Bridges over the River Wye
Bridges from Chepstow to Whitney-on-Wye - this page
Of the many little streams that begin on the slopes of Plynlimmon, two have particular significance: they are the officially named sources of the River Severn and the River Wye. The sources are only about 3 km apart. In principle, two nearby drops of rain falling near the summit of Plynlimmon could find their way into the two different rivers, and then they would go their separate ways, with no possibility of meeting again until the union many miles later, of the Severn and the Wye, near Chepstow.
Both rivers pass through or near well known and historic towns, and under famous and historic bridges. Other pages in this web-site describe the bridges of the river Severn: this page is devoted to the bridges of the Wye. The bridges will be described in order from mouth to source, though only a few of them have so far been photographed for this web-site.
You will see that the piers of many Wye bridges are surrounded by stone or concrete platforms. These are to avoid the deadly effects of scour, which washes away material from the bases of piers, sometimes to the point where the foundations are attacked. You can sometimes see the effects of scour around a timber post or a boulder that is embedded in a sandy beach, after the tide has receded. Many of these pictures were taken when the river was low; at other times of year the river would be much deeper, and the platforms would be well under water. The diagrams below, showing sections at right angles to the flow, show the general effect.
The first picture, taken in mid summer at a time of very low water in the river Wye, shows the very large depression that has been scoured out of the shingle. The piers will have been founded further down on good ground. The notice is for the benefit of people who wish to swim or paddle in the water, which is in any case dangerous because of swirling currents.
The Wye, like the Severn, rises near the top of Plynlimmon in Wales, and is fed by numerous mountain tributaries. Consequently, it is subject to occasional fierce flooding, which has taken away many a bridge in earlier times. Even now, who can say that an unusually strong flood will not do damage?
These pictures show the old bridge at Hereford, the second being a simulation of the level reached early in 2004, though without the turbulence that would have occurred. Early in 1795, a particularly severe flood affect a large part of the Wye valley, damaging or destroying several bridges.
In this list of seventeen bridge failures, three are attributed to scouring.
Builders and river users in the lower reaches of the Wye and Severn face yet another problem - one of the highest tidal ranges in the world. In the 18th and 19th centuries, when navigation went far up these rivers, the problem of providing clearance was added to the difficulties already presented by the creation of adequate foundations in these waters.
Why were the Wye bridges built where they were built? Click here.
This page is far from complete. Bridges that do not have a thumbnail picture or a link in this panel are not yet described in the page. Bridge pictures will be added when they are available.
Bridge Sollers - bridge being rebuilt
Going upstream from Whitney, we reach Wales: the Welsh bridges, listed below, are described in Wye Bridges Two.
B4594 near Erwood
40 Pont as Ithon A470
Rhaedr Gwy foot bridge
Rhaedr Gwy road bridge
Rhaedr Gwy foot bridge
Pont Marteg foot bridge
Pen-yr-ochr - Dolhelfa
55 Clochfaern ?
60 Pont Rhydgaled
To be continued . . . .
Details of the bridges which have been photographed so far are given in the following panels.
North of the Severn cable-stayed bridge, and west of the suspension bridge, just upstream of the mouth of the River Wye, a cable-stayed bridge with a main span of 770 feet/235 m takes the M48 (previously labelled M4) across the river, near the Welsh end of the Severn suspension bridge which carries the same road. Here are some pictures.
The second picture has been squashed sideways, to show the undulations in the steel deck, which sags between the supports. The high points are at the anchorages of the bundled cables into the deck, and at the towers, and are marked by horizontal black lines. Each cable contains twenty spiral strands, arranged in a triangular cross section with five layers, with 6, 5, 4, 3 and 2 strands per layer, respectively. The flat bottom of the section allows the cables to rest on the flat tops of the towers, held by simple clamps, avoiding the need for specially shaped saddles.
The stiffness of the box girder span is used to transmit torsional forces to the abutments, which are the only supports that are not on the centre line. This technique is used in many modern concrete spans and steel spans, supported either by piers or cables, because the simplicity provides a cost saving that is not lost by the cost of the torsional stiffness. For box girders on piers, the potential untidiness of two rows of piers is avoided.
The towers are also of steel box construction. Their height has been increased since these pictures were taken, and the single pair of cables on each span has been replaced by a set of cables in harp formation. These modifications were made because of greatly increased traffic. The sag in the deck has been decreased with the smaller distances between suspension points.
