Chicago flood

The Chicago flood happened on April 13, 1992. It was caused 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 of water. No one was killed or hurt during the incident. It caused an estimated $1.95 billion of damage.
The tunnels.
In 1906 a small tunnel system opened under the downtown. The streets were crowded with horse-wagons. The tunnels were meant to carry things inside with no horses. Coal and "ashes" (burnt coal) were always part of the business. Most tunnels were wide and tall. The walls were made of concrete about thick. The tracks were "gauge" (the distance between the rails) and an electric "trolley" wire was mounted on the ceiling. Two axle electric motor locomotives used electricity from the trolley wires. They pulled small freight cars.
There were up to of tracks under the downtown. They went under most streets in a space about by . The tunnel under Kinzie St. went under the Chicago River.
The tunnels were a failure. Not enough buildings connected with them and there wasn't enough business. Then trucks replaces horses and the tunnels had even less business. Most buildings stopped using coal and then there were no ashes. The tunnels lost money until they were closed in 1959. After then the city owned them. They are now used for telephone and other wires.
The bridge.
The Kinzie St. bridge is one of many drawbridges over the Chicago River (a railroad bridge next to it is left open). When it was built in 1909 it opened many times a day. It has a control tower where a bridge-tender could see both ends of the bridge when raising and lowering it. Now it does not open very often and nobody works there. "Pilings" (logs pounded into the ground) were bumpers to stop boats from hitting the bridge.
When the pilings were being changed one of the new pilings was moved a little. Nobody thought it was important. The company filled out some paperwork but didn't do anything with them. The city inspectors didn't check the plans or the work. Changing the pilings seemed simple so nobody was careful.
When the new pilings were put in they pushed an older pile into the tunnel. The concrete cracked and a little mud started leaking into the tunnel. An inspector for a cable TV company saw the leak and took pictures. He told the city. Nobody thought it was very important and work was slow.
The flood.
In the morning of April 13 the tunnel wall broke and water started coming in. The tunnels are below river level and filled up with water. Twenty four older buildings connected to the tunnels. Their basements started to flood. Most had doors closed and locked but the doors were not waterproof. The City Hall/County Building had to move legal paperwork out of the basements. Other buildings also saved things. The tunnels connected to two subways that were closed. Some places not connected to the tunnels also flooded. A low part of an Interstate Highway also flooded. All electricity was turned off and the downtown was closed.
A whirlpool was seen by the pilings on the southeast corner of the Kinzie St. bridge (that was where the bridge-tender's tower was). A large construction company started to put gravel and sandbags into the hole (the hole was the size of a car). Later quick-drying concrete plugged it. Concrete walls were built in the tunnel on both sides of the river. On April 19, six days after the flood started, the leak was stopped. Two days later the water started to be pumped out. It was pumped out slowly so no other problems happened. On May 21 the pumping was done.
After the flood.
After the flood the tunnels were cleaned out and fixed up. The tunnels were still strong, they were just wet and dirty. Before the flood the city was getting ten million dollars a year in rent from wire companies. Mud (and old train cars left behind) was taken out. Waterproof doors and walls were built and more "sump-pumps" put in. Now the tunnels are clean, painted, and still used.