When landscapers are done fixing up a 7 1/2-acre crater of muck at the Chicago Botanic Garden next year, the result will be more than pleasing to the eye. It may offer hope to the multitudes plagued by Canada geese at water detention ponds throughout the suburbs.
The crater appeared at the garden in April, when workers drained 16 million gallons of water from a lake known as the Great Basin. Eventually it will hold a $13 million water garden, the most expensive project in the garden’s history.
As the center of the emptied lake is deepened with earthmoving equipment, workers will use the muck to sculpt the shorelines, building shallow shelves that, when the lake is refilled, will be covered with only 6 to 12 inches of water.
The shelves will be planted with tens of thousands of plants native to Illinois wetlands, with an emphasis on tall shoreline and shallow-water plants: carex grasses, pickerel weed, sweet flag, bulrushes, arrowhead, swamp dock, lake sedge and giant bur reed.
Dashes of color from plantings of waterlilies, lotuses, water cannas and taro will interlace with the grasses.
The new shoreline should be not only attractive to the Glencoe garden’s 900,000 annual visitors, but also inviting to spawning fish, turtles and wild shoreline birds like herons, egrets and ducks (this sentence as published has been corrected in this text).
It won’t look so homey, however, to Canada geese, whose exploding population has taken up residence along more than 10,000 detention ponds built in the Chicago region in the last couple of decades.
Most of those ponds are surrounded by the open lawns of suburban homes and business parks. So if geese see an enemy approaching, such as a dog, it’s easy to get in the water quickly and swim away.
“There are thousands of detention basins in the Chicago area with nothing but flat, open turf grass growing right to the water’s edge,” said Jeff Mengler, a biologist at the U.S. Fish and Wildlife Service’s Chicago field office in Barrington.
“That’s the perfect habitat for Canada geese,” said Mengler, whose agency was one of several federal and state agencies that contributed funds and expertise to building the new shoreline. “The geese like flat, open spaces where they can easily see any approaching predators, plus the grass in the lawn is good to eat.”
By contrast, experts say, the geese feel uncomfortable around curtains of high grass, fearing hidden predators.
“If you have taller vegetation along the shorelines, the geese won’t stick around,” Mengler said.
Battling erosion, aiding water
Renovating the Great Basin is the first large-scale venture into water gardening at the garden’s sprawling 385-acre facility, of which about one-third is covered by artificial ponds and lakes. Government and private environmental groups are endorsing the project as a way to combat shore erosion and improve water quality in detention ponds–as well as controlling geese.
Though the Great Basin won’t be completed until September 2002, visitors starting Tuesday can see a similar, artificially planted wetland at the unveiling of the garden’s new Spider Island display area.
Designed by Michael Van Valkenburgh, a Harvard University landscape architectural professor, the 11,000-square-foot island will feature a path through meadows and stands of birches, alders and serviceberries. He also used the wetland grasses and plants along Spider Island’s shoreline to re-create the look of natural glacial lakes in the area.
Though the garden’s staff from the outset saw the Great Basin project as an ideal way to show visitors a model of shoreline and ecosystem restoration, the ecological message is almost secondary to other goals.
“We want to be the top aquatic garden in the world one day,” said Kris Jarantoski, the botanic garden’s director. “With more than six miles of shoreline on the property, if we don’t become the best in the world someday, something is wrong.”
It also is a way to open up more of the garden’s extensive grounds to strolling foot traffic, increasing what Jarantoski calls its “intensive display gardens” to 50 from 35 acres. That is needed, he said, because of the increasing popularity of the garden, which is expected soon to draw more than a million visitors annually.
“Our pathways can get pretty crowded on a good Sunday afternoon,” Jarantoski said. “The rule of thumb for a botanic garden is that you should have 50 acres of primary display gardens to accommodate a million people in one year.”
The garden is adding the new display acreage by building a series of footbridges to areas near the primary display grounds, Main Island. One of them is Evening Island, a five-acre crescent of land that forms the southern arc of the Great Basin.
Until recently, Evening Island had been noted mostly for a giant carillon bell tower standing on a hillside in a small forest of firs. The carillon remains, but under the design of renowned Washington, D.C., landscape architects James van Sweden and Wolfgang Oehme, many of the firs have been removed.
They have been replaced with stands of birches and sweeping meadows of perennials, flowering bulbs and shrubs selected to change the landscape’s color and form through the seasons.
On opposite shores on Main Island, the staff has planted an arc of flowering crab apples to frame the lake in the spring, and golden weeping willows and red-to-yellow sugar maples to do the same in the fall.
Waterlilies and lotuses
The most intensively planted part of the water garden will be the shoreline, with its tens of thousands of native grasses and colorful waterlilies and lotuses. Unlike the Spider Island shore, which is planted to re-create natural plant communities, the Great Basin shore will clump grasses and flowers according to artificial color schemes.
Still, the plants’ deep root systems will benefit the shoreline in much the same way as they do in more natural settings.
“The deep roots and the shallow water shelves they are embedded in are great for shoreline erosion control, combating erosion when winds blow high waves against the shore,” said Bob Kirschner, the garden’s curator of aquatics.
Similar plantings in suburban detention ponds also would work to naturally remove dangerous contaminants, including pesticides, herbicides, oil, grease and heavy metals.
The proliferation of such ponds in the last 30 years came as suburbs struggled to control flooding from increased runoff caused by paving over farmland for development.
The pools detain storm water so that it isn’t all dumped at once into rivers and streams, lessening the chance of floods. But once the ponds do release excess water, they release accumulated pollutants too.
Interested in broadcasting the benefits of using wetland plants to purify the water in detention ponds, the Illinois Department of Natural Resources, the Illinois Department of Commerce and Community Affairs, the Illinois Environmental Protection Agency and the U.S. Army Corps of Engineers all are helping fund the building of the Great Basin shoreline.
“It’s a great demonstration project,” Mengler said. “Hundreds of thousands of people go through the garden every year, and a lot of those people live or work near detention ponds. This is a good way to show the potential of improving them.”
