Fishing The Fly Scotland Forum

Matt Henderson

Floods in the south
« on: 04/02/2014 at 11:27 »
I keep hearing how the floods in the south of England could be prevented by dredging of rivers.  Is this actually true?  I'm guessing that a few people on here must know something about hydrology?  My take on it is, if it rains a lot then if the river capacity is exceeded it will flood?


Cheers

Matt

Rob Brownfield

Re: Floods in the south
« Reply #1 on: 04/02/2014 at 12:14 »
I shout at the TV every time I hear the "dredge the rivers, it stops flooding!"

Fact is, build a town, add roads, pavements and concrete and you have a problem. Water runs off quicker, so you have to build drainage channels. To take the water from those channels, you have to direct them into rivers. Doing this pushes the flood risk from the town, further down the river system.

Dredgeing rivers is great for those who live upstream, but those that live downstram are now more at risk as you have more water running off faster, to be me by high tides, that back the water up...but more water is trying to get down...so it backs up more...and so on.

The ONLY way to stop flooding is to allow water to be soaked up and released slowly....just like nature did before man interferred.

A great example can be see with the Dee and Don. The Dee tends to rise quickly (especially the Feugh) and drop quickly as most of the water runs of granite. The Don rises and drops more steadily as the rain water is held in the fields and moors that it runs through. Aberdeen Uni has done som studies on this...the papers are online somewhere. They show flows for the Dee and Don against equivalent rainfall.

Hamish Young

Re: Floods in the south
« Reply #2 on: 04/02/2014 at 12:20 »
Yes, it is true the flooding in some parts of Somerset could be alleviated by dredging the rivers.
But.......
The larger truth is that 'we' have made an arse of building in places where 'we' should not without a thought for lots of rainfall and the 'what if' factor.
Houses have been built on historic flood plains and that's just plain stupid.
More importantly though I would ask you to consider this, in some way the Somerset levels and indeed significant parts of Norfolk, Suffolk and Hampshire have been/are an artificially controlled or man made environment pretty much since man learned to say more than "ug" or a few years later "watch out for the nasty bitey dinosaur". OK, I exaggerate a little, but certainly since Roman times (what have the Romans ever done for us :?) 'we' have endeavoured to control our environment to improve agricultural yield or serve our purpose, this is patently evident in those counties and elsewhere if you car to look.
Controlled flooding of fields in Hampshire was a winter event as part of a managed water system, but this fell away post WW2.
When the husbandry of those environments is neglected, forgotten about or just simply abandoned there are bound to be consequences. That said, across Somerset and the likes of Norfolk and Suffolk, there have been significant historic flooding events that (by and large) the media chose to neglect to mention in their current report ("we're doomed Captain Mannering, we're all doomed") as obviously it's far worse now than it has been in the past.
That would be utter bollocks.
Fair play, on occasion, historic flooding has been more about coastal inundation flooding from the sea than flooding caused by precipitation but it would not be the first time that heavy rainfall combined with severe storm surge and high tides has caused significant 'backing up' of the low lying river systems and inland flooding.
It amuses/concerns me that in some ways folk in the south are saying that pumping will resolve this and the Environment Agency must take responsibility for this... and so on. Truth is if you don't manage and continue to look after something you've artificially created in the environment at some point nature will want it back, if you continually cut the budget of the body set up to look after the environment we have created what the hell do you expect to happen :? :!

Sorry Matt, I kind of went off on one there but, in my defence, it really pisses me off something chronic the way this is being reported.
I hope I answered your question.

H :cool:

Ben Dixon

Re: Floods in the south
« Reply #3 on: 04/02/2014 at 19:20 »
Quote
The larger truth is that 'we' have made an arse of building in places where 'we' should not without a thought for lots of rainfall and the 'what if' factor.
Houses have been built on historic flood plains and that's just plain stupid.

Main problem and one that can still be addressed

And, I am inclined to agree with the rest too Hamish.  Mess with something (anything) in nature enough and it will need to be managed for ever more or, it will simply break down.  Seems we never learn but doesn't help those caught up in it all, some of whom have been more or less underwater for months.

Ben

Euan Innes

Re: Floods in the south
« Reply #4 on: 05/02/2014 at 12:27 »
The Somerset Levels were named as such because that was where crops and livestock were produced in the SUMMER. The rest of the year they were left to their own devices, usually under water. As Hamish said, if you want to "manage" the water you better keep doing it and not do anything silly like build a house on it. But then greedy people with "voidaphobia" (fear of leaving any piece of land empty and not built on) came along and saw pound signs and the rest is soggy history.

If you want to control water then you have to do it like the Texans do it. Out the back of my brother in laws house in south west Houston there is a 200' wide, 30' deep drainage channel which most of the year is full of critters and snakes but when it gets to pissing down, and by feck does it piss down in Texas, every drain and culvert diverts water from roads and sidewalks into the drainage channel and then diverts it out of the city and seawards or lakewards. It's very effective but the builders in the UK would never consider the expense as worth it.
The Feugh by Strachan had some real efforts at containing it built a few years ago because the flooding used to be biblical, and for a wee while it worked. But the road to the Cairn O'Mount was cut off recently, and more than once as the defences started to fail. You cannot channel water to where you want it to go because eventually it will say "enough, I'm going that way".

The Somerset Levels also had help from two other local towns that had just built new estates, both of which got rid of their drainage problems by channelling the excess into the levels, because there was a river there. They were nice and dry and you all know what happened to the water....

Long ago Darwins best theories suggested that the stupid would die out and the strong would be left. Well that used to work, but doesn't seem to be that common these days.
One last thing. If YOU chose to live on a flood plain why should the Guv'ment have to bail you out (pun intended)? My upstairs toilet has just started leaking, so can I have a new one please Mr Cameron?  :mad

 :z1

Allan Liddle

Re: Floods in the south
« Reply #5 on: 05/02/2014 at 12:53 »
Yup agree with all you guys on this one.
Elgin in recent times has been through a wee bit of flooding (understatement) and as a result a mega million flood aleviation programme is under way. (Actually underway through a lot of areas in Moray as you'd see if you ever drive the A960.

But i still hear people stating that they could have slashed the cost by simply dredging the River Lossie.  What these people fail to understand is that digging down a river bed is only as effective in alleviating flood water as the depth of the water table and (in the case of Elgin) the fall height to the sea (about 2 meters in this case).  All you produce is sluggish easy silted areas that hold deep water.  Essentially the water in it can't go anywhere especially with the high tides we're getting at the moment.

Matt Henderson

Re: Floods in the south
« Reply #6 on: 05/02/2014 at 21:50 »
Thanks guys. I couldn't understand how deepening the rivers by dredging them would actually make any difference. It's not going to automatically increase the volume flow rate to decrease the flooding issue. Cheers. Matt

 




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