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• Type

  Map

  Title

  Map for Drochaid a’ Chaolais Chumhaing, An Caolas Cumhang / Kylesku Bridge, Kylesku (LB52497)

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Summary

Description

Drochaid a' Chaolais Chumhaing / Kylesku Bridge is a curved concrete box-girder bridge supported on two pairs of V-shaped concrete piers, spanning the deep sea inlet of An Caolas Cumhang. It was built between 1981-84 to the designs of Ove Arup and Partners for the Highland Regional Council. Built at a cost of £5.3 million, the main contractors were Morrison Construction Ltd. in conjunction with Lehane, MacKenzie and Shand. The bridge is located in Sutherland in the northwest of Scotland. It forms part of the North Coast 500 route between Ullapool and Scourie, and carries the A894 non-trunk road over the inlet where Loch a' Chàirn Bhàin, Loch Glencoul and Loch Gleann Dubh meet.

Spanning a total length of 276m, the bridge comprises a central span of 132m, flanked by two smaller spans of 72m. The portal frame means that it has a largely consistent navigable clearance of 24m along its length. The continuous curved deck is a hollow box girder of pre-stressed concrete, with a carriageway and a footway over. The deck is supported by two pairs of V-shaped concrete piers, which are located on either side of the channel. The piers are splayed outwards by 16m at the base, inclining upwards to converge at the deck. The carriageway and footway have aluminium parapets with three horizontal rails. The deck is inclined to accommodate the curvature of the bridge.

Statement of Special Interest

Drochaid a' Chaolais Chumhaing / Kylesku Bridge is a visually striking and technically innovative modern concrete bridge in a remote rural location. The early use of the curved form for the bridge enabled the character of the surrounding landscape to be preserved. Since it was first built, the quality of the bridge's design and its method of construction has been recognised through a number of prestigious awards, including the Scottish Award for Civil Engineering Construction and the Concrete Society Award. The distinctive sculptural form of the bridge means that it is instantly recognisable and provides a dramatic contrast to the rugged Highland landscape setting. Overcoming a long-standing communications barrier and transforming the socio-economy of this area, the Drochaid a' Chaolais Chumhaing / Kylesku Bridge continues the legacy of state-of-the-art bridge construction in the Highlands, which Thomas Telford pioneered with his masonry bridges nearly 200 years earlier.

It is one of Scotland's most architecturally distinguished bridges of the second half of the twentieth century and is among the most outstanding of its type in the country. This is now reflected in the bridge's growing status as tourist attraction along the North Coast 500 route, and in its use in a number of high-profile international advertisements.

Age and Rarity

Drochaid a' Chaolais Chumhaing / Kylesku Bridge was built between 1981-84 to replace a commercial vehicle ferry service that was established in 1975 by the newly-formed Highland Regional Council. An earlier ferry service had existed in the area since the early 19th century, initially carrying passengers across in rowing boats but later evolving to carry horses and carts. Shown on the 1st Edition Ordnance Survey map (surveyed 1875), the service operated between Kylesku pier and Eilean na Rainich. During the 1920s and 1930s, small ferries were established that were capable of carrying some cars. The roll-on-roll-off ferry the Maid of Glencou, introduced in 1975, was the first vessel capable of carrying fully-loaded commercial vehicles. The roads on either side of the loch were upgraded to modern two-lane roads at some point during the mid-20th century. This was financed under the Crofter Community Grant Scheme, which was introduced in the 1930s in an effort to improve communication networks between the remote rural communities in the Highlands.

Despite these successive improvements, the ferry service remained a significant bottleneck in the route north-south. Another disadvantage was that it only operated in daylight hours, which are very short during the winter months. The only alternative to crossing the loch was a 110-mile detour via the inland roads. It was therefore widely acknowledged that a bridge would provide a better long-term solution to the ferry but it was not until the late 1970s that it became economically viable.

