City’s nightmare 40 feet below the city: A look back at the Great Chicago Flood

During the Great Chicago Flood of 1992, 250,000 gallons of water had the city drowning by the hour.

The leak that sprung in the old freight tunnels under the city quickly turned into a major flood often referred to as the "unseen catastrophe.”

It was a calamity that filled the basements of buildings on State Street, LaSalle Street and even the Merchandise Mart. Water rose to 7 feet, then 10 feet and up. It cut power and evacuated trading floors at the Board of Trade and the Mercantile Exchange. It closed major retails stores like Marshall Fields and even left the Merchandise Mart wet and flooded.

Water poured in from the bottom up. But where was it coming from?

Back in September of 1991, wood pilings were driven into the Chicago River to act as bumpers for the Kinzie bridge house so passing boats wouldn't knock it over. Story has it, the contractor hired to install the pilings hit an  underground freight tunnel in the process creating a slow leak that got bigger and bigger with time until the tunnel gave way seven months later: April 13th, 1992.

WGN’s Julie Unruh talks to the major players about that day, what happened and the fallout – both politically and in the city’s infrastructure.