The most critical infrastructure you've never seen

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On Nov. 24, 1876, the U.S. Army Corps of Engineers saved St. Anthony Falls. On that day, they finished a cutoff wall, or dam, under the Mississippi River and below the thick but fractured limestone riverbed. The cutoff wall runs three stories deep and spans the river. It is an essential piece of Twin Cities infrastructure that no one can see and few know exists.

It has been 146 years since the Corps completed that wall, and we have no idea of its condition, or that of the surrounding geology. That's because no one accepts ownership, meaning no inspections, no maintenance and no emergency action plan.

If the wall failed and we couldn't get control, the river would begin cutting down its bed to level out the nearly 50-foot difference from above the falls to below it. Anything resting on the limestone — including the 3rd Avenue Bridge and the horseshoe dam — could collapse as the river ate away the soft sandstone foundation.

If the reservoir above the horseshoe dam drained, Minneapolis, the suburbs it supplies and the International Airport could lose their water. Minneapolis only has a three-day reserve.

The river would become a rapids for miles upstream, threatening more infrastructure. Billions in riverfront development depend on the St. Anthony Falls.

The Corps constructed the wall in response to a series of catastrophic events that occurred between 1867 and 1875, some natural and some caused by timber and flour millers. By 1874, the Corps recognized that only a cutoff wall could preserve the falls.

Why should we worry? In a 2020 article, National Geographic wrote, "Many U.S. dams were built with now-outdated standards and methods, as well as for different climate trends. What's more, dams need continual maintenance to keep operating safely over the decades. Valves break. Metal rusts." And, the author noted, "By 2025, 70 percent of them will be more than a half century old ... ."

While we should worry about dams that are half a century old and built with "outdated standards and methods," we should consider that the cutoff wall is nearly three times that age, and we know little about what might have cracked, crumbled or rusted. Standards and methods have certainly changed since 1876.

When the Corps completed the wall, Ulysses S. Grant was president, and Colorado was admitted to the union that year as the 38th state.

I don't know whether the cutoff wall will fail this year, next year or anytime in the next 146 years. No one does. And that should worry us. No one has thoroughly studied the wall or the adjacent geology since 1876.

After every disaster, the public, press and politicians ask three questions: who knew what, when, and what did they do about it? I have been working with Friends of the Mississippi River and the National Parks Conservation Association to answer the first two questions. We need the Minnesota Legislature to address the third.

We are simply asking for a study to inspect the cutoff wall and surrounding geology. Doing so at least once every 146 years seems reasonable.

The House government finance omnibus bill included $1 million for a study, but the Senate bill did not. We hope the conference committee will accept the House recommendation and move this long overdue inspection forward.

John O. Anfinson is a longtime Mississippi River historian and retired superintendent of the Mississippi National River and Recreation Area, a unit of the National Park Service.