Drought, then flooding? After the summer and fall of drought, and a winter worrying about whether the precipitation levels would be enough to carry people through the next season, rivers in the Midwest are now flooding due to heavy rainfall. Chicago has been particularly badly impacted by the heavy rainfall.
Midwest Storms: The Flood Report
As of Thursday, April 18th, flood warnings and flood watches were in place from northeastern Oklahoma to Missouri, northern and central Illinois, southern and central Wisconsin, and parts of Lower Michigan. While rainfall is heaviest in these areas, the weather report shows a band of rain from Texas into Canada.
Chicago has been particularly drenched: seven inches of rain fell on Chicago in twenty-four hours, and water filled up the storm sewer system. Normal April rainfall totals just under four inches in the city: That’s almost double the monthly rainfall in a single day. The storm sewer system had trouble holding all of the water, and there have been flash floods and road closures. Over 600 flights have been cancelled at O’Hare Airport.
Why is There Flooding in the Midwest?
Spring flooding occurs for a number of reasons. In the spring, warmer weather leads to snow melt, causing rivers to rise even when it is not raining. Combine this with heavy rainfall, and you have a recipe for flood conditions. Rain often falls and soaks into the ground, replenishing the groundwater and making its way slowly to rivers or lakes. When multiple heavy rainfall events occur one after another, the ground can become saturated with water, and the water simply flows across the surface to the nearest water body.
In urban areas, conditions are even more challenging. Urban and suburban areas often rely on storm water systems to move water from the streets into rivers, lakes, and the ocean because urban areas are covered with impermeable surfaces like roads and sidewalks. When water falls on the pavement, it doesn’t soak in and move slowly. Instead, it moves very quickly across the surface and into drains. During extreme weather events, this efficient water delivery system can get used to its maximum. The water from the drains rushes into rivers, hitting the rivers all at once and leading to a rapid rise in water levels.
Flood Mitigation: Slowing Down the Water
When we think of flood preparation, we often think about keeping it away from homes using levees – human-constructed barriers along the sides of a river. We may also think about the frantic sandbagging of homes that happens before and during a flood. However, there are longer-term solutions as well.
Using more permeable ground cover such as gravel will allow water to sink into the ground instead of moving quickly to a river. Creating wetlands or maintaining wetlands can help with water storage in rural areas, while in urban areas, street-side rain gardens near drains can slow down the water and bioswales can help filter and channel it. In fact, Chicago has created over 40 green infrastructure demonstration projects that include rain gardens, bioswales, and permeable pavement. However, this extraordinary rainfall has reached far beyond what’s normal in the areas that it has affected.
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