How about a wilder river? Imagine this Mississippi

A secret river runs through Minneapolis and St. Paul.

Almost no one knows that 30 feet beneath the surface of the languid Mississippi there are rapids. Not just a murmuring riffle or two, but a magnificent, roiling whitewater that once thundered for eight miles over massive boulders, around small islands and through the great river's only high-banked gorge on its way from St. Anthony falls to Fort Snelling.

Native people knew its perils, of course. The river was so fierce that in 1805 the explorer Zebulon Pike and his exhausted party strained to pull their boats upstream, resting on small islands that dotted the stretch.

The question now is: Why not restore these mighty rapids? With north Minneapolis' port closed to barge traffic, with downtown's St. Anthony locks padlocked just last week and with St. Paul's Ford plant demolished, there's no reason for keeping the dam that makes navigation possible on this stretch of the river. So why not crank open the gates at Lock and Dam No. 1 near Minnehaha Park and let the water flow swiftly and naturally?

With boulders and islands uncovered, the river's 100-foot drop between downtown Minneapolis and Fort Snelling would create a gushing spectacle during times of high water. These rapids would be a kayaking paradise and a sporting delight. Scores of eagles would soar overhead, drawn by all the fish that would mass in the oxygen-rich water and spawn in gravel beds under the swirling eddies.

Such rapids would make Minneapolis-St. Paul the only major city on Earth with a world-class whitewater running through it. "People are fascinated by wildly rushing water," said river historian John Anfinson of the U.S. National Park Service, hinting at the environmental and economic benefits restoration might bring.

Indeed, there's something magical about rushing water in an urban setting — the juxtaposition of the wild and the structured. Minneapolis and St. Paul have been working for decades to pivot the public's attention toward the Mississippi, just as scores of cities across the nation (the long list includes Chicago, Baltimore and Seattle) have been repurposing their industrial waterfronts for housing, parks, amusement piers and festival markets — and drawing millions of visitors in the process. Waterfronts are so alluring that cities without them (Dallas, San Antonio, and Scottsdale, Ariz., for example) are spending huge sums to "manufacture" the waterfront illusion.

But no one else has rapids.

The restoration idea has gathered momentum recently among environmental organizations pushing nationwide for the removal of what they consider to be unnecessary dams. A particularly influential group, American Rivers, announced in March that it's building a coalition to advocate for gorge restoration in the Twin Cities.

Still, a sober analysis of costs, benefits and environmental impact is needed before the rapids idea can be taken seriously. What, for example, might be the cost of neutralizing Lock and Dam No. 1? Would it simply involve opening the locks, or would the entire structure have to be removed?

With a narrower, faster river and a deeper gorge, what would be the cost of shoreline restoration? How would hydroelectric generation be affected? Would bridge safety be threatened by rushing water? What would be the potential for real estate, tourism, recreation and other enterprises along the gorge?

Those are just a few of the questions. Without more study, it's not known whether the entire dam would have to be removed, but based on similar projects in the Pacific Northwest, it's reasonable to expect a cost of at least $40 million and likely much more.

As for hydropower, the 17-megawatt capacity at Lock and Dam No. 1 would be lost. That's enough electricity to power 30,000 homes, according to Douglas Spaulding, co-manager of the Nelson Energy hydro project at Lower St. Anthony Falls. Moreover, Brookfield Renewable Power, the private firm that owns the historic power plant at Lock and Dam No. 1, would almost certainly expect tens of millions of dollars in compensation if the dam were removed before its federal license expires in 2034. The Nelson plant could also be affected if the water level drops below its outflow pipes, adding more expense.

No one should expect those costs to be offset by new real-estate development along the river. That's because parklands and expensive single-family homes already line the gorge, effectively blocking opportunities for large-scale development.

The demolished Ford plant is the lone exception. The city of St. Paul and its partners are planning a mixed-use, eco-friendly community on the 130-acre site. "The thought of losing hydro gives me pause," said Anne Hunt, the city's environmental policy director. "Sustainability and net-zero energy are big goals for this project, and hydro is a big part of the mix."

Then, too, there's the thicket of federal, state and local agencies that oversee the river and its banks, including the U.S. Army Corps of Engineers, the National Park Service, the state departments of Natural Resources and Transportation, two city governments and various watershed districts — all with competing interests.

Drama is hardly new for this segment of the Mississippi. Ten thousand years ago, when the enormous River Warren (now the comparatively small Minnesota River) was draining ancient Lake Agassiz, a Niagara-sized falls occupied the area of present-day St. Paul. As river flow dwindled, a much smaller falls migrated upstream, triggered by seasonal freeze-thaw cycles that eroded the soft sandstone below, with the harder limestone-shale cap-rock breaking off in large blocks. Those boulders remain in the riverbed today all along the stretch of river below the falls' current location in downtown Minneapolis.

The river ran wild until a partial collapse of the falls in 1869 led to a series of attempts to stabilize the stream. Although it was still wild enough in the 1880s to inspire the renowned landscape architect Horace Cleveland to create what became Minneapolis' Grand Rounds park system, taming the stretch below the falls became an imperative of the industrial era. Minneapolis boosters believed that the city could not thrive without riverboat traffic.

One result was a frenzy of construction in the early 1900s that turned the free-flowing Mississippi into a chain of gentle pools, stabilized by a series of 27 locks and dams built between Minneapolis and St. Louis. Flat water would enable barges laden with grain and other northern commodities to reach the seaport of New Orleans — and help control the periodic flooding of cities and croplands along the way.

Lock and Dam No. 1 opened in 1917 to promote navigation through the rapids and to provide a 35-foot head for a hydropower plant that enticed Henry Ford to build a giant auto assembly plant in a then-remote space between the cities. The project gave St. Paul jobs and electricity, while Minneapolis got the serene, navigable waterway that it craved.

But that rationale has now all but vanished. Ford closed the assembly plant in 2011. Commercial barge traffic to north Minneapolis' Upper Harbor Terminal ended in 2014 when the St. Anthony Falls locks closed to prevent invasive carp from heading upriver into Minnesota's northern lakes and streams. The only remaining purpose for what's still called the "Ford Dam" is to enable a privately owned hydro plant to generate and sell electricity and to accommodate a relatively small number of canoes, cruise vessels and collegiate rowing boats. For that, the Corps of Engineers spends $2.4 million a year.

For all the costs involved in restoring the rapids, it's hard to place a value on the cleaner water that rapids would bring, or on the pleasures of miles of whitewater surrounded by forested parkland in a major city crowded with outdoors enthusiasts.

Restoring the rapids might also be nature's way — and the best way — to keep invasive species like bighead carp and zebra mussels out of upstate Minnesota, according to University of Minnesota fisheries expert Peter Sorensen. "The preferred defense against carp is to clean up the river," he said, "and restoring the rapids would do that."

While it's too early for federal and state officials to stake out a position on rapids restoration, many midlevel managers are privately excited — even giddy — about the prospect.

Mike Davis, a mussel expert with the Minnesota Department of Natural Resources, views it this way: "Would anyone today seriously consider erecting a dam and burying what would be the longest white-water run through a major city anywhere in the world?" He answers himself emphatically: "Of course not."

Ron Way is a former environmental journalist and official with the U.S. Department of the Interior in Washington, D.C. He lives in Edina. Steve Berg is a writer and urban design consultant. He lives in Minneapolis.