SLHS Edstone Aqueduct

History - The Problem

The entire Stratford Canal was built to run roughly parallel to the Grand Union Canal not far away and compete with it by offering cheaper tolls.  Construction of the northern section by Josiah Clowes got as far as Kingswood but ran out of money in 1802.

William James ran much business north - south and took charge of the construction of the remaining southern section. By 1816 his surveyors knew that they needed to cross a wide valley and the river leading from the lake at Edstone House. The depth of the valley would require 4 locks to be constructed each side.

However locks were expensive, required maintenance and took barges considerable extra time to negotiate.

There was also a technical problem. A far as possible canal systems should always have locks facing the same way, not because it may be slightly quicker for the bargemen, but because where there is a change of orientation water must be provided or sent to waste depending, respectively, on whether one is at the summit or at the bottom of a valley.

Thus this section, going down one side and then up the other, would see water leave the canal system as a whole .

Navies knew that the canal ‘cut’ must be lined with ‘puddled clay’ to prevent water loss. Unrecoverable loss of water due to avoidable locks was a well known problem in the area in summer and could result in the canal being unoperable and thus considerable toll revenue would be lost. Obviously pumping water all year round is extremely expensive and requires 100% reliability otherwise a section of canal would eventually have to be closed and any system like this is dependent on its weakest link.

Further Information

1. Histories: Stratford Canal
   

2. Many technical details: Industrial Tour: Edstone Aquaduct

SLHS Picture & Document Archives..

1. Coming soon..

● Longest in England     ● Early example of prefabrication     ● Unusual towpath height

Located above Salters Lane near Bearley.

Problem Solved

The entire problem would be solved by an aqueduct. However this would be the longest ever built. Construction was overseen by William Whitmore in 1816. It features 35 prefabricated cast iron troughs each 2.7m x 1.5m. They have a towpath at trough base height and corresponding handrailings. Each is bolted to the next. It is supported on 13 brick parapets with extremely deep foundations because for cast iron nothing must move.

Another known problem for pre-Victorian Engineers is that being suspended in the air the entire structure is subject to considerable temperature changes and thus expansion and contraction. Thus the troughs cannot just be simply rested against one-another but huge bolts must be used because during contraction in cold weather the entire bridge and it’s thousands of tons of water will get shorter ! Thus the water seals at each end must be capable of moving around 200mm each. Likewise it is a little surprising that the bridge has not split side-ways due to the expansion of ice on the surface of the water, which can be seen to be at least 100mm thick, in a cold winter. One assumes that the cast iron is ductile enough to allow transverse bowing of the troughs by 9% which is the peak increase in width with ice at -4ºC. The position of the whole canal must snake it’s way to where the dead-straight aqueduct must lie. Unless, of course, one is to build a curved aqueduct -but don’t even think how dreadful the technical problems are if length changes are on a curve !

The fact that it still stands unaltered today is a testament to Mr Whimore’s excellent Engineering skills.

Closure -But Not Closure

Once the railways were established it was only a matter if time before the canal fell on hard times but it’s success made it last longer than many. Sadly by the 1930’s it was closed for trade. However the aqueduct remained useful to the GWR to top up it’s engines with relatively soft rainwater running in from each end via the installed feed pipe (see below right).

Thus there was no incentive to sell it for scrap. Steam ruled the railways until the early 1960’s but before then many volunteers were beginning to see a wealth of pleasure that could be had on Britain’s waterways. David Goodman (father of the webmaster) became Founder Treasurer of the Stratford Canal Society and through various pressure groups’ petition to central government in London Warwickshire County Council’s Plan to fill in the canal was averted (see Further Information below).

You can find out more about these here: Red Plaques

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