How Native Plants Reduce Flooding in Illinois


After the devastating Hurricane Harvey, and Irma on its coattails, urban planning and its role in coping with and minimizing flooding is on our collective minds. Cities are especially vulnerable due to their higher-than-average proportion of impermeable surfaces. Here in Chicago, we are mostly far from the terror of hurricanes, but, like much of the world, we have seen record levels of precipitation that has damaged buildings and homes and pushed sewage from our treatment plants into the river and the lake. 

There are many ways to prepare for flooding, but today, we’re focusing on the permaculture aspects that we could employ here in Chicago and Illinois. These include small scale things that citizens can do, from rain gardens and and green roofs, to bigger picture projects like restoring regional ecosystems such as prairie and wetlands.

Look to Prairie and Wetland restoration for macro-level flood management

Prairies are ecosystems with few trees and lots of tall grasses and forbs (herbaceous, flowering plants). These plants are very hearty and can reach water well below the surface soil. They can also survive in the relatively extreme temperatures of Illinois.

Although puzzling to early Europeans, Native Americans understood how to take advantage of the incredibly rich and fertile soil the prairie provided. Prairies can also withstand prairie fires, and in fact, these fires can help renew and rebuild the prairie by recycling plant matter into nutrients for new growth. Because of the fantastic soil in prairie country, grains (a type of grass) grow like weeds. Next time you hear someone call the midwest “corn n’ soybean’ land, you can blame the Europeans who decided to swap out prairie grasses for miles of monocultural wheat, corn and soybean fields, which use the riches of the prairies once diverse plantings as fodder for sandwich cookies and pot pie crusts. Today the Illinois prairie is just .001% of its former glory.

One such prairie restoration site is the Indian Boundary Prairie, just three and a half miles away from the South boundary of Chicago. “The Indian Boundary Prairie is part of what used to be the outer shoreline of Lake Michigan thousands of years ago,” says Chicago Conservation Director at The Nature Conservancy, John Legge. “As the glaciers melted and the land rebounded, the shoreline continually moved north, so you had a series of fairly subtle dunes that marked the former boundary of the lake, and swales which mark the lower boundaries,” he says. “We perform regular burnings with highly trained staff, and we rotate the location to give plants and insects time to recover.”

Visitors from hilly areas will sometimes marvel that on a clear day, you can see for miles in Chicago due to its flat surface.

With no natural drainage to speak of, such as a hillside or cliff, much of the water in a flat city would simply gather there if not for permeable surfaces with thirsty plants and soil. Back when the prairie had its full reign, precipitation had room to swell and subside, as it was drunk up relatively quickly and shuttled to deep roots by its grassland biome.

Take all of that away, and pave it over with decidedly non-permeable roads, and the water needs somewhere to go, stat. “Native prairie plants have much deeper and more extensive root systems that play a huge role in capturing and storing stormwater in a way that’s superior to lawn grass,” explains Legge. “In an area like Indian Boundary prairies where there is lots of pavement, the natural system ends up being important for absorbing stormwater that might otherwise contribute to localized flooding.”A research project being conducted on a portion of this prairie by Northwestern University Institute for Sustainability and Energy is finding out just how much water is being absorbed and purified by regional prairies, which could prove invaluable if developers decide to make the cost/benefit analysis of native plants and flood damage part of their local projects.

Fun fact: prairie grasses have such deep root systems because they adapted over thousands of years to survive fires that raged in the hot summers. The deep roots were able to survive the blaze, but invasive species and sun-greedy trees? Not so much. Eventually the fires and the prairies found synergy where only the hardiest grasses and plants survived.

Luckily, prairie restorations are alive and well, both in the city proper and not far outside of it. Winnemac Park has a thriving Prairie restoration, where black-eyed susans and pale blue asters thrive amongst grasses that cast human-sized shadows. Walking alongside it at sundown, you can almost imagine what it was like to see the sun sparkle off a prairie that stretched to the horizon. Humboldt Park is chock full of native grasses and even some wetland vegetation. If you go on a quiet morning, you might glimpse a turtle family basking in the sun.

“The mix of grasses and forbs is important for the overall native community, including lots of native insects and pollinators that have different flowering seasons,” says Legge. “A lot of prairie restorations in Illinois and elsewhere struggle with predominance of grasses or grasses in one or two particularly strong wildflower species, so part of what’s noteworthy at Indian Boundary is that most of the site has not been plowed and is therefore reflective of the native diversity on the site with minimal alternation.”

Wetlands take just four ingredients, according to Brian Huberty, Regional Wetlands Coordinator at U.S. Fish and Wildlife Services. “Water, vegetation, soil and time,” he says. But they are oft-misunderstood as “just cattails.” Huberty says that’s like comparing soybeans to strawberries: there are lots of different types of farmland, and there are lots of different kinds of wetlands. Think of wetlands like the amphibians of ecosystems: in order to qualify, they must spend part of their time partially underwater. Wetland types include marshes, fens, bogs, wooded wetlands and swamps.

