River Tay Dochart until it flows into Loch Tay at Killin. The River Tay emerges from Loch Tay at Kenmore, and flows from there to Perth which, in historical times, was its lowest bridging point. Below Perth the river becomes tidal and enters the Firth of Tay. The largest city on the river, Dundee, lies on the north bank of the Firth. On reaching the North Sea, the River Tay has flowed from west to east across central Scotland. The Tay is unusual amongst Scottish rivers in having several major tributaries, notably the Earn, the Isla, the River Tummel, the Almond and
Tay Rail Bridge Bouch had used the technique for viaducts including the Belah Viaduct (1860)) on the South Durham & Lancashire Union Railway line over Stainmore, but for the Tay Bridge, even with the largest practicable caissons the pier dimensions were constrained by their size. Bouch’s pier design set six columns in a hexagon maximising the pier width but not the number of diagonal braces directly resisting sideways forces. The engineering details on the Tay Bridge were considerably simpler, lighter, and cheaper than on the earlier viaducts. On these the machined base of each column section docked securely into a machined enlarged section