For immediate release
May 18, 2020

8:30 a.m. MWRD Storm update

Over the last 96 hours, the Chicago metropolitan area has seen between 6 to 8 inches of rainfall. The levels of rainfall varied across the region with more falling in the northern suburbs and less in the south suburbs. From May 14 to May 17, the National Weather Service reports that 7.88 inches of rain fell at O’Hare and 6.22 inches of rain fell at Midway with higher localized totals across the area. For the entire month of May, 8.19 inches of rain has fallen.

To mitigate the impact of the storm event, we have reversed the flow of the Chicago Area Waterway system to Lake Michigan at the Wilmette Pumping Station and at the Chicago River Controlling Works downtown to minimize overbank flooding.  There are several factors we consider when determining to release floodwater to the lake, including the rate the river water level is rising at each lakefront control location, whether the rainfall intensity is continuing or beginning to decrease, and the storm conditions on the radar.

Reversal incidents at each location includes:

• Wilmette Pumping Station reversed from May 15, 2020 at 2:30 a.m. to May 15, 2020 at 5:45 a.m.
• Wilmette Pumping Station started reversing May 17, 2020 at 3:45 p.m. and is still ongoing.
• Chicago River Controlling Works, downtown Chicago, started reversing on May 17, 2020 at 7:20 p.m. and is still ongoing. 

The Tunnel and Reservoir Plan is comprised of three systems and all are operating as designed. Combined they are currently holding more than 8 billion gallons. The current status of all TARP tunnels and reservoirs includes:

• McCook TARP System: 100% full, 4.970 billion gallons stored
  • Comprised of Mainstream Tunnel, Des Plaines Tunnel, and McCook Reservoir
• Calumet TARP System: 36% full, 3.017 billion gallons stored
  • Comprised of Calumet Tunnel and Thornton Composite Reservoir
• Kirie TARP System: Tunnel - 100% full, 71 million gallons stored & Majewski CUP - 243 million gallons stored

Currently the North Shore Channel and the Chicago River are higher than the lake. In order for the MWRD to reverse the flow of the Chicago Area Waterways, the river must be higher than the lake.

The U.S. Army Corps of Engineers provides data on the lake level.  

Storm event 5-18-2020_0.pdf