Thomas Telford's Bridges Over the River Severn
The Severn was once the busiest river in Europe, and in view of its length, it is not surprising that some of the bridges were built by great engineers such as Telford. One of his ideas was a standard cast iron bridge of about 150 foot span, which reduced the amount of design work he had to do. Several of these are still in use across the Severn, though one was never built. Telford planned to build such a bridge across the Severn between Gloucester and Over, but some of the notables in Gloucester would not allow the use of cast iron, though in fact the bridge would have been invisible from the city. Telford had to build a very flat masonry arch, which was much heavier than the iron design. This in itself was a source of extra expense, and matters were made worse when the crown of the bridge sank about 25 cm when the centring was eased. The soil data available to Telford had not been adequate. The alluvial plain west of Gloucester is such that the city is built only on the east of the river, apart from a small settlement on Alney Island, which suffers flooding almost every year. Nothing practical seems to have been done about this.
Among the many splendid arch bridges over the River Severn are some excellent designs by Thomas Telford, who built numerous elegant bridges in cast iron, some of which are still carrying vehicular traffic. He lived from 1757 to 1834. His career in civil engineering dates from around 1785. He designed magnificent canal aqueducts and bridges, probably the most famous being the Menai Strait suspension bridge, with a span of 580 feet/177 m, a record in 1826. The great flood of 1795, which destroyed or damaged numerous bridges over the river Severn and the river Wye, took only one of Telford's, that at Buildwas.
Thomas Telford was one of Britain's greatest engineers, but like Joseph Locke's, his name has been overshadowed by those of the Stephensons and more particularly by that of the younger Brunel, who seems to be the only engineer well known to the media and to most non-technical people in England.
To read more about Thomas Telford, try this book, which is excellent on both technical and historical topics, and is highly recommended - Telford's Britain by Derrick Beckett - David and Charles - ISBN0-7153-8558-7 - T. Another book about Telford is Thomas Telford by LTC Rolt - Longmans.
The Mythe Bridge near Tewkesbury
Near the junction of the Rivers Severn and Avon close to Tewkesbury another Telford bridge, this time of cast iron, carries the A438 over the Severn at The Mythe. The span is 170 feet/52 m. Some pictures are shown below.
The road narrows to one lane, with traffic lights permitting flow in only one direction at a time.
The road signs refer to a weak bridge with a weight limit of 17 tonnes. But of course when Telford designed this bridge it was only intended for horses and carts and pedestrians. Seventeen tonnes is a large load that would have been considered absurd at the time. The bridge is of cast iron construction with triangulated trusses, crossing the river in a single span. There is now a pronounced dip in the middle, seen in the picture of the roadway, and in the fifth picture, which has been squeezed, showing that the abutments must have moved slightly further apart, just as they have at Over.
At each side of the main arch there are several very narrow pointed arches, presumably to allow flood water through. Why did Telford not use a simple round arch at each end in order to reduce the resistance to flow? Perhaps these narrow arches were easier to build in a place where side-thrust was not desirable. Perhaps they are not for flood water at all. Perhaps he simply liked the design.
The Mythe bridge was manufactured in 1826 by William Hazledine, a well known builder of bridges. Apparently Telford was not the original designer at the site - a Mr Moneypenny is said to have started construction, before the contract was transferred to Telford.
Holt Bridge or Holt Fleet Bridge
Holt Fleet bridge, with a span of 150 feet/46 m, is rather similar to the Mythe bridge. It was built between 1826 and 1828, by William Hazledine. In 1928 it was strengthened. A curved sheet of concrete was made around all the lower ribs, and concrete was also added around upper ones. Given the techniques at the time, this was probably all that could be done, while allowing Telford's basic structure to show through. It was a sensitive piece of repair work.
The fourth picture shows a detail. The concrete encases the lower ribs of the arch over the full span and width. But the only upper ribs that are encased are the outer ones, except near the abutments, where all are encased.
Unlike the Mythe bridge, Holt Fleet bridge has two semicircular arches at each end, built in old red sandstone.
This elegant three arch bridge spans the River Severn at Bewdley, carrying the B4190 road. Some flood arches with grills can be seen at the right. Unfortunately the scale of the flooding in recent years has rendered such measures irrelevant, because of the very large volumes of water coming down from the Welsh mountains. Thomas Telford built this bridge in 1798.
Visit Severn bridges book for details of a very useful book by Chris Witts, who has spent much of his working life on the River Severn. This book, called "A Century of Bridges", includes information, a grid reference, and a drawing by the author for every bridge, even including notes about demolished bridges and some history. A Century of Bridges, ISBN 0 9532711 0 2, is published by River Severn Publications, Gloucester.
Another very interesting book by the same author is called "Along the Severn from Source to Sea", ISBN 1 873877 31 5. This book is published by Reardon Publications, Leckhampton, Glos.
Telford's Britain by Derrick Beckett - David and Charles - ISBN0-7153-8558-7
Link to Atlas of Thomas Telford's Bridges -
Biographies of Severn bridge designers -