Most flooding is not in the floodplain

Sewer Overflow, Nicollet Island Commission.
Sewer Overflow, Nicollet Island Commission.

In Illinois, a state study shows that most urban flooding occurs outside the FEMA-designated flood zone. This counterintuitive fact arises from historical patterns of building and water infrastructure construction and management, which are designed to move water off land and into (aging and deteriorating) sewer systems as quickly as possible.