Too much water?

[cee-dee]

I've been thinking.... (OK, so thinking's a bad idea?) about all this water we've had and the poor unfortunates that have been flooded.

Now, if you've got a pipe and it's full of water, it's full and if you try to put more water in to it, where you're trying to put more in, it will just not go.

Streams and rivers are not constricted like a pipe, I suppose they're more like half a pipe? So when they're full and more water is put in to them, the water spills over the sides. There's absolutely no way you can constrict it. OK, so you build the banks up and what happens? The extra water backs up all the storm pipes leading in to that water course?

Someone could say "Ah-ha, we can deepen that water course" but what'll happen then? I suppose some group or other will counter that by saying "Oh no ya don't, there's all the wriggly things that live there, oh no way can you do that"!!!!!!!!!!!!

What do we do? Put all the properties on stilts? Knock 'em all down and move the communities? Where to?

So, what's the answer then? What bright ideas can anyone come up with?

[upthecreekyetagain]

Contrast and compare!

[**bustysbargains**]

Amazing pics. Xx

[cee-dee]

So, the Severn has overtopped four foot "flood barriers", if the river was deepened by 5 feet it wouldn't overtop the barriers?

[suzieseaside]

And you would do that all the way to the estuary?? And maintain by regular expensive dredging?
Otherwise it would just cause problems downstream

[cee-dee]

Yes, all the way to the sea.

Well if you say regular dredging would be needed, how is it that regular dredging's not being done at the existing depths?

[upthecreekyetagain]

---

@cee-dee wrote:

So, the Severn has overtopped four foot "flood barriers", if the river was deepened by 5 feet it wouldn't overtop the barriers?

---

Not sure your logic is correct in that!

Dig a hole 3 foot deep and it fills with ground water to the top so you dig it another 2 foot deeper the water will still reach the top.

All a river is doing is channel the ground water, it may move the water from upstream faster downstream but the level won't change until the water upstream that is higher than the river bank downstream drops in level.

[cee-dee]

That is completely wrong because..... there was no water behind the barriers until they were overtopped.

Photos and videos exist which show that the river was level with the top of the barriers and there was clear ground behind the barriers.

[**bustysbargains**]

I read that although that barrier was over topped the barrier itself had failed because the amount and force of the water was pushing its way through underneath it.
I don't think anyone can plan for something as unpredictable as the elements, the last few years of flooding in places where it was not expected is proof of that.
Maybe the way to go now is build with the view to living with the water while its high and not trying to stop the floods. Flood plains are a natural occurance along our natural rivers, as has been said before why build on them?

[upthecreekyetagain]

Of course the barriers limit the level behind them - you're not understanding what I am saying - my fault.

The water in the river is coming from a level higher up than the level at which it is at.  Imagine a dam with a lake of water behind, (upstream flood plains, mountain run off etc) - below the dam is a culvert ten foot deep - sluice gates  in the dam open until the water in the culvert runs to the brim - now make the culvert deeper and again open the sluice gates, you'll have to open them wider but the water  can still reach the brim.

The situation at Ironbridge for example is that the water entering that stretch of water is coming from upstream, if you made the river wider or deeper at the point it is currently flooding all that would happen is that the water would flow faster and the store of water upstream would diminish more quickly but the level in the river wouldn't change all the time the water level upstream is higher than the banks down stream and the water is entering the river faster than it can flow.

What is needed is to hold the water upstream and slow down the speed at which it .enters the water course - flood plains hold the water, and branches, fallen trees etc slow the flow.

Another point that seems to be forgotten is that if you dredge a river by say 2 metres an awful lot of bridges will have to be strengthened or totally rebuilt as their foundations are compromised and at the same time the force of water against them increases.

[upthecreekyetagain]

---

@cee-dee wrote:

Yes, all the way to the sea.

Well if you say regular dredging would be needed, how is it that regular dredging's not being done at the existing depths?

---

Which would simply increase the risk of tidal flooding in the estuary area!

[cee-dee]

No, that's wrong!

To use your analogy of the culvert, sluices and the dam.... At the moment what you've got is your sluices already open and there's no more water to come from the dam (because you've opened the sluices at their design maximum). So, your ten foot culvert's overflowing now but if you make your culvert bigger/deeper, it won't overflow.

As to the bridges, what you say is correct SO.... you bypass them by building a tunnel similar to the Thames Tideway. QED.

Before anyone moans about the cost, think of the cost of that daft high speed rail line? The country's too small to take proper advantage of that, by the time it's got up to speed, it'll be time to slow down again.

[suzieseaside]

Ceedee, you keep saying everyone who doesn't agree with you about dredging is wrong, so I'm going to say that I think you are wrong. And anyway, do you have any idea how much repeated dredging of our rivers would cost, not to mention riverbank damage, stability, and ecological consequences?

We need to trap or slow down run off from the large catchment areas of our river systems, stop building in flood prone areas, and accept that flooding will be inevitable now and again in places after extreme rainfall events.