The extension of the United Kingdom's road and motorway network was a major post Second World War infrastructural investment. The role of transport infrastructure in supporting economic development was fully recognised but the provision of bridges and road improvement schemes, particularly in rural areas, was constrained by the high cost. As a result, the early schemes of the 1960s focused on improving the road networks that served the highest population centres and the major industrial areas. Key works from this early phase included the M8 (1965), the Tay Bridge (1966), the Forth Road Bridge (1964) and the Erskine Bridge (1971). By the 1970s focus had shifted north of the central belt in an effort to transform road connectivity in the Highlands, thus giving greater opportunities and economic benefits to these remote areas. Direct forerunners of the bridge at Kylesku were the Cromarty Bridge (1979) and the Kessock Bridge (1982), which were both constructed as part of the major road improvement scheme on the northeast coast.

Within the context of the post-industrial economy of the late-1970s, there was an economic strategy to encourage tourism within the more remote regions of the Highlands. It was hoped that this would provide a much-needed stimulus to the local economy but the provision of a bridge at Kylesku was vital to achieving this. In June 1978 the Highland Regional Council appointed the engineering firm of Ove Arup and Partners to design a bridge at Kylesku.

The contract was awarded to Morrison Construction Ltd., in conjunction with Lehane, McKenzie and Shand, and the initial value was £2.75 million. Works to the approach roads were carried out first in 1981-82 and the design of the bridge began in June 1981. The bridge was built in four main stages. The V-shaped reinforced concrete legs were constructed and then the two outer spans were built in phases. The central span was precast on a temporary jetty on the shore of the loch. Measuring 43m and weighing 640 tonnes, this was then transferred to a floating barge and lifted into place by cranes, with the concrete deck cast on top.

The bridge was completed in July 1984 and it was officially opened on 8 August 1984 by Her Majesty The Queen. The weather conditions during the construction phase were extremely adverse, which led to the final cost almost doubling to £5.3 million. Following completion, the bridge was given a number of awards that included the Scottish Award for Civil Engineering Construction (1984), the Concrete Society Award (1985), the Scottish Civic Trust Award (1986) and Annual Award of the Association for the Protection of Rural Scotland (1988).

The bridge opened up the coastal route to Thurso and improved connections between this part of the West Highlands and the rest of Scotland. This significantly reduced travel times and stimulated both economic development and the provision of services in the local area.

Completed in 1984 the Drochaid a' Chaolais Chumhaing / Kylesku Bridge is a more recent example of its building type (see Technological excellence or innovation, material or design quality for more information). Whilst road bridges are not rare in Scotland, the Drochaid a' Chaolais Chumhaing / Kylesku Bridge is a major bridge, which is a particularly significant and unusual example of its type. Concrete box girder bridges are a relatively common road bridge type in Scotland dating to the second half of the twentieth century, with early examples including the M8 White Cart Viaduct (1968) and the Kingston Bridge (1970). The Drochaid a' Chaolais Chumhaing / Kylesku Bridge may be of a later date for this type but its unusual form and impressive setting makes it a unique and highly distinctive example. The curved plan form is particularly unusual for its date (see Plan Form for more information). Another example of a curved box girder bridge is the Fosdyke Bridge in Lincoln (1989), which carries the A71 over the River Welland.

Instantly recognisable due to its striking curved design and spectacular setting, the Drochaid a' Chaolais Chumhaing / Kylesku Bridge stands out amongst its contemporaries. The recognition of its visual interest is also is reflected by its increased use in contemporary advertising (see Technological excellence or innovation, material or design quality and Close Historical Association). Although it is a later example, in the context of the modern era of innovation in road infrastructure that began in the 1960s, Drochaid a' Chaolais Chumhaing / Kylesku Bridge is among only a few landmark bridges in Scotland. Largely unaltered since it was first built, it is an artistic and technically innovative design that responds to a challenging local topography.

Architectural or Historic Interest

Interior

N/A

Plan form

The curved plan of the Drochaid a' Chaolais Chumhaing / Kylesku Bridge was selected as it used the natural contours of the surrounding landscape and the existing roads. This not only resulted in the most economical bridge solution but also one that harmonised with and preserved the natural setting.

