Kurt Leuthold, PE, LEED AP, Barr Engineering Co.

Greg Wilson, Barr Engineering Co.

Fred Rozumalski, Barr Engineering Co.

Daryl Jacobson, City of Burnsville

Leslie Yetka, Minnehaha Creek Watershed District

Track: Research

Abstract:

The Burnsville Stormwater Retrofit Study began in 2003 at a time where a paired watershed approach had not been used to monitor the treatment effectiveness of rainwater gardens and very few stormwater retrofits included rainwater gardens. In addition, there was skepticism about the long-term efficacy of infiltration practices and volume control requirements had only been instituted in a few, limited instances. The project partners funded the project with the intent of demonstrating how these practices would function in a retrofit setting.

In-person surveys of an area tributary to Crystal Lake, impaired for excess nutrients, revealed that one subwatershed area could secure 85 percent participation by the homeowners. Paired watershed monitoring was initiated to calibrate the runoff from the control and treatment subwatersheds. Seventeen rainwater gardens were designed and constructed at the end of the calibration phase. Homeowners and volunteers assisted with the plantings. After plants were established curb-cuts were installed to bring the rainwater gardens on-line and the treatment phase of monitoring was conducted. Results of the paired watershed monitoring indicated that stormwater runoff volumes were reduced by 90 percent.

A recently completed follow-up study of the project included an evaluation of the long-term efficacy and cost-effectiveness of rainwater gardens, based on supplementary monitoring to the original paired watershed study. The results evaluated whether properly designed and maintained rainwater gardens provide long-term treatment capacity and represent a cost-effective BMP for new and retrofitted residential development, based on comparison to literature for the life-cycle cost-effectiveness of other BMPs.

Project monitoring results, cost-benefit comparisons and recommendations for optimizing the design and maintenance of rainwater gardens will be presented, along with lessons learned.