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The Wisconsin Department of Natural Resources estimates that an average acre under construction loses 30 tons of sediment per year to downstream waterways. This large amount of sediment is partly due to high erosion rates – 35-45 tons per acre per year compared to one to 10 tons per acre per year for cropland erosion. Another reason is the water is moving fast. Storm sewers, ditches and grading installed early in construction provide good drainage, but they also create an efficient way to move storm water.
The buzz phrase in new development to install storm water and erosion control measures is "Low Impact Design" (LID). LID developments try to mimic the drainage patterns before development using techniques that infiltrate, filter, store, evaporate and detain runoff close to its source.
LID areas feature common open spaces, narrow streets, shorter set backs for driveways, smaller lots, and infiltration practices. LID manages and treats storm water through small and often cost-effective landscape features.
According to the Low Impact Development Center in Beltsville, Md., LID techniques often save money over conventional approaches.
"Case studies and pilot programs show at least a 25-30 percent cost reduction associated with site development, storm water fees, and maintenance for residential developments that use LID techniques," according to Urban Design Tools. Savings come from reducing clearing, grading, pipes, ponds, inlets, curbs and paving.
LID features include neighborhood designs such as reducing curbs and gutters, maintaining buffer zones along waterways, using infiltration swales, and conserving open space. Many of these landscape practices are attractive and property values increase as a result.
Steve McCarthy, a project manager for the Milwaukee Metropolitan Sewerage District, supports the idea of LID designs to manage storm water. Historically, that district has developed larger and larger conveyance systems to address flooding as development has moved into the floodplain. This response has been costly and largely ineffective, especially during major floods.
In the 1990s, two major flood events deluged the Milwaukee area. One was at the 100-year flood level and the other close to that, McCarthy recalls. Flooding saw Milwaukee's County Stadium under water. Over 600 properties were flooded in Wauwatosa causing $16.7 million damage.
McCarthy says taxpayers in the Milwaukee and Menomonee River watersheds have paid about $300 million to control flooding there since the 1990s, not including the Deep Tunnel project, which cost $1 billion, yet flooding continues.
He says it is time to look beyond traditional engineering to control storm water. McCarthy says the district now encourages green roofs, rain barrels, rooftop restrictors and wetland gardens, along with storm water ordinances, and restoring flood prone properties and natural depressions that act as storage areas.
On the roof
One LID practice catching on in some communities is detaining runoff on flat roofs with restrictors – wide metal collars that sit around the drains and look like manhole covers with vertical slots. Water is slowed as it is forced to enter these slots. Restrictors aren't cheap, though, at $500 each.
Green roofs are another LID concept. These roofs are covered with a waterproof membrane, soil and vegetation. Water is retained in the soil and much of it is used by plants or evaporated. Overflow from the roof exits through drains or downspouts. These roofs need to be carefully engineered so they do not become too heavy.
Some communities are experimenting with rooftop gardens to control roof runoff. These roofs are reinforced and a light soil is used. They have emergency drainage systems for extreme storm events.
In Germany, people sell rooftop-captured water. In New Zealand, people have concrete shingles and harvest rooftop runoff.
Building a two-story home instead of a more expansive one-story home also is a practical way to lessen the amount of roof area available for runoff.
Homeowners may ask their builders to design and tilt their driveways so that runoff is directed to the lawn instead of into the road and storm sewers. Grid or tire tread driveways allow more infiltration.
Some homeowners are moving to single car driveways or sharing a driveway with a neighbor to reduce the amount of pavement on their properties. Consider installing gravel trenches along driveways or patios to collect water and allow it to filter into the soil.
Channels along driveways may direct water to rain gardens instead of the road.
Walkways may be built from porous materials. Some subdivisions are locating sidewalks on only one side of the street and providing common walkways linking pedestrian areas.
Paver blocks are another driveway option. These blocks have spaces where water can infiltrate. Driveways can contribute 15 percent of the annual runoff from a residential area.
Siting and landscaping
By selecting a house in a mass transit corridor, you can take advantage of buses, commuter trains and bicycle routes.
Support the preservation of wetlands as natural filters that protect water quality, prevent flooding and provide vital open space.
Promote parkway corridors adjacent to streams and waterways for water quality, wildlife and other benefits. Homes may be sited so that clearing and grading is minimized and existing trees are left intact.
Steep slopes can be challenging, but provide a chance to try creative landscaping. Steep banks are difficult to mow and may lead to serious erosion if vegetation is not kept up. One consideration is planting ground covers to protect the soil from erosion. Check with a local nursery for plant species best suited for your area. Plants that adapt to a wide range of light and moisture conditions, require little care and provide soil erosion protection include juniper, wintercreeper, periwinkle and heathers.
Terraces, which create mini-gardens, are another option on steep slopes. Terraces prevent erosion by shortening the long slope into a series of shorter and leveler steps. This allows rain to soak into the soil where it falls.
Terrace costs vary depending on materials used and the area to be terraced. Terraces must be installed properly to ensure stable slopes. Slope steepness often dictates wall height. Check on local ordinances and building codes if considering a terrace.
Other techniques for LID landscaping include installing tree box planters. Trees beautify, provide wildlife homes, allow water to soak in, and filter pollutants.
Bielinski Development Company in Waukesha was chosen in a regional competition as one of three Model Conservation Development Projects of the Great Lakes region by The Conservation Fund for its 39-acre site in Germantown. The site was designed for 31 single family lots and nearly 60 protected open spaces, which integrated mature woodlands, restored prairie buffers, swales and a restored wetland, all of which help slow and cleanse storm water.
Small businesses can use many of the suggestions offered for cities and homeowners to curb storm water runoff. These include disposing of wash water where it will be treated. For instance at restaurants, handle grease and used cooking oil properly, cover dumpsters and do not store trash or chemicals near a storm sewer. Clean up any leaks or spills. Use de-icers judiciously on sidewalks.
In some cities, outdoor storage of scrap metal, coal and salt is a significant source of metals.
In some areas, street filters are taking root. Water is directed to a tree surrounded with biofilter material. There also are several options for replacing concrete and conventional asphalt with porous pavement. Bricks may be spaced to allow plants to grow in between and rain to infiltrate. Perforated concrete block pavers may be installed over a sand and gravel base allowing grass to grow in the perforations.
A Kwik Trip on Main Street in the City of Sun Prairie has rock infiltration trenches within the landscaping to trap oil and grease runoff and store storm water to meet the rate control requirements, as well as to infiltrate water into the ground. A shopping development on University Avenue in the Village of Shorewood Hills has incorporated storm water controls including porous pavement near storm drain inlets in the parking lots to trap pollutants so that water flowing into the storm drain and Lake Mendota is cleaner.
Natasha Kassulke is the associate editor of Wisconsin Natural Resources magazine.