All has to do with the Deep Tunnel project, they regulate the amount of storm water into the system so that they do not have to open the locks from the cal sag channel into lake Michigan...the nice thing about Chicago area is that all of our waste water heads south to the Mississippi, not into the lake system...at least it is nice for the great lakes people...southerners..not so sure ...
Also there are retention ponds here in oak lawn, they use valves to regulate the release from the retention ponds, the whole sewer system is dated to about the 1920's - next big MWDR project is revamping the storm drainaige system from Burbank south..This is the first year in about 10 years that our street corner has flooded, so there has been a lot of rain here, all the ground is soaked ,nowhere else for the water to go..
NwBie