The felicitously named Tunnel Business Magazine looks at Chicago's Tunnel and Reservoir Plan (TARP):
Flooding became an increasing problem with the development of the areas surrounding Chicago occupying what had previously been drainage areas for the City. In the 1960s, officials began researching regional solutions to its various water and drainage difficulties. The Federal Clean Water Act of 1972 led to TARP's designation as the solution of choice and construction began in 1975.
Via the always-wonderful BLDGBLOG.