Observations regarding the Whitchurch Canal Breach

[Heartland]

With the publication of the Interim report, several questions have been raised,

 

In trying to find the cause or causes they have delved into a new realm

It is suggested that there was a long term leak and that the canal had been deepened there. Along with this was a possible suggestion that boaters turning their propellors may have contributed to the breach.

 

If the embankment had been weakened by piling and the use of this spot as a popular mooring location. Boats arriving and leaving might have an effect on the bed of the canal and if so is this something that needs to be addressed.

 

There is also the effect of water getting behind the waterway wall or piling and what damage that might cause over time. For those who have seen the Bridgewater videos it is clear that water is passing past the coffer dams and behind the walls to exit on the drained sections. With time water in such locations might freeze in winter and on freezing to ice expands creating a larger hole. An again is this an issue engineers should consider.

 

[David Mack]

7 minutes ago, Heartland said:

For those who have seen the Bridgewater videos it is clear that water is passing past the coffer dams and behind the walls to exit on the drained sections. With time water in such locations might freeze in winter and on freezing to ice expands creating a larger hole. An again is this an issue engineers should consider.

The UK climate isn't cold enough for the ground to freeze to any significant depth,so freeze damage isn't really a problem. Unlike much of the northern part of continental Europe or North America where ordinary houses all have basements as you have to put the foundations that deep anyway to get below the zone of winter frost heave.

[PeterF]

41 minutes ago, Heartland said:

If the embankment had been weakened by piling and the use of this spot as a popular mooring location. Boats arriving and leaving might have an effect on the bed of the canal and if so is this something that needs to be addressed.

This area is quite often exposed to frantic and frenetic engine revving and prop thrashing. Coming from Grindley Brook there is a left hand curve often with boats moored on the towpath (right hand) side followed by the VMs on a right hand bend with boats moored on the offside, with a lift bridge with the lift bridge landing opposite the VMs, in a very busy location, with the current to deal with, with lots of novices in their first day (many in their first 10 minutes) of narrow boating. We have been hit several times whilst moored on those VMs, seen boats pinned across the canal, by the current, seen lots of last second full power reverse to avoid collisions. All on a sand based embankment. This location perhaps inadvertently brings a large number of factors into play that could cause prop wash damage to the canal bed.

Edited April 2 by PeterF

[Col_T]

I can see that the scenarios @PeterF describes could have some kind of scouring effect, but wonder whether this effect would be diminished because the boats would be moving for most of the time. The idea being that the scouring from a moving boat would / might create a shallow trench rather than a deeper pit. Once the ‘emergency’ is over, the throttle would be closed and the scouring stops. This, of course, is not the case when a boat is tied up with the engine running in gear for whatever reason.

[David Mack]

This area is used by boats setting down and picking up crew to operate the lift bridge, as well as those mooring for longer periods, so it is likely to see more manoeuvring close to the bank than areas that are just visitor moorings.

[Quattrodave]

On 02/04/2026 at 17:34, Heartland said:

If the embankment had been weakened by piling

 

I may be misunderstanding here, but wouldn't piling be reinforcing the bank?

We are talking about what is often refered to as 'Armco' arn't we??

[Stroudwater1]

23 minutes ago, Quattrodave said:

 

I may be misunderstanding here, but wouldn't piling be reinforcing the bank?

We are talking about what is often refered to as 'Armco' arn't we??

I would have thought the same but a  long time ago (1970s) a breech up by Llangollen happened. It was “sorted” with pilings but it failed very rapidly leading to a second breech and hence the concreted trough. Others will know why it happened. 

[MrX]

The piling was not long enough. This was covered on the original thread. 

 

By hammering  1.8/2.1m piles in the top of the embankment the structure was compromised and a route was provided for water to get under the canal bed and cause the piping effect. That's what happened. Piping.

 

I did mention this at the time ! 

 

The only type of piling which would work in this scenario is 30ft Larsen piles. Mickey Mouse campshed piles are the wrong thing. 

 

Embankments like that are supposed to have outward angled stones or slabs.

 

Not tinny piling. 

 

 

Edited April 3 by MrX

[David Mack]

1 hour ago, Quattrodave said:

 

I may be misunderstanding here, but wouldn't piling be reinforcing the bank?

We are talking about what is often refered to as 'Armco' arn't we??

The issue is if it extends down all the way through the puddle clay lining, and creates a leakage path through to the sandy embankment material below, which can then get washed out over time.

[jonesthenuke]

The report says the old piling failed by lining (rotating) into the canal. This may have caused a gap in the clay liner on the bottom of the canal. The new piling was installed with crushed rock fill behind it (as seen in various videos). This would allow water flow behind the piling as the old and new piling would not have been joined together. This leaves the possibility that clay base of the canal or whatever was sealing the side walls had failed and water would be permeating into the embankment which we now know was constructed of sandy material. I suspect a sand embankment saturated with water is more likely to slip. Thus the breach. To me this looks like the new piling etc was an inadequately designed repair to a failing embankment.

