Stormwater Management: Permeable Paving & Rainwater Harvesting


When heavy rain falls cover Chicago, it’s not only inhabitants who feel overwhelmed by rushing water–it’s our sewer systems. Even with an expensive and complex underground deep tunnel that has helped reduce flooding and the rush of raw sewage into Lake Michigan, what can be done on a smaller scale? Is it possible to manage stormwater with permeable paving and rainwater harvesting?


Many in Chicago know: our history with waterways is not exactly a love story, with polluted rivers and sewer overflows that are still a serious issue, so much in fact that our Friends of the Chicago River established overflow action day initiatives to encourage urbanites to use less water on rain-heavy days. In the 1970s, Chicago’s Metropolitan Water Reclamation District started a massive public works project entitled the Tunnel and Reservoir Plan (TARP), better known as “The Deep Tunnel”, designed to hold excessive storm water in huge underground areas until it can be processed by treatment plants after flooding has subsided. The plan, due to be completed by 2029, has an ambitious goal of creating swimmable Chicago rivers.

Deep Tunnel System (Cred: David Schalliol | Slate)

Even with riverside pool parties potentially in our future, the system still reaps problems. “It’s a marvel,” states Karen Hobbs, former deputy environmental commissioner, “[but] we have this tendency in this country to think we can build our way out of stuff. And we can’t always build our way out.” The deep tunnel system in Chicago has rendered some clean water success, but these colossal infrastructure projects are incredibly expensive and environmentally problematic. More water running off into our combined sewer systems means more energy used in water treatment to clean that water. Moreover, Chicago still floods. What if there was a more sustainable (and potentially less expensive) solution?

In what has been called a “vision for a green oasis” for Philadelphia, a green infrastructure overhaul is already underway for a more ecological and efficient stormwater management system. The plan for the 25 year project is to reduce Philadelphia’s combined sewer overflows by 85%. This will be accomplished by converting the city’s landscape into a “giant sponge” using rain gardens, permeable paving and large-scale trees lining the streets which will improve air quality and restore ecosystems. Is this a benchmark that Chicago can achieve?


Increased awareness about the economic and environmental impact that stormwater overflow can have on a community has accelerated conservation efforts for both home owners and developers. Paving and landscape material options are more sustainable than ever and are highly effective at reducing stormwater runoff and pollutants.

Pervious pavement, also known as porous pavement or porous concrete, acts as a sponge by soaking up water and filtering it down through the gaps to the loose sand or gravel beneath the surface. Unlike impervious surfaces, permeable pavement treats, detains, and infiltrates stormwater runoff in areas where there is little to no landscape to absorb excess water. These pavements have multiple applications including sidewalks, alley ways, parking lots, or along gutter zones and in some instances, entire roadways.

Unlike impervious surfaces, permeable pavement can help keep polluted stormwater out of the sewer system. Pollutants like animal waste and vehicle fluids that collect on roadways and sidewalks mix with stormwater, then collect and heat up under the sun on impervious surfaces. Eventually, this hot polluted mess flows into the sewer which empties into our waterways. This creates a perfect recipe for a meal that algae loves to devour causing our rivers and lakes to be inundated with algae clouds that block sunlight and upset the fragile ecosystem. Cities and citizens can improve water quality by adding pervious surfaces during new construction and replacing portions of existing roadways, walkways and driveways.

Section showing how permeable paving and landscape collects rainwater and disseminates stormwater (Cred: Smart Cities Dive)


  • Reduce the concentration of pollutants entering the waterways
  • Trap pollutants
  • Mitigate the heat island effect caused by evaporation
  • In colder climates, can promote thawing and melting of ice and snow
  • Increased traction for pedestrians, bikers and vehicles during rainy or icy conditions
  • Less maintenance and, on rainy days, reduction of puddling and icing
  • Requires less roadway salt for deicing in the winter
  • Reduce the need for retention ponds or storm sewers with new construction
  • Channel more water to landscaping and tree roots, decreasing need for irrigation

The most commonly used permeable pavement surfaces are: interlocking concrete pavers, concrete grid pavers (aka Turfstone), pervious concrete, and porous asphalt. Other options include amended soils, or landscape rocks that add texture and contrast while maintaining high functionality.

