Rain Gardens: Nature’s Flood Control

Rain Gardens: Nature’s Flood Control

By: Sarah Voska, Bluestem Ecological Services, and Angela Duea, Lieberman Management Services

The recent heavy rains and flooding have caused trouble in Northern Illinois community associations. Water has seeped into homes, clogged gutters and downspouts, and pooled in places that cause asphalt damage. Moreover, it is predicted that the amount of rainfall will only increase in our area. A 2016 report by the US EPA, “What Climate Change Means for Illinois,” found that the biggest risk to Illinois would come from heavy rains, flooding and drought. Spring & Fall rainfall and thunderstorms are expected to intensify, something we certainly saw this spring.

While precipitation in Illinois overall has increased by 5-10 percent over the last 50 years, this rain is coming in shorter time spans, leading to increased risks of flooding. Northern Illinois originally had vast tracts of wetlands, which naturally absorbed excess rainfall, but extensive land developments have eliminated this natural flood control.

During flooding events, the ground becomes supersaturated with water, and excess water gushes into the storm water drains, fills up basements and serves as breeding ground for mosquitoes. In the city of Houston, flooding in 2015 and 2016 (prior to Hurricane Harvey) caused $1 billion in damages to 16,000 buildings. Geologists and urban planners were able to tie the devastating flooding back to over-development in wetlands and floodplains; paving over some 38.000 acres of wetland since 2000 (Time Magazine).

By restoring the types of habitat and water filtration systems that historically existed in the area, Houston, and other forward-thinking cities, has a chance to protect their waterways and their communities from destructive floods.

Rain gardens are a flood control solution that is designed by planting tolerant plants in a natural slope or depression. They are considered “tolerant” because they are capable of soaking up large quantities of water during heavy rains while still surviving in dry spells. They slow the flow rate of storm water, and absorb greater than usual amounts of water into the soil. Whether you contour the land to direct the water towards storm drains/ surface waterways, or you plant along current flow paths, rain gardens serve as a great way to manage flood events.

By slowing the water, rain gardens also  protect shorelines from erosion and recharge groundwater aquifers. Rain gardens are typically constructed with native plants, that is, plants that have historically been part of the Illinois landscape since pre-development. Native plants provide the most benefit in rain gardens because they are habituated to Illinois climatic conditions and soil types. Their deep roots help secure the shoreline and give the plants a high tolerance for droughts or flooding.
Some native plants that do well in a rain garden include:

  • Turtlehead Chelone glabra
  • Cardinal Flower Lobelia cardinalis
  • Joe Pye Weed Eupatorium purpureum
  • Swamp Mallow Hibiscus moscheutos
  • Blueflag Iris Iris virginica var. shrevei 

Rain gardens also filter the water as it flows through them. This can help protect your community association’s lake or decorative pond from pollutants including lawn chemicals, oil and heavy metals. Because of the topography of many neighborhoods in the Chicago Metropolitan area, lakefront areas can convert into waterslides during heavy rains, especially as runoff from roofs and roads joins the mix. Natural shoreline buffers can reduce runoff by 40 percent or more, with most of that water trickling into the groundwater supply instead.

Rain gardens also filter out sediments, which can cause silt barriers in waterways. In areas where drinking water is sourced from shallow water aquifers (pockets of freshwater located underground between the soil and the bedrock), rain gardens help ensure the quality of groundwater.

Rain gardens and shoreline buffers can provide a means of natural pest control: they are unfavorable to mosquitoes, and deter geese, who don’t like the grasses taller than their necks. Instead, these natural areas become habitat for desirable species such as sand-hill cranes, dragonflies (which feed on mosquitoes) and butterflies. Native shorelines and buffer gardens can improve the health of your beautiful lakes, bringing them back to center stage in your community. Encourage your homeowner’s association to plant a rain garden this year!