Photo by Caitlin Abrams
Island built with Legos
“Buy land,” Mark Twain supposedly quipped, “they’re not making it anymore.” That old investment chestnut, however, turns out to be wrong. That’s because they—and there are a lot of “theys”—make new land all the time.
At present, the most extravagant acts of land creation are taking shape on scattered reefs in the South China Sea. There, for the better part of the decade, China has been frenetically constructing large artificial islands, complete with military-grade airstrips.
But these days, a lot of land building is also happening in Twain’s old stomping grounds. He could see it for himself were he to ride another steamboat up the Mississippi River.
If all goes to plan, Pig’s Eye Lake will become the newest addition to the island-building boom by the end of 2021. That’s when the U.S. Army Corps of Engineers expects to finish work on the construction of a little archipelago of new islands at Pig’s Eye, an isolated, 638-acre backwater of the Mississippi River located about four miles downriver from downtown St. Paul. (The work will be done in partnership with Ramsey County Parks & Recreation and a private contractor.)
The public plans call for seven islands of varying sizes, elevations, and shapes, complete with benches, willows and larger trees, marshes, and protected coves. In total, they will cover about 40 acres. (For purposes of comparison, Minneapolis’s Nicollet Island spans 48 acres.)
The following year, a similar undertaking should start about 45 miles downriver at the head of Lake Pepin, just south of Bay City, Wisconsin. The technical details of the Pepin project have yet to be ironed out. But the corps currently expects to construct four islands in a shallow backwater known as Catherine Pass.
“Island building is new to the metro, but it’s not new to the river and it’s certainly not new to the corps,” says Nate Campbell, project manager for the $15.6 million Pig’s Eye project.
In fact, the construction of artificial islands on the upper Mississippi dates back to 1986. At that time, river ecologists were growing concerned about the disappearance of aquatic vegetation in a broad, windswept backwater located on the west side of the river, between Wabasha and Winona.
The problem at Weaver Bottoms began with its wind fetch-—the term hydrologists use to describe the distance wind travels across a body of water before it strikes land. Because a big wind fetch fosters more intense wave action, it can stir up muck and erode shorelines. That, in turn, increases the turbidity of water. With less sunlight penetrating the shallows, aquatic weeds go into decline, affecting the fish, waterfowl, and other wildlife that rely on vegetation.
In the end, areas with big wind fetch can turn into what is, ecologically, little more than a watery desert.
At the same time that the degradation of the habitat at Weaver Bottoms was stirring concern among researchers, the U.S. Army Corps of Engineers faced its own problem. It needed to dispose of the copious volumes of sand and sediments it continually dredged from the Mississippi as part of its core mission: maintaining a nine-foot-deep navigational channel for boat and barge traffic.
The result: The corps turned its worthless dredge “spoils” into something useful. That is, two new islands, dubbed Swan and Mallard. Situated in the middle of the 5,500-acre backwater, the islands help reduce the wind fetch. After years of tinkering, Weaver Bottoms is now a favorite stopping point for thousands of tundra swans as they head south each November. It has also, unsurprisingly, become a magnet for birdwatchers.
The corps’ Tom Novak, who has worked on many island-building projects, says the corps has been refining its island-building techniques ever since Weaver Bottoms. In fact, he says, they’ve built so many islands in the intervening years that he’s lost an exact count. “Maybe 50 to 100,” he guesses.
One major difference: The corps built Swan and Mallard to sit about eight feet above the river’s normal low water level. That’s about twice as high as newer islands, which are designed to “overtop” in periods of high water.
In many regards, the islands the corps now designs mimic those that the river creates through its own natural processes. They typically feature skinny, irregular shapes with tapered points and stretches of sandy beach. Many of these “artificial” islands are facsimiles of the historic islands that were first submerged and then eroded after the corps built the locks and dams on the upper river during the 1920s and ’30s.
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So how does one go about building an island? Construction techniques vary, depending on the circumstances. The fastest and messiest method employs hydraulic dredges. These are essentially floating vacuums, powered by enormous diesel engines, that suck sand and water from the river bottom through a pipeline.
