In 2006, the Shakopee Mdewakanton Sioux Community (SMSC) constructed the largest green roof in the upper Midwest its new Water Reclamation Facility. The 31,000-square-foot green roof contains more than 45,000 plants, including native prairie grasses and flowers. The greenoof system disperses significant amounts of water back into the atmosphere through evaporation and transpiration. During dry spells, the plant life on the roof can be supported using reclaimed wastewater from the treatment process itself, yet another benefit of the high level of treatment the facility provides.

 

Research

The Shakopee Mdewakanton Sioux Community recognize the research opportunity presented by the Wastewater Reclamation Facility (WRF) green roof and its ability to answer some of the unanswered questions for Midwest green roofs. Five research projects are currently being conducted (started in 2007):

• Looking at building heating and cooling on and inside the WWTF and an adjacent building without a green roof.
• Determine plant and irrigation influence on soil moisture to optimize water retention.
• Examine influence of irrigation amount on percent cover of roof over two growing seasons.
• Establishment of Sedum by seeds, cutting, or plugs and various irrigation levels to determine optimization of upfront cost and final “green” cover.
• Competition of Sedum and native prairie vegetation under irrigation conditions past establishment.
• Explore pollinator usage of native prairie plants used in the green roof vegetation.
  

 

Plants

A mixture of plants native to Minnesota and traditional green-roof vegetation (stonecrop) were planted on the roof in summer 2006 [plant list on side bar of internet]. By the end of the first full growing season in 2007, the green roof had achieved 60% vegetative cover. Stonecrop makes up the majority of the understory, while the native grasses and forbs make up the mid- and upper- canopy. The vegetation receives water from rainfall and an irrigation system. Water from the irrigation system is the treated discharge from the WRF.

Stonecrop, native grasses, and some native forbs did very well in the first growing season. Both stonecrop and native forbs were utilized by local pollinators. In addition to planted species, the green roof also host several kinds of volunteer plants. These surprisingly include wetland species like cattail, willow, and cottonwood.

 

Temperature Study

One of the benefits often attributed to green roofs is temperature regulation. Green roof advocates claim that shade and evapotranspiration produced by the vegetation will keep roof temperatures lower; this in turn will reduce the need for cooling during periods of warm weather. Additionally these same processes will aid in mitigating the urban heat island effect which exists in developed areas.

One of our ongoing research projects will address these potential benefits. We are currently recording air temperatures at five different heights to create a temperature profile from a height of one meter above the green roof to 1.5 meters above the floor directly below the green roof. A similar profile is being monitored in another area of the building that has a typical membrane roof with no vegetative cover. A comparison of these data sets will show whether there is a significant difference in air temperature above a green roof and whether any temperature differences are translated to the interior of the building.

 

Soil Moisture Study

Traditional roofs are designed to respond quickly to precipitation events and efficiently move water off of the structure, this water typically ends up in a storm drain. During a storm event this process can lead to flash flooding and erosion. With a green roof the opposite is true. One of the advantages of a green roof is its ability to retain water which can be taken up by plants and transpired back into the atmosphere or slowly released through the drainage system.

We are currently gathering soil moisture and precipitation data on a small section of our green roof. This data will allow us to quantify the response of green roof soils not only to precipitation events, but also to periods of dry weather

A Rain Garden is a garden that is designed specifically to collect and infiltrate rainwater that falls on nearby impervious surfaces. Downspouts from rooftops are directed to the rain garden and swales direct water from impervious surfaces like sidewalks and driveways.

The benefits of Rain Gardens are:

• Rain Gardens reduce storm water runoff which:
• Reduces the amount of pollutants such as sediment, nutrients and metals that enter lakes, streams, wetlands, and rivers
• Rain Gardens are beautiful
• Rain Gardens attract Butterflies and Birds
• Rain Gardens are low maintenance once established

For more information on Rain Gardens, including manuals to construct one in your yard see the links below.

Links

University of Wisconsin – Rain Garden Manual
www.clean-water.uwex.edu/pubs/pdf/home.gardens.pdf

Minnesota Pollution Control Agency – Rain Garden Manual
www.pca.state.mn.us/publications/manuals/stormwaterplants.html

Applied Ecology – Rain Garden Manual
www.appliedeco.com/RainGarden.cfm

Minnesota DNR list of Native Plant Suppliers and Landscapers by Region
www.dnr.state.mn.us/gardens/nativeplants/suppliers.html

Minnesota Conservation Volunteer Rain Garden Article
www.dnr.state.mn.us/volunteer/mayjun04/raingardens.html