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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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February 2003

Cities on the spot

Capital investments and storm water utility fees.

Natasha Kassulke

Detention ponds
Stenciling to street sweeping
From streets to swales
Paying to curb pollution
One county's storm water story

In August 2001, the cities of Franklin and New Berlin received awards from the Milwaukee Metropolitan Sewerage District for managing storm water and reducing flooding risk.

How did they earn the honor? Franklin scattered retention and detention ponds throughout the city. Any development or redevelopment in that community must now have ponds to control storm water runoff. Homeowners in the Lake Point Estates subdivision planted native vegetation in backyard commons to capture runoff and reduce the need to treat a pond in the subdivision for weeds.

Other options to manage storm water in cities may include street sweeping. Installing and maintaining these options comes with a cost.

Detention ponds

Detention ponds are speed bumps to slow storm water.

These ponds are popular in subdivisions and areas with multi-family dwellings. Some businesses use these ponds to control runoff from roofs and parking lots.

Creating a wet detention pond takes advance planning, though. It can take a year to seal a pond that might be used to detain runoff at a construction site. The pond also needs an adequate water supply to prevent sediments from re-suspending once they've settled out.

These ponds come in various shapes and sizes. Some take advantage of natural land contour depressions. Ponds designed for removing pollutants, though, have to have enough storage capacity to hold all the runoff from a 1.5-inch storm. Storm water ponds are most effective in removing pollutants when they have permanent pools of water three to eight feet deep.

Pond surface area is another consideration. The more surface area a pond has for each acre of land it drains, the higher the percentage of pollutants it will remove. Another factor is the distance between the inlet and outlet. Overall, the pond should be at least three times as long as wide. This design maximizes detention time and allows more sediment to settle out.

DNR monitoring found that storm water ponds can remove 90 percent of suspended solids, 65 percent of phosphorus, 70 percent of lead and 65 percent of zinc found in runoff.

A DNR grant to the City of Delafield in 2002 studied the feasibility of dredging Nagawicka Lake and the Bark River and building two storm water retention ponds to control sediment runoff. Sediment on the lake and river bottoms from storm water runoff makes navigation difficult for anglers, swimmers and boaters. Retention ponds would filter runoff before it reaches the lake and river or seeps into wells.

Landscaping is another consideration so the basin can provide habitat for frogs, birds and insects. All storm water ponds should have gentle side slopes and a safety shelf – a 10-foot-wide ledge about one foot underwater on all sides of the pond. Plantings around the edges discourage swimming and wading.

An outlet should be located in the embankment and the pond should have an emergency overflow if large storms exceed the outlet capacity. Pipe openings should be covered with trash racks to keep people and debris out.

The Southeastern Wisconsin Regional Planning Commission estimates construction costs of $35,000 to $110,000 per pond surface acre, which includes engineering, excavation, fill, compaction, inlet and outlet installation, landscaping, legal fees and contingency.

Annual maintenance costs for mowing, pruning and litter pickup, and cleaning the outlets are usually three to five percent of capital costs.

The City of DePere saved $750,000 on a $1.2 million project by using a storm water system with ponds rather than a conventional sewer system.

Stenciling to street sweeping

Youth groups are stenciling DUMP NO WASTE beside storm drains in many communities to get people thinking about where storm water ultimately winds up – in the lakes.

Most municipalities also do some kind of street sweeping to remove pollutants that are not only ugly and harm water quality, but are hazards for bicycles.

Regular street sweeping can help keep storm drains clear of debris. © Robert Queen
Regular street sweeping can help keep storm drains clear of debris.

© Robert Queen

Street sweeping is important in areas where vehicles frequently start and stop. Shopping mall parking lots and busy intersections collect cadmium, zinc, copper and hydrocarbons from brakes and exhaust. New generations of street sweepers are better at removing these fine particles.

From streets to swales

Cities have several options for making streets more environmentally friendly by: narrowing streets, reducing the length of streets, exploring alternate street layouts and more.