A curved form was unusual for bridge design during this period, as it was perceived that bridges should be straight (Nissen, J. in Kylesku Bridge Reunion, 30 Years, 2014). Its use meant that the design and construction process was particularly complex (Transport Scotland). The use of curved elements in road bridges did not become common until the mid 1990s when companies began to manufacture curved pre-cast concrete elements in an effort to create more visually appealing bridges (International Federation for Structural Concrete, Precast Concrete Bridges, 2004: 20).

Showing innovation its plan form, Drochaid a' Chaolais Chumhaing / Kylesku Bridge therefore has special interest under this heading.

Technological excellence or innovation, material or design quality

With the emergence of new building materials and construction methods in the post-war period, there was a new-found belief in the ability of architecture and engineering to overcome natural barriers, thus connecting previously isolated areas to areas of larger population and modern transport links.

Composite steel and concrete box-girder bridges became popular during the 1960s for being relatively cost-effective, low maintenance and straightforward to construct. The uninterrupted profile and reduced massing of the bridge type meant that it became the dominant structural form in road bridge design. By the 1970s there were at least 40 box-girder bridges on Britain's motorway network, the earliest being Salmesbury Bridge in Lancashire (1956-58). Stays were incorporated in some designs to achieve longer spans, which can be seen in such notable examples as the Erskine Bridge (opened 1971 – listed category A) and the Wye Bridge of the First Severn Crossing (opened 1966 – listed grade II). Following the collapse of two box-girder bridges in Australia in the early 1970s during their construction, more stringent codes of practice and independent design checks were introduced.

The rapid expansion of the road and motorway network during the 1960s and 1970s meant that large numbers of concrete bridges were built, with the emphasis being on economy and durability rather than style. By the late 1970s and 1980s more concern was being given towards the aesthetic appearance and silhouette of bridges. As a result, the cast in-situ method of constructing concrete bridges became favoured over the use of precast elements as this led to a more slender deck, which was perceived to be more refined and visually appealing.

The Drochaid a' Chaolais Chumhaing / Kylesku Bridge is a bold design that has used modern construction materials and civil engineering techniques to great aesthetic effect in its remote rural context. The bridge was specifically designed to respond to the particular characteristics of this exposed site. As a result the bridge has a unique form that makes it one of the most iconic bridges within the United Kingdom. This considered approach makes it an early and particularly notable example of the shifting ethos in bridge design during the late 1970s and 80s, towards solutions that were more elegant and more sympathetic to their setting. This is supported by the fact that before construction began the scheme was presented for consideration by The Royal Fine Art Commission for Scotland in 1979. They commented that the bridge design was '…aesthetically exciting and elegant…' and that they would be '…pleased to give their wholehearted approval…' for it (The Structural Engineer 1985: p.71).

The design of the bridge, its materials and methods of construction were chosen due to the challenging nature of the remote site, where standard design and construction techniques would not be suited. The primary concern was to provide the most economical bridging solution that was also aesthetically pleasing. As the deep waterway has steep sides and strong tidal currents, the bridge had to clear the channel and be constructed without temporary supports in the water. A clearance height of 24m was dictated by the Department of Trade and therefore wind resistance was a strong consideration as prolonged periods of gale-force winds are not uncommon in this area. Other requirements were that the bridge had to be durable and relatively low-maintenance and pre-stressed concrete construction was selected as the best method for this reason.

A box girder bridge was selected for Kylesku as the profile of this bridge type, with no external stiffening, gave a streamlined appearance and as there are no traps for dirt or moisture, it is also a very durable type. The overall form of the bridge is simple but the proportions and streamlined appearance add to its design quality. The inclination and tapering of the V-shaped piers serves to create a slender form. Visual interest is added by the geometry of the piers themselves, while the curved approach and deck means that the view of the bridge changes as you move.

Out of the four potential routes, that chosen allowed the bridge to have the shortest span possible, making it the most economical choice. In order to preserve the natural landscape as much as possible, the bridge followed the natural contours of the site, which generated the unusual curved plan (see Plan Form). As the route incorporated the existing approach roads, costs were reduced further as no substantial rock excavation was needed. In order to accommodate this horizontal curvature, the width and angle of the carriageway is varied along its length. The use of the V-shaped concrete piers served to further reduce the length of the central span. The piers were paired and inclined at the base as a way of providing stability against the substantial wind loads. Their geometrical form was also carefully designed to ensure that each pair looked like a single entity rather than four individual supports.