Note the light traffic on this road, the motorway M4 which runs from London into Wales. These pictures were taken almost thirty years ago. As traffic built up, it became clear that a new Severn crossing was needed. This is described in the page about cable-stayed bridges. The road over the earlier crossing was renamed M48, and the M4 now follows the new route. It is much harder now to take pictures with no vehicles, and to avoid the vibration which persists after vehicles have passed.
To read more about the old and the new versions of this bridge click here.
Other sites about the M48 Wye and Severn bridges Construction
A few miles upstream we come to Chepstow, which once possessed a unique railway bridge, designed by Brunel. This bridge was both asymmetrical and inelegant, and only comprehensible when seen as a sort of test bed for the Royal Albert Bridge at Saltash. Its main span was an iron truss with a tube as the top member, in compression, and very few tension members. Here is a simplified diagram.
This bridge, as well as a truss, can also be seen as a very simple suspension bridge, self-anchored by the tube, or as a very simple cable-stayed bridge. It was used from 1851 to 1962, when it was replaced by the bridge shown below. The new spans were built on land and were slid in under the existing spans, which were then dismantled. The site itself is asymmetrical, with a vertical cliff on the east bank of the river, and low ground on the west.
Whereas Brunel's main span had been constructed mainly above the railway line, the new main span is mainly below, there being no significant navigational requirements. The new bridge uses some of Brunel's piers: the stumps of the unused ones being visible also. The main span is based on two very deep trusses, while the land spans are plate girders.
As you see from the pictures above, very close to the railway bridge there is a road bridge, which is of more recent date, carrying the A48. Placement of bridges in close proximity is fraught with aesthetic problems, and engineers often go to great lengths to solve them. The design of over-bridges on motorways often takes into account the possible clashes of alignment with others that drivers can see at the same time.
The transition from the box-girder main span and the side spans of the road bridge is made using a half-oval shape under the bridge. A more familiar type of transition is represented by the stress-reliever that is fitted to many plugs where the cable enters. A couple of bridge pictures are also included. Whenever a structure includes a sudden change in dimensions, there will be a stress concentration, which can be a source of failure, especially when fatigue is possible. Fillets and gussets are among the features that are used to reduce these concentrations. Mushroom heads on concrete columns can greatly reduce stresses in the concrete floor they support. More about this can be found in the pages about attachments and cracks. The Chepstow picture includes a side span of the railway bridge.
Here are more pictures from Chepstow.
At Chepstow, the designers of the road bridge decided to copy Brunel closely, building one wide span and numerous smaller ones. The piers are cylinders of about the same diameters as Brunel's the main differences being that the new ones are concrete, with stiffening walls connecting them. The main span is a steel box-girder, while the side spans are plate girders. The transition between them illustrates a very important principle: avoid sudden changes of stress whenever possible. Accordingly, the bottom plate of the main span does not suddenly end: there is a curved transition section into the first side span.
The new spans were slid into place under the old ones from a position on land to the west of the bridge. Demolishing the old spans was not a simple task, because the iron tubes were stressed by the suspension bars, and would have released energy if these bars were simply removed. Stored energy is of course present in any structure, but it presents a particularly severe problem in pre-stressed structures, where the forces can be great.
Chepstow's third bridge as we go upriver is the oldest, dating from 1816. It was designed and built by John Urpeth Rastrick and John Hazledine, in cast iron. As so often with arches, there is a slight sag in the main span. Loads are now restricted to 24 tonnes, which is far more than the designer and builder could have foreseen. The new A48 bridge takes most of the traffic now, while the old bridge carries the B4228. Note the very substantial piers, and the way that the thrust of each arch is carried through to the next one. An earlier bridge had a large pier in midstream, with wooden construction on the English side and masonry on the Welsh.
More pictures of Chepstow's old bridge -
Our first stop upstream from Chepstow is Tintern, but before reaching the undistinguished footbridge that was once a railway bridge, we look at the ruins of the Cistercian abbey, founded in 1131 and dissolved, along with hundreds of other religious establishments, by Henry 8th. What men can create, men can destroy. Enough remains to show that the abbey must have been a beautiful building. Now the only colours in the windows are the colours of nature outside, and the only roof is the sky. Good times to see Tintern abbey are spring and autumn, outside the tourist season. Already, having hardly begun our journey up the Wye valley, we get a taste of its beauty. Click here for pictures of Tintern abbey.
