Category Archives: Previous attempts to cross the Estuary

Acknowledgements and further reading

Readers seeking further information on the historical context to the modern estuary crossings are advised to consult the two sources from which most of the material in the previous chapters has been taken.

Stephen Jones generously invited the Trust to make use of relevant material from his book, “Links with Leviathans” the third volume of his trilogy; “Brunel in South Wales” now published by The History Press of Stroud, Gloucestershire.  Chapter 4 of the book, entitled “Severn Gateway”, covers all aspects of early transport links across and around the lower estuary in great detail and was an invaluable aid to the Trust in covering the story.

The essential source for a real understanding of the construction of the Severn Railway Tunnel was written by Thomas Walker, the contractor who assumed responsibility for the project in 1877. His  comprehensive book entitled “The Severn Tunnel. Its construction and difficulties (1872-1887” was published in 1888.  Facsimile editions by Kingsmead Press of Weston-super-Mare were published in 1969 and 1990.  The website’s ‘page’ on the tunnel is based almost entirely on information obtained from that book.

In terms of engineering achievement, the 19th century railway tunnel beneath the Estuary undoubtedly ranks alongside the two great twentieth century bridges.  However, with the passage of time and the virtual absence of any visible indication of its presence on the ground, the importance of the railway tunnel in the economic development of South Wales, and its stature as an engineering achievement, could easily be forgotten or overlooked.  To help restore the balance, a fairly lengthy coverage of its construction has been provided on this website, to increase public appreciation of the project and the enormity of the achievement it represents.  The story deserves to be better known.

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The Decision to use Inclined Hangers

 

Choice of Deck Cross Section.

The previous item of ‘more detailed information’, entitled “Background on choice of design for First Road Crossing”, describes the circumstances which led to the catastrophic collapse of the Tacoma Narrows Bridge in the USA in 1940. Initial work on the Severn Bridge started shortly after that and there can be no doubt that its designers were well aware of the potential consequences of neglecting the lessons learned.

In the late 1950s, using an anemometer mounted on a mast 110 feet (33 m) high (the height of the proposed Severn Bridge deck) and an array of instruments mounted on the then existing Severn Railway Bridge, some 3 miles (5 km) upstream, a spectrum of data on local wind speed, direction and inclination, was established over a width of about 300 feet (90 m). This information would be put to good use when the 1/100-scale model options for the Severn Bridge deck were tested in a wind tunnel at Bedford. At that stage, it was assumed that the deck design would follow American practice with a stiffening girder, about 33 feet (10 m) deep and of open-lattice truss construction, as had been proposed in the 1930s.

However, in the late 1950s, the Government stipulated that the new Forth Road Bridge would take priority over the Severn. The Forth Bridge would, not surprisingly, be designed on the same principles as those being developed for the Severn Bridge, although the main span across the Forth would be slightly longer, at 3300 feet (1008 m). Mott Hay and Anderson were appointed in association with Freeman Fox and Partners to design the Forth crossing using a conventional design for the stiffening girder, consisting of a horizontal concrete slab, above a latticed steel-work construction (a truss) that supports it.

There was a new development on the Forth Bridge in that the road deck was made of stiffened steel panels resting on cross girders at the top chords of the trusses. These panels were light in themselves and the overall dead weight was also kept to a minimum by specifying a thin layer (c 1 ½ inch or 40 mm) of mastic asphalt as the running surface. Nevertheless, the total dead weight of the Forth deck was some 18,000 tons which required the towers, main cables and anchorages to be designed to cope with this load plus the weight of the traffic on the deck. Construction on the Forth proceeded about two years ahead of the Severn.

This delay allowed different deck cross-section to be considered for the Severn Bridge, 4 of which are illustrated below.

At an early stage in the design process for the deck, it was necessary to test the 1/100 scale models of the various options being considered for this crucial item, using a wind tunnel to check the strength of the deck, when exposed to the strongest side winds that might occur.  It was also necessary to ensure that the deck would not start oscillating during a less powerful but steadier wind flow. However, very early in the first part of this procedure, the model fixings in the wind tunnel failed and the model was completely destroyed. During the delay that followed, the Consultants, Freeman Fox and Partners, were moved by inspiration to develop an unprecedented design for the deck section, quite different from anything that had been tried before.  It was based on the technology developed to design aircraft wings.

A problem.  The box girder would clearly have no difficulty in coping with anticipated lateral wind forces but during the later stages of the tests, a slight movement had been seen from the model while it was being subjected to a less powerful but steady wind. This led to concerns, and then to doubts about the box girder’s ability to resist oscillations. The presence of this small amount of movement was worrying, given the absence of any obvious source of damping.  The wind-flow over the welded box girder was so smooth and undisturbed that there was very little chance that the deck cross-section itself would be able to provide a worth-while contribution to any damping.

So the search was on for a fresh energy-absorbing element that could be relied upon to eliminate any embryonic oscillation that might occur. The Consultants were seeking an independent source of energy which, when transferred to the deck, would be capable of denying embryonic oscillations the opportunity of becoming uncontrolled and divergent.

The introduction of Inclined Hangers

The choice of the welded box girder for the bridge deck, was widely welcomed, although it would not have been accepted, if there had been any real doubt about finding a reliable source of energy which could be transferred into the deck to ensure that there would be sufficient dampening of all the oscillations that might seek to establish a foothold.  In a second major innovative move, the Consultants decided that all the hangers used to suspend the deck from the main cables, would be hung in an inclined pattern, as shown on the following diagram. The purpose of this move was to increase the structure’s ability to prevent the deck from oscillating.

The pattern for inclined hangers.

The introduction of inclined hangers gave the Consultants a game-changing opportunity to prevent any embryonic oscillation that might form in the deck from developing into an uncontrollable and divergent oscillation. Engineers have long known that certain elements of a suspension bridge act in a very similar manner to the equivalent items on a washing line. They have been aware that, if an additional garment is hung on a washing line, away from the centre, the point on which it hangs, will sag and, more importantly, it will move a short distance towards the nearest point on the washing line that is held fast by a fixed support.

Similarly, when a vehicle travels over a suspension bridge, the deck will not only dip down a little at the moving point of the load, the whole deck will move a short distance longitudinally towards the nearest tower, whether the vehicle is travelling towards, or away from, that tower. The bridge deck is often called the stiffening girder because it spreads out the tensions among the hangers, in order to avoid excessive local sag under an exceptional load.

