Subsequently as a consulting engineer, he helped develop the caisson and popularised the use of lattice girders in railway bridges.

)[2][page needed] Others had had similar ideas, but Bouch put them into effect, and did so with an attention to detail (such as design of the ferry slip) which led a subsequent President of the Institution of Civil Engineers[3] to settle any dispute over priority of invention with the observation that "there was little merit in a simple conception of this kind, compared with a work practically carried out in all its details, and brought to perfection.

Bouch did the initial survey for the Edinburgh Suburban and Southside Junction Railway, laid out tramway systems in Edinburgh, Glasgow, Dundee and London, and designed the Redheugh viaduct a road bridge across the Tyne at the same height as and not far upstream of Stephenson's High Level Bridge.

Bouch designed the first Tay Rail Bridge while working for the North British Railway, and the official opening took place in May 1878.

The subsequent public inquiry revealed that the contractors to the railway company sacrificed safety and durability to save costs.

Sloppy work practices, such as poor casting of the metal, and the re-use of girders dropped into the estuary during construction, were factors in the bridge's collapse.

Analysis of the archives has shown that the design, which featured cast-iron columns with integral lugs holding the tie bars, was a critical mistake, because cast iron is brittle under tension.

Many similar bridges had been built using cast-iron columns and wrought iron tie bars, but none used that particular design detail.

His assistant, Charles Meik, conveyed the impression that he "was aptly named", implying that he had no real influence over the design and construction.

[12] Thomas Bouch bought a country house in Moffat, "his health", already not good, "more rapidly gave way... under the shock and distress of mind" caused by the disaster.

"In his death", said the journal of the Institution of Civil Engineers, "the profession has to lament one who, though perhaps carrying his works nearer to the margin of safety than many others would have done, displayed boldness, originality and resource in a high degree, and bore a distinguished part in the later development of the railway system".