11 a.m. Storm Update: MWRD continues to manage flow after yesterday’s storm

After a night of heavy storms, the Metropolitan Water Reclamation District of Greater Chicago's (MWRD's) Tunnel and Reservoir Plan (TARP) is protecting the quality of the region's water resources and mitigating flooding for 3.71 million people served through combined sewer systems.

TARP consists of three reservoirs and four tunnel systems. At this time, TARP is holding more than 2.4 billion gallons of water. Here is the breakdown:

• McCook Reservoir is approximately 51 percent full holding 1.8 billion gallons. The McCook Reservoir has 3.5 billion gallons of capacity, serving central Chicago and 36 municipalities covering 252 square miles on the Des Plaines and Mainstream Tunnel Systems.
• Thornton Composite Reservoir is approximately 8 percent full holding 600 million gallons. The Thornton Composite Reservoir has 7.9 billion gallons of total capacity, including 4.8 billion gallons of combined sewer capacity, serving 91 square miles on the Calumet Tunnel System, covering the South Side of Chicago and 13 south suburban municipalities.

Before severe storms, the MWRD lowers the levels of the Chicago Area Waterway System at its Lockport Powerhouse to provide added capacity in local waterways. On Tuesday afternoon, the MWRD issued an overflow action alert encouraging homeowners and businesses to conserve water, when possible, to provide more capacity in the sewers.

"Our staff is working to manage billions of gallons of water at our seven water reclamation plants and through our Tunnel and Reservoir Plan which is operating to protect our water environment and mitigate flooding," said MWRD President Kari K. Steele. "We encourage everyone to conserve water when rain is predicted."

When it rains, stormwater flows through smaller, local pipes owned and maintained by local municipalities. This water then flows to the MWRD's large intercepting sewers that convey wastewater from homes and stormwater from local sewers to the MWRD's water reclamation plants for treatment. In heavy rainfall, the water flows past the MWRD intercepting sewer and falls into a TARP tunnel to help keep this water from overflowing into our waterways and backing up in our basements. TARP has huge capacity, but water must pass through local sewers first before it even reaches the TARP system.

Learn more about TARP and other MWRD programs

How you can help prevent flooding