The purpose of employing inclined hangers is to take advantage of the opportunity to generate more frequent switching of the tensions between each pair of hangers that is connected directly to any of the cable clamps. As a result, the tensions in each of the hangers, and the bridge deck, will be in an almost-continual state of change. These changes will be related to the lengths of the hangers involved, and the angle between each pair, in each case.  This means that the longer hangers on each side of the towers are effectively only subject to a change in vertical load from passing vehicles. Those near the centre of the main span and those towards the ends of the side spans suffer, not only the changing vehicle loads, but the much more significant reversals in tension due to the relative longitudinal movement of the deck in relation to the cable clamps to which they are attached.

Preparations. The deck of the bridge is freely suspended from the two catenary cables, using 172 hangers on each cable. And because the cables hang in catenary in the vertical plane, the two lines of lower anchorages, one on each side of the deck, that are attached to the surface of the deck to receive the hangers, are also in the same vertical plane. The next step was to wrap clamps around the cables at locations set at positions along the cables equivalent to 60ft apart horizontally.  Each clamp was provided with a double eye to secure the top ends of the two hangers in each pair together, before they are allowed to diverge from each other as they go down to meet the deck. The lower ends of the hangers have to be moved 30 ft longitudinally, but in opposite directions, in order to be fastened into the two double deck anchorage eyes that had been fixed to the surface of the deck to receive them, and to provide the hangers with their relevant inclinations.  The other halves of both these deck anchorages will be occupied by hangers from the cable clamps that are their nearest neighbours on either side

Both sides of the deck were treated as described in the above paragraph and, as a result, there is a single line of double sockets at 60ft centres on each side of the bridge deck. These lines are parallel to each other and identical in other respects. In every case, the cable clamp is located, horizontally, at the mid-point between each pair of sockets from one of the lines on the bridge deck.

Lateral restraints and vertical rockers have been provided at each tower and anchorage, to restrain the horizontal and vertical movement of the ends of the deck but permit longitudinal movements of the deck, unhindered. So the deck is restrained laterally and vertically, at both sides of the towers, but permitted the move with traffic loading and thermal expansion. The ends of the side spans are restrained vertically, laterally and longitudinally at the anchorages.

What actually happens?  To cover the various activities that ensue, it is worth starting from a period of shutdown, when the deck will be lying in its position of equilibrium and before the traffic arrives, any two hangers involved will each carry half of the total tension that goes up through the cable clamp to the main catenary cable above. The total tensions carried by both of the cable clamps will remain similar at all times because the dead loads they carry are constant and virtually identical.

The process of additional damping will start with the build-up of vehicles running across the bridge in each direction. Each time that happens, the bridge deck will dip slightly and make a small longitudinal movement towards the nearest tower, similar to the garment on the washing line. The displacement will be proportional to the weight of the vehicle. The first tranche of vehicles will add to the tensions in the hangers, and provide many small longitudinal movements of the deck, which will soon coalesce into a distinct movement in one direction. The actual distances moved by the deck would be more correctly described as being the algebraic sum of the movements in a particular direction. Quite quickly, the deck will have moved a significant amount longitudinally, one way or the other, and this will enable the system to click, autonomously, into a higher gear. (Remember that the direction of these additional movements is governed by its location in relation to the positions of the towers, not by the direction in which the vehicle was travelling).

Now consider what will happen when the deck has made a fairly short movement in a particular direction. The system will react to a longitudinal movement of the deck, destroying the parity between the tensions in the two adjacent hangers. The system will move from point A to point B, in the time that the deck took to move to its new location, just like when an extra garment is added to a washing line, the difference between them may not appear to be very significant but it must be remembered that the crucial triangle at the centre of the issue is wholly comprised of steel which can be very demanding in such circumstances, a fact that is borne out by the contents of the next paragraph.  And it must be remembered that the effect of the movement will probably impinge upon every pair of hangers that serves the deck – the whole caboodle. Think about it!

There has however been an important down-side to the use of inclined hangers.  Depending upon their length and position on the deck, some of the shorter hangers are subject to increased fatigue damage, due to the frequency of the switching of the tensile stresses within each pair of hangers that shares a common cable clamp on one of the main cables.   This is a sure sign that there has been ample switching of tension within the pairs involved. The shorter hangers might need to be replaced after a fairly short time in service. No traffic restrictions are needed, while the hangers are being replaced but the additional maintenance charges are significant.

The previous paragraphs illustrate how the idea of suspending the deck of the Severn Bridge using hangers erected in an inclined pattern, had made it possible for large tensile stresses to be redistributed within each pair of hangers that share an upper cable clamp.  It was exactly the kind of new energy source that the consultants had been  seeking to combat the possibility of an oscillation developing within the completed structure, similar to the one that destroyed the Tacoma Narrows bridge in 1940.  It is particularly intriguing that the actual source of that additional energy should be the ‘live load’ that crosses the bridge.  However, the consultants concluded that the most sensible approach would be to avoid situations that could lead to a hanger becoming slack, or otherwise overstretched under extreme live loading conditions, and they were supported in that decision by the government Department for Transport. 

Manufacture of the hangers.  The above demonstration of the ability of the inclined hangers to provide a new source of energy that must be generated from the live load of traffic, raises questions about the construction of individual  hangers.  The dead load of the bridge deck is extremely uniform throughout its length and so all cable clamps (at 60 ft centres) would carry basically the same share of that weight.  At the same time, the average daily live load borne by each cable clamp  would be virtually identical.   It was also clear, at that stage, that more than 50% of all the hangers would be long enough to be treated in exactly the same manner as if they had been hung vertically.  This all suggested that the current practice of the day, based on a multi-strand configuration, would probably be adequate.  At the same time, there was strong support for developing a strand that would further strengthen the structure against the possibility of oscillations by maximising the amount of hysteresis in the hangers (this work was undertaken but very little has been said about it since).  These deliberations resulted in a strand that contained a total of 178 separate wires, made up from the following three sizes, 0.118 ins, 0.133 ins and 0.339 ins with a lay of 7.5 d.  The resulting strand would provide a maximum working load of 100 tons and a breaking load of 225 tons.  At this stage the way forward was clear for the suspending of all the longer hangers from cable clamps and making the necessary connections to the sockets that would be fixed to the deck to receive them.  But before that work started the possible need for a modification to the system outlined above, in order to cope properly with all the shorter hangers, was undertaken. 

The initial system for supporting the bridge deck that was used to suspend all the longer hangers is described in the above with a section of main cable on one side of the deck, with the two hangers in one pair, coming together directly underneath the main cable to which they are both fixed using a special connection attached to the base of the cable clamp.  Lower down, on the top of the deck, a line of sockets had been fixed to the deck  at 60 ft centres, to secure the lower ends of the hangers.  Each cable clamp was positioned directly over the mid-point between two sockets.  An initial examination confirmed that that this arrangement, in the form described above, would not be able to cope with the shortest hangers.  This meant that a modification was required together with a decision concerning the point at which the modification would need to be introduced.  

