The project just completed work on one of the major reservoirs used by the system. The Thornton Reservoir is a limestone quarry that can hold 8 billion US gallons (30,280,000 m^2)<p>Here's a video of the reservoir taking in 400 million gallons after a heavy rainfall last week:<p><a href="http://www.dnainfo.com/chicago/20151203/south-chicago/watch-400-million-gallons-of-stormwater-rush-into-chicagos-grand-canyon" rel="nofollow">http://www.dnainfo.com/chicago/20151203/south-chicago/watch-...</a>
I went on a tour to the bottom of the reservoir before it opened and it is massive. An engineering feat started almost 30 years ago coming together with this site and several move over the next decade to add capacity to the system in different areas of Chicagoland.
In The Netherlands (Rotterdam) we have something similar to deal with extreme water amounts: <a href="https://www.youtube.com/watch?v=xODdtcEdp5w" rel="nofollow">https://www.youtube.com/watch?v=xODdtcEdp5w</a>