Pumping Water From Flooded Villages

[puternut]

A number of times over the past month we have seen on the news that the fire brigade is pumping massive amounts of water from certain areas so that the flood waters might recede a little quicker.

My question is where is it pumped to?

Are they just moving it from the floodsite to the nearest river? Isn't that river at flooding point too? If so, will it not affect the next town/village just down river?

Am I being really thick here but I have asked two relatives and they aren't sure either.

[jomifl]

You can dredge the rivers all you like but it s the pinch points such as bridges that limit the maximum flow.

[Hypognosis]

Sorry Peter - took too long to write my post.

Clarification on mine: I'm concentrating only on what would be gained by dredging, over and above what the drains are already doing.

I did mention flow rate but completely disregarded the other dimensions of the river.

Personally, I don't think the dredging will stop the banks from being breached in future but it may mean that any flood will clear more quickly and/or the spring tide will top out a few cm lower than it just has done. The locals are basically right but I'm not sure if my reasoning is the same as theirs.

[Hypognosis]

Correction!

For every kilometre of dredge 10m wide by 1m deep.. (10,000 m^3)

you can empty 20,000 square metres of water 50 cm deep

which is a square 141.4m x 141.4m

About 1 field's worth (or a small housing estate, perhaps).

[modeller]

I believe in Holland the main purpose was to reclaim land from the sea not just to drain swamps. That's why they built the dykes , primarily to keep the sea out.
In East Anglia they changed their policy in recent years to allow flooding on the coast to cope with tidal surges and rising sea levels rather than trying to hold it back. Maybe a total rethink is needed in Somerset rather than throwing money at it.

[EDDIE51]

You can't dredge canals and rivers with a dredger (ship )far too shallow you have to do it from the bank with a loading shovel (JCB)

[youngmafbog]

Stop building on Flood plains, or if you do build appropriately.

And don't expect the rest of the taxpayers to bail you out when it all goes wrong.

[Hypognosis]

"The pumping operation is currently centred on the areas of Curry Moor, Moorland and Langport. "

http://www.bbc.co.uk/news/uk-england-somerset-20575152

For what it's worth, Google Earth shows that the canal upstream from Bridgewater is about 20m (~65ft) wide at the banks, maybe half that in the stretches photographed at low(er) tide. Well beyond the reach of a JCB, so the most they could manage would be to peck at the riverbank (which explains the environmentalist concerns viz otter/water vole et al) and just hope that the river redistributes silt from the centre out to the edges again by the following year.

If draft is a major issue then a canal barge conversion is the logical step. How did they manage the upkeep, historically, I wonder?

Trouble is, though, since the Dutch did their handiwork, half a dozen bridges have gone up on the stretch to Langport, Muchelney etc.

I can't help thinking that a better fix would be to cut a complete new river-sized canal but Labour-cost-wise, it's 150 years too late to bring in navvies.

[Hypognosis]

@youngmafbog

allegedly, if they build houses on a brownfield or inner-city site, they have to pay VAT.

If you build on greenfield sites, there's no VAT to pay.

Rural planning committees do all they can to stop picturesque villages (churches tend to be found on raised ground) having new housing estates plonked onto their outskirts, so the only places the property devlopers can make a buck is on the flood plain.

Stilts are a great solution but we forget that they shout to the potential buyer about there being something fudamentally wrong about the site. The developer's game is to sell someone a pup and be completely unaccountable for it after the deeds have changed hands. (Caveat emptor etc)

Insurance companies are the buyer's only recourse but it's turning nasty out there and this individualisation of premiums has already reached the stage of separate flood insurance or no offer of flood insurance at all because they have mapping tools and know who gets hit, where and how often.

I'm not in a flood affected area myself and I feel the original 'spirit' of insurance was "shared risk". Yes, it feels like we're collectively subsidising people for living in the wrong place but the alternative is patently unfair. Fire, theft, flood - what's the difference, in the long run?

[ludwig]

I think further down the river they're pumping it back into the fields to stop the river overflowing again.

[mushroom25]

//You can't dredge canals and rivers with a dredger (ship )far too shallow you have to do it from the bank with a loading shovel (JCB) //

the problem with that is that the dredged material is "contaminated waste" and can't just be left on the bank, or spread on the fields.

[Hypognosis]

Paterson speaking now. (BBC Parliament)

[EDDIE51]

mushroom , then that massively increases the already high cost of dredging.
The ideal solution is to build dams and reservoirs up in the hills so the water can be stored where it falls and then released slowly to help in times of water shortage
( what's the betting we have a hosepipe ban again this summer?)
but. that in itself creates huge problems. In the end it is all down to ''You can't beat Mother Nature''

[Hypognosis]

@EDDIE

Re: Reservoirs

I don't live anywhere near there but, looking at the surrounding land in Google Earth, the nearest hills are several miles away and aren't a convenient shape. What you really need is a longish (capacity), narrow (so the wall isn't too expensive) valley, elevated at the pointy end.

You could build a wide, shallow reservoir with an earth bank perimeter (gravel-pit style) but that would wipe out a huge swath of farmland because the terrain is so flat.

Monbiot's article was suggesting that we plant more trees on the uplands. The root system and forest floor debris are highly absorbant and broadleaf trees transpire through their leaves, sending water vapour away in the breeze (albeit only from spring to autumn).

Conifer leaves are superbly designed for *not* losing water through transpiration, hence Monbiot emphasising the need for broadleaf trees. Admittedly, conifer forest floor can get a foot deep in needles and soak up a rainstorm's worth and release it slowly, which makes up for the deciduous trees being bare in the winter, somewhat, although the runoff is slightly acidified (the Scandinavian acidified lakes problem was as much down to their own plantations as from our power station exhausts).

On flatland, it should be too difficult to change the field ditches to run round three sides of each field (picture a castellated pattern) and cause the water to have to travel 3 times further than before before it gets to the river. Depending on the dimensions of the ditch, it adds further capacity.