The project is part of an effort to treat stormwater in an area covered in concrete.
Walkers made their way along the Promenade bike and walking trail in Edina. A $1.8 million water feature would add a pond with an island that would drain into a brook that flows south, with a rapids and perhaps a waterfall.
Visitors to Edina’s Promenade, the sculpture-lined bike and pedestrian trail that winds from Centennial Lakes to the Galleria, may someday stroll along a gurgling stream and pond.
The water features were approved in concept last week by the Edina City Council. It’s part of a two-part plan to improve handling of stormwater in the area as well as to add beauty and complete the Promenade.
The scenic part of the $1.8 million project is a pond and stream to the east of the Byerly’s site, which is being redeveloped. The pond would have an island and drain into a brook that flows south, with a rapids and perhaps a waterfall.
“The stream is more of a parks feature and is supposed to be appealing to the eye,” said Ross Bintner, city environmental engineer.
Swinging benches and places to sit would be installed along the rock- or concrete-lined stream, with three or four spots to add public art. Walkways would cross the water. Because the elevation drops about 10 feet from the pond area to the spot where the stream will disappear into the earth, waterfalls or rapids could be installed, planners said.
The pond would draw its water from Centennial Lakes. The “lakes” are actually stormwater ponds. When the water level is high enough, Bintner said, the pond and stream would be filled, with the stream eventually sending water down into the ground and back to Centennial Lakes. The pond and stream may aerate the water and allow some pollutants to settle, but their main purpose is to add a water feature to the Promenade, Bintner said.
The other part of the project, an underground stormwater treatment structure, would do the real work in treating stormwater before it flows into Centennial Lakes and goes on to Nine Mile Creek. Bintner said the area around Centennial Lakes is more than 60 percent impermeable surfaces such as concrete and asphalt.
Those hard surfaces send polluted water pouring through stormwater pipes toward Nine Mile Creek, which is why the Nine Mile Creek Watershed District is interested in helping to pay for the project.
Just under the Promenade path and lawns, drain tile would spread water from Centennial Lakes underground, where it would be available to tree and grass roots. Shallow rock trenches edged with plants also could suck up some of the water. Water that isn’t taken up by plants would infiltrate into the ground.
Kevin Bigalke, the watershed district manager, told City Council members that the district is interested in the project because it could educate people as well as treat stormwater. Signs or kiosks explaining the purpose of the project could be erected on site or put on the city website, he said.
“We have a real prominent opportunity to showcase how stormwater management can be done in an innovative yet aesthetically pleasing way,” he said. “If it strictly goes underground, it becomes out of sight, out of mind.”
Council members asked Bintner why a series of rain gardens, the cheapest of the four measures that were considered to treat water on the site, weren’t recommended. The rain gardens would have cost an estimated $307,000, compared with $395,000 for the underground treatment with shallow gardens and a rock channel.
Bintner said officials concluded that the rain gardens would have looked out of character with the more formal landscaping of the Promenade.
With one council member absent, the vote to approve the design process and partner with the watershed district was 3 to 1, with member Joni Bennett voting no. Bennett said she was concerned about spending a lot of money on a small area when the city is still developing a priority plan for parks and there might be more pressing needs elsewhere.
The pond part of the project would cost about $1.2 million, including the water feature, areas for public art, lighting, controls, pedestrian walkways, stream crossings, design and half the cost of a pump station. That would be paid for with $600,000 in park dedication fees that came from development in the area and tax-increment-financing money.
The remaining $667,000 for the underground stormwater system, shallow gardens, rock channel and the remaining cost of the pump station would be paid for with city stormwater utility money and funding from the watershed district.
The project will come back to the City Council in the spring when contracts for construction are awarded.