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Quick question - there are one or two embankments referred to as "puddle banks", the best known at Braunston. Does their construction differ from other embankments? And was there a reason for this? I'd assumed they were built entirely of clay but this is only an assumption.

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6 minutes ago, Paul Evans said:

An article on the Chesterfield Canal Society website (https://chesterfield-canal-trust.org.uk/gallery/photos/staveley-puddlebank/ ) suggests that the Staveley Puddlebank was built entirely of interlocked clay blocks. Does this help you?

 

 

 

Thanks Paul, yes it does

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No doubt there is a link to clay, but thinking of Staveley leads me to look at another use of the word.

 

In the iron industry, a puddler, was a person who worked up iron in a furnace called the puddling furnace. This was a reverbatory furnace where heat was brought down onto the balls of metal being worked up to a malleable state.

 

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I have no factual information on where the name comes from. But thinking from an engineering perspective, I reckon it may be along the following lines.

 

The early canals were built mainly along contours, following every twist and turn of the contour, as boaters can attest. The construction involved digging out soil from the uphill side and moving it across the line of the canal to form a bank on the downhill side, usually with the towpath along the top. There was generally no movement of soil along the canal. So unless there was a convenient source of clay nearby, the canal would not have a specific waterproof lining, just the existing local soil, which might be puddled a bit by getting cattle to trample it. Consequently these banks were probably reasonably porous, but on the other hand surface runoff from the land on the uphill side would replenish the water.

 

Forward a few years and canals were now built straighter, with deeper cuttings and higher embankments, and this necessarily involved longitudinal movement of soil from cuttings to embankment sections. The cuttings would often meet groundwater, so except in the driest weather, they didn't lose (much) water, and they were not usually clay lined. But the embankment sections, above ground level on both sides, would leak unless lined. And so it became practice to import puddle clay to line them. Hence the name.

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I am no canal engineer, but you cannot go digging a canal and expect water to stay in the dug cut without a sealant - clay, but 'puddled' clay. Brindley famously gave a demonstration of how regular clay would not hold water, until it was 'puddled' or pummeled by kneading well. Then it would hold water. The equivant was said (by some) to have been done by running some cattle along the clay bed to do the pummeling or puddling.

 

Puddle banks I have always taken to be places where large amounts of the required clay was kept until required. I seem to recall there was a puddle bank along the Slough arm somewhere.

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2 hours ago, David Mack said:

Forward a few years and canals were now built straighter, with deeper cuttings and higher embankments, and this necessarily involved longitudinal movement of soil from cuttings to embankment sections. The cuttings would often meet groundwater, so except in the driest weather, they didn't lose (much) water, and they were not usually clay lined. But the embankment sections, above ground level on both sides, would leak unless lined. And so it became practice to import puddle clay to line them. Hence the name.

 

Interesting idea, and as far as I'm aware that is how the Bridgewater Canal works - lined on the embankments and not in the cuttings

2 hours ago, Derek R. said:

I am no canal engineer, but you cannot go digging a canal and expect water to stay in the dug cut without a sealant

 

Maybe you can't expect it but it's what several early canals did - St Helens Canal, Exeter (much earlier), indeed anything pre-Brindley

2 hours ago, Derek R. said:

Brindley famously gave a demonstration of how regular clay would not hold water, until it was 'puddled' or pummeled by kneading well. Then it would hold water

 He did, but I think he picked the technique up from French canals - I suspect it was the Duke rather than Brindley who had been to France though

 

2 hours ago, Derek R. said:

Puddle banks I have always taken to be places where large amounts of the required clay was kept until required. I seem to recall there was a puddle bank along the Slough arm somewhere.

 I can see where you are coming from, but at least two canal embankents, Braunston Puddle Banks on the Oxford, and Staveley Puddle Banks on the Chesterfield, are canal embankments carrying the name. The latter was proposed by Brindley but probably built by Hugh Henshall

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6 minutes ago, magpie patrick said:

 

 

Maybe you can't expect it but it's what several early canals did - St Helens Canal, Exeter (much earlier), indeed anything pre-Brindley

 

I could be wrong but aren't sections of the GU unlined due to the height of the local ground water?

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2 minutes ago, tree monkey said:

I could be wrong but aren't sections of the GU unlined due to the height of the local ground water?

 

I don't know the specifics but it wouldn't surprise me - puddling was common but nowhere near universal, it was blimmin expensive if it wasn't needed

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In the case of Braunston I’d always thought it likely to be way of describing a form of construction where the embankment is formed from the material that also retains the canal water.

 

A railway embankment - and presumably the major works on later canals such as the SU main line - would generally consist of a clay core overlaid with ash or soil to form the finished profile. Hence there is an engineered structure beneath the line of way (iron or water) above.

 

In the case of Braunston the canal is carried over relatively flat lower lying land. I suspect there is no proper embankment structure beneath the canal and the construction is broadly two parallel bunds of clay laid on top of a prepared bed formed by localised cutting and filling as necessary, and quite possibly with a clay lining between the ‘banks’.

