Fall 2011 Department Article
Sidewalk Slurry
When rain falls in the city, dangers flow into rivers. How can we curb them?
By Martha Coventry
Photography by John Linn
 | |
| PEGGY KNAPP: “People think, ‘If it comes out of the tap and it’s cheap, I just don’t have to think about it.’" |
Rainfall is not good news for city rivers.
When water flows off rooftops, lawns and parking lots, it brings all sorts of unpleasant things along with it, including oils, chloride from road salt and trace metals. It also picks up phosphorus, nitrogen and sediment. Instead of then soaking into the land and filtering down to the aquifer, that now polluted water runs full tilt into street gutters, which usually funnel it directly to the nearest lake, river or stream.
That water is called urban runoff. Phosphorus and nitrogen from fertilizers, pet waste and decaying leaves and grass clippings feed algae and weeds, which in turn suck up the oxygen in the water. Sediment clouds the water and blocks sunlight from reaching the bottom. As a result, water quality greatly diminishes and aquatic life suffers.
Water is not high on most people’s worry list, especially in Minnesota, said Peggy Knapp, director of programs for the Freshwater Society based in Excelsior. “People think, ‘If it comes out of the tap and it’s cheap, I just don’t have to think about it,’” she said. But urban runoff needs everyone’s attention.
When water flows off rooftops, lawns and parking lots, it brings all sorts of unpleasant things along with it, including oils, chloride from road salt and trace metals.
Larry Baker, a research professor at the University of Minnesota’s Department of Bioproducts and Biosystems Engineering, says we have to tackle urban runoff with a host of inventive approaches, technologies and incentives. Here are three promising solutions:
Rain gardens:
When the city of Burnsville on the Minnesota River decided to see if it could capture storm water at the source, it paired two similar neighborhoods: one was the control; the other built rain gardens, which are depressions in the earth planted with native grasses, flowers and other vegetation to hold and absorb rainwater runoff. Monitoring over three years showed that runoff volumes were reduced by nearly 90 percent in the rain garden neighborhood and that most gardens captured the first 0.9 inches of rainfall—an important finding when you consider that 90 percent of pollutants run off in the first inch of rain.
Rewarding success:
The Blue Star program, sponsored by Friends of the Mississippi River in partnership with several watershed districts and The Irwin Andrew Porter Foundation, encourages communities to take a rigorous online self-assessment of their storm water management policies and practices. The assessment rates cities in a number of areas, like green street design, runoff control standards for new development and the extent of their public education programs. Forty-one communities have participated thus far. Cities that earn a score of 60 percent or higher are publicly recognized as Blue Star Award winners and are listed, along with their scores, on the Blue Star Leaderboard (bluestarmn.org/leaderboard). “This award allows cities to inspire each other to protect clean water, while helping educate citizens about urban runoff,” said Trevor Russell, watershed program director for Friends of the Mississippi River.
Reducing leaf and grass runoff:
The Mississippi Watershed Management Organization (MWMO) worked with St. Anthony Village in Minneapolis to figure out the best way to reduce nutrient pollutants in urban runoff. MWMO bought the village a leaf vacuum truck on the condition that it sweep its gutters at least six times a year, versus the normal two. Now St. Anthony Village is keeping at least three times more organic material out of the watershed than before. A similar program is at work in Prior Lake. IQ
When water flows off rooftops, lawns and parking lots, it brings all sorts of unpleasant things along with it, including oils, chloride from road salt and trace metals. It also picks up phosphorus, nitrogen and sediment. Instead of then soaking into the land and filtering down to the aquifer, that now polluted water runs full tilt into street gutters, which usually funnel it directly to the nearest lake, river or stream.
That water is called urban runoff. Phosphorus and nitrogen from fertilizers, pet waste and decaying leaves and grass clippings feed algae and weeds, which in turn suck up the oxygen in the water. Sediment clouds the water and blocks sunlight from reaching the bottom. As a result, water quality greatly diminishes and aquatic life suffers.
Water is not high on most people’s worry list, especially in Minnesota, said Peggy Knapp, director of programs for the Freshwater Society based in Excelsior. “People think, ‘If it comes out of the tap and it’s cheap, I just don’t have to think about it,’” she said. But urban runoff needs everyone’s attention.
When water flows off rooftops, lawns and parking lots, it brings all sorts of unpleasant things along with it, including oils, chloride from road salt and trace metals.
Larry Baker, a research professor at the University of Minnesota’s Department of Bioproducts and Biosystems Engineering, says we have to tackle urban runoff with a host of inventive approaches, technologies and incentives. Here are three promising solutions:
Rain gardens:
When the city of Burnsville on the Minnesota River decided to see if it could capture storm water at the source, it paired two similar neighborhoods: one was the control; the other built rain gardens, which are depressions in the earth planted with native grasses, flowers and other vegetation to hold and absorb rainwater runoff. Monitoring over three years showed that runoff volumes were reduced by nearly 90 percent in the rain garden neighborhood and that most gardens captured the first 0.9 inches of rainfall—an important finding when you consider that 90 percent of pollutants run off in the first inch of rain.
Rewarding success:
The Blue Star program, sponsored by Friends of the Mississippi River in partnership with several watershed districts and The Irwin Andrew Porter Foundation, encourages communities to take a rigorous online self-assessment of their storm water management policies and practices. The assessment rates cities in a number of areas, like green street design, runoff control standards for new development and the extent of their public education programs. Forty-one communities have participated thus far. Cities that earn a score of 60 percent or higher are publicly recognized as Blue Star Award winners and are listed, along with their scores, on the Blue Star Leaderboard (bluestarmn.org/leaderboard). “This award allows cities to inspire each other to protect clean water, while helping educate citizens about urban runoff,” said Trevor Russell, watershed program director for Friends of the Mississippi River.
Reducing leaf and grass runoff:
The Mississippi Watershed Management Organization (MWMO) worked with St. Anthony Village in Minneapolis to figure out the best way to reduce nutrient pollutants in urban runoff. MWMO bought the village a leaf vacuum truck on the condition that it sweep its gutters at least six times a year, versus the normal two. Now St. Anthony Village is keeping at least three times more organic material out of the watershed than before. A similar program is at work in Prior Lake. IQ
Initiative foundation | 405 First Street Southeast | Little Falls, MN 56345 | (320) 632-9255
