Monument record MDR9697 - Leashaw Bridge, Cromford Canal, Lea Shaw, Crich

Leashaw Bridge is an original bridge of the Cromford Canal, built 1792-4 at the same time as the canal. It is a simple hump-backed bridge of local rough coursed gritstone. The string course follows the line of the deck. It was presumably designed by the engineers Jessop & Outram. Arched recesses in the bridge narrows indicate 'Brindley Gates'. This style is typical of small canal bridges of the period and developed from the earlier bridges over the Trent & Mersey Canal, designed by Brindley. The bridge provided access from Leashaw Farm up a track to Leashaw Road. The towpath passes under the bridge on the west bank. (1) Because the canal ran so high up the side of the valley, it was essential to be able to close off sections of the canal in case of a breach. The conventional manual technique of inserting stop planks was good for planned maintenance, but no use for an emergency. In an attempt to provide gates that would automatically close, many canals adopted what have been dubbed 'Brindley Gates' after the famous canal engineer on whose canals they were first used. At Leashaw Bridge contractors relining the canal revealed parts of the gates during dredging. The gates pivoted across the width of the canal bed, which was stone lined in such places. If a breach occurred to the right of the bridge, the flow of water would force the left-hand gate to rise, thus blocking off any further flow, and vice versa. Indicative signs on the canal today are elongated narrows such as at Leashaw and several other bridges, including Whatstandwell where an additional tell-tale is the arched recess in the masonry, clearly visible form the towpath, inside which the gates would have rotated. (2)