Most tunnels have just one function - they allow traffic to go under a mountain or hill as an alternative to going over the mountain or cutting a big gap in it. Expensive to build and maintain.
So to find this tunnel in Cairo that provides a dual function was special. Yes, it takes US-51 under the Canadian National Railroad line, the tunnel was also built to function as a flood control gate, protecting downtown Cairo from the Ohio River.
It is a riveted steel plate floodgate that operates as a counterweighted structure that was originally designed to be lowered into place during floods. The flood gate was built by Stupp Brothers Bridge and Iron Company of St. Louis, Missouri. No longer used, it has been replaced by modular flood control gates that are stored off-site which would be inserted into a slot into the abutment of another nearby bridge in the event of a major flood today.
Clever engineering.
[Review 1244 of 2024 - 199 in Illinois - 22267 overall] read more