Canal-side Subsidence

[TheFew]

Hello,

I am looking for a little advice on how best to proceed with a small problem.

My garden backs onto a canal, where we have some steps leading to a small walk way and a mooring (as can be seen from the below pictures).

Today whilst using the walkway the ground collapsed under foot!

It seems that the walkway is made of a inch thick layer of concrete/aggregate atop a bed of soil, and it seems that the underlying soil has been washed away, leaving the top layer suspended in mid air and unable to support the weight of a person.

So I need to repair the hole (and possibly the whole length of the walkway), but I am not sure how best to go about it.

Your advice would be gratefully appreciated.

Thanks.

P

 

[jeds]

Break it up with a bar. Compact the loose material down and add a new topping. Hoggin would be a good option. That's self-binding clay based sandy aggregate. You should be able to get it from your local sand and aggregate supplier.

 

[KenGMac]

TheFew, Hi.

I would be very cautious! in this matter, what may? have occurred is that the so called fines [the tiny small particles] have been washed out by some sort of ebb and slow flow of the Canal, or? there may be a leak in the Canal wall that are generally constructed to be capable of retaining the Canal water.

Several potential problems appear to me including, who "owns" the Canal Bank, to be precise do you or the Canal operator "Own" the bank and how far from the water line does this "ownership" extend?

I would suggest that you carefully consider an approach to the Canal Owner / operator / owner to enter into discussions as regards how to repair this problem? why, because if your repair subsequently fails then you who have instigated / Instructed / undertaken the repair could be held responsible for the damage? just one way of looking at what could be a bigger picture.

As an aside, somewhat tongue in cheek? your Property Insurance will NOT provide cover for so called " River and Coastal Erosion" But this Canal is neither a river or indeed a coast? There is a very interesting spin on the Insurance Policy Wording going on here, should you need to involve your Insurer, in general terms if it is not a so called "Specific Exclusion" as above then all bets are off?

Apologies if I appear the doom and gloom merchant here but there are far too many variables to tender a proposal to undertake a repair, suggest you discuss locally with neighbours what has occurred historically? there could be precedents to follow?

Ken.

 

[bernardgreen]

I would suggest that you carefully consider an approach to the Canal Owner / operator / owner to enter into discussions as regards how to repair this problem?

That is essential before you do anything.

The legalities of ownership of the land and the riparian rights assigned ( or not assigned ) can be legal minefield when carrying out any repairs to river , stream or canal banks.

 

[^woody^]

Do you have riparian rights, or does the Canal and River Trust own the bank? If they do you can get them to fix it.

Otherwise, I'd advise against involving the Trust unless you want to incur a hefty fee for the privilege of their advice and inspections. Just break it and fill it as per jeds.

Check there is no wildlife nesting though.

 

[TheFew]

Thanks for the replies. We rent this section of the bank from the Canal and River Trust. I have sent them an email advising them of the situation, but it is unclear to me if they will fix it or if it will default to me having to do it (i await their reply).

In the meantime i would appreciate ideas on how best to repair (thanks to Jeds - i had not heard of Hoggin before) so i am forearmed when i do speak to them.

Thanks.

 

[^woody^]

We rent this section of the bank

Check your agreement carefully, don't rely on them telling you what they think it is.

 

[TheFew]

We rent this section of the bank

Check your agreement carefully, don't rely on them telling you what they think it is.

Like all good agreements it is unclear and hints towards us being responsible. A re-read is required however.

 

[WabbitPoo]

can you see water under that hole? if so, no point in pouring rubble in as it'll just disappear into the canal.......

 

[bernardgreen]

Repairing the bank of a canal is NOT a DIY project. Since your area is affected then almost certainly the adjacent properties will also be affected. Any repair to your area alone will affect the rate of errosion of the adjacent properties.

Repairing / maintaining the bank of the stream ( 3 foot wide 2 foot deep ) along our garden required a new "foundation" to be created below the bed of the stream for a retaining wall to be built on. The alternative was gabions but profiling them into the bank upstream and downstream from our land would have been difficult to achieve. ( profiling reduces the turbulance and errosion )

 

[^woody^]

Repairing the bank of a canal is NOT a DIY project

It's not just a case of the OP filling a hole then?

 

[bernardgreen]

It's not just a case of the OP filling a hole then?

No... definately not if he can see water or very wet mud at the same level as the water in the canal. It might work as a short term "repair" to regain use of the path but the reason the bank has been erroded has to be found and dealt with as well. The extent of the errosion and or water logging of soil has to be determined. Are the steps on solid ground or water logged earth ?

Is the canal a river made navigable and hence has a ( strong ) flow or is it a purpose built canal with no signifcant flow. Is there a lot of traffic on the canal disturbing the water. A boat moored by the bank will deflect flowing water onto the bank to speed up errosion.

 

[^woody^]

He can't fill it with concrete or a cement sand/soil mix either? That wont go anywhere.

If the canal is leaking, then that's not the OP's problem to remedy because he does not own the canal, nor the canal wall.

 

[TheFew]

can you see water under that hole?

Yeah there is water in the hole, which can be seen to move as water in the canal moves.

 

[TheFew]

It's not just a case of the OP filling a hole then?

No... definately not if he can see water or very wet mud at the same level as the water in the canal. It might work as a short term "repair" to regain use of the path but the reason the bank has been erroded has to be found and dealt with as well. The extent of the errosion and or water logging of soil has to be determined. Are the steps on solid ground or water logged earth ?

Is the canal a river made navigable and hence has a ( strong ) flow or is it a purpose built canal with no signifcant flow. Is there a lot of traffic on the canal disturbing the water. A boat moored by the bank will deflect flowing water onto the bank to speed up errosion.

I think the steps are on a thin layer of concrete with water-logged mud underneath. They may have been undermined slightly.

The canal is the Kennet and Avon canal, so purpose built. Traffic is low at the moment, but will speed up as the weather improves.