The Included angle.  It soon became clear that the critical item when dealing with shorter hangers is the angle ‘included’ between the two hangers at the point where they come together under the cable clamp to which they are both fixed..  This angle will be quite small In the case of the longer hangers but consider what would happen if it reached the 60 degrees shown on the diagram above (note, an angle of 60 degrees has been chosen just to simplify the mathematics).  The triangle that includes both of the hangers and the line of the deck beneath them, approximates to an isosceles triangle.  This means that these hangers are inclined at an angle of 30 degrees to the vertical.  Because of that, only 86% of the tensions in the hangers (i.e., the sum of the vertical components of these tensions) would be used to support the weight of the bridge deck, together with the live load of traffic on it.  The other 14%, the horizontal components of the tensions in the two hangers, would cancel each other out, being dissipated into the bridge deck.  And at the mid point of the span where the main cable drops lower, approaching the centre of the bridge, the included angle between the two hangers would need to be larger still in order to conform with the model.  

The chosen modification involved a simple change to the rules that are implied in the model that is described above.  Having reached the point chosen to make the change, the consultants extracted the included angle at that point and decreed that it should apply to all subsequent operations that would otherwise have adopted a wider angle between hangers.

Changes in hanger tensions due to longitudinal movements of the deck

This diagram shows an elevation of a short length of the support mechanism developed for connecting the bridge deck to the main catenary cable when viewed from one side.  The cable clamps, that transfer the loads from the hangers to the main cable, are positioned along the cable at 60 ft intervals, horizontally, and they each have to secure two hangers, one from either side.   The eyes that are used to fix the hangers to the deck are located mid-way, horizontally, between the cable clamps to either side.  They are fitted along a line just off the flat area on top of the deck, where an additional section of box girder has been welded on to the main box girder, to provide the short cantilever that  carries the footpath and cycle track at the side of the deck.  (see Deck Section Diagram in Main Elements).

  Once decisions were taken on the dimensions of the spans and the towers, together with the shape of the main cable and the horizontal space between the cable clamps, there will be no scope for adjusting hanger lengths.  They will simply be a matter for calculation   

The purpose behind the introduction of inclined hangers is to produce a situation in which the energy stored in the hangers will increase and decrease much more rapidly and by larger amounts than would be the case with vertical hangers. This should provide the structure with much greater potential for dampening embryonic oscillations of the type that destroyed the bridge at Tacoma Narrows. The Severn Bridge has already given good service for more than 50 years and, with adequate maintenance, should continue to do so for the full 120 years of its design life, and beyond.

Unfortunately, there is a downside to the introduction of inclined hangers. It is extremely important that components of the structure that are active in suspending the deck, should remain in service for long periods. And when necessary, they must be capable of being removed and replaced, without requiring traffic restrictions. The rapid fluctuations in traffic loading associated with inclined hangers, and the additional loads that are imposed, make these hangers especially vulnerable to fatigue failure. This is particularly true of the shorter hangers located in the central area of the bridge. The situation is manageable but it requires significantly more maintenance than was originally planned.

It has been shown that the level of stress for hangers in an inclined pattern could rise to at least twice the maximum level experienced in a pattern of vertical hangers, especially where the hangers are short and near the centre of the main span. And it has been established that the relative fatigue life of an individual hanger on that bridge can be expressed, mathematically, as being inversely proportional to the fourth power of the range of stress involved. When this formula is used to explore the effect of doubling the range of stress in a hanger, as in the present circumstances on Severn Bridge, it confirms that we should expect the fatigue life of some of these hangers to be reduced to one sixteenth of the life that would apply if the hangers had been in a vertical pattern (the fourth power of 2 being 2 x 2 x 2 x 2, which equals 16).

It should have been no surprise, therefore, to find fatigue failures of wires within hangers on the Severn Bridge after only six to ten years service. After a period during which individual hangers that had failed, were replaced ad hoc, a wholesale strengthening programme for the bridge put in hand. All hangers were replaced using stronger and less fatigue-prone strand construction, and new designs of socket were installed.

Mott Hay and Anderson continued in their role to design and supervise the construction of the crossing, but now jointly with Freeman Fox and Partners. Motts led overall and designed all the foundations. Freeman Fox were responsible for the steel superstructures. The superstructure of the main suspension bridge was a major technical advance on all previous long-span road bridge designs.

A total of three suspension bridges were built with inclined hangers, between 1965 and 1980, all with Freeman Fox and Partners as main consultants. It is interesting to note that the inclined hangers on the Humber Bridge have proved less prone to such problems, possible because of a less severe traffic loading pattern. On the other hand, those of the first Bosphorus Bridge have been so fatigue prone, probably because of a traffic loading pattern even more extreme than on Severn, that they were all recently replaced by new vertical ones. Suffice to say that, to date, no other major suspension bridge has been fitted with a system of inclined hangers.

At the time, the Severn Bridge was hailed not only for its majestic appearance but also for its technical excellence. The all-up weight of steel in the Severn Bridge, 3,240 feet (988 m) span, was 19,000 tons for the deck, cable suspension system and towers compared with 39,000 tons for the earlier Forth Bridge which had a main span only 60 feet (20 m) longer.

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The Severn Railway Tunnel

Preparatory work

It was while working on the ferry piers for the Bristol and South Wales Union Railway in 1862–63 that Charles Richardson first began to pursue the idea of replacing the ferry with a railway tunnel beneath the estuary.  However, it took him three attempts, over a period of ten years, to get the plan accepted.  His first approach, in 1865, was rejected because the GWR were in the process of seeking an Act of Parliament for a project, proposed by John Fowler, for a new double track, mixed-gauge railway, 41 miles (70 km) long, from Wootton Bassett to Chepstow, crossing the Severn at Oldbury Sands.  And by 1869, Richardson’s scheme also had competition from two other tunnel proposals.

Plan showing the Severn Railway Tunnel

Richardson’s estimate for his tunnel, and for the short lengths of railway at either end, was £730,000.  The tunnel’s chances of success improved dramatically when, in 1870, the newly elected chairman of GWR, Daniel, later Sir Daniel, Gooch, denounced the Fowler project (see previous paragraph) as an extravagance.  Apparently he had come to realise that the director who had been pressing the case for this project at Board meetings, had been doing so to further his own interests.  After further lobbying, Richardson’s scheme was adopted by the GWR Company in 1871 and, the following year, the Severn Tunnel Bill was approved by parliament.  Construction began in 1873, with Richardson as Chief Engineer and with John (later Sir John) Hawkshaw as Consulting Engineer.

