Judging by the erosion shown at the Commerce Street crossing in Norwalk, the river must have been flowing right through the Wall Street tunnel!
It did indeed flow through the Wall Street Tunnel. By the time the floodwaters reached Norwalk the Norwalk River had been rushing down its whole 17 mile length in a torrent breaking Mill Pond dams*** along the way as it went; and in addition, in northern Norwalk the floodwaters from the Silvermine River got added ---- so..... there was one hell of a lot of water rushing into Norwalk!
Also --- and I suppose this is probably mentioned somewhere else in this thread --- there were TWO 1955 floods. The one that destroyed the Naugatuck, and Farmington, and Quinebaug rivers was Hurricane Diane on August 19-20. The one that washed down the Norwalk River basin (and Silvermine, and Rippowam rivers) was October 14-15. That one was NOT a hurricane, rather a somewhat localized pocket of extremely heavy rain centered in northern Fairfield and southern Litchfield counties.
*** This has nothing to do with the thread but I can't resist throwing in a personal note: one of the Mill Pond dams washed out was on the property of Stonehenge Inn on Route 7. It was rebuilt for sure --- and one day just three weeks short of the 20th anniversary of the flood there was a photo taken atop that very Mill
Pond dam of my wife and me on our wedding day. Thank God we're going strong 36 years after that photo!!!