The single track railway bridge at Tintern has become a footbridge. From a distance it looks quite attractive against the landscape, but seen close up it is a rusting hulk, in great need of some attention. Some of the truss members are flat: others are flanged - it's a question of ties and struts. Like other Wye bridges in a flood plain, Tintern bridge has side arches. More pictures -
Next comes the delightful village of Brockweir, with a road bridge based on a lattice truss. It is tempting to think that a plate girder might have been simpler. Indeed it might, but at the time of its construction, it was easier to make small pieces of metal than large ones, and much easier to transport them. Contrast this with the old and the new railway bridge at Chepstow. This bridge shows very well the technique of thickening the compression bearing top plates in regions of greater stress. This bridge crosses the Wye in a deep narrow valley: it has no side arches.
The main road crosses the Wye at Bigsweir, on an attractive iron bridge with flood arches. It was originally a toll bridge, and the small toll house remains, on the right bank of the river. This bridge was designed by Charles Hollis, and opened in 1827. Trees at all four corners make good photographs difficult to obtain. More pictures are shown below -
A footway is cantilevered out from the railway bridge on the upstream side. The truss bridge is on a gentle curve, at a skew to the river, with the pairs of piers aligned along the river. Diagonal ties connect the columns. This is especially important for a curved railway bridge, to take the lateral force as a heavy train takes the curve. A change in direction means a change in velocity, which is an acceleration, which requires a force. The sway of the piers with each passing train might be slight, but the cumulative effect of a cyclic force can lead to fatigue cracking.
A spider has built its ephemeral web under the bridge. Completely recyclable - the spider eats it before building the next one - it has, like many another natural product, elastic properties that the works of man cannot yet reproduce. The web is ephemeral, but compared with the era of spiders on this planet, the age of modern industrial man is but a moment in time.
Not far south of Monmouth are the remains of two old railway crossings that converge on the right bank of the river. The downstream viaduct stops short of the river in a huge wall of masonry, but the other still crosses the river by means of a truss that is now rusting away. The decks of the truss spans comprise many transverse metal arches. Plants are growing on both the viaducts and the truss. This will accelerate the process of decay, as the roots force their way into the masonry, and the plants build up dust and soil around their roots on the truss, retaining water and speeding up the rusting process.
Near Monmouth the A466 road crosses the Wye on a multi-arch bridge which has been widened, as you can see from one photograph. The old arches are semicircular, but the new ones are much flatter. This reduces the resistance to flow in time of flood, as compared with long narrow arches. The road also crosses there flood relief arches, which are shown in the last two pictures.
Monmouth itself is not quite on the river Wye: it lies on the left bank of the river Monnow. But it is worth mentioning here because of the Monnow bridge, a famous fortified bridge, built towards the end of the 13th century, on the site of a 12th century timber bridge. Above the gateway are openings that allowed the guards to drop unpleasant things on intruders. The bridge now connects Monmouth with Overmonnow. Downstream of the Monnow bridge, a pipe bridge crosses the river, and not far from the confluence of Monnow and Wye, the A40(T) crosses the Monnow on a fairly standard concrete beam bridge.
The next bridge above Monmouth is a suspension footbridge at Biblins. It possesses many of the attributes of large suspension bridges, except that the hangers are all the same length, so the deck dips with the cables. In these pictures, you can see the main cables, the saddles which carry them over the towers, and one of the attachments to the anchorages, which are heavy concrete blocks. One the features which is now seldom seen is the series of cables which pass outwards and downwards from the deck, to limit the amplitude of wind-induced oscillations. Such cables were sometimes employed during the 19th century. A notice reminds people that oscillation is bad for the bridge, though some engineers from eight to eighty years old might find it difficult to resist the temptation to see how easy it is to excite a small amount of sway. Here are some pictures of the bridge at Biblins.
A short distance upstream from Biblins we find the river Wye flowing through a deep and narrow valley. Since it could not originally have flowed up and over the hill, we have to wonder whether the land rose very slowly, even as the river was cutting down through the rock. At any rate, the top of Symonds Yat rock affords splendid prospects of the river, which flows past both sides of the rock, and of a part of the county of Herefordshire. As in many other stretches of the Wye, we see steep ground on one side, and flat on the other, as if the river's meanders have taken it to the limits. Though there is no bridge at Symonds Yat, you can cross from Symonds Yat East to Symonds Yat West and back, by means of a ferry. A stout cable spans the river in a taut catenary. A smaller cable has a loop round the main cable, and is connected to a large punt. The operator throws the loop forward, and then relies on friction to pull the boat.
Going upstream from Symonds Yat we find Huntsham bridge, a tidy truss which rests on two old piers in the river. The clean appearance is produced by the use of hollow box section steel members. The bridge is very narrow, providing only just enough room for vehicles to move in one direction at a time. This was probably the result of using the existing piers. Also, on such a small road, the expense of a two-lane bridge might have been hard to justify.