As the article in the link below says, river deepening will not prevent flooding during extreme river flows - the amount of water held by a floodplain is usually vastly more than the channel volume, even a deepened channel. Dredging is not a magic bullet.

https://www.theguardian.com/commentisfree/2014/jan/30/dredging-rivers-floods-somerset-levels-david-c...

[cee-dee]

The idea of debate is to put forward your point of view and points pass back and to as people do that.

My last post was to refute something that was clearly not correct.  My point wasn't that dredging was correct and allowing flooding on "flood plains" was incorrect. The anomaly used was incorrect.

Getting back to the point of it all..... dredging is not taking place at the moment to keep the "troublesome" rivers flowing so why say that if the rivers were deepened throughout their length they would need continual dredging?

More dredging may well be necessary around the estuaries and would that be a bad thing anyway? Take the River Dee for instance, large ships used to get up as far as Chester but the estuary has silted up now but even so it's the upper reaches of the Dee where there's flooding.

Dredging may not be a magic bullet but doing nothing helps no-one.

[cee-dee]

Heck, just noticed I've put "anomaly" instead of "analogy" 

Returning the the dam/culvert analogy..... Some people (??) want to reintroduce Beavers to create natural dams and hold back "flooding" above the headwaters. Well, we've beaten the Beavers to it!!! On the Severn there's the dam on it's tributaries, Lake Vyrnwy and the Clywedog, on the Dee there's Bala Lake (OK, it was natural but it was enlarged with a dam) as well as Llyn Celyn, on the Wye there's the Elan Valley reservoirs.

Soooo, all those are supposed to regulate the flow of their rivers and maintain a stock of water for drinking etc. The thing is, when they're full, they're full?

[suzieseaside]

Re your comment about 'continual' dredging - I didn't say continual but it has to be repeated after major flooding events and heavy precipitation like we have been getting this winter because they silt up quickly again - that's stated in the linked article I posted.

I worked a lot in the Humber Estuary. That is dredged frequently to keep the busy shipping channels open but the sediment dumped outside the estuary soon comes back in plus a huge amount of sediment comes down the rivers that join just west of the Humber Bridge. The Humber Estuary is usually brown from the heavy sediment load in suspension, which settles out. Anyway it is a major shipping channel and no doubt repeated dredging is very expensive but necessary because of the amount of maritime traffic.

The Dee Estuary is a bit different I think. Bit rusty on that but I think it needed to be dredged to allow shipping of large aircraft wings ( ?? Might be totally wrong) but there were conservation issues and they allowed development of salt marsh??

Not only is my memory not quite as good but I just broke my specs and can see burger all!!!

[upthecreekyetagain]

I know flooding has been a big story recently but I think the Environmental Agency have been doing a pretty good job.

It seems that around 2,000 houses have been flooded in the recent months, a tiny, tiny percentage of the 4 or 5 million houses considered at risk of flooding and an even smaller percentage of the total housing stock of around 25 million.

It's all a question of diminishing returns.

[cee-dee]

I live way above flood level, on a ridge about 500 feet above sea level and my standing joke is that if I get flooded, there's no hope for the rest of you!

I've just seen a bit of news on the BBC news channel about Snaith and the flooding there and here's a link to a web page:-

https://www.bbc.co.uk/news/uk-england-humber-51656111

It seems some houses were built there as little as a year ago? Are they mad?

As to estuary dredging, yes, quite true that silt does "build up" but also a lot of it is "shifting sands"? The sea causes movement of the sands etc around there?

Really, there's only two options, 1/ do nothing and let nature take its course or 2/ try to do something about it.

If you let nature take its course, some of the rivers and estuaries will "silt up", others may "be clearer" for a long time. After a time, the sited up estuaries and rivers will cause the flooding of more and more land.

Much as people would like it, you can't have it all ways.

See my post about the dams? We, acting as "beavers" have built our dams in an effort "to control" those rivers I mentioned but when our artificial "beaver dam flood plains" (the dams/reservoirs we've built) are full, they're full and that's that! It'd be the same with real Beavers and their dams. Great ideas so long as it's someone else's land that the Beavers are flooding?

[cee-dee]

Building houses on known areas with a risk of flooding? No, they wouldn't do that would they? They're not allowing building in such places are they? 

Oh yeah? Wanna bet?:-

https://www.bbc.co.uk/news/uk-wales-51786881

[upthecreekyetagain]

That's the problem - and if you read the linked report from that the developers say the plans include steps to mitigate the risk of flooding - I'm sure they do, just as the development on the other side of the river to us is unlikely to flood because of ground raising, drainage and pumps - doesn't help,the surrounding area much though - all it does is push the flood risk on to someone else!

[cee-dee]

"Steps to mitigate the risk of flooding." Hmmmm, that means reduce the risk, it doesn't mean the risk is ended, finished, stopped or that they'll never get flooded.

https://www.bbc.co.uk/news/uk-wales-51712267