 

 

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2 hours ago, magpie patrick said:

 

I don't know the specifics but it wouldn't surprise me - puddling was common but nowhere near universal, it was blimmin expensive if it wasn't needed

 

It would indeed, and there must be lengths which are river fed (The Bulbourne and Gade for two) that are fed by natural water sources.

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4 hours ago, tree monkey said:

I could be wrong but aren't sections of the GU unlined due to the height of the local ground water?

When we had water shortages a few years back Tring Summit was down about a foot -18 inches. CRT initially closed it, but then arranged a trial passage by a deep drafted boat, which got through with few problems, so they reopened the canal. Thereafter, although it still didn't rain, the level remained constant. The assumption was that the groundwater table in the chalk through the summit cutting at that time was about 12 inches below the normal (on weir) water level. Presumably in wetter times, it is higher, meaning that although the cutting is through porous chalk, there isn't much water lost through leakage. The same sort of thing must happen elsewhere.

Edited by David Mack
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Puddle is a little more complicated than is generally thought, and I suspect clay was not used extensively. The Austrian canal engineering book I have recently translated - hopefully available soon from the Railway & Canal Historical Society - gives the lining of a canal as being created by suitable soil mixed with small stone, which was then made watertight in layers. Rees' Cyclopedia and some contemporary specifications for canal building does confirm this. The Austrian book - the author visited England in 1795 - then suggests that using clay was an English invention developed by Brindley. If the use of clay for a canal lining was relatively unknown, then Brindley's presentation of the system in Parliament does become more understandable. The major problem with using clay for a canal would be the difficulty in moving sufficient amounts before the canal was built. I would expect that the use of clay was widely known by millwrights in the UK, but only used where suitable supplies were within easy reach of the section of canal to be lined. A clay lining would only need to be around one foot thick, while the earlier system using suitable soil required a thickness of around three feet. Historically, a canal had a 'lining' where it was necessary to make it watertight, though a lining was not necessary where the existing soil could be made watertight, or where the water table was high enough to keep the canal filled. 'Puddle' was the term used for a clay-filled trench which made the boundary between existing soil and a new embankment impermeable, such as on a reservoir dam.

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  • 2 months later...

When we first encountered Braunston Puddle Banks 50 years ago, there was a large heap of puddle clay stored next to the point where the dredgings were unloaded as the embankment was quite wide there. I always assumed that the local clay was  suitable for repairing the canal so some was stored where it could be easily accessible in case of need. Some of the wartime photos of the bomb damage to this embankment should show the original construction methods but I don't have them currently to hand. I recall that the reconstruction gang were working too slowly and were replaced!

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On 26/06/2021 at 19:33, tree monkey said:

I could be wrong but aren't sections of the GU unlined due to the height of the local ground water?

I was told that the GU and marinas in the Calcutt area did not need puddle clay because the natural blue lias did the job/

.

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The more contemporary articles I read about making canals water-tight, the more I think that they did not use clay as we know it now as a sealant. That was only introduced after canals opened, when it would be cheap enough to transport. The water-tight layer was made from suitable earth from local excavations mix with small stones and loam. It was only when repairs became necessary that clay was used. Suitable clay is not found everywhere, so puddle banks may have been created where suitable clay was stored after being delivered by boat. There were also clay pits, where the clay was sourced, and I know of two on the L&LC, one on the Leigh  branch, which I think is still the main local source, and one below Dean Lock which is now overgrown, with several old wooden boats sunk in the basin.

 

Confusion is also created by the way the term 'puddle' has changed in meaning. It traditionally meant a vertical wall of clay between the original ground level, and any new material above, and could be called a 'puddle trench'. These were used during construction of dams for reservoirs and, depending on circumstances, between the original ground and earth thrown up to create the towpath. The water-tight layer forming the bed of a canal was called the 'lining'. This term now seems to have been replaced by 'puddle', or 'puddle lining'.

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Another, more recent, report about puddle comes from G R Jebb's paper on Maintenance of Canals, with special reference to the Mining Districts, for the 1888 Royal Society Conference on Canals. Describing maintaining canals where there is subsidence, he says (about images which I do not have):

The cross-section shows how the canal has been maintained. When the first swagging (subsidence) began, a puddle wall, 3 feet in thickness, was constructed on either side of canal, with a slope of puddle on the canal side, and these puddle walls were raised from time to time as required, the space between the slopes being filled up with mud dredged out of other parts of the canal, or with marl. Either of these materials is better than clay, as they seal up more readily any incipient cracks in the puddle walls. Of course, embankments have to be formed outside the puddle, and raised and strengthened as the ground goes down.

 

Again, another confirmation that clay was not the best material for making a canal water-tight, and that locally-sourced materials could be better. I suspect that clay was used where it could be dumped directly over a problem area of the canal bed. This would ensure that it was kept wet, and was probably easier to work underwater than other materials because it kept compact.

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Two interesting points to come out of this

 

My basic question, perhaps now well articulated, was "why are there two embankments on the canal system known as puddle banks? What distinguishes them?" At least part of the answer is that the meaning of the term "puddle" has changed

 

Second - clay wasn't anywhere near universal as a lining as people suppose. That's is of great relevance on canal restoration as it probably explains a lot of futile ground investigations trying to find clay lining! 

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