C O N T E X T 1 1 0 : J U LY 2 0 0 9 23 remain to reinstate the canal to its full length, creating a continuous waterway between London and the Lake District. Ask the majority of people what they imagine when they think of canals and they will describe a canal lock. However, the 42 remaining miles of the Lancaster Canal form one long continuous lock-free ‘pound’, making this effectively the longest canal pound in Britain. Instead of locks, the Lancaster Canal derives its character from the simple and robust Rennie-designed bridges, built from local limestone and sandstone. Having stood as a memorial to the skills of Rennie and his assistants for around 200 years, these unpretentiously elegant structures are now under increasing threat from vehicular damage. British Waterways, the public corporation responsible for the Lancaster Canal, finds itself having to address three distinct issues in relation to these bridges. It works with partner agencies to devise strategies to reduce the instance of bridge strikes; carries out high-quality and often extensive works to damaged bridges that may be listed; and manages the associated health and safety concerns, as the majority of these bridges have a heavily used canal and towpath running below – an area of risk where stone parapets are being dislodged. One recent example where an inter-agency solution has been developed is at the Grade II listed Crooklands Bridge, south of Kendal. The limestone bridge, dating from around 1818, was completed to Rennie’s original design under the direction of the resident engineer, John Fletcher. It has been struck repeatedly over the past three years. On one occasion in 2007 the bridge was struck and damaged while undergoing repairs from a previous strike. The hessian sheet protecting the lime mortar had not yet been removed and British Waterways had not yet been able to photograph the work. The problem at Crooklands is exacerbated by the road crossing the bridge on a sharp bend at its western end, and the fact that the bridge is busy with heavy lorries. Following the 2007 strike, which left around ten linear metres of the bridge parapet on the towpath below, British Waterways worked in association with a local volunteer group (the Lancaster Canal Trust), seeking to engage with Cumbria County Council to agree variations to the road layout in an attempt to reduce the number of vehicle strikes. Progress with these discussions was slow.While there was general agreement regarding the repairs required, a technical question was raised as to whether or not the use of lime mortars in the repairs was leaving the bridge weakened and susceptible to further damage. British Waterways’ heritage policy is to use traditional materials during repair works to historic structures. It was successfully argued that the use of lime mortar represented best practice and was protecting the overall integrity of the structure. BritishWaterways further argued that the use of lime mortar allowed the mortar joints to become ‘sacrificial’ elements of the structure, avoiding greater damage to the original stonework. The council formulated a change to the road markings which would direct heavy goods vehicles towards the middle of the road when approaching the bridge, to encourage vehicles not to cut the corner. The highway alterations at Crooklands Bridge appear to have had a degree of success, although it was apparent from a recent inspection that the parapet had suffered a number of minor impacts following the works. Different problems have been experienced at the Grade II listed Borwick Bridge, which crosses the Lancaster Canal to the north of Carnforth. This bridge, dating from around 1797, is constructed of locally-sourced sandstone. Serious damage was caused when around five metres of its stone parapet was totally demolished by a vehicle crashing through the bridge parapet and landing on the towpath below. As this bridge is sited on the section of canal still in use, British Waterways had a responsibility to reopen the canal and return the highway to a safe state as soon as possible, while ensuring that the integrity of the historic structure was maintained. Initial assessment of the damaged stonework showed that little of it would be suitable for re-use during repairs to the bridge. The local sandstone is comparatively soft, and the stone blocks that were recovered had in most cases been badly damaged by both the impact of the crash and the drop of around 15 feet to the towpath below. Sufficient details were available for an insurance claim to be pursued. As is often the case with such The Grade II listed Borwick Bridge before (left) and after repair work
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