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Water table and cellars flooding

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Joined 24-04-2006
Posted on Monday, 24 April, 2006 - 12:16 pm:   

Hi all
We are just about to exchange on a lovely house on Wood Vale, just by the Horniman Gardens. But I've found out that last year the cellar flooded with a metre (gulp!) of rainwater. The cellar was already "tanked" so it was waterproof. But the tanking people say that because there is a drain in the corner of the cellar, whenever there is pressure on the water table, the cellar will flood.
Now I know nothing about such things but we're on the side of a hill. Can a water table run that high? Is SE23 prone to such things? Does anyone else with a cellar in SE23 have any experiences to share please??
Joined 24-03-2004
Posted on Monday, 24 April, 2006 - 01:11 pm:   

A water table can be at any depth below the ground but as you say will tend to be influenced by topography. It will certainly not be down towards sea level / level of the Thames, though. It can be trapped above lower levels of impermeable clay. It seems reasonably likely that the cellar flooded after heavy rain when the ground was temporarily saturated, rather than the actual water table being higher than the cellar floor (although this is quite possible, no reason why the water table couldn't be 3m below ground). If you look further down the page you will see that there is indeed some discussion about this. Problem of clayey soil I suppose; your foundations are likely on the first layer of decent clay so any water may just sit in the more permeable topsoil and fill and be unable to drain away.
Doesn't having a drain rather defeat the object of the tanking?! Better surely a sump with a pump...
If the tanking is intact then the water must have come through the drain. Perhaps there is some way of sealing the drain when it isn't required - the seal might have to take a considerable pressure, up to say 0.3 bar. It may also be worth looking at whether your tanking will withstand the water pressure without being "blown" off the wall.
Joined 19-04-2006
Posted on Tuesday, 25 April, 2006 - 05:07 pm:   

Wood Vale - isn't that in Forest Hill??
Joined 18-03-2005
Posted on Tuesday, 25 April, 2006 - 05:56 pm:   

The Horniman Garden side of the road is in Lewisham and the other side of the road is in Southwark. I suspect Woodvale would also be part of the geography known locally as UDB.

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