Jan 13, 2010

Managing Runoff One Sprout at a Time

The Chicago Botanic Garden (CBG) is the second most visited public garden in the U.S. The garden is the home of millions of plants, and it is a recognized center of education, research and conservation.

In September 2009, CBG opened its new Daniel F. and Ada L. Rice Plant Conservation Science Center, which includes a 16,000-sq-ft green roof garden on top of the building.

The green roof garden project was designed to allow scientists to study what plants are best suited to grow in extreme environments, provide insulation and decrease the urban heat-island effect, increase the roof’s lifespan and reduce storm water runoff from the structure into the rainwater glen surrounding the building. Additionally, it will help remove carbon dioxide from air and pollutants from water, absorb sound and create habitat for insects, birds and the like.

SWS Editorial Director Neda Simeonova looks out over the green roof garden.

North to South

The green roof garden consists of two sections–north and south. The north section of the garden, the Josephine P. & John J. Louis Foundation Green Roof Garden North, was planted with a mix of plants currently accepted as good for green roofs, as well as exotic and native plants that have potential for green roof use. The south section, the Ellis Goodman Family Foundation Green Roof Garden South, was planted with North American native plants only.

“Both sides of the garden feature a display component, and half of it is an evaluation site,” said Richard Hawke, plant evaluation manager for CBG. “This project will look at different environmental conditions, landscapes and geographic areas that are similar to the conditions that you may find on a green roof.”

CBG initiated green roof plantings in summer 2009.

Construction of the new center started in 2008; however, planning for the green roof project started a year earlier, and plants were planted in August 2009, according to Hawke. “This is a fairly young green roof, so we haven’t analyzed specific storm water runoff data, but this will start in early 2010,” he explained.

The planting beds were constructed of several layers, including a waterproofing layer; two layers of hard foam insulation; a root barrier fabric; a drainage tile to allow water to drain away from the roots; a filter fabric to keep the growing media from clogging the drainage holes; and growing media as the top layer.

Public Access & Education

The green roof garden is open to visitors of the garden. This provides an opportunity for the public to watch the evaluation project progress in the coming years.

“The public is very interested in green roofs,” Hawke said. “What I find most interesting is that they are really interested in the energy savings and other environmental aspects such as rainwater runoff.”

Urban areas generate considerably more storm water runoff than natural areas. Green roofs are designed to absorb the water and release it slowly over a period of time, as opposed to conventional roofs where storm water is discharged into the sewer system and could lead to combined sewer overflows.

Staff will begin analyzing storm water performance this year.

National studies show that more than 80% of storm water retention can be achieved through the introduction of vegetative green roof systems. As a result, green roofs have begun to sprout all around the country.

CBG’s trials for innovative rooftop gardening will allow it to monitor plant health, aesthetics and survivorship of plants and be able to recommend plants that are low maintenance, absorb water and nutrients from rainfall and cool the building below, while providing an aesthetic retreat.

Editor’s note:

Managing Editor Caitlin Cunningham profiled the Daniel F. and Ada L. Rice Plant Conservation Science Center’s rainwater glen in the December 2009 edition of SWS RunOff.

About the author

Neda Simeonova is editorial director of Storm Water Solutions. Simeonova can be reached at 847.391.1011 or by e-mail at [email protected].

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