Someone told me that the increase in flooding

mikedobson

is caused by the proliferation of out of town shopping malls which introduce huge areas of concrete in to areas that were hitherto considered unsuitable for development. To wit, towns are where they are because they naturally evolved within existing non-flood plains, the extension of non draining ground into areas where the water table was already higher with no compensating drainage created elsewhere is what has caused the increase in flooding. Or it could be the rain.

Or am I just being daft.

Crapaud

mikedobson wrote:

is caused by the proliferation of out of town shopping malls which introduce huge areas of concrete in to areas that were hitherto considered unsuitable for development. To wit, towns are where they are because they naturally evolved within existing non-flood plains, the extension of non draining ground into areas where the water table was already higher with no compensating drainage created elsewhere is what has caused the increase in flooding. Or it could be the rain.

Or am I just being daft.

It could well be true. There was a telly prog, a year or so ago, that argued that the trend for monoblocking gardens and driveways was putting shed loads of water into a drainage system that wasn't designed for it, and overloading it. The water was previously soaked up by dry earth and vegetation.

It might not be the cause of the flooding, but it won't be helping.

unclemalc

mikedobson wrote:

is caused by the proliferation of out of town shopping malls which introduce huge areas of concrete in to areas that were hitherto considered unsuitable for development.
Or am I just being daft.

ITS A FACT... :shock:
The main problem is that the water that drains away from the concrete is lost into the drains whereas the water that used to be soaked up returned to the water supply. Our future will be governed by water supply and, as usual, this country is NOT prepared for i) flooding ii) drought, and we are supposed to be an 'advanced' nation.
Watch this space.

DavidBelcher

mikedobson wrote:

is caused by the proliferation of out of town shopping malls which introduce huge areas of concrete in to areas that were hitherto considered unsuitable for development. To wit, towns are where they are because they naturally evolved within existing non-flood plains, the extension of non draining ground into areas where the water table was already higher with no compensating drainage created elsewhere is what has caused the increase in flooding. Or it could be the rain.

Or am I just being daft.

Not daft at all - the underlying principle, that there's an impervious layer through which excess water won't drain off, is the same as that which led to the Lynton and Lynmouth floods in the '50s, though in that case the impervious layer was naturally-occurring rock below the Exmoor topsoil (the moorland had basically absorbed all the rain it could and was like a saturated sponge) [1].

David

[1] We studied this in GCSE geography; amazingly I still remember it 18 years later!

ddraver

YAY I can geek out on Geology!!

Its less to do with where it is soaked up or not but how FAST that water gets to the river system

If it hits soil and mud it will have to percolate through the soil (throughflow) over the soil (run off) or through the groundwater (groundwater flow) where it may be soaked up/or transpired back into the atmosphere by trees etc. It also takes a week (give or take) to reach the river by which time the river has dealt with the increased influx of water

however ALL rainwater that falls on a concrete city will be swept straight into the sewer system and then DIRECTLY into the river thus the time between peak rainfall and peak flow in the river channel is much shorter causing greater flooding for a shorter amount of time. In short the water takes an hour to rweach the river which has no time to get rid of the excess before it has to flood

Civic engineers need to get it into their heads that the floodplain of the river still counts as the channel to us geologists. thus if you build on a flood plain it WILL flood (unless you also build significant flood defences

Obviously other factors are involved like how saturated the ground is prior to the storm (the main issue with the tewkesbury floods last year) and local geology and soil type (clay soil will not lwet any water soak into the soil and thus run off will be significantly higher than a sandy soiled area) and many others

cougie

I dont think that a couple of out of town malls would make much difference apart from in the area. But as they say - the more we pave the country - the more water cant soak naturally into the ground.

Than again - its been raining soldily all day here. Thats a lot of rain...

toshmund

The programme mentioned earlier, was "The One Show" - which had a feature in Sheffield. Did an experiment with traditional block paving and some new design which had some kind of interlocking system. New system was a lot more porous and let the water pass through.

They also mentioned legislation coming out in the near future (if it is not in force by now...) that the government were going to bring out the need to have planning permission, for block paved driveways/patios. Link below to a DIY forum (ooherr! "Lovely bit of anaglypta there Cyril!?")

http://www.diynot.com/forums/viewtopic.php?t=130359

hammerite

There is a new development being built a few hundred yards off the boundary of my village, it's quite a large development and it's no coincidence that along with groundworks for the new roads etc..... they've also added in plenty of lakes and parkland to take the water in.

Same as Milton Keynes, pretty much all built on a flood plain. The city has a network of balancing lakes to take care of the water that would otherwise speedily be heading into the Great Ouse http://en.wikipedia.org/wiki/Balancing_lake