Lindsay Farquharson: 'Repair and Maintenance of Historic Bridges'

95 Repair and maintenance of historic bridges Lindsay Farquharson Introduction Courant of 17 November 1725 as ‘hardly possible for a single man’, would not have been fit for General Bridging Perthshire’s Past was a three-year project Wade’s purpose which was the rapid movement of delivered by Perth and Kinross Heritage Trust (PKHT) large numbers of troops and wheeled vehicles such and supported by the Heritage Lottery Fund (HLF). as gun- and baggage- trains to and from isolated The project ran between October 2008 and September forts and barracks. 2011 and focused on the preservation and promotion of The first road Wade constructed and improved the 18th-century military roads, bridges and associated was that along the Great Glen, effectively connecting monuments in Perthshire. planned and existing forts (Fort William, Killiwhimen The project had three key objectives: to deliver a and Inverness). Wade then turned his attention to creating programme of outreach and education, to improve access and improving two major lines of north–south communi- and interpretation and to carry out a programme of repair cation so that those troops stationed in major strongholds and enhancement at seven bridges that comprised an such as Stirling and Edinburgh and barracks such as essential part of the 18th-century infrastructure. This Perth could be rapidly deployed to the Highlands should paper addresses the last aspect of the project and outlines trouble arise. Finally he improved communication to his some of the considerations involved in the repair of new fort at Killiwhimen by branching off the Dunkeld historic bridges. to Inverness route at Dalwhinnie (Illus 1), (NLS GB233/ MS.7187). General Wade left Scotland in 1740 but before he left he entrusted his road-building programme to Historic background of the bridges Major Caulfeild who had been in service with him from at least 1729 (NAS GD1/369/55). It was a position In 1725 General George Wade, Commander in Chief, Caulfeild was to keep until his death in 1767. North Britain initiated a massive overhaul of the military As with the roads, the construction of bridges before infrastructure in Scotland by constructing and strength- the military investment into Scotland’s infrastructure ening forts and barracks and connecting them with would have been a matter for the Commissioners of a network of roads across the Highlands. It was an Supply or individual landowners and, as such, their ambitious and expensive undertaking designed to construction would have been intermittent. Without a impose Hanoverian control on a population, many bridge the crossing of rivers, especially by foot, could of whom were dissatisfied with the ruling regime be treacherous and there would have been long waits and had therefore allied themselves with the Jacobite until the water had fallen to a potentially manageable cause. Much-needed repairs were carried out at level. Ferries were rare except on the wider rivers and major strongholds, such as Edinburgh Castle and even then their usefulness could be limited depending Fort William, and two new forts were constructed at on the size of the boat. In many cases, especially in the Inverness and Killiwhimen (Fort Augustus), both of Highlands, the boats could only carry three or four which commanded key passes, thereby preventing the people with no room for horses (Burt 1822, 287). In rebels descending into the Lowlands. Scotland had short, river crossings could severely hamper the quick been garrisoned many times before, most recently after and easy passage of troops and therefore a programme the 1715 rebellion but the Highlands remained largely of bridge- building became essential for the security impenetrable to the British forces and their forts and of the Highlands. barracks isolated. Wade, however, had spent time in The masons working on the bridges would have been Minorca and had witnessed how a good road could civilians and appear to have largely used traditional improve military effectiveness. As early as 1724 Wade Scottish construction methods and techniques. In the notes in his report to King George the disadvantageous Tummel contract, Wade gives general dimensions for the situation in which the regular soldiers found themselves bridge and requests that it be well made, of good quality due to the mountainous terrain of the Highlands which materials and easily passable for wheeled carriage or was made ‘still more impractical for the want of roads cannon (NAS, GD1/53/97). He does not, however, give and bridges’ (NAS GD112/47/1). any further direction as to building methods or design. There were of course roads in the Highlands prior A more distinctive style of bridge is generally associated to General Wade arriving in Scotland and maps such with those built under the supervision of Caulfeild as Herman Moll’s A Pocket Companion of ye Roads and his four engineers and may be exemplified by the of ye North Part of Great Britain called Scotland 1718 bridge at the Spittal of Glenshee. It