The Panel for Historic Engineering Works (PHEW) ICE South West member is David Greenfield BSc PhD CEng MICE.
If you are interested in finding out more about PHEW and/or becoming involved, please contact David Greenfield using the following contact details.
This entry in I.K. Brunel's diary is dated 21 July 1828. He was 22 years old, and was touring the West Country while recuperating from serious injuries received during a disastrous inundation of the Thames Tunnel which had nearly killed him. During the previous three years he had assisted his father, Marc Isambard Brunel, in the pioneering project to drive a 1,200ft long tunnel beneath the Thames between Wapping and Rotherhithe.
By that time, Marc was one of the most celebrated engineers in Europe. He had enthusiastically encouraged his precocious son to follow him into the profession by ensuring he had an early grounding in technical and mathematical matters, followed by experience assisting Marc in projects ranging from suspension bridges to steam engines. So, even though he was only 22 the younger Brunel's opinion on the merits of a crossing of the Tamar at Saltash would have a sound basis - not least because Marc had himself already considered the feasibility of a bridge at this site.
In 1822 Marc, assisted by his son, designed two suspension bridges for the French Government, which were to be shipped out to Ile de Bourbon (now Réunion) in the Indian Ocean the following year. With spans of little more that 122ft, they were modest structures when compared with the 361ft span Union Suspension Bridge over the river Tweed, which had been completed two years earlier to the design of Samuel Brown and which was then the longest span suspension bridge in Britain. Now, in early 1822, Brown had been engaged by Plymouth and Cornish entrepreneurs to design a bridge to span the Tamar at Saltash, capable of carrying "all coaches, chaises, waggons, carts, horses, and foot passengers", so that the deprived country west of the Tamar could be "raised to an equal degree of improvement with other districts of England".
Brown's preposterously over-ambitious proposal of a 1,000ft span suspension bridge 90ft above the river naturally attracted Marc's attention; by way of comparison, the present Tamar Road Bridge is only 100ft longer and was the longest suspension bridge in Britain when it opened in 1961. Brown had reduced the proposed span to 830ft by December 1823, when the promoters sought Marc's opinion on what he referred to as "Bridges of that description when carried to an excess of bearing". He responded, "My observations are on the terror which is likely and unavoidably to be felt at the Bridge, being at an undue height, when passing over it. The middle is likely to sink down very rapidly." The proposals were abandoned soon afterwards.
Less than ten years later the younger Brunel, with some assistance from Marc, would be designing a suspension bridge of his own – over the Avon at Clifton, Bristol. And he would return to the Tamar estuary in the 1850s with his own proposals for an innovative structure to carry traffic (rail traffic in this instance) into Cornwall – the Royal Albert Bridge, which has become a lasting monument to his engineering genius.
By David Greenfield
Image Sources
Top image: Bristol University Library
Bottom image: Plymouth & West Devon Record Office
For more about bridges over the Tamar, see:
http://www.ice.org.uk/ICE_Web_Portal/media/southwest/Bridges-over-the-River-Tamar---ICE-South-West.pdf