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Mokidugway

UK infrastructure and flooding

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Having worked in civil engineering for some years I feel there something amiss with our infrastructure , not on about the 2000 EU rivers dictat please :)..

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Being a geologist originally, I can't help but see it all (flooding) as a natural process.

I mean, if you build a house on the alluvial fan of a mountain river in the lake district, at some point the river will come an add another layer (or cut a new channel through it) like it has done for millennia. It's not the pretty little babbling brook that cut deep ravines and made the alluvial fan - you can tell from the size of the rocks in it - but raging torrents that happen from time to time.

Same applies for that lovely, fertile, organic rich silty alluvium of a flood plain. That was laid down as flood waters became static then slowly drained away. They'll be back again.

'The past is the key to the present' was the first thing we were taught in the subject. It's what I see when I look at the landscape; the processes that formed it and continue to shape it, often dramatically, not what it looks like most of the time, which can lull you into a false sense of security.

There is only so much we can do to engineer our way around it. We can build defences, but these will be topped or eroded away by a torrent at some point.

Better to build in the safest places. While everywhere is either being eroded away or deposited on, you do have and end to the scale where these processes are the slowest. Has been a factor in my past choice of home location.

I despair when I see a new development being built on a floodplain anyway. It's not called that for nothing.

 

 

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2 minutes ago, scottish skier said:

Being a geologist originally, I can't help but see it all (flooding) as a natural process.

I mean, if you build a house on the alluvial fan of a mountain river in the lake district, at some point the river will come an add another layer (or cut a new channel through it) like it has done for millennia. It's not the pretty little babbling brook that cut deep ravines and made the alluvial fan - you can tell from the size of the rocks in it - but raging torrents that happen from time to time.

Same applies for that lovely, fertile, organic rich silty alluvium of a flood plain. That was laid down as flood waters became static then slowly drained away. They'll be back again.

'The past is the key to the present' was the first thing we were taught in the subject. It's what I see when I look at the landscape; the processes that formed it and continue to shape it, often dramatically, not what it looks like most of the time, which can lull you into a false sense of security.

There is only so much we can do to engineer our way around it. We can build defences, but these will be topped or eroded away by a torrent at some point.

Better to build in the safest places. While everywhere is either being eroded away or deposited on, you do have and end to the scale where these processes are the slowest. Has been a factor in my past choice of home location.

I despair when I see a new development being built on a floodplain anyway. It's not called that for nothing.

 

 

Exactly SS.

If one chooses to live in areas prone to flooding (and ALL of the reported areas in last couple of weeks plus the Somerset levels a couple of years ago have flooded for centuries) then that's the risk. Flood defences built properly can sometimes alleviate the worst, but when the rainfall in record amounts falls then it's inevitable there will be floods.

The only day-to-day activity that the Environ agency should be stepping up is dredging - the locals are the daily eyes and ears on that one and a few of the problems caused in some of the towns and villages this last few weeks have been exaggerated by build up of debris - the Tadcaster bridge destroyed yesterday is one such flashpoint - locals were telling the authorities to clear tree debris for weeks because large tree branches (thick ones) were constantly smashing into the bridge structure.

 

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One of the problems is increasing population so this will lead to increased building on flood plains as well plus increased concrete generally which also increases run off which increases flooding risks. 

Building flood defenses will also stop the natural replenishment of soil and natural fertilizer of grass lands. Farmers would then have to resort to more artificial means increasing pollution levels. Once built defenses have to maintained so it's not a simple case of spend once and then issue has gone away. Indeed if they don't calculate properly the defenses could be simply to small. We also need to look into ways of slowing the water and in some cases trapping it. The water can then released in a controlled manner at a later date which may also be useful for drought control as well.

If we're going to build on flood plains build houses that can with stand it. Yes it will cost more in the short term but less in the long term.   

WE've got to be very careful of the knee jerk reaction.

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3 hours ago, Bristle boy said:

 

The only day-to-day activity that the Environ agency should be stepping up is dredging - the locals are the daily eyes and ears on that one and a few of the problems caused in some of the towns and villages this last few weeks have been exaggerated by build up of debris - the Tadcaster bridge destroyed yesterday is one such flashpoint - locals were telling the authorities to clear tree debris for weeks because large tree branches (thick ones) were constantly smashing into the bridge structure.