The construction of what would become the longest railway tunnel under water in the world at that time, turned out to be a classic example of an engineer’s extreme fight against adversity.  It is surely the leviathan of all Victorian railway tunnels and one of the nation’s finest engineering achievements.  An excellent and detailed account of the works is contained in the book written by Thomas Walker, the contractor who assumed responsibility for their completion, after progress under Charles Richardson stalled, in 1877. The description of events, given below, is based on information obtained from that book.

The bold attempt fails

The original intention had been to put the work into the hands of an experienced contractor but Richardson was not satisfied with any of the bids he had received from contractors.  He was convinced that, by using the GWR Company’s own direct labour force, he could complete the job for 25% less than would be the case if he accepted any one of the bids he had received from contractors, and so he decided to go ahead on that basis.   However, four and a half years later, all he had achieved was one winding shaft and 1,600 ft (490 m) of 7 ft by 7 ft (2.1 m x 2.1 m) heading under the river.  In August 1877, the Directors of GWR intervened and instructed that tenders should be invited for the remaining works.

Appointment of the contractor

Sir John Hawkshaw, 1877

Sir John Hawkshaw, 1877

Only three tenders were received in response to the new invitation and Hawkshaw, acting as consultant, recommended acceptance of the tender from Thomas Walker, an experienced contractor in whom he had full confidence.  However, the Directors took the view that Walker was asking too much for contingencies.  In order to minimise their exposure, should a disaster occur, they decided not to enter into a contract with him until the ground had been proved by the completion of the 7 ft x 7 ft heading right through the length of tunnel under the river.  In the meantime, the heading was to go ahead using direct labour.  Certain other relatively small items of work were also allowed to proceed, some by using smaller contractors, others by direct labour.

The first major incident

Thomas Walker

The pace of the work picked up significantly but, on 18 October 1879 when the headings, that were approaching each other from either side of the river, were only 138 yards (125 m) apart at the east end, a great inrush of water occurred at the west end.  Within 24 hours, water had filled the works on the west side, up to the level of the tide.  Fortunately, the safety measures that had been put in place, enabled all the men working in the tunnel to escape with their lives.

There is little doubt that all the men who ran for their lives on that day were convinced that the river had broken into the tunnel.  However, when the initial shock had subsided and it became possible to rationalise events, it became clear that the point at which the water had broken in was not under the estuary itself but a short distance from the west bank.  We now know that the influx of water came from the “Great Spring”, a major aquifer that carries extremely pure water down from the Brecon Beacons and directly into the Estuary below low tide.  To day, over 130 years later, 20 million gallons (90 million litres)of valuable spring water are still being pumped out, each day, from the point at which the tunnel had had been cut into this aquifer. At the time, this flow represented the daily intake of either Liverpool or Manchester – or about one sixth of the consumption of London.

The aftermath

The ingress of the Great Spring, no doubt, caused GWR Directors to ponder their previous statements about the amount requested by their chosen contractor for contingencies.  Their reaction, to what had happened up to that point, was to invite Hawkshaw to take full charge of the works, as Chief Engineer, with authority to act as he thought fit.  Hawkshaw intimated that he was prepared to accept, but on condition that he be allowed to let the works to Thomas Walker.  The Directors concurred but still wanted the length of 7 ft by 7 ft heading to be completed under the deep channel known as “The Shoots” before any major works were undertaken elsewhere.  They asked Hawkshaw to seek a price for this element, alone.

Walker responded, suggesting that his 1877 tender should still stand, though modified to allow for the lapse of time and the amount of work still to be done.  He was prepared to concentrate on completing the heading under the river, as soon as he had dealt with the influx of water and pumped the workings dry.  This suggestion was agreed by all parties and the works were handed over to Walker on 18 December 1879.

Richardson’s Departure.

The events described above inevitably led to the departure of Charles Richardson from the project.  Great credit is due to him for the conception of the scheme and for its safe passage through the unpredictable Parliamentary procedures.  He also developed a system for successfully aligning the two headings with unprecedented accuracy.  However, while his administrative and conceptual expertise remained untarnished, his ability to drive a difficult project through to fruition, had been called into question.  The extent to which his difficulties stemmed from a lack of expertise or commitment on the part of the GWR direct labour force, is difficult for us to judge in the 21st century.  But before Richardson leaves the stage, it is worth mentioning that generations of boys, both young and old, should be grateful to him for conceiving the idea of inserting three layers of rubber into the cane handle of a cricket bat, a device that soon became adopted universally and is still employed, worldwide.  It is on record that several of his professional colleagues, including Brunel, often complained about the amount of time that he spent playing cricket!

Longitudinal Section of the Railway Tunnel

Dealing with the Flood Water

In January 1880, while Walker was setting up and organising pumping operations, Hawkshaw decided to lower the position of the tunnel under the Shoots Channel by 15 ft (4.6 m), preserving the previous gradient of 1 in 100, eastwards towards Bristol, but increasing the gradient westward to 1 in 90. It was possible to make this change without incurring large additional costs because the almost completed heading would still be wholly within the template of the amended tunnel. The greater security that this represented, against the threat of the river inundating the works, allowed him to authorise Walker to commence work at other points. Walker was then able to put in hand arrangements for recruiting and housing a very large work force (the maximum number employed, at any one time, eventually reached more than 3,900).

The immediate task was to seal off the heading into which the spring water had entered. Although the heading itself was quite short and wholly under dry land, it interconnected with the main heading in the Sudbrook pumping shaft. This meant that a shield had to be positioned in the shaft to seal off the problematic heading on both sides of the shaft.  Like so many other operations involved in the construction of the tunnel, the task was bedevilled by practical problems and pump breakdowns.  Divers were called upon to perform superhuman feats at what were extreme depths for the best survival equipment available at that time.

Sudbrook Pumping Station

A good example of this came about when Walker realised that, in order to clear all the water from the Great Spring out of the tunnel, it would be necessary to close an iron door in a headwall that had been left open, inadvertently, when the men evacuated tunnel on the day the inundation occurred. The job was given to his most experienced diver, who had to negotiate all kinds of obstacles in walking for 1,000 ft (310 m) though the flooded heading, all in darkness. The diver’s air pipe was connected to a static pump at the start point which meant that a very long length of pipe had to be dragged out behind him.  And because the water in the heading was under considerable pressure, the air pipe pressed hard against the top of the heading, producing a great deal of friction.  Even with several assistants to help convey the air pipe forward, the diver was unable to complete the assignment. The problem was only overcome when the engineers discovered that a Wiltshire man, named Henry Fleuss, had just developed a new type of diving helmet that connected directly to a cylinder of compressed oxygen strapped to the diver’s back – a very fortuitous piece of timing.