"Now, we are asking city engineers to design infiltration trenches that run down the middle of the street – as they have done in Cross Plains – to filter pollutants and slow water flow," says Roger Bannerman. "This is a new concept that some cities still haven't been sold on yet."

The key is to design streets for the minimum required pavement width needed to support travel lanes, on-street parking and emergency, maintenance and service vehicle access. Cities also still need engineering and storm water controls that safely handle the big storms – 100-year storm events.

"There has to be some balance," Bannerman says.

With that in mind, Bannerman says there are options for cities to curb storm water runoff, while maintaining safety and comfort. These include incorporating landscaped areas to reduce impervious cover. Where the slope permits, vegetative channels should be planted in the street right-of-way to convey and treat storm water runoff.

A business or city could reduce the overall area of a parking lot by providing a parking ramp and using pervious pavement or paver blocks, which are porous. Storm water treatment of parking lot runoff includes bioretention areas, trees and planters, and filter strips.

Applied Ecological Services, Inc., (AES) an ecological consulting, contracting and restoration firm in Brodhead, designed landscaping for a housing project that featured prairie and wetland management supported with native seed and plant materials by Taylor Creek Restoration Nurseries, the company's 300-acre prairie and wetland nursery.

AES supports using alternative storm water management systems such as those found at Prairie Crossing, a 678-acre residential development 40 miles northwest of Chicago in Grayslake, Ill. Jack Broughton, AES, marketing manager, says the community adopted conservation designs to reduce runoff rates and volumes and to reduce pollutant loads.

Storm water is routed into swales, rather than storm sewers. The swales provide initial storm water treatment, primarily infiltration and control sedimentation. The prairies diffuse the water and soils retain contaminants, slowing storm water velocity.

The development expects to about 60 percent of the land is devoted to open spaces. Residents raise rain gardens and take part in prairie burns, retain 65 percent of its storm water , reduce nutrient loads and reduce heavy metal pollutants by 85 to 100 percent.

Maintenance costs for storm water controls are expected to drop, downstream conditions have improved and there's less flooding. A sign of success has been thriving populations of nongame native fish (Iowa darter, black-nosed shiner, blackchin shiner, pug-nosed shiner, and banded killfish) in the 22-acre lake.

Paying to curb pollution

Purchasing street sweepers and other projects to curb storm water pollution can be costly. To pay for them, many municipalities are creating storm water utilities and adding a fee to utility bills.

"Storm water utilities get people to notice that there is a problem and they charge the people who contribute the most to the runoff," says UW-Madison engineering professor Ken Potter.

Shopping malls, even churches, schools and other tax-exempt entities are subject to storm water fees because the utility creates a user fee, rather than a tax. These fees also may be used to finance flood control.

Most storm water utilities set residential rates based on average amount of paved area. Some communities use zoning classifications. Fees on water bills average $15 to $20 per single or two-family dwelling per six months.

Prior to charging a storm water utility fee in Madison, storm water management was financed through property taxes. John Pfender, a DNR urban storm water specialist, says new utilities are being formed in Wisconsin at a rate of about two to four per year.

Natasha Kassulke is the associate editor of Wisconsin Natural Resources magazine.

One county's storm water story
In 2002, Dane became the first Wisconsin county to implement countywide standards to reduce runoff from development to protect lakes, rivers and streams.

The County's storm water management ordinance calls for storm water plans to be included in any development that creates 20,000 square feet (about .5 acre) or more of paved surface – parking lots, roofs and driveways. It also requires temperature control on runoff to reduce thermal pollution, which hurts cold-water trout streams.

The ordinance sets standards but does not mandate practices that must be used. Recommended runoff and erosion controls include installing buffer and filter strips, grassy swales, deep tilling, planting trees and native plants, installing oil and grease filters, and sediment traps.

One project working to meet the standards that went into effect in August 2002 is the St. Francis addition subdivision located at the end of Brewery Road in the Village of Cross Plains. Storm water control practices at St. Francis include infiltration areas such as grassy swales in the boulevards to meet water rate control, thermal, and sediment requirements. Narrower streets mean less impervious areas and less runoff.