--Illinois State Water Survey Report
Why do rivers flood?
Basically, flooding is water flowing onto previously dry land. The primary driver of flooding is precipitation—in general the more precipitation, the more water rises and spreads out, “flooding” more land. Other factors that significantly increase flooding in river systems include increased discharge from upriver, obstructions that constrain conveyance of water downriver, and loss of flood storage.
And, record-breaking floods are increasing. So-called 'hundred year floods' are now happening more often, increasing not just in frequency but in severity. As these floods have increased, so have the costs. And science tells us there will be more of these catastrophic flood events in the future.
What is a floodplain and why are floodplains important?
A floodplain is a relatively flat area along a river onto which river waters spread during a flood; they are some of the most valuable places on Earth, both for people and wildlife.
Floodplains provide a river more room as it rises, thereby reducing pressure on manmade flood protection structures such as levees and dams. They act as natural filters and improve our water quality. They recharge aquifers, the underground sources of water for many communities and agricultural production.
And, floodplains are home to some of the most biological rich habitats on Earth, providing critical wildlife habitat and many outdoor recreational opportunities.
Floodplains provide many benefits to people and nature.
What is the urban/rural connection between rivers–why should people in Chicago care about restoration efforts happening downstream along the Illinois River?
From a flooding standpoint, the Chicago area can generate a lot of storm water during rain events because there are so many impervious surfaces like rooftops, parking lots and roadways. Water runs off these impervious surfaces instead of infiltrating into the groundwater or being stored, and it makes its way to the Illinois River, increasing the river’s flows. Poorly managed, this storm water contributes to flooding downriver, which can lead to high flood-damage costs felt throughout the state.
What can we do to mitigate flood damages?
It's time for a different approach. We need a coordinated and systemic approach that helps eliminate such hardship and loss. We need to start being proactive rather than reactive when it comes to investing in flood management.
Repairing and rebuilding structures on the floodplain again and again doesn't solve the issues long-term, and we need to find a way to invest in designing a system that more cost-effectively handles more and larger floods, while providing so many other benefits. For every dollar we spend on mitigation efforts now, we can save $4 in future damages and receive numerous other added benefits as well.
We need to work with nature, not against it. At Emiquon we're working to include nature as part of our flood management plan. Give the river room to better accommodate these flood events. Having more room and eliminating pinch points upstream, can lower flood stages and associated damages upstream as well as downstream. And natural areas like Emiquon not only reduce risk for people – they provide ecological benefits by improving water quality and providing habitat for fish and water fowl – which can provide economic boosts for tourism, fishing and hunting. Some of these areas can be safely flooded during the largest floods, helping reduce flood stages.
According to the Illinois State Water Survey Report, if just 14 percent of the existing leveed floodplain along the Illinois River were allowed to flood during a 100-year flood event, 40 percent of the remaining leveed floodplain would be protected from overtopping or breaching. In other words, by allowing a relatively small portion of the floodplain to flood, additional protection is afforded to a much larger portion of the leveed floodplain.