 

 A lot of bridge damage has been caused by large trees coming down and either blocking the arches so it acts like a dam or literally knocking chunks out.
while this can never be stopped entirely it's important that debris is removed as soon as possible.
Trees on the banks are good to hold material with their roots but in the past were usually pollarded or coppiced so that the tops were more compact and less likely to fall in.   
The reduced dredging is all part of plans set out in 2004, the purpose in a nutshell was to "Encourage the rivers to reconnect with the flood plains"
Well it worked in spades, job accomplished.
Unfortunately most of the water voles and such that are more important than houses, fields and farms will now be in the sea though.

EU Water Framework Directive - Making Space for water:
http://www.look-up.org.uk/2013/wp-content/uploads/2014/02/Making-space-for-water.pdf

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2 hours ago, Mokidugway said:

More trees on upland slopes might help ...

Most definitely. Greatly reduces the rate of surface runoff.

Scottish government have a major reafforestation programme; plan is for a new 1000 km2 over the period 2012-2022. 

Not specifically targeted at flood mitigation, but that's one of the reasons it's seen as a good idea. That and forestry is a much more productive used of wild Scottish land than folk in tweed flat caps shooting wee birds for fun.

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29 minutes ago, Woollymummy said:

http://www.forestry.gov.uk/fr/infd-7zveqv

 

good stuff about slowing down catchment waterflow

This is close to me and while I agree with some of the ideas it is annoying to see it being widely promoted in the media as having "saved Pickering"
The reason Pickering didn't flood after Christmas is that there was probably less than 50mm over two days in the catchment - it wouldn't have flooded anyway.
Most of Pickering's floods have been after violent summer thunderstorms not low impact winter rains spells like this.
The Met Office rainfall chart confirms Pickering and the Moors had little more than average rainfall through December.
My own weather site recorded 15mm  on the 25th and 18mm on the 26th.
To those with geographical problems the North York Moors and Pickering are not in the Pennines but near the East coast :)

https://pbs.twimg.com/media/CXymfTGWkAA_r5R.jpg

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They hardly mention they also built a substantial concrete dam nearer the town, it has a restricted exit culvert so fills slowly if the stream rises substantially, and continues to release for several hours afterwards.
This is far more likely to have useful effect than a few rotting logs which will silt up behind and/or get carried away within 2 or 3 years.
Incidentally the catchments on the southern side of the moors are already largely forested since the 1950s, and the forest has in the past been blamed for increasing floods as it was mostly planted on peaty moorland. The trees needed improved drainage to establish.

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Oops, thought it was probably too good to be true, oh well. Thanks for clarification....

I think the dam they built was what they were referring to as a bund. Not sure.

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http://www.pickering.gov.uk/download/659/

Yes it's quite a substantial structure which took two years to build.
There's a large earth walled dam and the outlet is a narrow concrete channel so normally the (quite small) stream passes unhindered.
The day after Boxing day there was some water ponding  in the area but the channel was till running unhindered.
But mainly we just didn't have the rain anyway so portraying this as a wonderful success story is premature especially whn they aren't even aware of the full scheme.
The trouble is it's being used as an argument about proper alleviation schemes, presumably because it looks cheaper.
The valley in question is already quite well wooded, and the areas with debris dams aren't farmland.
Pretending this is a miracle solution to suit other areas is rather naive.
 

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4 hours ago, 4wd said:

Incidentally the catchments on the southern side of the moors are already largely forested since the 1950s, and the forest has in the past been blamed for increasing floods as it was mostly planted on peaty moorland. The trees needed improved drainage to establish.

Aye. Forest is good on hillsides for lowering overland flow rates and holding the soil together, reducing landslides. Draining upland peat bog 'sponges' to plant forest is not a solution of course!

Even simple things like ploughing fields along contours rather than down/up slope can make a difference.

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I feel the emphasis in dredging being the best solution is too simple and may not work, but I don't know if I am just being suspicious, wish I knew more about it. Got flooded about 15 years ago before we moved uphill and am always glad we made that move.

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I'm not sure at all. But, regarding homes already placed on flood-plains, regular dredging would seem to be the most prudent option, in the short-term. In the long term, a total ban on areas liable to flooding might be a better option...Will our government countenance such a ban? I doubt it; short-term political gain is their #1 priority. 

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If you look at old pictures of rivers, they were wider and deeper than they are nowadays, so perhaps dredging is still needed to keep the water within the banks.  Farmers also had lots of ditches for drainage - that they were allowed to dredge - they don't seem to now.

Not the whole answer but I  do believe it would help.

