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The newsletter I sent on Tuesday explaining what happened during the major storm of June 30–July 1 didn’t tell the whole story. It was worse than I thought. Thanks to some of the responses I received, I realized that I had failed to account for the intensity of the storm. I had been provided with information about the duration of the rainstorm, but not about its intensity and there were several additional factors that added to the drama and damage this storm caused.
Permit me, then, to add to the account.
First, it’s important to note that the ground was already saturated because there were really three storm events in one day — two rainstorms of lesser intensity and then a big unleashing just before 10 p.m. Moreover, evaporation was occurring at about half its normal rate, meaning the ground was staying saturated longer. When the ground is saturated with water and can’t absorb any more, this adds to runoff and loads more water into the sewers through leaking pipes and illegal connections (see “infiltration and inflow”).
Second, I had been thinking that some places, such as Wilmette, received more than three inches of rain over the six hour duration of the storm. But the reality was different. I called my friend and meterologist Rick DiMaio who was able to provide me with more specific rain data.