CNT Green Infrastructure Out-Weathers the Storm of the Century
On September 13th and 14th, 2008, the Chicago Region experienced a 2-day rainfall that was indeed the “Storm of the Century”. It was the largest storm ever recorded in the 119-year history of the Metropolitan Water Reclamation District of Greater Chicago. The Storm also, at 6.83 inches over two days, nearly met the definition of a 100-year storm in Chicago. Rivers surrounded houses, an interstate highway and several other arterials were closed for days, and thousands of basements were flooded throughout the region.
But CNT and St. Margaret Mary Parish found a small silver lining beneath the clouds on Chicago’s north side.
Two major church buildings on the St. Margaret Mary property, long among the first in their neighborhood to suffer from water damage during storms, weathered the storm of the century by soaking the rain’s torrent into re-opened ground where it fell. CNT had installed green infrastructure features at the church during 2007. These natural drainage systems protected the church from harm and kept about half a block’s runoff out of the sewers, also out of the record combined sewer overflow to the Lake.
Three green infrastructure features did the trick. The largest is a bioswale, or garden, in a cutout in the main parking lot that collects water and transfers it into the soil, thus bypassing the sewer system. In addition to relieving the sewers from the sanctuary building, the elementary school and the rectory, the bioswale serves as an arrestingly beautiful accent in the church courtyard and a traffic organizer. Two rain gardens are located in the lawn fronting the rectory. They divert runoff from the roof to the soil and replaced a massive hedge with two attractive native features.
The third improvement was installed in a large parking lot at the rear of the site, adjacent to the activities center. This building has been plagued by water frequently backing up into its first-floor gymnasium. CNT determined that a major cause of this flooding was a sewer line from the parking lot that joined the drainage from the building through a single line to the undersized street drain. CNT arranged for Ozinga, a local cement contractor, to donate a demonstration site for their Filtercrete brand of pervious concrete. A 15 by 15-foot square of asphalt pavement was removed from around each of the two parking lot drains and replaced with Filtercrete. Now, most of the runoff from the parking lot never enters the problem sewer.
And Father James Barrett of St. Margaret Mary explained the benefits of green infrastructure to his congregation:
“At St. Margaret Mary, we were very fortunate in that there was little rain damage… Since we put the water permeable concrete in the Activity Center parking lot and the bioswale in the church parking lot, there has been no water in either building… Thank you Ozinga Concrete Company and the Center for Neighborhood Technology. You saved us hours in clean up costs.”
And 20 miles south of Chicago at Our Lady Gate of Heaven Church, CNT also installed a bioswale. The parking lot there had frequently been filled with up to two feet of water. Now instead of remaining flooded for about three days, the lot is usable within a day.
CNT uses the installations at the two churches for research under funding from the USEPA. The bioswales and rain gardens are instrumented with a rain gauge and water level meters so that the performance of the green infrastructure can be measured for a period of years. Plans have been made for monitoring the performance of the Filtercrete, as well. The performance on September 13th and 14th will be thoroughly analyzed along with many other storms in coming years.
The bioswales are 650 and 900 square feet in area, draining pavement six times their own areas, and can be replicated elsewhere for approximately $10,000 to $12,000. The rain gardens are each 100 square feet in area and 10 inches deep. They each manage water from a roof area of about 600 square feet. The native plants in them, one plant per square foot, can be purchased for $2 each. The cost of the pervious pavement patches will depend on local availability, but should cost less than $5,000 apiece.