Chicago Flood
The Chicago flood occurred on April 13, 1992, when the damaged wall of a utility tunnel beneath the Chicago River opened into a breach which flooded basements and underground facilities throughout the Chicago Loop with an estimated 250 million US gallons (1,000,000 m3) of water.
Rehabilitation work on the Kinzie Street Bridge crossing the Chicago River required new pilings. However, when the City of Chicago specified that the old pilings be extracted and replaced by the new ones, the Great Lakes Dredge and Dock Company reported back that the old pilings were too close to the bridge tender's house, preventing proper removal without the risk of damaging or destroying the house. The City of Chicago then gave permission to install the new pilings 3.5 feet South from the old pilings. Unbeknownst to the crewmembers that began work at the site, beneath the river was an abandoned Chicago Tunnel Company tunnel that had been used in the early 20th century to transport coal and goods. One of the pilings on the east bank was driven into the bottom of the river alongside the north wall of the old tunnel. Although the pilings did not actually punch through the tunnel wall, the clay soil that was displaced by the piling eventually breached the wall, allowing sediment and water to seep into the tunnel. After some weeks, most of the clay between the water and the breach had liquefied which rapidly increased the rate of flooding in the tunnel. The situation became very serious because the flood doors had been removed from the old tunnels after they fell into disuse.
A telecommunications worker inspecting a cable running through the tunnel discovered the leak while it was still passing mud and forwarded a videotape to the city, which did not see anything serious and began a bid process to repair the tunnel. The CTC tunnels were never formally a public responsibility, as most of them had been dug clandestinely, many violated private property, and the collapse of the operator had failed to resolve ownership and maintenance responsibilities. Meanwhile, the mud continued to push through until the river water was able to pour in unabated, creating an immediate emergency.
The water flooded into the basements of several Loop office buildings and retail stores and an underground shopping district. The city quickly evacuated the Loop and financial district in fear that electrical wires could short out. Electrical power and natural gas went down or were shut off as a precaution in much of the area. Trading at both the Chicago Board of Trade Building and the Chicago Mercantile Exchange ended in mid-morning, having a global effect, as water seeped into their basements. At its height, some buildings had 40 feet (12 m) of water in their lower levels. However, at the street level there was no water to be seen, as it was all underground.
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