Batavia Illinois – The 5th Ward

Author: Jim Fahrenbach

Batavia’s Fox River Dam has been in a state of slow collapse since 1974. As with any piece of civil engineering in dire need of repair, the problem has finally become hard to ignore.

With the Depot Pond arguably reaching a critical stage, the current City Council will soon be commissioning a feasibility study to decide and align on the next steps for the failing structure.

Complicating any path forward is a stark financial reality: significant state or federal funding to replace or remove the dam is no longer available. This means any “next step” may have to be funded almost entirely by Batavia taxpayers.

This isn’t the first time the city has faced this decision. To understand the options on the table, it’s worth looking back at a comprehensive 1998 study and the pivotal public vote that followed (other options, including removal, have been proposed since then).

https://www.bataviail.gov/AgendaCenter/ViewFile/Item/9050…

A Decisive Moment: The 2003 Referendum

Back in the early 2000s, a plan to replace the dam was eligible for both state and federal funding. However, in a 2003 non-binding referendum, Batavia voters rejected the project.

Though not legally binding, the City Council at the time chose to honor the result and did not proceed nor did they fix the issues with the existing dam.

In the years that followed, the state of Illinois proposed a few alternatives for partial removal and replacement, but nothing gained traction.

History of Structural Failure

The Batavia Dam dates back to the early 1800s when it powered local mills. By 1916, it was a concrete dam with an S-shaped spillway. Structural problems began to surface in the early 1970s.

In 1934 a survey reported the dam was 5.8 feet high with a spillway length of 328 feet. The dam holds a storage capacity of 169 acre-feet, making it a crucial structure for managing water levels and mitigating flood risks in the area.

A 1974 report from the Illinois Department of Natural Resources was grim, noting that an abutment wall had collapsed and a 15-foot section of the dam’s crest had been destroyed by undermining.

This breach, combined with the dam’s age and complex flow patterns from an upstream island, has led to its continued failure, especially during major storms. While temporary fixes have been applied over the years, a permanent solution has been needed for decades.

The 1998 Study: Three Investigated Options

In 1998, the University of Illinois used a 1:30 scale physical model of the river to test three potential replacement structures. The goal was to find a solution that could handle floods ranging from 2-year to 500-year events.

https://vtchl.illinois.edu/fox-river-batavia-dam…/

https://www.ideals.illinois.edu/items/12287

Alternative I: The “Bathtub” Spillway

This design featured a conventional spillway with a U-shaped “bathtub” section extending upstream.

• Pro: It improved upstream flow and was successful at concentrating flow toward the center of the structure, away from the banks.
• Pro: It efficiently dissipated energy for most flood events (up to a 100-year flood).
• Pro: It maintained flood stage levels comparable to the existing dam.
• Con: Its efficiency declined significantly during an extreme 500-year flood.
• Con: High-velocity water exiting the “bathtub” could be a concern for scouring the riverbed, though the area’s bedrock might mitigate this risk.

Alternative II: The Rock Dam

This option would replace the concrete dam with a structure of large boulders designed to emulate natural rapids.

• Pro: It was seen as more economically feasible and aesthetically pleasing.
• Pro: The irregular surface provided strong energy dissipation.
• Con: It offered few hydraulic improvements and actually resulted in higher flood stages than the existing dam.
• Con: Flow remained concentrated at the edges of the channel, and downstream turbulence was more erratic.
• Con: A major concern was that the dam’s porous nature could dewater the upstream Depot Pond during low-flow summer months, harming recreation.

Alternative III: The 2-Sided Spillway

This innovative design consisted of a modified spillway with two crests joining at a vertex anchored at the tip of the upstream island, designed to handle the separate flows from each side.

• Pro: It produced excellent upstream and downstream flow characteristics, proving most successful at managing the complex hydraulics caused by the island.
• Pro: It significantly reduced flood stages for all tested flows, in some cases by as much as half a foot.
• Pro: It created a highly uniform and desirable downstream flow, eliminating problematic cross-channel currents.
• Con: The primary concern was the potential for a “submerged roller”—a dangerous, recirculating current at the base of the dam that is unsafe for recreation. The report noted this might not occur if the riverbed is solid bedrock but recommended precautions if the design were chosen.

Conclusion: A Decision Revisited

The 1998 study identified the 2-Sided Spillway as the most effective hydraulic solution while ruling out the Rock Dam.

In 2025 the engineering challenges remain similar, but the financial landscape has changed dramatically.

The decision that was deferred over two decades ago has now returned, and is now more expensive, while demanding a permanent solution for the future.