Multiple rounds of heavy rain fell between July 2 and July 4, leading to flash flooding in streets and rising river levels across the greater Chicago region, with some municipalities reporting 8 to 10 inches of rain over the 48-hour period.
According to the MWRD, its two largest Deep Tunnel reservoirs are nearly at capacity.

Thornton Reservoir nearly full after heavy storms over weekend

The Thornton Reservoir, which serves many surrounding south suburbs, is nearing capacity after storms swept through the area this past weekend. FOX Chicago’s Joanie Lum has the latest on its condition.

This weekend’s heavy rainfall in the Chicago area has helped to fuel record amounts of stormwater being stored in Cook County’s reservoirs, nearly 20,000 Olympic-size swimming pools’ worth.

A soggy start to summer with near-record rainfall has left Chicago’s Deep Tunnel stormwater retention system almost full.
The Deep Tunnel, which was constructed over the course of more than five decades, is a system of underground tunnels and reservoirs that captures and stores stormwater and sewage that could otherwise overflow into waterways.

The Thornton and McCook reservoirs, designed to hold billions of gallons of rainwater, are nearly full.
As of Monday, July 6, the Metropolitan Water Reclamation District (MWRD) had stored over 13 billion gallons of stormwater in its deep tunnels and reservoirs following severe weekend storms that dumped 3.77 inches of rain on the Calumet Water Reclamation Plant alone.