St. Louis, Mo., hides four miles of River Des Peres in tunnels beneath Forest Park
(UI) — Deep beneath Forest Park lies a hidden system of tunnels carrying the River Des Peres, which is nearly half of the river’s roughly 10-mile course, according to Fox 2 Now. The enclosure was originally implemented to mask the foul conditions of the open stream during the early 1900s as St. Louis expanded.
Today, that system remains vital. The tunnels carry mixed wastewater and stormwater to Lemay Treatment Plant through what’s known as the Forest Park Junction Chain, where flows from multiple lines converge, Fox 2 Now reports.
MSD officials caution that this is not a navigable river. They warn of dangerous sewer gases and rising water levels during storms. Modern tunnel work now relies on massive TBMs—making the hand-dug, 29-by-23-foot tunnels constructed over a century ago a remarkable engineering achievement.
To bolster capacity, MSD plans a new network of 15–16 miles of deeper tunnels - up to 250 feet underground - to add roughly 300 million gallons of capacity. That project is scheduled for completion by the late 2030s.
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