September 11, 2006

In 2000, Burnsville (MN) Mayor Elizabeth B. Kautz and the city council convened a town hall meeting of all citizens who live on and around the water bodies in Burnsville to address the issue of storm water runoff and its effects on the city’s lakes and ponds.

The meeting was an initial step in a process to inform residents what the goals should be for the water bodies in the city of 60,220 and what citizens could do to achieve these goals.

Under the guidance and facilitation from Burnsville city staff, residents presented to the city council goals and strategies for protecting and improving the lakes in the city.

Two key goals identified were: improving water quality and eliminating any existing flooding issues.

Water clarity was identified as a key indicator of water quality. Water clarity goals in the range of 5.5 to 7 feet were established for all the major lakes in the community.

In 2002, Kautz and the city council adopted a Water Resources Management Plan reflecting the goals identified by the citizens. The city provided $27 million in funding over a 15-year period to achieve the storm water management and lake water quality goals.

One of the strategies was evaluating the benefits of installing rainwater gardens in neighborhoods surrounding the city’s lakes. The idea was to focus on areas where the storm water run-off was not currently receiving any type of pre-treatment (e.g. ponding) prior to entering a nearby lake. If run-off could be infiltrated into the ground via rainwater gardens, it would reduce the volume of run-off and subsequently the amount of pollutants that would make their way into the area lakes.

The Rushmore Drive neighborhood provided an excellent location to test this practice and the Burnsville Rainwater Garden Project was soon underway. The neighborhood is strategically located in the watershed of Crystal Lake, where storm water run-off from the yards and streets flowed directly into the lake prior to this project. Crystal is a 280-acre lake in Burnsville that is highly valued as both a recreational area and a natural resource.

Funding for the project was provided via a partnership between Burnsville and the Twin Cities Metropolitan Council.

To protect Crystal Lake from excess phosphorus and large volumes of storm-water runoff through a rainwater garden, the system is designed to soak vast amounts of water into the ground, rather than routing it via storm sewers to Crystal Lake where it is detrimental to water quality.

This is nationally significant because:

• It is new technology.

• Rainwater garden systems work! Stormwater runoff is reduced by more than 90 percent.

• The paired watershed study proves the effectiveness of rainwater gardens in reducing storm water runoff.

The gardens were designed to add visual unity to an existing 1980s neighborhood. In all, 17 gardens were constructed – 13 along Rushmore Drive and four in a backyard swale that drains to Rushmore Drive. The gardens feature limestone retaining walls, colorful perennials and shrubs, and gradual side slope. They were designed for easy maintenance.

The contractor began construction on the rainwater gardens by cutting the sod, excavating below grade, backfilling the depressions with topsoil and compost, and installing edging and retaining walls. Homeowners became involved by planting their own gardens with the help of the project team.

Construction costs: $8 per square foot. Homeowner education, design and construction supervision costs: $4.50 per square foot. Funding was provided by Burnsville and a grant from the Metropolitan Council.

Two similar watersheds – a control site and the rainwater garden neighborhood – were monitored prior to and after installation of the new stormwater treatment practices. Runoff rates and volumes were collected in the storm sewer pipe at the outlet of each watershed. After collecting data two seasons before and two seasons after the project’s implementation, the results are in, and the project is an overwhelming success.

The paired watershed study determined that the rainwater gardens have reduced runoff volumes by approximately 90 percent, confirming that existing residential neighborhoods can be successfully retrofitted with rainwater gardens and provide high levels of runoff reduction and stormwater quality improvement. In addition, the high participation rate among homeowners indicates that rainwater gardens can be viewed as a valuable amenity to property owners.