Green Infrastructure Data Quantification and Assessment In the Calumet Region
The Center for Neighborhood Technology, Our Lady Gate of Heaven Parish and the U.S. EPA are demonstrating how the Calumet region can reduce flooding and create beauty. The project is designed both as a demonstration for emulation throughout the region and as a research site to gain performance data for use by engineers and regulators to design green infrastructure.
Our Lady Gate of Heaven Parish is located in Chicago’s South Side Calumet region. Historically, it has been plagued by flooding that is common in its poorly drained neighborhood, much of which was wetland that was filled with slag from nearby steel industries. When storms hit Our Lady Gate of Heaven, up to two feet of standing water collected in its parking lot and many nearby streets and properties were flooded. Because the church shares its space with a public school, both parishioners and students were burdened.
By employing Green Infrastructure, Our Lady Gate of Heaven has significantly reduced its flooding problem. The vegetated swale created in this project re-established natural drainage with limited loss of parking space and achieved aesthetic, educational, and social benefits for the community. The vegetated swale (or bioswale) will absorb about 100,000 gallons of stormwater runoff per year—enough water to fill a typical high school swimming pool. This stormwater runoff that could have otherwise caused flooding and potential sewer overflows now drains back into the natural hydrological cycle. Initial observations from school staff at the church indicate that, even in heavy storms, flooding in the parking lot is reduced by approximately 75% and standing stormwater drains off within hours instead of days.
Background
Before the Calumet region of Chicago and its suburbs was settled in the mid 19th Century, it included some 22,000 acres of wetlands, as well as dune and swale complexes and other features created as the glaciers retreated some 10,000 years ago and Lake Michigan retreated to its current basin. The land and waters were teeming with wildlife.
Railroads began to radically change the region before the Civil War. Urban development began with the introduction of a steel plant owned by Brown Iron and Steel Company1 in the 1870s and continued with additional steel plants by Republic Steel, Acme Steel, Wisconsin Steel, Southworks (part of United States Steel), and dozens of other major facilities serving the steel and other industries.
In those years, drainage conditions were so poor that elevated sidewalks and streets (6-8 feet above the rest of the ground) were constructed in many areas so that people could get around without slogging through standing water. As a solution, the Chicago Tribune noted ‘There is plenty of material for filling…in the mountains of slag surrounding the rolling mills.’2 Slag, a waste product of smelting iron ore before it is alloyed with carbon to produce steel, was indeed used to fill in the wetlands and lift vast areas above the water table. Unfortunately, it blocked natural drainage patterns which are still beyond the capacity of the City to completely fix.
The communities located in the Calumet area were devastated as the steel industry disappeared in the last few decades of the 20th Century. The increased level of activism that resulted included groups that were concerned about the trend toward using Calumet open spaces as dump sites. There was also an increasing appreciation that some remaining wetlands were homes for rare and endangered plant communities and birds. The work of these pioneering activists has been answered by the City of Chicago. Now there is widespread restoration of natural landscapes and plans for innovative facilities for education and tourism.
Site description
Our Lady Gate of Heaven Church, which was constructed in 1948, is located twelve miles south of Chicago’s Loop and two miles west of the Indiana border. The parking lot covers 17,000 square feet along the west side of the church and school. CNT selected the site based on a history of flooding complaints received by the City of Chicago for the area, along with the potential for public education and participation the site represents. This project’s vegetated swale was designed to drain most of the west half of the parking lot, intercepting stormwater from 7,000 square feet of pavement, before it reaches the sewer system.
The construction of the vegetated swale was ridden with challenges. The swale was originally designed to be 100 feet long and 10 feet wide. This area was calculated as proportional to the drainage area—a rule of thumb being that infiltration features function most effectively when sized at 10-15% of the drainage area. Soil borings revealed that the parking lot was constructed on top of approximately 6 inches of soil overlying 12-18 inches of slag. In some places, the slag proved to be impenetrable with small construction equipment, a skid steer loader with a hydraulic breaker attachment, along with jackhammers. As a result, the size of the swale was scaled down to a size of 66 feet by 10 feet; Thus, the bioswale is 660 square feet in area and receives water from 7,000 square feet of pavement. The excavation was expected to last several days, but ultimately took more than two weeks to complete.
Swale Design and Monitoring
The vegetated swale at Our Lady Gate of Heaven Parish is designed to be typical of a bioswale located in a parking lot. To promote infiltration, the swale contains a series of soil layers to a depth of 43 inches. The first layer of material that was placed into the trench is four inches of sand two inches of which is mixed into the sub-grade soil, followed by 12 inches of open-graded aggregate base (3/4-inch crushed limestone), a layer of filter fabric, a minimum of 12 inches of amended soil, and two inches of mulch. The amended soil layer slopes to within four inches of the pavement, yielding a maximum soil depth of 27 inches
The plants in the bioswale were selected based on several criteria: they must represent the plant communities in the Calumet region prior to development; they must be sustainable in the environment of a parking lot; and they must be distinctive enough for maintenance by people who are not experts. Ten species were selected and purchased in one-gallon containers.
To protect the garden and avoid damage to cars, tree stumps salvaged from tree removal activities in Chicago were installed along the edges of the swale.
Conservation Design Forum designed the bioswale. Jacksons Blacktop and Construction excavated the swale and removed the slag. The garden, was constructed and plants installed by Greencorps, a job-training program within the Chicago Department of the Environment.
Rainfall data and the performance of the bioswale will be measured through a rain gauge, three monitoring wells, and a soil moisture meter. Each piece of equipment is configured to record data at five-minute intervals; the data will be downloaded at least once every thirty days. The rain gauge was installed on the roof of the church building. The three monitoring wells each contain a water level meter. One will be used to quantify the amount of water stored above the ground surface in the bioswale, one to quantify the amount of water stored in the aggregate layers, and one to document the water level in the subsoil beneath the bioswale. A soil moisture meter is installed at a depth of approximately 6 inches in the engineered soil portion of the swale. The monitoring system was installed and the monitoring will be conducted by Hey & Associates, a consulting firm with experience monitoring other best management practices in Chicago.
Monitoring began in October 2007. The equipment, after initial testing, was removed in November to prevent damage from freezing, but will be ready for monitoring beginning in the Spring. Observations by church staff indicate that the swale is effective at reducing flooding in the parking lot. In a major storm on August 23, 2007 that deposited 2.15 inches of rain, the swale limited flooding of the parking lot to approximately 25% of the area that was inundated prior to the swale’s construction, with water draining off within two days. (The swale was not constructed in the lowest portion of the parking lot, but was located where the area of pavement draining into it was appropriate to the area of the swale (roughly a 10:1 ratio).
The total cost of materials, labor and plants for this swale was $22,781. Approximately $7,000 of this cost was due to the presence of the slag beneath the site. The project also incurred additional design and engineering costs of $7,500.
Public Involvement
Our Lady Gate of Heaven Parish rents space to Banner Academy, a Chicago public school. CNT will begin, in the Spring of 2008, to work with the Southeast Environmental Task Force, church parishioners, and Banner Academy staff and students to utilize the bioswale as a cornerstone for a public involvement program. The program will bring the community closer to the natural features of the Calumet region and will demonstrate opportunities for improving their community through reductions in flooding and enrichment of biodiversity.
Figure 1: The bioswale at Our Lady Gate of Heaven Church
Figure 2: Details of the bioswale at Our Lady Gate of Heaven Church, including three monitoring wells.
Link to Photo Gallery.
