Low impact development (LID) is an approach to stormwater management that mimics a site's natural hydrology as the landscape is developed. Stormwater is managed on-site and the rate and volume of predevelopment stormwater reaching receiving waters is unchanged. The calculation of predevelopment hydrology is based on native soil and vegetation (Minn. Stat. 115.03, subd. 5c).
Low impact development principles complement, and sometimes replace, traditional stormwater management systems, which historically emphasized moving stormwater off-site with curbs, pipes, ditches and ponds.
Green infrastructure is an approach to wet weather management that is cost-effective, sustainable, and environmentally friendly. Green infrastructure management approaches and technologies infiltrate, evapotranspire, capture and reuse stormwater to maintain or restore natural hydrologies. The terms "low impact development" and "green infrastructure" are used interchangeably.
- Water is a resource
- Reduce impervious surfaces to allow water to soak into the ground where it lands
- Use natural systems to promote infiltration of water
- Protect ecologically important areas of proposed developments
- Vegetated filter strips at the edges of paved surfaces<
- Residential or commercial rain gardens designed to capture and soak in stormwater
- Porous pavers, porous concrete, and porous asphalt
- Narrower streets
- Rain barrels and cisterns
- Green roofs
There are hundreds of low impact development/green infrastructure practices installed in Minnesota. Here are some sites with case studies.
- Minnesota Erosion Control Association
- Association of Landscape Architects
- Washington Conservation District
- Ramsey Washington Metro Watershed District
- Capitol Region Watershed District
- Minnesota Green Roofs Council
- Many LID practices prove to be attractive amenities to a neighborhood, using them may increase property values.
- Using LID practices and structures may reduce the overall cost of stormwater management
- LID practices encourage rain to soak into the ground where it falls, there are fewer opportunities for water to collect pollutants and reach nearby waters.
- MPCA and stakeholders are exploring how LID practices may help cities and townships achieve certain stormwater regulatory requirements under the Clean Water Act.
Comprehensive planning and ordinance development are the first step in encouraging low impact development practices. Communities throughout Minnesota are incorporating low impact development in comprehensive plans and are re-writing zoning codes and ordinances to encourage and allow these practices.
- Model Community Conservation Subdivision District
- Natural Resources Performance Standards
- Hanover. Through a grant from the MPCA, the city conducted a review of their ordinances and codes and made modifications to allow and encourage low impact development and conservation design. For more information, go to the city of Hanover's Web site.
- Crow Wing County Zoning Ordinance: Riparian lots with impervious surfaces exceeding 15 percent are required to have in place a stormwater management plan designed to treat water runoff before it reaches the lake through natural filtration, rain gardens, berms or other common sense approaches based on the particular characteristics of each property. Stormwater plans implemented since the ordinance has been in effect have reduced phosphorus by approximately 16 pounds or 4 tons of algae in our lakes and streams. The ordinance also includes conservation design language.
Rain gardens are another tool that can be used in established suburban or urban areas. Raingardens in numerous communities in Minnesota are already reducing urban runoff. The garden is located near the street or in a shallow depression where runoff can be diverted into it. Native perennial plants are recommended in rain gardens with hardwood mulch to reduce weeds. Minnesota is blessed with multiple resources for rain gardens including the Blue Thumb program, Metro Blooms and others.
There are multiple benefits to rain gardens, but in order for them to capture the rainwater, it is critical that they be designed, installed and maintained properly.
For useful information on design specifications, operation and maintenance and other information for rain gardens and bioretention facilities, go to the Minnesota Stormwater Manual.
Trees and shrubs
Known as “vertical rain gardens,” trees offer multiple benefits, including managing stormwater runoff. When planted properly, trees can capture rainwater and runoff. The rainwater benefits the trees and there is reduced runoff going into lakes, rivers and streams. The City of Minneapolis has done extensive work in their downtown on urban tree planting. See a case study on the Deep Root's website. Other projects that include tree trenches are the renovation of the Maplewood Mall and the Central Corridor Light Rail Project.
For useful information on design specifications for tree boxes and tree trenches, including design specifications and case studies, go to the Minnesota Stormwater Manual.
Stormwater reuse and rainwater harvesting
There are several systems available to collect rainwater, ranging from a simple rain barrel to an extensive underground collection system. For example, the new Minnesota Twins stadium, or cisterns at the Minneapolis City Hall building.
For useful information on stormwater reuse, go to the Minnesota Stormwater Manual.
Green roof technology began in Europe and has now spread worldwide. In Minnesota there are numerous green roofs, including U of M buildings, the Walker Library, the Prairie Technologies building in Rockford, the Lebanon Hills Visitor Center in Eagan, and the Minneapolis Public Library. Green roofs filter, absorb and detain rainfall. The specialized soil and plants reduce runoff by holding back and slowing down water that would otherwise flow into the storm drains. The Minnesota Green Roofs Council maintains a list of green roofs in Minnesota.
For information on green roofs, go to the Minnesota Stormwater Manual.
Permeable pavement (pavers, porous concrete or porous asphalt) allows rainwater to pass through instead of allowing it to run off. It is recognized by EPA as a Best Management Practice (BMP) for stormwater and can remove pollutants that would otherwise wash directly into rivers and lakes. Pervious pavement is ideal for parking lots, sidewalks and road shoulders. There are many porous pavement applications in Minnesota.