 

PS I am not a civil engineer and would be interested if someone suitably qualified commented on this

[MrX]

 

It's obvious that these sheets were ordered to be fitted by someone who didn't understand what they were doing. The overriding objective would have been to provide a useful path and deep edges without considering the fact that it was an embanked section of canal. It's blatantly obvious to anyone with a modicum of engineering understanding that it was the wrong thing to do. 

 

mm

 

 

Edited April 3 by MrX

[matty40s]

12 hours ago, MrX said:

 

It's obvious that these sheets were ordered to be fitted by someone who didn't understand what they were doing. The overriding objective would have been to provide a useful path and deep edges without considering the fact that it was an embanked section of canal. It's blatantly obvious to anyone with a modicum of engineering understanding that it was the wrong thing to do. 

 

mm

 

 

 

My mistake 

Although gybeho is obviously still here....

Edited April 4 by matty40s

[David Mack]

2 hours ago, jonesthenuke said:

The report says the old piling failed by lining (rotating) into the canal. This may have caused a gap in the clay liner on the bottom of the canal. The new piling was installed with crushed rock fill behind it (as seen in various videos). This would allow water flow behind the piling as the old and new piling would not have been joined together. This leaves the possibility that clay base of the canal or whatever was sealing the side walls had failed and water would be permeating into the embankment which we now know was constructed of sandy material. I suspect a sand embankment saturated with water is more likely to slip. Thus the breach. To me this looks like the new piling etc was an inadequately designed repair to a failing embankment.

 

PS I am not a civil engineer and would be interested if someone suitably qualified commented on this

When originally installed the toe of the piles would be embedded in the canal bed, and the top would be restrained by tie rods attached to the waling beam (the 'armco') which are anchored to shorter piles driven well back from the canal edge. Thus the piles are supported top and bottom against side loads from the towpath material. There have been failures with this sort of approach where the top anchor piles have failed, allowing the tops of the sheet piling to move forwards, and that could open up a gap in the puddle behind the piles. But with older piles, such as these installed in the 60s and now around 60 years old, it may be that the piles have corroded through to the extent that they can no longer take the loads imposed on them - you can sometimes see older sheet piling which has rusted through at around water level. In this situation the pilign may fail in bending while the top remains restrained, with the middle of the pile moving forward into the canal, and similarly creating a gap behind the pile at puddle level.

[Ange]

5 hours ago, matty40s said:

 

I thought you wanted out of the forum, have your account deleted etc.

Why come back at all?

Your other account @Gybe Ho is still.there.

Interesting. Thank you Matty.

 

Mod Q maybe?

This isn't the hotel California Gyberish.

Please leave.

[MrX]

10 hours ago, matty40s said:

 

I thought you wanted out of the forum, have your account deleted etc.

Why come back at all?

Your other account @Gybe Ho is still.there.

Gybe ho has nothing to do with me. I'm magnetman/andrew.

 

People are allowed to come and go from the forum if they want to it's just I can't get into my other account. 

 

 

 

 

[Gybe Ho]

1 hour ago, MrX said:

Gybe ho has nothing to do with me. I'm magnetman/andrew.

 

 

I am reassured to read that the Magnetman brain worm is not living in my skull.

 

The Mods seem to be approving two month old posts.

[Gybe Ho]

11 hours ago, matty40s said:

 

I thought you wanted out of the forum, have your account deleted etc.

Why come back at all?

Your other account @Gybe Ho is still.there.

I cannot speak for @magnetman but The Mods agreed to delete my account last August. Perhaps Brigade 77 vetoed that.

[MrX]

It actually is me but I can't get into my magnetman account because I've changed the email to a burner email address as a slightly anorakish way to block myself.

 

It's a non functioning account. 

 

I have no idea what the email or password is because I wrote it on a piece of paper then put it in the fire.

Edited April 4 by MrX

[Graham Davis]

14 hours ago, MrX said:

The piling was not long enough. This was covered on the original thread. 

 

By hammering  1.8/2.1m piles in the top of the embankment the structure was compromised and a route was provided for water to get under the canal bed and cause the piping effect. That's what happened. Piping.

 

I did mention this at the time ! 

 

The only type of piling which would work in this scenario is 30ft Larsen piles. Mickey Mouse campshed piles are the wrong thing. 

 

Embankments like that are supposed to have outward angled stones or slabs.

 

Not tinny piling. 

 

 

So you have inspected the breach site at close quarters, with the full permission of CaRT, have you?

And exactly what are your qualifications? Please state them.