has a gently sloping show them to be fairly extensive. However, many of parapet rising to a peak above the crown, generally the existing roads, described by the Edinburgh Evening with lower arches to provide a wider span (Curtis Tayside and Fife Archaeological Journal vol 18 2012, 95–104 96 Lindsay Farquharson Illus 1 Scotland’s military roads and strongholds. (©Perth and Kinross Heritage Trust) Repair and maintenance of historic bridges 97 1980, 485). However, earlier and later examples of Repair, maintenance and enhancement bridges being built to this pattern in Scotland are not of military bridges unknown. As with Wade it is likely that Caulfeild and his engineers would have provided the masons with Over the years 2005–06, Perth and Kinross Heritage general dimensions and instructions based on their Trust carried out a low-level condition survey of the earlier survey results rather than any detailed written bridges on the line of the military road, using as a specifications (Ruddock 2008; Farquharson 2011). baseline the historic data held in the Perth and Kinross The bridges that survive are of masonry arch Heritage Trust’s Historic Environment Record. The construction; although records of General Wade’s information held in this record largely comprised brief expenditure show that at least two of the 35 bridges notes compiled mid-20th century giving a general mentioned were of timber with stone abutments. The description and condition assessment, sometimes masonry bridges built around this period tend to supplemented by photographs and engravings. The comprise a single arch made up of flat and irregularly 2005–06 survey looked primarily at continued shaped stones. Spandrel walls are of rubble masonry, survival of the bridges, current condition and an most commonly roughly dressed boulders and field initial identification of maintenance and repair needs. gatherings bedded in lime mortar. Between the spandrel The final selection of bridges was informed by the walls there would be a fill of earth and gravel, most survey but also by more prosaic considerations such as likely from the excavation of the bridge foundations. landowner permissions, accessibility and the best result The main purpose of the fill would be to provide a that could be achieved with the budget at hand. Also, solid foundation for the carriageway. There may have on the whole, any bridge that still carried a significant been a waterproof clay layer separating the carriageway amount of traffic was not considered for repair by the and arch, although many historic bridges relied on Trust as, in many instances, this would have involved the structure’s permeability to allow the free passage the consideration of larger-scale engineering works, of water. Gutters in the carriageway are likely to which was outwith the scope of the project. Rather the have been provided, although this can be difficult project focused on maintenance and repair designed to establish. The cobbled surface of the carriageway to retard future deterioration, works to enhance the has often been resurfaced with asphalt to provide a cultural resource and very low-level engineering works wearing surface for modern farm vehicles or have under the advice of a structural engineer. Only one of grassed over. However, gutters were reported during the bridges, that at the Spittal of Glenshee, still carried the consolidation of a military bridge at Corgarff, traffic but was included as the works were minimal Aberdeenshire (Addison 2001). The use of lime-based and not intrusive. A list of the project bridges, their mortars would also have provided the bridge with location and brief descriptions of repair, maintenance a pathway for the movement of moisture through and enhancement works are presented in Appendix 1. the structure and allowed the structure to dry out However, most of the bridges showed a series of similar (McKibbens et al 2006, 33). Finally, a lime harling challenges and considerations – the presence of bats, would be applied to provide a weatherproof coating vegetation growth, deterioration of materials and scour – to protect the joints and pointing, particularly from which are discussed in more detail below. wind-driven rain. Traditional harling was a mixture of aggregate and lime binder. As with all lime-based Dealing with bats materials, it is permeable and worked by impeding the passage of water to the face of the walls by absorption Bats are known to roost in old bridges, partially in and allowing rapid evaporation from its large surface the soffit. Any repair works such as re-pointing and area (ibid). repair to masonry can disturb bats and result in the Records of expenditure show an ongoing programme loss of cracks and holes necessary for roosting and of maintenance during the period of military investment hibernation. Bats and their roosts are protected under of the infrastructure, particularly under Caulfeild, with the Conservation (Natural habitats, &c) Amendment the most common including re-pinning, re-pointing, (Scotland) Regulations 2007.

Load more