Thames Barrier

[Moodyman]

I know there have been a number of posts/threads on this subject over recent weeks but I was having a chat with a non-sailing friend in the pub the other evening and he asked me that if the Barrier has ben closed on a number of occasions in recent weeks on a rising tide what happens to all the water which is held back by the Barrier. Now I know that it's designed to let the ebb tide though so as not to impede the flow of water, but to be honest I couldn't answer his question regarding the incoming tide. Although I live in London I haven't been to the Barrier for some years and can't recall if there are additional defences to stop the tide overflowing the banks.......otherwise where else has it to go.

This might sound a stupid question but can anyone enlighten me.

 

[NUTMEG]

Don't quote me but I seem to recall that the river bank downstream has been raised by an additional meter or so. I suspect that the marshes right down the estuary are there to act as holding areas and in very bad conditions the downstream settlements, Canvey etc, are seen as expendable to protect the capital.

 

[Richard Shead]

I know there have been a number of posts/threads on this subject over recent weeks but I was having a chat with a non-sailing friend in the pub the other evening and he asked me that if the Barrier has ben closed on a number of occasions in recent weeks on a rising tide what happens to all the water which is held back by the Barrier. Now I know that it's designed to let the ebb tide though so as not to impede the flow of water, but to be honest I couldn't answer his question regarding the incoming tide. Although I live in London I haven't been to the Barrier for some years and can't recall if there are additional defences to stop the tide overflowing the banks.......otherwise where else has it to go.

This might sound a stupid question but can anyone enlighten me.

In a nut shell it rises...but not to stoopid levels. The problem is when we have flood water coming down meeting the tide coming in thats when the probs start. I live in Teddington / Twickenham and we will flood if the barrier is not in place with lots of flood water coming down. Nothing too serious through and it will flow past Tedd and flood up to Hampton Court.

The barrier is only there to stop the incoming tide so not in place for long periods of time so wont flood (yet...)

Sorry just re read your piece, ignore all of the above! I thought you were talking about the water that can't escape..

 

[bedouin]

I don't thinking stopping the tide flowing into the centre of London will have an appreciable difference to the level of water downstream - that is connected to the estuary, the north sea and the rest of the oceans. If you can measure the impact at all downstream it could only be an inch or two.

 

[mjcoon]

I don't thinking stopping the tide flowing into the centre of London will have an appreciable difference to the level of water downstream - that is connected to the estuary, the north sea and the rest of the oceans. If you can measure the impact at all downstream it could only be an inch or two.

Yes, exactly; the tide isn't like a wind-driven wave that will leap into the air when it meets a solid wall. The dynamic effect must be there but quite small.

Mike.

 

[Tam Lin]

I believe they did a lot of work in the estuary to make sure the barrier didn't cause problems elsewhere.

 

[CAPTAIN FANTASTIC]

Hydraulic mathematical modelling is used to input ground level data, atmospheric data etc and simulate upstream and downstream situations; the models are calibrated regularly to ensure accuracy when simulating scenarios such as high upstream flooding against high incoming tide etc. The results are very accurate and effective for predictions.

 

[oldgit]

Anecdotal evidence and sloppy observation suggests that we on the Medway see a rise in water levels when barrier is raised.
Perhaps half a metre over prediction !
One day, no doubt,we will "enjoy" the efforts to protect Westminster and Kensington.

 

[bedouin]

Anecdotal evidence and sloppy observation suggests that we on the Medway see a rise in water levels when barrier is raised.
Perhaps half a metre over prediction !
One day, no doubt,we will "enjoy" the efforts to protect Westminster and Kensington.

But there is a fallacy in that - the reason they raise the barrier is that they expect tides well above the normal prediction.

The Thames barrier protects a fairly small area of water - so the amount of water it prevents from flowing into the centre of London could not possibly equate to a noticable amount as far away as the Medway.

 

[Twister_Ken]

It was designed to protect against tidal surges, but is far more often deployed to prevent rain water flooding. In that role it's closed at about half tide, leaving the tidal Thames above the barrier to act as a run-off basin for the freshwater Thames. The barrier is then re-opened when, as the tide ebbs, the downstream level drops below the upstream level.

I live close to the tidal Thames above the barrier, and am used to seeing the current flowing upstream as the tide level rises. When the PLA does a 'freshwater' close, the river level rises, but the current is still going downstream. Slightly discombobulating.

 

[Alan ashore]

Yes, exactly; the tide isn't like a wind-driven wave that will leap into the air when it meets a solid wall. The dynamic effect must be there but quite small.

Mike.

Actually I think from decades of sloppy observation that in the context of the river, the tide is very much like the wave your kids make at one end of the bath, which slops along it. I'd guess that the dynamic effect of hitting "the wall at Charlton", will be significant (but not something to worry about) for a few miles downriver, but I cannot believe for a minute it is detectable in the Medway.

 

[DJE]

The barrier is the upstream end of the Thames Tidal Defences Scheme which includes walls, bank raising, and tributary barriers all the way down to Southend and Sheppey. It kept many of us very busy for much of the late seventies and early eighties. The local authorities and water authorities paying for the downstream defences were given a payment known as the "Reflected wave contribution" to cover the additional height of wall needed to deal with the effects of closure of the main barrier.

 

[Marmalade]

aren't there other barriers (eg creekmouth at Barking) that protect tributaries from surge when the main barrier closes?