These days, the dredges employed by the corps are capable of pumping 8,000–10,000 cubic yards of this slurry in a 24-hour period, according to Novak. While hydraulic placement is efficient, it’s not the ideal approach for all applications.
“You’ve got to control that ‘chocolate milk’ because you don’t want a plume going down the river,” Novak notes.
The most common technique for island building is a straightforward mechanical process using backhoes and bulldozers and barges. It’s slower than employing a hydraulic dredge, but not as slow as a third method: the seed-island approach.
This practice involves the strategic placement of rocks in areas of flowing water. These spots gradually accumulate sediments, in effect mimicking the river’s natural island-building process.
Because Pig’s Eye Lake is a backwater—that is, it’s connected to the main river channel but lacks any current—seeding wouldn’t work. And with heavy pollution from a now closed dump on the north side of the lake, the contractor may choose not to dredge sediments off the bottom.
The islands of Pig’s Eye may end up being constructed the old-fashioned way, with an estimated 2,000 bargeloads of dredged materials shoved 12 miles upriver by barges. For the Lake Pepin project, most of the spoils will have to be shipped even farther—some 22 miles.
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If you’re picturing a new Manhattan, though, you may want to ratchet down your expectations. These islands will be smaller and much closer to the water’s surface. First and foremost, the Pig’s Eye project constitutes a habitat improvement project: Wading birds, ducks, fish, and other riverine creatures will be the prime beneficiaries. Pig’s Eye Lake is broad and very shallow—typically only two to four feet deep, though it fluctuates with the river level. That profile makes wind fetch a big problem. As with Weaver Bottoms, a reduction in wind fetch should make the water a little less turbid and more hospitable to wildlife.
Another hope? The new islands will slow the steady erosion of Pig’s Eye’s wetlands—the marshy shoreline areas that also provide valuable habitat. Judging from aerial photographs, the corps’ Campbell estimates that more than 100 acres of wetland has been washed away at Pig’s Eye since the 1950s—a significant loss of habitat.
Pig’s Eye has long existed out of the public eye. It’s one of the least visited parks in St. Paul. Yet as news of the island-building project has spread, a few politicians and private citizens have raised complaints. Some fret that the construction could exacerbate pollution problems by stirring up contaminants on the lake bottom.
Noting the proximity to the St. Paul Downtown Airport (which sits across the river from Pig’s Eye), the Federal Aviation Administration has filed its concerns that the new islands might create too much prime “loafing habitat” for big birds, such as Canada geese, swans, and pelicans. The FAA, according to a database, has recorded 70 “wildlife strikes” at the airport.
But that number counts collisions over the course of almost 30 years. And Pig’s Eye Lake already holds one of the largest nesting sites for colonial waterbirds in the state. It’s one of only four places in Minnesota where yellow-crowned night herons are known to nest.
“There’s been some uninformed commentary about the project,” says Whitney Clark, the executive director of the environmental nonprofit Friends of the Mississippi River. “I see a lot of ecological benefits, and I don’t think there are any significant downsides.”
Some recreational users seem happy that Pool 2—the 32-mile stretch of the Mississippi that runs from the Ford Dam, in St. Paul, to Hastings—has finally won some attention from the corps.
At Weaver Bottoms, the water has become much clearer, says Greg Genz, a lifelong river rat who serves as the vice president of Friends of Pool 2. The improvement is so dramatic, he adds, that you can sometimes see the bottom at a depth of five feet. Farther downriver, another island-building project near Stoddard, Wisconsin, has won rave reviews from area anglers. “The fishing just exploded,” Genz says.
But the island-building bonanza on the upper Mississippi —and the considerable expense and effort it requires—underscores another reality. As it stands, the Mississippi River is a highly engineered body of water. Prior to the construction of the locks and dams, it was, in the parlance of ecologists, a “braided river”: much shallower in most spots and laced with innumerable channels and islands. Many of these riverine features have since vanished.
Of course, as long as the dams remain in place, the Mississippi will never be a natural river again. But with a few new islands, it will look, and act, a bit more like the river that Mark Twain cruised.
