Dredging? So how does that help?

[watson1959]

Forgive my ignorance, but watching the news and the heartbreaking stories of loss, people keep suggesting that dredging would help.

I see how dredging would help river users but I dont understand how it would help to alleviate the current situation.

Surely cleared waterways just mean faster river flows, and the present water/rainfall levels would still cause overflowing.

If I de-scale my plumbing to improve the flow, there is still only so much water I can force through the pipes....

What am I missing?

 

[macnorton]

A 2" pipe carries more water than a 1" one.

There is a previous post on this that gives the for and against in the lounge.

 

[sailorman]

A 2" pipe carries more water than a 1" one.

There is a previous post on this that gives the for and against in the lounge.

No it doesnt, it all depends upon the pressure exerted on the water

 

[2Tizwoz]

You can change the pressure with a pump but as gravity alone is available in a river channel making the channel bigger by dredging is required.

Of course if it's suggested to those responsible that dredging may destroy some wildlife the cost can become too great.

 

[Phill]

No it doesnt, it all depends upon the pressure exerted on the water

A 2" pipe will carry more than twice the volume of water that a 1" pipe will.

 

[elton]

I don't agree that dredging a river could prevent flooding. It's done to ensure it remains navigable, that's all. Rivers will always find a course, that's how they exist in the first place. A dredged river might hold a bit more water, but they don't exist to contain water, they're just paths to the sea.

 

[sailorman]

A 2" pipe will carry more than twice the volume of water that a 1" pipe will.

Not if the 1" has a pump & the 2" doesnt

 

[prof pat pending]

Not if the 1" has a pump & the 2" doesnt

FGS If you have nothing sensible to say don't bother
A 2" pipe obviously carries more water than a 1" and you can't pump the volume of the Thames

I don't agree that dredging a river could prevent flooding. It's done to ensure it remains navigable, that's all. Rivers will always find a course, that's how they exist in the first place. A dredged river might hold a bit more water, but they don't exist to contain water, they're just paths to the sea.

As for not preventing flooding, no, it probably won't, but what it would do is allow a larger volume of water to escape between the storms which haven't been happening every day

 

[sailorman]

FGS If you have nothing sensible to say don't bother
A 2" pipe obviously carries more water than a 1" and you can't pump the volume of the Thames



As for not preventing flooding, no, it probably won't, but what it would do is allow a larger volume of water to escape between the storms which haven't been happening every day

Tetchy tonight Prof

 

[2Tizwoz]

http://www.bbc.co.uk/schools/gcsebitesize/geography/water_rivers/river_landforms_rev3.shtml

I don't agree that dredging a river could prevent flooding. It's done to ensure it remains navigable, that's all. Rivers will always find a course, that's how they exist in the first place. A dredged river might hold a bit more water, but they don't exist to contain water, they're just paths to the sea.

Whilst some of what you state is true temporary in channel storage has minimal effect. If a river isn't dredged it will meander. That's the problem.

 

[funinthesun]

FGS If you have nothing sensible to say don't bother
A 2" pipe obviously carries more water than a 1" and you can't pump the volume of the Thames



As for not preventing flooding, no, it probably won't, but what it would do is allow a larger volume of water to escape between the storms which haven't been happening every day

The dimwits blaming the jubilee river struggle with this one, I feel so sorry for those flooded but you just can't account for the wettest period for over 200 years.

 

[boatone]

Isn't it time to at least accept that we are faced with an exceptional weather event and that no routine dredging over recent years would have made that much difference to the disaster we are watching unfold because there is simply too much water both in the ground and on the surface? I don't believe any government would have made decisions and implemented major protection schemes that would have prevented what we are seeing now. The existing circumstances would simply not have been foreseen as they are extreme beyond any worst case planning scenario that might have been played a few years back.

 

[Alan ashore]

Isn't it time to at least accept that we are faced with an exceptional weather event and that no routine dredging over recent years would have made that much difference to the disaster we are watching unfold because there is simply too much water both in the ground and on the surface? I don't believe any government would have made decisions and implemented major protection schemes that would have prevented what we are seeing now. The existing circumstances would simply not have been foreseen as they are extreme beyond any worst case planning scenario that might have been played a few years back.