The Great Spring was eventually contained behind a long ‘cement’ headwall, 8 ft (2.5 m) thick, into which a door had been inserted. At a later stage, pumps were installed to take the water away to prevent it causing further damage – and to take advantage of the commercial potential thus available.

Other unexpected difficulties

At the end of April 1881, when the process of ‘breaking up from the initial 7 ft by 7 ft  (2.1 m x 2.1 m) heading to the required dimensions of the tunnel was underway on the Gloucestershire side, water suddenly burst in from the roof of the tunnel near the Sea Wall shaft. This time it was sea water; the river had broken in!  Fortunately the hole, which was close to the bank on a stretch of water known as the Salmon Pool, was not very large. The shape of the surrounding rocks was such that the Pool retained a minimum of 3 ft (1 m) of water even at low tide, making it impossible to locate the hole by sight. A number of men were called upon to walk slowly across the area, holding hands as they went, until one fell into the hole and had to be pulled out by his colleagues. The water was allowed to rise in the tunnel to the same level as the river itself and then, at high tide, a schooner was loaded with puddle clay and moved into position so that the hole could be plugged, using alternate layers of bagged and loose clay.

In December 1882, a major incident occurred, causing more than three hundred men to abandon their possessions and stampede out of the tunnel, shouting “The River is in”.  When the initial panic subsided and it it became possible to carry out a preliminary assessment, it became clear that the situation was not as bad as feared. In fact, the expected flooding of the tunnel did not occur. After a thorough investigation, it became clear that the panic was caused by a sudden surge in water from the Great Spring which had been damned behind a berm in an upper heading.  The level of this water had risen steadily and, after over-topping, it had washed it away the berm and surged into the lower heading. The men’s reaction was hardly surprising, given the conditions under which they were working. They naturally assumed that their worst nightmares were about to be played out.

On the 9th of February 1883, a terrible accident occurred as men on the night shift gathered round the bottom of a lift shaft, waiting to be brought up for supper.  Four or five men had just entered the cage at the bottom, when an iron skip at the top of the shaft was inadvertently allowed to move over the lip and fall 140 ft (c 45 m) on to the cage below, killing three men before bouncing into another group, standing by, where another man was killed and two seriously injured.

There was another emergency on 10 October 1883, when a great surge of water entered the works from the Great Spring, very much exceeding the capacity of available pumps. It swept the men and their iron skips, like so many chips, through the door leading out of the heading and into the finished tunnel, where the men were able to recover. None of the men were seriously injured but three colts were drowned. Headwalls were rapidly built to contain the flood, as water rose up against the pumps to a height of 52 ft (16 m). At first, it seemed that the works might have to be abandoned as all the available pumps, working to capacity, failed to make any headway against the floodwaters for several days. But eventually, the pumps slowly but perceptibly started to gain the upper hand, much to the relief of everyone involved. It seems that water from a nearby subterranean reservoir had suddenly been released but fortunately proved to be more manageable than seemed likely. It has been calculated that the maximum flow during this incident must have been about 27,000 gallons (c 125,000 litres) a minute, 16,000 gallons (c 70,000 litres) more than the available pumping power could lift.  Never the less, the Great Spring had been safely imprisoned again by the 3rd November.

Then, on the night of the 17th of October 1883, only a week after the Great Spring had renewed its assault, a tidal wave flooded the low lying area on the Sudbrook side. On a night when one of the highest tides of the year was expected and, during an exceptional storm, a tidal wave described as a solid wall of water, 5 or 6 ft high, swept in and entered the living accommodation provided for the workforce. About 90 men had just descended the Marsh shaft to continue opening up the heading into a full tunnel, near the western portal, when flood water over-topped the mouth of the shaft and fell into the workings. Three men attempted to climb a ladder out of the shaft in order to escape from the flooded works beneath; two emerged unscathed but the third was thrown off the ladder by the weight of falling water and killed. The water rapidly flooded the area at the base of the shaft, driving the men up the completed tunnel which rose at a gradient of 1 in 90. In the meantime, a workforce was rapidly gathered on the surface to build a make-shift wall around the top of the shaft in order to prevent additional water entering the works. Then a small boat was lowered down the shaft, to ferry men back to the base of the shaft where the water had by then risen to within 8 ft of the crown of the tunnel. Some had to wait hours for their turn in the boat but, by the morning of the 18th, the last remaining survivors emerged.

Completion

The incidents described above, and many other unexpected difficulties that bedevilled the operations, are all vividly described in Walker’s book, each one requiring men to work at the limit of human endurance and ability, while using the most advanced technology available at that time.  On several occasions, it seemed that the task would prove to be beyond the capability of the men responsible but, with outstanding skill and perseverance, they managed to overcome all these obstacles and complete the task.

The first train journey through the tunnel took place on 5 September 1885.  A special coal train ran through from Aberdare to Southampton on 9 January 1886, but it was not until the end of 1886 that the tunnel was opened to regular traffic.  The construction of the 4 mile 628 yd long tunnel took almost fourteen years to complete.  The final cost was £1,806,248, two and a half times Richardson’s original estimate and nearly double Walker’s 1877 contract price.

The opening of the tunnel for regular passenger services on 1 December 1886 marked the end of Brunel’s unique steam ferry railway, the last crossing by the steam packet taking place the previous evening.  Over thirty years later, a ferry was re-introduced at New Passage, this time in order to transport cars and other road vehicles across the Estuary.  And later, with the inexorable growth in the car use after the Second World War, British Rail introduced an occasional piggy-back car-carrying service, through the tunnel.  Both these services ceased when the Severn Bridge opened on 8 September 1966.

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The Bristol and South Wales Union Railway

An improved ferry service – after a long gestation

In 1844, Brunel started to consider the possibility of reviving the direct route across the Severn, via the New Passage, by bringing together the convenience of a railway and the flexibility of a steam ferry.  The idea had much to commend it but for various reasons, it did not get underway for another 14 years.   Brunel himself was involved from time to time, although he was also working on many other projects during this period.

The first positive proposal along these lines, known as the Bristol and South Wales Junction Railway, was approved by Parliament in 1846.  It comprised a branch line from Bristol to the pier at New Passage, a further short length of track on the opposite side of the Estuary to connect from the ferry pier at Portskewett to the SWR, and a ferryboat to run between the two piers.  The timber piers, designed by Brunel, were to be approximately 500 ft (155 m) long to accommodate the full length of the train and to reach out into the deeper water.  Financial problems led to the abandonment of the scheme in 1853.

Another project based on a similar principle and entitled the Bristol, Wales and Southampton Railway was brought forward in 1854.  A “steam bridge” across the river was proposed, at the same point, with the railway carriages being hauled onto the ferry boat, thus allowing people to stay in their seats.  This project also failed from a lack of investment.

