wildlife in the area,” explains Jeff Guerrero, WBK Water Resources Engineer. “Connecting the stream means the return of a lot of micro-invertebrates, which in turn expands the diversity of the ecosystem.”
The stacked limestone barrier of the Warrenville Grove Dam was replaced by with native plant-life in a lively river.
Project Highlight: Warrenville Grove Dam
Built in Illinois on the West Branch DuPage River in the late 1930s, the Warrenville Grove Dam was constructed of a reinforced concrete upstream face supported by a concrete footing. Quarried limestone slabs laid in mortar made up the stair stepped downstream face of the dam. The dam’s total height was approximately 8.5 feet above the downstream river channel bottom.
The structure was negatively impacting fish passage, recreational use, and water quality within the pooled areas created by the dam. Removal meant the return of a free-flowing river, eliminating the barrier to aquatic migration upstream. Beyond simply removing the dam, WBK engineers kickstarted the re-naturalization with the addition of a variety of native plants, as well as site design and restoration of an island for public recreation.
The WBK Water Resources team were brought in to create engineering plans for the removal of Ryerson Dam, replacing the barrier with a series of rock riffles for improved water quality.
Project Highlight: Ryerson Dam
The Ryerson Dam, located on the Des Plaines River in Lake County, Illinois, was a run of river structure constructed of steel sheet that extended 97 feet across the river, with a 70-foot spillway in the middle. The Lake County Forest Preserve District contracted with WBK to manage the final design and engineering for the removal of the dam and re-naturalize the area.
The purpose of this dam removal project was to restore the ecological health of an impounded segment of the Des Plaines River. By removing the dam and allowing for re-creation of upstream channel conditions, this project restored the natural ecological functions and processes of a free-flowing river. In addition, the WBK team added riffles to oxygenate the water, going from a stagnant, lake-like pool to a vibrant, active river free of barriers to fish migration and mussel dispersion upstream.
Thoughtful Mediation
Whether it’s for public safety or environmental restoration, dam removal has become increasingly important for municipalities and forest preserves. Once removed, untold budget and time are saved by no longer needing to allocate resources for their maintenance, allowing the river to return to its natural state. Eliminating these barriers of recreational or aquatic passage, WBK has lived up to its mission to mediate the built and natural environments.