Wetlands are a low maintenance ecosystem that have an “almost limitless capacity to store carbon,” says Huberty. This is good news for climate change. Even better, Huberty says, is that we have slowed wetland loss to a crawl. “People have gone from draining and filling them, to saying ‘hey, maybe there’s a reason why we keep these things,” he says. Beyond storing carbon, wetlands can handle fluctuations in water (wild rice in particular loves wetlands that see lots of water level fluctuations) making them an ideal “sponge” for heavy rains. “They are basically like stormwater holding ponds, but overtime, they have much more functionality,” says Huberty. “You get plants not only absorbing water, but also transporting it back into the air through transpiration.” They also clean effluent. “Most people don’t realize how the wetlands settle the sediment in rivers and uptake all the excess nutrients as well as holding some of the bad contaminants,” says Huberty. Wetlands are especially helpful during huge influxes of water.

What the Dutch Can Teach Us about Living Near Water // Notes from Sweet & Salt: Water and the Dutch (Tracy Metz and Maartje Van Den Heuvel)

The Netherlands know a thing or two about living with the constant threat of flood. Afterall, much of their country is below sea level; the water held at bay with dikes and polders (the later referring to pumping water out of a space formerly occupied with sea until it is dry enough to inhabit.) Referring to the Zuidplaspolder near Rotterdam (90% of Rotterdam is below sea level and the Zuidplaspolder is seven meters below), Metz and Van Den Heuvel have this to say: “landscape architect Adriaan Geuze has issued an impassioned plea for his countrymen to stop pumping themselves into the abyss ”however characteristic these polders may be for the Dutch landscape.”(78, Dikes and Polders).

Beyond these ways of keeping water out, the Dutch have fashioned ways to simply adapt to incoming water. “Water is coming back into the city…As a result of climate change, it rains more often and harder; sewers cannot handle the load and the streets are flooded. Cities are looking for new ways to keep the water out, or collecting it temporarily…Some believe the future will be on the water, with floating houses, parks and even power stations.” (175, Wet City)

Using creative architecture, the dutch build floating homes; and say if they win the 2028 Olympic bid they will build a floating athlete’s village. In addition, they are also adding green roofs to absorb falling water, a floating park called The City Water Lounge Rotterdam (complete with whirlpool), “climate plazas” with pools clarified by reeds that can be used dry or wet to give the sewers a reprieve. (178, Wet City).

It’s interesting to think of these methods being used in Chicago. We already have docks and large ships with dining rooms and margaritas; why not invest in floating infrastructure in areas that are likely to experience large influxes of water during storm events? Inspired by the dutch, our Kayak River Park and native plantings along the Chicago River bring the ideas of floating entertainment and recreation to, and on, the water, while allowing room for native species to go about their business. Read more about our floating river islands and river conservation here.

Look to individual buildings and homes for micro-level flood management

Green roofs have been rather trendy for their ability to protect buildings from heat gain, provide vegetation for a hyperlocal feast, and more. But they provide another benefit: absorbing rainwater before it can cause roof damage. Excess stored water may even cool the surrounding air by evaporating for another bonus. Native plantings are ideal for roof gardens because they require less maintenance and water.

Think of bioswales as a more sophisticated gutter. Comprised of plants (the bio part) and a shallow trench (swale), bioswales divert accumulated water away from sidewalks and streets while the plants, sandy soil and gravel filter out harmful chemicals, sediment and other pollutants before water flows into a permeable pipe or sewer. The longer the swale, the more it allows water to spread out and settle, giving sewer systems adequate time to process water before the dreaded Combined Sewer Overflow. This permaculture technique can also prevent erosion when implemented in less urban areas with more land.

Rain gardens are less space intensive than bioswales, which in the city are better suited to serving blocks and areas, not individual homes. These gardens are sunken to help divert water from the street and can have a big impact that is visible on a personal level. Follow the path of your gutter during a rainstorm to figure out where to dig. The water will naturally flow there. The Chicago Botanic Gardens recommends planting native perennials with deep root systems to deal with storm-sized influxes of water. The deep roots help the plant maximize its absorption of H20, while also anchoring it to the ground during strong winds and aggressive rains.

Did you forget about your good old friend trees? Trees prevent soil erosion, absorb water through their roots to prevent flooding, and even pass it along to other trees via a frankly magical communication system that was well documented in this episode of Radiolab.

In conclusion, there are lots of ways we can tweak our built environments to be more flexible for weather events. Not only do the above solutions require minimal infrastructure and maintenance, they replace valuable habitat for animals and insects, which bring just a little more nature into the city.

We hope you’ve learned something about how native plants reduce flooding in Illinois. Do you have a rain garden, rain barrel or bioswale near you? Have you visited some restored prairie in Illinois or in the CPD? Let us know in the comments.