A Digression

Isambard Kingdom Brunel

Three years earlier, in 1854, when construction of the bridge over the River Tamar at Saltash was well underway, the new Duke of Beaufort had consulted Brunel about the possibility of bridging the Severn Estuary at Old Passage.  On 30 May 1854, Brunel replied through the Duke’s agent, in the following terms;

“I should be very glad, if the Duke thinks seriously that it would benefit his interests, to look seriously into the question and give the best advice I can.  And if I should be able to suggest a feasible plan and there should be friendly people ready to make it, I shall have the satisfaction of bridging the Severn, as well as the Tamar.”

Brunel is on record as saying that he believed there would be a bridge or a tunnel across the estuary within fifty years.  Although the Duke did not take the matter further, Brunel obviously kept the exchange in mind because, in April 1857, probably while attending the public inquiry into the B & S W U R, he made a sketch of a design with obvious similarities to that of the Tamar Bridge.  Under the drawing, Brunel had written ” Severn Bridge.  Q: is 1,100 ft practical”.

Brunel’s sketch for a bridge across the Severn Estuary

Development of the Bristol and South Wales Union Railway

Finally, a scheme was brought forward by the new Bristol & South Wales Union Railway Company (B & S W U R), this time with strong Welsh backing and with the chairman of the SWR on board.  A public enquiry was ordered by the Admiralty and it opened in the New Passage Hotel on 25 March 1857.  Opposition was raised by the City of Gloucester and the Gloucester & Berkeley Canal Company, as well as owners of small craft and the steam packet Wye, that ran between Chepstow and Bristol.  Those who opposed the scheme had the mistaken impression that a chain ferry would be used.  Brunel, who had become engineer for the project in 1855, explained that this was not the intention; the project would be based on a train ferry and confined to passenger and light goods only.  An Act of Parliament for the B & S W U R was obtained in July 1857.

Charles Richardson

In September 1858, a contract for the 11½ miles (18 km) long single line railway from Bristol to the estuary was awarded to Rowland Brotherhood, with Charles Richardson as resident engineer, working under Brunel.  From the junction with the existing railway, ½ mile (1 km) east of Temple Meads Station, the line would include five local stations.  The piers leading into the river were the most innovative items, incorporating floating pontoons at the ends of the timber piers on to which the trains would run, with stairs and lifts down to the pontoons.  The piers extended far enough out to provide sufficient water for the steam ferry boat to come alongside at any state of the tide.  The pontoons floated with the tide and were therefore at the same level as the boat when it came alongside.  Sadly, Brunel died in 1859.

The full system from Bristol to New Passage, across the ferry, then on to the link to the SWR, for Cardiff, was achieved by November 1863, with the formal opening taking place in January 1864.  Initially, there were five trains a day, each way, and a single ferry, called “Relief”.  The route became so popular that other vessels were used from time to time to provide additional capacity.  Eventually, a second ferry was ordered from the Glasgow shipyard and named “Christopher Thomas” after the chairman of the company. This system now forgotten, was a marked improvement on anything that had been used previously and with the prospect of a tunnel still only an aspiration should be remembered as a major step forward.

Old photograph of New Passage Hotel

Present day photograph of what was the New Passage Hotel, from the foreshore

Sketch of the Ferry Pier at Portskewett

Remains of the Portskewett Pier, with the Second Severn Crossing in the background

New Passage Hotel and Ferry Pier,
on the opening of the Bristol and South Wales Union Railway in 1864

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The Coming of The Railways

Early proposals

The coming of railways encouraged engineers to explore other ways of crossing the estuary, especially for journeys between Bristol and the important and growing industrial areas of South Wales.  The coastal section of the South Wales Railway (SWR) had been completed as far west as Haverfordwest by 1854 and it soon began to displace shipping as the chosen method of transporting goods and people from one South Wales coastal town to another.  But the problem of negotiating the ferry at Old Passage remained.  Despite the improvements brought about by Telford, the ferry crossing was still treacherous in bad weather.  On a good day, the time taken to travel between Bristol and Cardiff, by coach and ferry, would be about seven hours.

The Post Office had considered installing a chain ferry during 1836.  James Meadows Rendel surveyed both the Old and New Passages but reported that tidal currents were too strong for his system which employed a steam engine on the ferryboat to pull, or warp, itself along a submerged chain.

By 1852, the SWR was connected by Brunel’s Chepstow railway bridge up the western side of the estuary to Gloucester.  This facility, together with the line between Gloucester and Bristol, provided a more attractive journey between South Wales and Bristol than was available using a coach and ferry, via the Old Passage route.  Accordingly, patronage of the Old Passage ferry declined rapidly and, by 1855, the use of steamboats could no longer be justified.  Attempts were made to keep the ferry open, using sailing boats, but eventually the passage closed.

Not enamoured with the circuitous route through Gloucester, the railway companies started to look into the possibility of crossing the Severn somewhere between Gloucester and Bristol.  This would provide a shorter route between South Wales and Bristol and it would please the colliery proprietors in the Forest of Dean who were seeking a less costly route for transporting their coal to English markets.  Also, the Great Western Railway Company (GWR) had concerns about the steep gradients in the Stroud Valley, between Gloucester and Swindon.

Proposed Rail Crossings of the Lower Estuary

Early proposals for bridges in the vicinity of the ancient ferries included an ambitious 20-arch railway viaduct by Charles Blacker Vignoles in 1834.  He, like Brunel, had considered the possibility of tunnelling under the Severn.

Thomas Fulljames, Chief Engineer to the Bristol and Liverpool Junction Railway Company, proposed a more practical scheme, published in 1845. He suggested two possible designs for what he described as the Aust Bridge, in the vicinity of the Old Passage, just a few hundred yards below the line of the present crossing. It took advantage of several rocky outcrops that were exposed at most low tides

Two designs for a bridge at Old Passage by Thomas Fulljames

James Walker FRS was commissioned by the Admiralty to report on the proposals.  Fulljames argued that his first design “could be achieved with perfect safety to navigation”.  Walker disagreed, saying it would be objectionable on account of a pier, which “would be directly in the middle of the navigable channel”.  Navigation was a most important consideration in 1845 and shipping trade through the line of the Old Passage exceeded 600,000 tons per year with the largest ships drawing 19 feet (6 m) of water.  Mr Walker found no fault with the second design, but the Aust Bridge was never built. James Williams, first class pilot for 13 years seems to have had the last words – “it will not do at all”

In 1845, S B Rogers of Monmouthshire proposed a toll-free road crossing at the English Stones. It consisting of 21 arches of 350 ft (about 100 m) span and which would be at least 120 ft (about 40 m) above high water mark. It was to have “shops, bazaars and a lighthouse”. However this scheme was not well received by entrepreneurs or navigation interests.

