1805 - Pontcysyllte Aqueduct
Canals, far more than roads, established the vital supply lines of the Industrial Revolution, offering big economies in the long-distance movement of heavy goods such as coal or grain, where transport costs are high in relation to their intrinsic value. The maximum capacity of a cart was only a few tons, even with up to eight horses hauling it. A canal barge could carry a much heavier payload - and with only a single horse. To cut down on expensive civil engineering works, canals tried to follow a flat course around the land's contours, using locks to change levels. If this was not possible, cuttings, tunnels, bridges, aqueducts and embankments had to be constructed to cope with the problems imposed by the geography of the area. The first British canals were opened in the mid-18th century and a network of waterways quickly spread across the country until the coming of public railways in the 1830s emphatically halted their growth. Nevertheless, they continued to provide a cheap, if slow, alternative means of transport for heavy bulk commodities until the large-scale advent of the motor lorry in the 1930s sent them into a terminal decline. Would it be practicable today to transfer some long-distance bulk transport from the motorways back to the canals?
Many of our rivers are navigable and in times past they formed an important channel of communication. Canals, however, were the real lifeline of British industry in the 18th century and after. Dug by labourers armed with nothing more than picks and shovels, they were far more practical than roads for the economical long-distance transport of heavy goods. To keep them level, some extraordinary feats of civil engineering were called for and at Pontcysyllte in Clwyd, Thomas Telford's thousand-foot aqueduct of 1805 carries the Shropshire Union Canal over the River Dee, 127ft beneath. The structure itself is less than 12ft in width, with a path 4ft 8in wide cantilevered out over the water for the towhorses. This left barely seven feet for the passage of barges which, to carry the maximum payload, could be anything up to 70ft long. The overhanging towpath was a novel and elegant solution to a major design problem. Earlier iron aqueducts had even narrower troughs and outside towpaths, but water did not flow easily in the tight space between the hull and the walls of the trough, and considerable effort was needed to haul the boat along. The additional width under the towpath at Pontcysyllte greatly reduced both drag and spillage. Iron railings guard the outer edge of the towpath but, on the navigation side, the water is only a few inches below the unprotected lip of the trough, and one looks straight down on the foaming, tumbling Dee, so very far below. For sheer white-knuckle drama, no fairground ride can match it. To cross in silence aboard a horse-drawn boat, separated by only a slim thickness of iron plate from the waters beneath, must have been a truly awesome experience. Though commercial traffic has long vanished, the aqueduct at Pontcysyllte -pronounced Pont-ker-shulty —is still regularly used by pleasure craft. Reflecting its importance, it is scheduled as an Ancient Monument.
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