Although it is not a particularly large example of its type, the construction of Drochaid a' Chaolais Chumhaing / Kylesku Bridge was challenging because of the complex geometry of the bridge and the exposed nature of the location (Transport Scotland). The temporary works required during the construction process were particularly complicated, as the bridge only became structurally stable once it was complete. The achievement of both the design and construction process is reflected in the number of awards that were received following the completion of the bridge (see Age and Rarity).

Established in 1946, Ove Arup and Partners are a world renowned consulting engineering firm. Their other notable works erected in the United Kingdom during the second-half of the 20th century include the Kingsgate footbridge in Durham (1966), the Royal Commonwealth Pool in Edinburgh (1965), the Galafairydean Stadium in Galashiels (1963) and more recently the Queensferry Crossing near Edinburgh (2017).

Setting

Located in Sutherland in the northwest of Scotland, the bridge crosses the deep sea inlet of An Caolas Cumhang where Loch a' Chàirn Bhàin to the west, connects with Loch Glencoul and Loch Gleann Dubh to the east. The mountainous landscape setting provides a dramatic backdrop to the bridge, with the rounded peaks of Sail Ghom and Sail Gharb to the southwest being particularly notable features within this remote location. The bridge's streamlined design creates a bold contrast to the rugged nature of the surrounding landscape. Due to the curved nature of the bridge, the inclined V-shaped piers and the angle of the approach roads, views of the bridge itself are ever-changing. The sweeping curve of the bridge follows the contours of the landscape as closely as possible, creating a sculptural and elegant form that sympathetically contrasts with the ruggedness of the natural setting.

Regional variations

There are no known regional variations.

Close Historical Associations

There are no known close historical associations with a person or event of national importance. However, the structure does has significant historical, social, economic and cultural associations with the Highlands from the time when it was opened until the present day.

The bridge was regarded as an important national infrastructural achievement when it was completed and was duly opened by Her Majesty The Queen on 8 August 1984.

Construction of the bridge saw the cessation of the long-established ferry service between Kylesku and Eilean na Rainich. This is reflective of the changing culture of the Highlands, which has undergone successive schemes of imposed improvement since the early 19th century. Before the Industrial Revolution the Highlands had a busy network of communication routes along its coastline and inland waterways. Efforts during the 19th and 20th centuries used civil engineering schemes such as new bridges, roads and canals, as a means of connecting and modernising such remote areas with the main population centres and industrial areas. This ultimately had an impact on the traditional Highland way of life and therefore the replacement of ferries with bridges is an emotive and poignant reminder of this.

With its numerous waterways and a legacy of innovative engineering, Scotland has a rich bridge building heritage. The Drochaid a' Chaolais Chumhaing / Kylesku Bridge is an example of how civil engineering works can affect the economy and way of life of rural communities. This has distinct parallels with the pioneering civil engineering works of Thomas Telford, which transformed the Highland regions in the early 19th century. Telford oversaw the construction and repair of hundreds of miles of new and existing roads, bridges and harbours. This large-scale and wide-ranging feat of civil engineering served to open up Scotland to the north and west of the Great Glen and Telford's roads remain the backbone of the modern road network in the Highlands today. The bridge at Kylesku can be seen as a continuation of Telford's work in the Highlands, which began over 200 years ago.

Having opened up the coastal route to Thurso on the north coast, the construction of Drochaid a' Chaolais Chumhaing / Kylesku Bridge was a major facilitator of the North Coast 500 (a 516-mile circular route that hugs the north coast of Scotland), which was set up by the North Highland Initiative in 2015 to boost tourism and stimulate economic opportunity in the region. The bridge is a now key point of interest along the route, with car parks provided on either side to enable visitors to stop and take photographs of it against the backdrop of the wider landscape. The visual interest in the bridge is further illustrated as it has featured in a large number of international advertisements, for luxury car brands in particular.

References

Bibliography

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