Sketch of railway viaduct, proposed by S.B.Rogers in 1834

Other early proposals for a railway crossing on the lower Estuary were concentrated on the short stretch between Sharpness and the Horseshoe Bend at Arlingham. The very first was in 1810 when the Bullo Pill Railway Co. started to tunnel under the Severn, south of Newnham, primarily for its own benefit. The company had acquired the rights of the Newham Ferry and began to construct a road tunnel that would have enabled adapted tramroad wagons to gain access to the eastern side. However, a major influx of the river brought work to a halt and it was never resumed.

On behalf of the SWR, Brunel brought forward a proposal for a timber viaduct that would cross the river from Hock Crib to Framilode on the Arlingham Bend, about 5 miles (8 km) above Sharpness. In his report, James Walker described the proposal as being “at about the very worst place on the river for navigation” and the scheme was rejected by Parliament in June 1845.

Later, in 1865, a scheme by Sir John Fowler was rejected as an ‘impediment to navigation’. Like several other rejected proposals in this area, it would have been located above the entrance to the Sharpness to Gloucester Canal. There is, however, an interesting footnote to this tale. Sir John continued to develop designs for a Severn Crossing, with spans of up to 1,000 ft (310 m) and based on the use of steel, until, in 1872, the GWR obtained parliamentary powers authorising construction of a tunnel under the estuary.  At that point, Sir John took his plans up to Scotland where, assisted by Sir Benjamin Baker, he developed them further until the design emerged for what was to become the world famous cantilever bridge that now spans the estuary of the Forth.

The ill-fated Severn Railway Bridge

Eventually, in 1871, engineers George William Keeling and George Wells Owen, on behalf of the SWR, put forward a scheme for a railway bridge, to be located just above Sharpness. Parliament gave approval to the scheme in 1872. The design, for what became known as the Severn Railway Bridge, was for a conventional single line viaduct 4162 ft. long, comprising twenty-one spans supported on huge cast iron cylinders. The bridge was to be situated half a mile above the entrance to Sharpness docks and the canal to Gloucester.

Severn Railway Bridge, as built

It is rather surprising that investors were prepared to support this project at the time. Work did not begin until 1875 and, by that time, construction of the railway tunnel under the Estuary, on the direct route between South Wales and Bristol, had already been underway for two years. However, part of the motivation behind this investment was undoubtedly to support mining interests in the Forest of Dean and many of the investors were sceptical about the tunnel ever being completed.

The fate of the many earlier attempts to obtain authority to construct a rail link across the lower Severn Estuary indicated a general reluctance on the part of Government to approve a scheme if it were deemed to be a hazard to navigation. All the previous attempts, mentioned above, were abandoned, at least in part, because they failed to surmount that hurdle. It is therefore surprising and – with hindsight – rather disturbing, that construction of the Severn Railway Bridge should have been allowed to proceed.

Severn Railway Bridge after collision

Disaster struck on the night of 15 October 1960, when two self-propelled fuel barges missed the entrance of the Gloucester to Sharpness Canal. In the dense fog, both skippers attempted to get back to the canal entrance but the two vessels collided and became locked together. Minutes later, with a combined weight of 858 tons, they struck one of the piers of the railway bridge. The debris from the cast-iron pier of the bridge and the two adjacent spans crashed down onto the barges, igniting the fuel.  Five of the eight crewmen on board the barges lost their lives. The bridge was not replaced. Apparently, it had been hit many times previously but the cost of substantial protection around the bridge piers had always been considered prohibitive.

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History of Estuary Crossings

The River Severn

Throughout recorded history, until well into the Industrial Revolution, the most efficient method of transporting heavy goods was by river and coastal water. It is, therefore, not surprising that the majority of large urban settlements in all parts of the world are located in close proximity to an effective waterway.

The River Severn is the longest river in Britain. It played a crucial role in the economic development of the post-medieval nation. Prior to the development of canals, it carried a greater volume of traffic than any other waterway in Europe. Rising on the slopes of Plynlimon Fawr, it meanders through central Wales as far as Shrewsbury and then turns south, passing under the famous Iron Bridge at Coalbrookdale and several bridges designed by Thomas Telford. His bridge at Over, just downstream of Gloucester, was opened in 1830 and remained the lowest road crossing of the estuary until the M4 motorway was opened in 1966.

The golden age of water-borne transport came immediately before the coming of the railways, when all possible use was made of this mode. By 1800, small river craft were able to navigate up the river as far as Shrewsbury; while Bewdley was considered to be the upper reach for larger vessels. With the construction of new waterways such as the Staffordshire and Worcestershire Canal which gave access to the Black Country, the Severn played an even more important role in the economy of the region. Access up as far as Gloucester, was improved by the opening of the Gloucester to Sharpness Canal in 1827, after a tortuous gestation.

During the late 18th century, most roads in this country were in such a poor state that manufacturers often had to go to very great lengths to transport their goods. An example of this was the route chosen, in 1775, by a company from Wellington in Shropshire to deliver a consignment of pig iron to Chester, 60 miles (97 km) further north as the crow flies. The journey began with the iron being transported by cart to the Severn, to be loaded on to Bristol-bound riverboats. On arrival in Bristol, the material was transhipped to sea-going vessels and then taken right around the coast of Wales, into the mouth of the Dee, and so to Chester. This example, involving a journey of over 400 miles (644 km) by water with two trans-shipments, speaks eloquently about the state of the roads at that time.

Ancient crossings of the lower Severn estuary.

Crossing the river has always been hampered by the high tides and fast currents, causing a real problem for all the peoples who have inhabited its boundaries. An ancient crossing route has been identified from the end of an ancient ridge-way over the Cotswolds to Shepperdine on the English side and onto the Beachley peninsula on the Welsh side. After the retreat of the ice, this route would have been used by the first settlers, their primitive rafts taking advantage of the tidal flows to go E-W on the ebb and W-E on the flow. This crossing probably survived through the Roman period and into mediaeval times, as indicated by the location of the southern end of Offa’s Dyke, part way down the Beachley Peninsula.

No record survives of the efforts made in early times to provide a regular ferry service but there is archaeological evidence indicating shipping trade across the Estuary. The first record of a regular ferry is from AD 1131. It was used by monks at Tintern Abbey, under a grant from Winebold de Balon who owned the land. The ferry plied across at the narrow point between Aust to Beachley. This ferry route was maintained down the following centuries and is known as the Old Passage.