+1

 

[guernseyman]

Isn't it time to at least accept that we are faced with an exceptional weather event and that no routine dredging over recent years would have made that much difference to the disaster we are watching unfold because there is simply too much water both in the ground and on the surface? I don't believe any government would have made decisions and implemented major protection schemes that would have prevented what we are seeing now. The existing circumstances would simply not have been foreseen as they are extreme beyond any worst case planning scenario that might have been played a few years back.

I would be surprised if the Environment Agency worked to a worst-case scenario rather than having a range of scenarios with differing probabilities. It is perverse to argue that dredging wouldn't have made much difference when the Agency thought it would. They are not saying it would have completely solved the problem, but would have been one part of a probable solution. On its own dredging would have been a relatively quick partial solution.

 

[Alan ashore]

... On its own dredging would have been a relatively quick partial solution.

I don't join the dredging debate because I have NO IDEA whether it is a better or worse use of funds than any other measure, but feeling pedantic tonight, dredging has never struck me as "relatively quick" Surely dredging has to be more or less a continual activity, like painting the Forth Bridge?

 

[funinthesun]

I don't join the dredging debate because I have NO IDEA whether it is a better or worse use of funds than any other measure, but feeling pedantic tonight, dredging has never struck me as "relatively quick" Surely dredging has to be more or less a continual activity, like painting the Forth Bridge?

guess who would end up paying for the dredging, an increase in the flooded villagers precept or thames boaters? I wonder.

 

[apollo]

Isn't it time to at least accept that we are faced with an exceptional weather event and that no routine dredging over recent years would have made that much difference to the disaster we are watching unfold.

So why did they build the Jubilee River then? And why did Maidenhead not flood and Staines did? Jubilee River was political dredging to make up for the silted river it bypasses, its just that EA didn't pay for it.
It is painfully obvious it would not have stopped any flooding at all, but it may not have gone as high and may not have lasted as long.

 

[boatone]

Looks like someone - yes, believe it or not it was the EA - was proposing major works back in 2004 to extend the Jubilee:
http://www.nce.co.uk/news/water/flo...o-seek-jubilee-river-extension/787320.article

The plans are a resurrection of a study carried out in 1992, which was thrown out because of the high cost.

Also some interesting background to the Jubilee here:
http://www.thamesweb.co.uk/floodrelief/relief_bckgrnd.html#anchor668028
This includes the following regarding Windsor & Maidenhead:

This area floods about once in five to seven years and there was a flood of this magnitude in 1990, which affected around 500 homes. The last major flood occurred in 1947 and had a return period of 1 in 56 years.

Clearly, without the Jubilee, Windsor and Maidenhead would have been severely flooded this time but the Jubilee was a £100 million capital project, not just a bit of dredging. To put that in perspective that is 5 times the annual budget handed down to the EA for the routine management and maintenance of the non tidal.
The Jubilee was never expected to just be the Maidenhead Windsor stretch. It was proposed that a similar scheme would extend eventually all the way down to Teddington. If THAT had been implemented then there really would have been major relief for those now suffering so much downstream of Windsor.

 

[Aquafan]

Regardless of how much benefit dredging would be to reduce the impact of floods, the Thames needs dredging. Last year the river was full of shallow spots left over from the floods of last year, heaven knows what the river will be like this summer, maybe the EA will pay for damaged props. somehow I doubt it.

 

[boatone]

Regardless of how much benefit dredging would be to reduce the impact of floods, the Thames needs dredging.

No disagreement from me over that but, in the current climate, the best we can expect is that depths in the fairway (the middle third as the EA define it) are maintained as per the declared depths in each stretch. The EA clearly take the view that depths bankside, i.e. outside the fairway, are the responsibility of the riparian owners. I don't give much/any hope for change in that policy unless there is a really major seed change in attitudes to the Thames as a public waterway with major new income from whatever source, be it public or private.