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THORNTON TOWNSHIP, Ill. — Here are WGN News, we’re suckers for a good time-lapse video – especially when it’s informative, like this one from the Metropolitan Water Reclamation District of Greater Chicago.

Their video, filmed last week, shows the Thornton Composite Reservoir taking on water for the first time.

“A stormy Thanksgiving holiday resulted in 400 million gallons of combined sewage and stormwater flowing into the reservoir where the water level reached 17 feet,” according to their YouTube page.

And:

Though this is a lot of water, it’s only five percent of the reservoir’s 7.9 billion gallon capacity. The water will remain in the reservoir until it is pumped up to the MWRD’s Calumet Water Reclamation Plant to be cleaned.

FIVE PERCENT!

According to The Chicago Tribune, the reservoir cost $429 million and is designed to ease flooding on Chicago’s South Side and in 14 suburbs, including Calumet Park, Dolton, Markham, Riverdale and South Holland. It’s been nicknamed, “The Grand Canyon of the South Side.”

A little more info from their YouTube page:

A major part of the Tunnel and Reservoir Plan (TARP, or “Deep Tunnel”), the Thornton Composite Reservoir provides flood protection benefits for 556,000 people in 14 communities throughout the south side of Chicago and south suburbs. It also protects 182,000 homes, businesses and other facilities and improves water quality in the Calumet Rivers and Calumet-Sag Channel by preventing combined sewer overflows.