Plan showing the ancient ferries

The alternative ferry route, across the English Stones, might, in fact, be the older of the two. However, it was closed by Cromwell, following the drowning of Parliamentary troops marooned on the English Stones in 1645. After it reopened in 1718, it became known as the “New Passage”.

The early ferries were not for the faint hearted. Daniel Defoe described the Old Passage crossing from Aust to Beachley as an “ugly, dangerous and very inconvenient ferry over the Severn”. Travelling to Wales in 1725, he decided that the alternative route via Gloucester was the safest and surest way, taking account of the weather and seeing the sorry state of the ferry boats at Aust;

“The sea was so broad, the fame of the Bore of the tide so formidable, the wind also made the water so rough, and which was worse, the boats to carry over both man and horse appeared so very mean, that, in short, none of us cared to venture. So we came back, and resolved to keep on the road to Gloucester”.

The Contribution of Thomas Telford

The route from the west bank of the Severn, opposite Bristol, through South Wales was in a poor state of repair throughout the eighteenth century and frequent calls were made for its improvement. Reductions in journey times became of pressing importance in the 18th century, as markets increased in scale and reach with the establishment of Empire and the impact of the Industrial Revolution. By the early 1800s steam pickets were plying between West Wales and Southern Ireland. In 1823, the Post Master General sought to improve the Mail Coach route between London and Milford Haven and he called upon Thomas Telford to advise on what should be done.

The advantage of replacing the long diversion around Gloucester whenever the ferry services were interrupted was evident to Telford and he believed that the value of the reduced journey times would justify the building of a permanent crossing. In modern times, major estuarial crossings have far outstripped other public works in economic gain, providing returns in the region of 200% in the first year alone.

Telford’s opinion of the New Passage crossing near the English Stones was unequivocal; “One of the most forbidding places at which an important ferry was ever established, a succession of violent cataracts formed in a rocky channel exposed to the rapid rush of a tide which has scarcely an equal on any other coast“.

Telford’s first proposal was a crossing from Uphill Bay in Somerset to Sully Island on the west side of Cardiff (this is similar to the line of the proposed Severn Barrage). It is possible to imagine Telford staring across the swirling waters in awe and excitement at the prospect of engineering such a structure and the wealth it would generate for the area. However, the proposal was rejected.

Telford then considered the Old Passage which crossed at the narrowest point on the estuary. At that time, his two suspension bridges were in the course of construction in North Wales, so it came as no surprise when, in 1824, he suggested a similar solution for the Severn at the Old Passage. However, his suggestion was not taken forward because, at that time, the route to Dublin via Holyhead carried more political clout than the South Wales route to southern Ireland. Nevertheless, on 26 November 1825, plans were announced for improvements to the Old Passage, including a new ferry and improved landing facilities on both sides of the estuary.

A short diversion — The Old Wye Bridge at Chepstow

Before moving on, the reader might be interested to learn about the existence of an old and historically-important road bridge situated less than 3 miles (5 km) from the western end of the Severn Bridge.

To the historically minded, the name of Chepstow conjures up visions of the medieval castle and Brunel’s magnificent Railway Bridge.  However, just upstream from the new Wye Crossing at Chepstow, there is a very interesting Grade One listed, five span, cast iron bridge which passed its 200th Anniversary in 2016.  Carrying the main road from Gloucester to South Wales, it was built to replace an older, wood and stone, bridge that had been struggling to cope with the prevailing conditions on the River Wye.

The tidal range at the Chepstow Bridge is only marginally less than that at the nearby Severn Bridge which, at 40 ft (14 m), is the second highest in the world.  This means that, for long periods every day, the view of the bridge on the water is constantly changing as water rushes up and down.  The bridge has five spans so there are four piers in the river that navigators need to avoid.

In 1811, in response to a request for bids to replace the old bridge, Watkin George of Cyfarthfa, Merthyr Tydfil, and John Rennie had each prepared designs for new cast iron spans on the existing piers and Rennie also prepared a design for a 250 ft (76.2m) span cast iron arch flanked with 72 ft (22m) span masonry arches.  These bids were all rejected, mainly on grounds of cost.

The Old Chepstow Bridge – The Chepstow Museum holds various prints of older bridges that had spanned the river at this point.

In 1812, a collision occurred between a vessel and one of the piers, causing 6 deaths and significant damage to the bridge.  This proved to be the catalyst for action.  The foundation stone for a new bridge, at the same location, was laid in 1813.  The following year, a contract to design and construct the new bridge was let to John Urpeth Rastick, Robert Hazledine, Thomas Davies and Alexander Brodie of Bridgenorth Ironworks.  Rastick was responsible for the design of the bridge and he supervised its construction.  Some of the ironwork was cast at Calcutts Ironworks in Shropshire, which was owned at the time by Brodie, and later by Hazledine.

The central span of the bridge is 112 ft (37 m) long and it is flanked by two 70 ft (21.6 m ) spans and then two end spans of 34 feet (10.5 m).  The overall length is about 487 ft (149.4 m) and it is 20 feet (6.1 m) wide. The piers and the abutments from the previous bridge were reused after being strengthened by a surrounding cover of large rectangular stone blocks (ashlar).  The deck for each of the graduated spans is supported by five, shallow lattice, cast iron arches (four of the outer lattice arches are visible on the photograph, opposite) and these elements, together with the vertically curved road profile and the decorative lamp standards, all contribute to the bridge’s attractive appearance.

Decoration at the centre of the old Chepstow bridge

The bridge was opened on 24th July 1816.  The original contract price was £17,150, and the total scheme cost, including fees, was £22,116.  This was less than half of Rennie’s earlier bid.  The centre span was strengthened by the addition of steel ribs in 1889 and further extensive repairs and reinforcement were carried out in 1979-80.

When built, the new structure became the third largest cast iron bridge in the world.  It is now the largest surviving bridge of its type and era. The bridge carried the only trunk road into South Wales until 1988, when the Chepstow Inner bypass was opened.  It continues to carry local traffic across the river.

The design is generally considered to having been inspired by the work of Thomas Telford who built several cast iron arch bridges that can still be seen in Mid and North Wales.  It therefore provides an opportunity for visitors to the area to see what Thomas Telford would probably have provided, had he been called upon to do so.

Rastick [1780-1856] is better known as a railway engineer and locomotive builder. He helped Richard Trevithick develop his ideas for steam engines and built a locomotive for him in 1808.  In 1829 he built the first steam locomotive to run in the USA.  In 1829, he chaired the judging panel at the Rainhill Trials for the Liverpool and Manchester Railway which led to the approval of Stephenson’s “Rocket” and he built many railways in Britain, including the London & Brighton Railway.

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