Sir Thomas Bouch (25 February 1822 - 30 October 1880) was a railway engineer in Victorian Britain. He was born in Thursby, Cumbria and lived in Edinburgh. He is the inventor of the caisson and the train ferry (roll-on roll-off). He designed the first Tay Rail Bridge. Queen Victoria travelled over it at the official opening, and she awarded him a knighthood in recognition of his achievement.
However, the Tay Bridge collapsed on December 28, 1879 when it was hit by strong side winds. A train was travelling over it at a time, and 75 people died, among them Thomas Bouch's son-in-law.
The subsequent public enquiry revealed that the railway company sacrificed safety and durability in favour of stringent cost-cutting. Sloppy working practices such as poor smelting and the re-use of girders dropped into the sea during construction were factors in the bridge's collapse. As the engineer, Thomas Bouch was blamed for its collapse, however (his assistant Charles Meik merely left an impression that he "was aptly named").
Bouch's design for the Forth Rail Bridge had been accepted and the foundation stone laid, but the project was cancelled due to the Tay Bridge Disaster. It was later revised by Sir Benjamin Baker.
Thomas Bouch retired to Moffat, his health deteriorated, and he died while the public enquiry into the disaster was still underway. He is buried in Dean Cemetery in Edinburgh.