The restoration of the Kennet and Avon Canal stands as one of the 20th century’s greatest testaments to the success of volunteer effort and determination. Closed to navigation in 1954, restoration began tentatively in the early 1960s, with slow progress until the early 1980s when fundraising gathered momentum and the Job Creation Scheme funded the solution to the most challenging civil engineering problems. It was re-opened along its full length by the Queen in 1990.
The canal is a ‘watershed canal’ joining the two rivers from which its name is derived, but John Rennie’s original 1794 design would have required a 2½ mile long tunnel under Savernake forest in order to store sufficient water in the ‘summit level’ to feed the locks on both sides. William Jessop’s 1796 suggestion to divert the canal at Wolf Hall to save substantial cost was thus enthusiastically accepted. This reduced the tunnel to a mere 500 yards, but required further locks to reach the higher contour and the need for a steam pumping engine to raise water to this higher level.
An Act of 1796 authorised the construction of a pump house at Crofton, near Marlborough, to supply water to the summit level from springs at nearby Wilton, and by 1809 the building was complete and the first engine ready to begin pumping. The canal opened at the end of 1810, but more capacity was needed and a second Boulton and Watt engine added in 1812.
The latter is still running today and is the world’s oldest steam engine still carrying out its function in its original location. ‘Cornish’ boilers were installed in 1843 and the first engine exchanged in 1846 for a Sims combined engine, which still runs today. Soon after the closure of the canal the tall boiler chimney became unsafe and was reduced in height in 1958, rendering the boilers unviable and forcing closure. Nine years later the Kennet & Avon Canal Trust purchased the pump house from British Waterways and immediately began restoration of the engines, opening them to the public in April 1970.
Essential repairs were made to the building from 1968, but by 2016 a backlog had built up to such a degree that the Trust needed to make an application to the National Lottery Heritage Fund to safeguard the future of the building and its unique machinery. Constant battering by rain-charged westerly winds and the vibration from the rocking of the twin 6 tonne beams had taken its toll, so a programme of considered conservation was devised.
In November 2017 the Bath office was appointed to refine the NHLF scheme to implement the ‘delivery’ phase of the project. working with Crofton’s management team which monitored the implications of the structural repairs on the functioning of the engines. A decision was made to allow the ‘steaming weekends’ to continue with public access throughout the construction phase, posing some logistical challenges. Of these, perhaps the most difficult was the need to re-support a main beam carrying James Watt’s impressive ‘parallel motion’; an ingenious set of precision-engineered linkages which eliminate rotational stress on the huge piston rods at their connection to the rocking beam. Only a ten-day ‘window’ was available to carry out this complex task, so contingency plans were needed! In the event. all went well and the next public steaming ran without interruption.
Throughout 2018 the pump house and adjoining boiler house were sensitively repaired with the Georgian brickwork repainted on the prevailing side, the boiler house re-slated and its lantern recreated, window and door joinery repaired and a programme of beam-end repairs where buried in damp walls. The 15m vertical shaft beneath the building, up which the water is pumped, required various iron tanks and structures within it to be de-rusted and resupported as a safety measure. New facilities were created, notably a new brick toilet block accessible to all, and improved staff facilities. However, the second portion of the project. including an oral history archive, advanced engineering monitoring and new interpretation material throughout the building, has continued right into 2021 and the education outreach will continue for many years to come.
Georgian engineering structures are an uncommon breed, but when they contain working machinery of unparalleled importance in our industrial and transport history, their conservation is doubly satisfying.