Next we find a disused railway bridge, an old plate girder bridge resting on cylindrical piers. It is now only used as a footbridge, and is a good viewpoint for watching kingfishers. Nearby, large factory buildings slowly crumble, reminding us of the once thriving industries of the Forest of Dean.
Kerne Bridge, dating from 1828, is a splendid sight, comprising five fine arches, two of which only come into play in times of floods, which are more frequent than people would wish, though here they affect only the fields. The symmetry of the bridge has been spoiled by the addition of a ramp at the south-east end, to bring the road up to the level of the B4234, which is on the the slope of the hill behind the bridge. Note the decoration of the voussoirs - only simple radial cuts, but effective in lifting the design. It is little touches like these which reveal how much the builders regarded their work as more than simply utilitarian. In the water below the bridge you may see trout, and you may also see a kingfisher fishing from the branches above the water, or flying under the bridge at high speed.
Wilton bridge, completed in 1599 to replace a wooden bridge, carries the old A40 road over the river Wye near Ross-on-Wye. Details and photographs.
Bridstow bridge, completed in 1960, carries the A40 trunk road over the river Wye near Ross-on-Wye. It is 353 feet/108 m long, and comprises two cantilever sets and a suspended span. Details and photographs.
A few miles upstream from Ross-on-Wye, Foy bridge, a small suspension span, crosses the river. Trees prevent a good photograph being obtained. The deck is stiffened by a truss. The cables are slightly kinked at the centre. The plaque reads "ROWELL & Co Ltd ENGINEERS WESTMINSTER".
The anchorages are unusual: the eyebolts that hold the main cables, also link to cables that are connected to the feet of the towers. Perhaps this defines the geometry of the whole bridge when the eyebolts are tensioned. Another unusual feature is the use of long bolted clamps, not only near the anchorages, but near the towers as well. Short cables hang over the towers; these are clamped to long sections that hold the deck, and to shorter sections that connect to the anchorages. The deck has no apparent means of stiffening, and will oscillate gently in both torsion and translation, though with fairly strong damping. The inscriptions on the towers read "LOUIS HARPER A.M.I.C.E. MAKER ABERDEEN", though it was designed by E G Davies of Hereford.
The last picture illustrates a fault that is rare in real suspension bridges, but not uncommon in models - the hangers are too stiff. The picture has been compressed vertically by a factor of five to make this clear.
After Sellack Boat we find Hoarwithy bridge, based on steel I-beams, and Holme Lacy, based on concrete I-beams: these are modern spans. These are shown below. Note the weight-saving cellular construction at Holme Lacy. The earlier Hoarwithy bridge was an iron truss.
Next we come to Hereford, which has a railway bridge, two footbridges and two road bridges over the Wye.
Going upstream, we find the railway bridge first, a rather undistinguished plate girder bridge with the usual flood arches for the Wye. This bridge and the next appear to be in the country because no building was done on the flood plain.
Then we come across that rare find, the pleasant Victoria suspension bridge of 1897, in a position where it can be well seen and photographed. This example has tie-bars rather than cables. Note the unusual truss work on each side of the span. The trussed tower is typical of small suspension bridges.
One is ribbed, two are pointed, and all are different. You can clearly see the signs that the bridge has been widened. Every pier has a wide anti-scouring platform, because the piers are wide and the arches are narrow. The bridge was built in 1490, and had a gate that was demolished in 1782. The bridge was widened in 1826.
One of the pleasant features of the river Wye is that when the water is low, you can walk out on the shingle in many places, and with waders, you can walk right across. The river is very popular with anglers. We see also the tower of the cathedral, one of the Three Choirs cathedrals. This building is perhaps on a more human scale than those at Worcester and Gloucester.
Close to the old road bridge is the new one, which appears to be a very flat arch, an impression which is emphasised by the surface treatment. Unfortunately, the "arches" which have been indicated on the surface have not been provided with fake abutments: the arch shapes just stop at each end.
The first bridge upstream of Hereford is at Bridge Sollers; this bridge has been replaced by a fine new one, and no picture of the old one will appear in this page. Change must occur, and we cannot indefinitely preserve every old structure, but we surely need to conserve the finer examples.
The new bridge is a beam bridge, based on continuous non-haunched steel I-beams, treated so as to obviate the need for painting. A stable surface layer has rapidly formed, which will prevent further corrosion or rusting. The design is neat, with two narrow concrete piers of streamlined shape, ideal for this river with its tendency to flood after storms in the mountains upstream. No doubt quite soon in the life of this bridge, the piers will be almost completely submerged.