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2 minutes ago, interested & confused said:

If you look at old pictures of rivers, they were wider and deeper than they are nowadays, so perhaps dredging is still needed to keep the water within the banks.  Farmers also had lots of ditches for drainage - that they were allowed to dredge - they don't seem to now.

Not the whole answer but I  do believe it would help.

Indeed, dredging is not the whole answer, i&c. But, as a part of a properly thought-out and coordinated long-term policy, it could go a fair part of the way towards a real solution? In the mean time, a flock of pigs just flew past my window!:D

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The rivers that have been causing issue in North and East Scotland are for the most part stone bottomed fast flowing mountain rivers that have never been dredged and never will be, so a lot of the babble about EU directives and dredging are hot air. Indeed in England, problems appear to have been made worse in some locations by deepening and straightening of river channels to speed water away from agricultural land only to add to problems downstream. There does appear to also have been a lack of modelling, planning and foresight with flood protection - ie not modelling in enough detail and inadequate consideration to downstream consequences. 

Of some major flood alleviation schemes that have been built in the last few years around the Moray Firth, only the River Ness one in Inverness has consisted off simply building a higher wall around the river and that is because it's at the lowest part of the river and is to protect areas from tidal not fluvial flooding. The major cost with the Forres and Elgin schemes have been the alleviation aspects rather than banks, walls and berms, where a condition of building the schemes were problems downstream had to be lessened not worsened, so huge water retention areas have been created around Forres.  These schemes have also been built to 1 in 200years + climate change allowance or better (HM Government standard is 1 in 100 years). There is also a requirement for critical new infrastructure to be considered against 1 in 1000 year events.

Under Scottish building control and planning rules new development areas  in locations within the 1 in 200year flood zones are generally prohibited, buildings within existing communities or developments within such zones are required now to meed much greater flood resilience building standards. This appears to be in stark contrast to the situation in England where HM Government is actively encouraging building on floodplains, and allowing the building of lower quality housing with no attempt at flood resilience  in wholly inappropriate areas for short term private profit at long term cost to residents and the public purse (with such developments adding to the rate of run off and increasing problems downstream even more).

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How do the recent Scottish floods square with the media's sudden desire to imagine 'changes in upland  management' as a new whipping boy?
The Dee won't have changed much other than far more trees. 
Regarding dredging, the way it should work is start downstream and work up - letting your ditch spill over because if you clear it the water goes away quicker isn't a very sensible approach.
There are plenty of example of lowland rivers which require periodic removal of silt at certain points.
It is hardly in dispute that for various reasons this work has been much reduced over the past decade or two.
Many lowland rivers require regular management or they can soon reclaim large areas of land.
On the Derwent below Malton the river is relatively narrow and lined with planted willow to reduce bank erosion - these were coppiced in rotation until recently when the EA decided it should only be be done if a specific issue arose. Now they almost meet in the middle and the channel is easily blocked causing major wash outs of the bank.
 

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How do the recent Scottish floods square with the media's sudden desire to imagine 'changes in upland  management' as a new whipping boy?

In the Dee catchment they don't, there will certainly be more trees in the catchment than was the case post World War II, but its likely if there were fewer trees things might have been worse. A tendency to grouse moor monoculture and overgrazing doesn't help, but that is not a new issue.

We appear to be talking about a 1 in 500year event (or worse) in the North East of Scotland, certainly on the Dee. It's the highest level ever recorded on official gauges which go back to the 1920s in some cases, but anecdotal evidence (which will require some research to verify) such as the height attained on the Bridge of Dee arches suggest the River hasn't been higher since the Bridge of Dee opened in 1527. That it's unscathed is a bullet dodged because it carries around 40,000 vehicles a day on the A90 trunk road despite a width restriction (for pedestrian safety). There was also a quite unusually uniform and unconsolidated snow blanket across the Southern Cairngorms when the rain from Storm Frank started falling, which had the effect of releasing a longer period of precipitation into the catchments in one go.

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Does also help when councils actually clear drains http://www.real-whitby.co.uk/whitby-flooded-in-torrential-downpour/

Sheffield still has the same problem where the council doesn't clear drains. End result damage to road surfaces as well as unnecessary flooding. Short term cost savings out weighed by long term costs.

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Yes they'll even go through the motions of clearing the silt trap every now and then, but studiously ignore the actual drain has been blocked for years.
Sometimes it's just some trivial thing like the outlet needs 5 minutes spade work.
Locally I took charge of them myself years ago.

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