- City of Shoreview YouTube Video
- Ramsey-Washington Metro Watershed District
- City of Owatonna
- North St. Paul Living Streets Project
For information on permeable pavement systems, design specifications, operation and maintenance and case studies, go to the Minnesota Stormwater Manual.
Ribbon curb, or curbless streets, sloped to vegetated areas, allow rain from streets to drain into raingardens or vegetated swales on adjacent property. By eliminating curb and gutters, there are fewer infrastructure costs and water can drain into the structure and soak into the ground.
Open space development
Sixty percent of the 241-acre Fields of St. Croix development in Lake Elmo is left as open space. Some of these areas of open space treat stormwater and wastewater by a series of cells planted with wetland vegetation. At the Wild Meadows development in Medina, more than 200 acres of prairies and woodlands have been restored; 58 percent of the development will be left as open space to help restore natural hydrologic functions. At the 245-acre Inspiration development in Bayport, constructed wetlands, rain gardens and a network of swales collect runoff from yards, rooftops and driveways; over half of the development is in a permanent easement. The Minnesota Land Trust maintains a list of conservation developments in Minnesota.
- City of Owatonna: A Low Impact Development grant was awarded to design and implement low impact development techniques in the community. Two porous alleys and several rain gardens were installed. For more information, go to the City of Owatonna Web site.
- City of Hanover: A grant was awarded to the growing community of Hanover to protect and conserve its natural resources and manage stormwater on site. Hanover changed its Comprehensive Plan and Zoning ordinances to encourage low impact development.
- Federal and state grant projects: A number of Low Impact Development projects have been funded by Clean Water Legacy Grants and federal 319 grants: Crow Wing Soil and Water Conservation District, Ramsey Washington Metro Watershed District, Aitkin Soil and Water Conservation District, Gun Club Watershed Management Organization, Minnehaha Creek Watershed District, Brown's Creek Watershed District, Capitol Region Watershed District, Stevens Soil and Water Conservation District, Stearns Soil and Water Conservation District, Pope Soil and Water Conservation District. Descriptions of these projects can be found on the Board of Soil and Water Resources (BWSR) Web site.
- Maplewood Mall Retrofit Project: The first retrofit of a shopping mall in Minnesota, this project includes infiltration tree trenches, rainwater gardens, porous pavement and a cistern. The project also includes an educational and interpretive element which will include public art, signage and exhibits. For more information, go to the Ramsey-Washington Metro Watershed District website or to the Minnesota Erosion Control Association's (MECA) website.
- Central Corridor Light Rail Project: The central corridor will connect the cities of Minneapolis and St. Paul. This highly urbanized corridor is comprised of commercial and industrial land uses. The current drainage system conveys untreated runoff from approximately 111 acres of impervious surface directly to the Mississippi River. Four types of green infrastructure practices have been installed: integrated tree trench system, stormwater planters, rainwater gardens and infiltration trenches. For more information, go to the Capitol Region Watershed District Web site.
Funding available for green infrastructure
State of Minnesota Watershed Project Funding: Funding opportunities for watershed projects around the state are available through federal and state funds. These funds are awarded through either competitive watershed grants (such as federal Section 319 and State Clean Water Partnership) or non-competitive processes (Clean Water Fund). For information about other water-related funding opportunities at the MPCA: Financial Assistance Grants and Loans.
The Clean Water Revolving Fund, also known as the Clean Water State Revolving Fund or simply SRF, is established under the federal Clean Water Act and state law to make loans to for both point source (wastewater and stormwater) and nonpoint source water pollution control projects. The PFA prepares an annual Intended Use Plan (IUP) based on a Project Priority List developed by the MPCA. The IUP describes the projects and activities eligible for funding during the state fiscal year. This fund includes an allocation for green projects. For more information, see the Clean Water Revolving Fund page.
Clean Water Land and Legacy Amendment: Funds are available for green infrastructure projects through the Board of Water and Soil Resources. Check the web site for information on availability of funding and also examples of green infrastructure projects that have been funded with Clean Water Land and Legacy Amendment funding.
Watershed Districts: Cost share programs are available through many watershed districts. Contact your local watershed district to find out if you are eligible for project funding. Contact the Minnesota Association of Watershed Districts for more information.
Soil and Water Conservation Districts: Cost share programs for green infrastructure projects may be available through your local soil and water conservation district. Contact the Minnesota Association of Soil and Water Conservation Districts.
Low impact development on brownfield sites
Brownfields redevelopment and green infrastructure both produce economic and environmental benefits by improving urban areas, protecting open space and preventing further pollution of the nation's waters. However, in order to prevent further environmental damage by infiltrating precipitation through contaminated soil, onsite stormwater management must be done carefully, using particular design guidelines.
- A recent seminar addressed brownfields and stormwater management.
- For more information on brownfields and stormwater, visit the EPA's Low Impact Development webpage.
Tools are being developed through this project to enable and promote the implementation of low impact development and other stormwater management techniques. For more information, go to the Minimal Impact Design Standards page.
- Case Studies Analyzing the Economic Benefits of Low Impact Development and Green Infrastructure Programs (U.S. EPA)
- Green infrastructure resources (U.S. EPA)
- A Conservation Design Development Prototype in Hanover, Minnesota
- Low impact development - An introduction for Minnesota businesses
- Minnesota Stormwater Manual v3.0 - Wiki
- Low Impact Development Center
- EPA "Reduce Runoff" video
- Green Infrastructure