Interlocking concrete pavement are separated by joints filled with stones that allow water to filter through and stream down to a soil subgrade. The stones located in the joints allow stormwater permeability and help filter pollutants. The pavement is available in a variety of colors, is durable, and can be installed mechanically, saving time and money. Outdoor patio grids surrounding pools and fire pits maintain an attractive look while entranceways in commercial spaces provide an ideal runoff system.

Concrete grid pavers allow rain water to gradually filter through and reach the earth to help irrigate and beautify lush landscaping. This gradual approach of water filtration decreases the rate of erosion (often an issue in suburban areas) and maintains a unique appearance. The cost-effective alternative works well in driveways, walkways, parking areas, and other pedestrian spaces.

Pervious concrete contains “a large volume (15 to 35 percent ) of interconnected “voids” containing little to no sand, allowing water to pass through more readily to the soil bed below. The composition is a blend of cement, coarse aggregates, and water — this combination provides sufficient pollutant filtration and stormwater retention.

Porous asphalt allows for water to seep through to a stone bed retainment center and then into the soil below the pavement. The pavement is slightly coarser and more expensive than traditional asphalt. However, the material is highly effective in stormwater management and shows little wear and tear–even after 20 years.


You can invest in a sustainable lifestyle at home and assist the city’s stormwater management system at large. With rain barrels and rain gardens, your backyard can morph into a micro stormwater management system, funneling stormwater runoff into surrounding foliage to absorb into the ground instead of flowing directly into the sewer.


A rain barrel is an above ground storage tank system that captures rainwater and runoff from rooftop gutter downspouts and stores it for future use. Typically, barrels are available in 50 gallon drums and can be relatively simple to construct or purchase. For every inch of rain that falls on one square foot of your roof, you can collect just over half a gallon of water. If you want to collect more than 50 gallons from one downspout, you can add a second barrel to the system and connect it with an overflow hose. The harvested rain water can be used to water your garden or to bathe your dog who decided to roll around in the mud. Rain barrel water is naturally free of chlorine, lime, and calcium, making it a better preference for plants, and that mischievous dog.


The purpose of a rain garden is to improve water quality in nearby bodies of water, and they do this by cutting down on the amount of pollution reaching creeks and streams. Rain gardens are constructed in a downside depression slope, collecting stormwater runoff from impervious surfaces (rooftops, driveways, sidewalks) and slowly filtering it in to the ground. The soil and native plants in the gardens naturally filter out pollutants, reducing the amount of contaminated water flow. The Chicago Botanic Gardens suggests planting “native perennial plants with deep root systems” to deal with the large influx of water from big storms. Plant those that require more water at the deepest trench of the garden with more drought tolerant plants towards the perimeter.


Bioswales can achieve similar goals as rain gardens by filtering stormwater, however on a much larger scale. The trenches consist of native grasses, rocks and various vegetation, making them more aesthetically pleasing than typical concrete gutters. The swales assist in diverting water runoff from sidewalks and streets and filter out harmful chemicals and pollutants naturally and efficiently.


In addition to rain gardens and pervious pavements installed in commercial developments and residential areas, can the city follow suite? Chicago has some instances of stormwater management through green streets infrastructure, but it’s an expensive undertaking and one that requires collaboration with private developers to redesign and retrofit the streets. There have been four pilot propositions in the green alley program, using recycled materials, permeable pavements, reflective surfaces to absorb heat energy, and energy-efficient lighting.

So what’s in the way? Permeable pavement can cost “two or three times greater” than regular concrete or asphalt. The benefits, we would argue, certainly outweigh the costs (both financial and environmental). Regardless whether Chicago takes a significant green infrastructure leap or not, incorporating stormwater management systems, on a micro level in and around your living space, can have a big impact.