Chicago Deep Tunnel Nears 100% Capacity After 8 Inches of Rain, Raising Flood Risk
Updated
Updated · Chicago Sun-Times · Jul 6
Chicago Deep Tunnel Nears 100% Capacity After 8 Inches of Rain, Raising Flood Risk
3 articles · Updated · Chicago Sun-Times · Jul 6
Summary
11 billion gallons of stormwater are now sitting in Chicago’s Deep Tunnel system, the first time the anti-flooding network has come close to full capacity.
More than 8 inches of rain over 30 days — including over 3 inches on July 3-4 — saturated soils and pushed McCook to 96%-100% full and Thornton to 94%.
11 south suburban communities now face river-flooding threats, while Chicago logged sewer overflows into the Chicago River, nearly 600 flooded-street complaints and almost 400 basement-water reports since Thursday.
McCook has already hit capacity six times in 2026, after filling only five times total from 2021 through 2025, underscoring how repeated wet periods are straining the system.
Experts say Deep Tunnel alone cannot prevent flooding as heavier, cumulative rainfall linked partly to climate change grows more common; a McCook expansion is not due until 2032.
Why is Chicago sitting on millions in federal flood aid while basements keep flooding?
Chicago's billion-dollar Deep Tunnel is full. Are green spaces the only answer left?
Chicago’s Deep Tunnel System at the Brink: 13 Billion Gallons Captured, Flooding Risks Rise After July 2026 Storms
Overview
In early July 2026, Chicago faced intense rainfall that pushed the Deep Tunnel system to its limits. The Metropolitan Water Reclamation District's reservoirs and tunnels captured 13 billion gallons of stormwater, but key reservoirs like Thornton and McCook neared maximum capacity. With more rain forecasted, the system’s ability to protect the city was threatened, as its buffer for additional precipitation was greatly reduced. This heightened the risk of localized flooding and overflows, making the speed of water treatment and discharge critical for community safety. The situation highlights the urgent need for both infrastructure upgrades and adaptive strategies.