The System Built To Prevent Massive Floods In Chicago Near Capacity After 'Stunning' Rainfall

Key Points:

• Chicago's Deep Tunnel stormwater retention system is nearly full due to an unusually rainy start to summer, with the Thornton Reservoir at 94% capacity and the McCook Reservoir completely full.
• The Thornton Reservoir, serving the South Side and 13 south suburban municipalities, holds 7.4 billion gallons of water, marking its highest level ever recorded and raising concerns about potential river flooding if it reaches capacity.
• The McCook Reservoir, which serves central Chicago and 36 municipalities, has reached capacity six times this year, surpassing the total number of times it was full between 2021 and 2025; its expansion to increase capacity is expected to be completed by 2032.
• Chicago has experienced significantly above-average rainfall since June 1, with some areas like Midway Airport recording the second wettest start to summer since 1928, and Independence Day weekend bringing more rain in 48 hours than the typical total for July.
• Illinois has seen a long-term increase in annual precipitation and more frequent heavy rain events, contributing to flooding challenges, though drier weather is forecasted for the early part of the coming week before storms return later.