A single model run

It was 7 o'clock in the evening, and my head was buzzing with an excess of terrible coffee as I stared at my computer screen, watching the clock tick down on what I hoped would be my last simulation run of the day. The model in front of me was inexorably crunching the numbers for what had, up until now for me been a fairly esoteric research question. Could a modeling approach based on probabilities help communities with limited knowledge of the properties of their underlying soils implement nature-based flood control solutions?

As a freshly-minted post-doc, this project was a final capstone on work I'd already completed - and defended - as part of my PhD from UIUC. For the community of Calumet City, IL, it was a matter of cold, hard cash. Needless to say, I was more than a little nervous.

Calumet City is a community on the south side of the Chicago metropolitan area. As with many of the smaller communities on this side of the city, budgets are tight, particularly for infrastructure rehabilitation. This is especially true for Calumet City, which has been historically prone to flooding not only due to its proximity to the Little Calumet River, but also as a result of acres of impervious new development. These layers of new asphalt and concrete cover over the soils and vegetation which would normally capture and soak away some of that water. Instead, most of the rain which falls on Calumet City is now funneled over the relatively flat topography and directly into local backyards and alleyways.

However, Calumet City has been blessed with a range of different soil types, including several veins of highly permeable sand left behind by the windings of the river over time, which have been papered over by the encroaching concrete jungle. This project was a collaboration between state geologists, landscape architects, civil engineers, and local communities to try and piece together the hydrogeologic landscape of Chicago's south side... and in the process help communities living there decide how to rethink their infrastructure to prevent flooding in the face of a changing climate.

My role in all of this - and the reason why I was sitting in a basement running model simulations rather than enjoying the late summer evening - was to look at how likely a given piece of green infrastructure was to fail, given its location, its design... and the type of soil it was sitting on top of.

Green infrastructure is fancy term for any engineered solution that makes use of natural processes to treat and soak water into the ground at its source before it can become nuisance flooding. When designed correctly, it can offer a multi-benefit, low-cost alternative to our traditional approach of stormwater pipes, ditches, and ponds. However, the very thing that makes green infrastructure so attractive - its flexibility - also makes it challenging to model and accurately predict. Think of green infrastructure like a sponge, with each different layer of soil being a different type of material in that sponge. Some soils, like sands, like to soak up water, like a loofah fresh out of the packet. Others, like clays, are like an old, dried out sponge that's been sitting out on the counter for a while - they'll absorb water, but only begrudgingly. And not every soil behaves the same all the time: the amount of rainfall, the types of plants and animals living in the environment, and the amount of compaction can all affect a soil's ability to absorb water.

And so, the need for probability-based design: a way to capture those uncertainties and provide concrete guidance on where green infrastructure should be placed in an urban landscape, and how that green infrastructure should be designed. It was a multi-stage process, integrating soil maps and analysis from the geologists, the modeling analysis from my department in civil engineering, and the design expertise of our landscape architecture colleagues.

The model runs became maps; the maps became design sketches; the design sketches became stakeholder workshops, and presentations, and... And then it was over. As I packed up my office to leave my summer post-doc for my first "real person" job, I had to wonder - had it all really meant anything?

Five years later, I received an email from my old mentor and friend, Dr. Ashlynn Stillwell, who had been my advisor on the Calumet City project. It was a photo of one of seven new Green Alleys that were in the process of being constructed across the city as a direct result of our work. The project is part of a much larger network of over 400 green infrastructure projects funded by the Metropolitan Water Reclamation District of Greater Chicago, which are anticipated to retain a net of 800,000 gallons of water per storm event. And Calumet City's participation was all thanks to our little project, which helped to launch the city's entire green infrastructure program.

Sometimes, all you need to spark change is a single model run.