Nature’s Flood Control
by: Sarah Voska (Sept. 2018)
A 2016 report by the US EPA, What Climate Change Means for Illinois, found that the biggest risk to Illinois will come from heavy rains, flooding and drought. Spring & Fall rainfall and thunderstorms are expected to intensify, something we certainly saw this past year. While precipitation in Illinois overall has increased by 5-10% over the last 50 years, this rain is coming in shorter time spans, leading to increased risks of flooding. During flooding events, the ground becomes supersaturated with water, and excess water gushes into the stormwater drains, fills up basements, and serves as breeding ground for mosquitoes. In the city of Houston, flooding in 2015 & 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, have a chance to protect their waterways and their communities from destructive floods.
Rain gardens are 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 stormwater, 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 have the added benefit of protecting shorelines from erosion and recharging 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.
Rain gardens also filter the water as it flows through them. This can help protect your lake 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% or more, with most of that water trickling into the groundwater supply instead. Rain gardens also filter out sediments, which can cause siltation 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 geese, who don’t like the grasses taller than their necks, and dragonflies feed on mosquitoes. Instead, these natural areas become habitat for desirable species such as sand-hill cranes, dragonflies and butterflies. Native shorelines and buffer gardens can improve the health of your beautiful lakes, bringing them back to center stage in your community.