 

Or are you another keyboard warriors who thinks he knows everything, but really knows beggar all?

[Stroudwater1]

The pilings are all too obvious to see for quite a distance and are indeed usual BW ones,  pretty short, not sure how old they are though perhaps from the 80s? There were images of ones nearby that were rusted out. 
 

I suspect that Magnetman has read the initial report that seems to suggest  that?

 

 

[jonesthenuke]

I remain unconvinced by the piping suggestion. The new piling has considerable rock fill behind it  (I accept this is at the only remaining point on the piling), this suggest to me that the original bank material which behind the old piling fell into the canal. If this was the puddle clay lining then at least part of the water seal was lost. I doubt it is in CRTs interest to  suggest such a root cause though.

[David Mack]

2 minutes ago, jonesthenuke said:

I remain unconvinced by the piping suggestion. The new piling has considerable rock fill behind it  (I accept this is at the only remaining point on the piling), this suggest to me that the original bank material which behind the old piling fell into the canal. If this was the puddle clay lining then at least part of the water seal was lost. I doubt it is in CRTs interest to  suggest such a root cause though.

That would still result in a piping failure of the embankment. 

We are unlikely to ever know with certainty what the cause was, since the original failure point will have been destroyed by the subsequent washout of large quantities of water and embankment material. That said, once the washed out material has been removed the two culverts beneath the embankment can be properly examined to see if either of them did or did not contribute to the failure.

[jonesthenuke]

1 minute ago, David Mack said:

That would still result in a piping failure of the embankment. 

We are unlikely to ever know with certainty what the cause was, since the original failure point will have been destroyed by the subsequent washout of large quantities of water and embankment material. That said, once the washed out material has been removed the two culverts beneath the embankment can be properly examined to see if either of them did or did not contribute to the failure.

I may be getting lost in the terminology and perhaps you can clarify. Piping suggests a small through wall leak of the embankment which would get larger as the bank material is washed out. I was think that saturated bank material would suddenly slip, though perhaps this is less likely in a free drawing sandy material rather than mud/clay.

 

I fully realise the material has been washed out thus leaving little evidence, however there is some visual evidence that the cause was not the culverts.  All the material is on one side of the bank. If either culvert had failed then I would expect to see red sandy material at the outlet of the culverts on the non breach side of the canal and none is visible.

[David Mack]

"Piping" is a term for internal erosion within a body of soil (regardless of where and how that water came from).

Google's AI summary says "Geotechnical piping is a form of internal erosion where seepage water removes soil particles, creating hollow "pipes" or tunnels that can cause catastrophic failures in dams, levees, and excavation walls."

In this case the seepage water presumably came from the canal, but that could have been as a result of leakage down the line of the sheet piling, or some other hole or crack in the puddle lining, or as a result of the puddle layer having been damaged by extensive propeller activity.

Canal linings are rarely completely impervious. Puddle clay installed 200+ years ago, using manual methods, was never going to be as effective as a modern engineered solution with a variety of specialised techniques and equipment. Then add in a couple of hundred years of wear and tear, general degradation, random repairs, climate change etc. etc. There will always be water seepage through embankments, but as long as the situation is stable, and no material is being washed out, then everything is fine. And if internal erosion does occur, it can be a long time before the resultant void grows to the size where it is no longer self supporting and collapses. There may be no visible signs this is happening until a significant collapse occurs.

Its actually quite surprising that there aren't more failures of this type.

[MrX]

5 hours ago, jonesthenuke said:

I may be getting lost in the terminology and perhaps you can clarify. Piping suggests a small through wall leak of the embankment which would get larger as the bank material is washed out. I was think that saturated bank material would suddenly slip, though perhaps this is less likely in a free drawing sandy material rather than mud/clay.

 

I fully realise the material has been washed out thus leaving little evidence, however there is some visual evidence that the cause was not the culverts.  All the material is on one side of the bank. If either culvert had failed then I would expect to see red sandy material at the outlet of the culverts on the non breach side of the canal and none is visible.

 

I think it was not the culverts.

 

It was a water path inside the embankment. 

 

The CRT female staff member did actually say this within days of the failure. She used words (or very similar) "when you get a water path... It unravels..."

 

This is because people who know what happened could immediately see what the cause was. The piling creates a wet/dry interface and also a vertical surface down which water would move. The piling is not long enough and was rusted through. 

 

This water, possibly assisted by animals, made is way under the canal bed and across the embankment gradually creating a hollow section which then collapsed into itself. A self filling leak. The resulting movement of water (water follows gravity as can be seen with locks) which was making it's way to a hole which is now blocked then creates a pressure wave which blows the outside of the bank away. 

 

I have not read the report. This was my original theory from when the event occurred. 

 

magnetman

 

.