Who would have thought that there could be a disadvantage to the narrow piers at Bridge Sollers? This picture of the bridge at Newbridge-on-Wye reveals what it is. The large tangle of old tree branches would probably not have become impaled on the old type of wide masonry piers. This mass of wood not only increases the effective width of the pier - it decreases the effective span.
Moving on from Bridge Sollers we encounter the magnificent brick bridge at Bredwardine, with six arches, two of which are for flood water only. Like the Kerne bridge, Bredwardine bridge has to contend with different levels at the ends, but unlike Kerne, Bredwardine is unashamedly asymmetric. The builder has placed most of the slope at the lower end, which has the merit of raising the whole bridge, a major concern in time of flood. In a strategic position overlooking the eastern end of the bridge there was a motte and bailey. Another bridge in such a location is Loyn bridge, which was overlooked by an earthwork known at one time as Castle Stede. Pictures of Loyn bridge can be found elsewhere in this site.
To deal with the occasional very fast flow, the has cutwaters and large platforms against scouring. On each side, only two of the cutwaters are taken right up to form refuges for pedestrians; this avoids the monotony that might have resulted from uniformity. At about deck level there is some modest decoration. Unusually for such large brick arches, keystones are included. Large drainage channels allow water that runs down the hill to the bridge to escape into the river, rather than flood the road, which has its lowest point quite near the bridge. This bridge is situated in a pleasant setting from which it can be well seen.
The bridge is not the original: it is a faithful copy built in 1922, the original bridge having become unsafe. The older bridge had already needed repair after the flood of early 1795. One wonders what would happen today if such bridges were to be declared unsafe. Already some rather uninspiring designs have replaced older Wye bridges. Whitney toll bridge
The next bridge, at Whitney, is also noteworthy, for it is a toll bridge and a grade II listed building. The income was decreed as tax free by a 1779 Act of Parliament. The original masonry bridge, built in 1779, was washed away by the river, as were two subsequent efforts. One of these events was caused by the great flood of 1795. The current bridge dates from early in the 19th century. It is not obvious that wood is more durable than stone, but it is probably a lot cheaper to replace when the floods take their toll. Normally we associate tolls with massive modern undertakings, but there are several places in England were ancient toll rights are exercised. These can spoil your travel plans if you reach them unexpectedly in the middle of the peak traffic period. There is such a toll bridge at Eynsham, near Oxford, which creates very long queues, and another one near Bath.
The three wooden spans at Whitney are propped beams, as you can see from the top left corner of this photograph. (Or could they be considered as three-segment four-hinged arches with stabilisers?) The general views are looking upstream, and on the far side of the cutwaters you can see the sheets of metal which protect the timbers from flood water and debris.
In the diagrams above, the deck was assumed to be in segments which spanned the piers. But if the deck were continuous, the compression in the centre of the spans would induce tension above the piers, in order to maintain the same total length, as in the first diagram below. The assumption here is that the deck is fixed at the ends. Such a bridge is somewhat indeterminate in both type and forces. The deck could be post-tensioned or post-compressed to attain a situation with the same polarity of stress throughout.
In the second diagram, we revert to a segmented deck, but with the joints near the props. Now the bridge is based on cantilevers.
We see that what looks like a simple structure allows of several different interpretations, depending on the exact mode of assembly. Unfortunately, it is not possible to get close enough to the bridge to examine the details.
Note the iron sheets which shield the wooden cutwaters against the ferocious flood waters and floating debris which sometimes hit the bridge. All along the Wye valley, you can see bridges with extra spans to accommodate flood water, and as we ascend the river, we see cutwaters, and platforms around the piers to combat scouring, a great enemy of bridges. The piers were originally essentially planar structures: the present shielding being a 20th century addition.
You will have noticed that the thrust of the two masonry arches is contained by the piers, Roman style, for they must have been placed before the timber was added, and they survive if the timber is washed away. The Romans were very conservative about the ratio of span to width of pier, reasoning that floods or enemy action, in destroying one span, would not take out the rest. With such a design, the arches could, if required, be built one at a time, using the same centring throughout. For arches in which the thrust propagates throughout the bridges, all the spans must be built together.
Building sturdy arches of small span with wide piers may seem like a good idea, but this type of construction reduces the area available for the flow of water. Compare the open construction at Bredwardine, downstream and up-page. Admittedly, there the river is rather wider, which helps greatly.
As we go upstream, just before reaching Hay-on-Wye, we enter Wales. For bridges in Wales, please see Wye Bridges Two.
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