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Oh Dear (Flooding)


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#1 ProDave

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Posted 27 December 2015 - 10:20 AM

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Very topical

Posted Image

Shows the problems with the present planning process

#2 Nickfromwales

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Posted 27 December 2015 - 10:26 AM

Maybe they're for river boats? :o
Regards, Nick

#3 ProDave

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Posted 27 December 2015 - 10:29 AM

It would make a great marina.

to me it shows the stupidity of the planning process. Look at all the existing houses above the flood level. Why build there?

I doubt it was a developer saying "this would be a great place to build houses" rather the developer saying "this is the only place they will give us planning permission to build houses" If that is correct you have to ask why is the planning process so stupid to allow permission in unsuitable places yet deny it in places more suitable for housing.

#4 jsharris

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Posted 27 December 2015 - 10:45 AM

One issue is that it is a lot cheaper to build houses on flat sites and flat sites are very often flood plains. The extra costs of building on even a slightly sloping site are enough to seriously hit the profits of the developers, hence the continuous pressure to build on flood plains.

Our site isn't, perhaps, typical, but it is a sloping site and that slope added around £50k in total to the development cost, just for one small house. About 2/3rds of that additional development cost was compensated for by the plot price being lower than typical for the area, but even so there was a premium that we paid for building a house on a slope. In fact I suspect that there were a lot of unseen additional costs because of the slope. As an example, the week before last I had 2 tonnes of sandstone paving delivered for the patio. The truck couldn't get up the slope of the drive so dropped the pallets at the bottom, and I had to spend 4 or 5 hours moving the stone out of the way. This has happened maybe a dozen times, with materials having to be shifted just because of the slope of the site, and although I've done most of the shifting if I were a developer then that has to be an added cost.

Edited by jsharris, 27 December 2015 - 10:46 AM.


#5 SteamyTea

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Posted 27 December 2015 - 10:52 AM

Isn't that just a materials handling issue.
If you had had 200 tonnes delivered would have found a way around it.
I think we also get hung up on 'traditional' building methods. When I was a kid we lived in houses 'on stilts'. It was the norm where we were in the Far East (western design housing for western workers).

But I do hope the speculator that owns that land takes a huge hit on it. Where is it and can we look at the planning application.

Edited by SteamyTea, 27 December 2015 - 10:53 AM.


#6 jsharris

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Posted 27 December 2015 - 10:59 AM

View PostSteamyTea, on 27 December 2015 - 10:52 AM, said:

Isn't that just a materials handling issue.
If you had had 200 tonnes delivered would have found a way around it.
I think we also get hung up on 'traditional' building methods. When I was a kid we lived in houses 'on stilts'. It was the norm where we were in the Far East (western design housing for western workers).

But I do hope the speculator that owns that land takes a huge hit on it. Where is it and can we look at the planning application.

Yes it is, but yet again it comes down to the traditional approach and natural conservatism of the big developers. You can solve the logistic problems of building on sloping sites, but it will add cost, and with margins being small developers will do all they can to reduce costs.

#7 SteamyTea

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Posted 27 December 2015 - 11:07 AM

It would make for an interesting university project that would. "Where is the best place to save costs on a difficult site".

Maybe less on kitchens and bathrooms would be a good start or on very expensive windows and doors.

#8 ProDave

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Posted 27 December 2015 - 11:14 AM

I would love to know if it really is the developers choosing a flat site that is prone to flooding in preference to a sloping site that never floods.

#9 jsharris

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Posted 27 December 2015 - 11:31 AM

View PostProDave, on 27 December 2015 - 11:14 AM, said:

I would love to know if it really is the developers choosing a flat site that is prone to flooding in preference to a sloping site that never floods.

My experience of the process is that sites are almost always identified for development by an "agent" acting for a landowner. A bit of gentle digging reveals that these agents are almost always working for developers. They concentrate on finding the easiest and cheapest land to develop and then create a very good case to the planners as to why that land should be developed to meet local housing need. They can be very creative in wording their proposals and, until recently, the EA and flood risk wasn't even looked at closely until very late in the planning process. By that point most of the persuading had been completed and the EA only had very limited input into the consultation process, and often found their advice watered down or ignored. Sometimes this was for a good reason - the inadequacy of the EA flood risk mapping has been known, or suspected, for a fairly long time, so planners have been reluctant to refuse permission on the grounds of flood risk, they were more likely to just impose a condition on the developer to include mitigation measures, some of which may well have had little or no real effect.

Whether this is changing, so that flood risks are taken as valid planning reasons to refuse permission to develop I don't know. I'd like to think that flood risk should prohibit development is sites like the one at the start of this thread, but I doubt it will.

Edited by jsharris, 27 December 2015 - 11:32 AM.


#10 ferdinand

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Posted 27 December 2015 - 12:46 PM

It's the Dale View development in Whalley, Lancs.

Photo taken from the A59.

https://www.google.c...!7i13312!8i6656

Ribble Valley District Council.

"The site has been subject to ground investigations which were commissioned by Bloor Homes. The ground report and a topographical survey can be made available to interested parties upon request. "

For sale on Rightmove here:

http://www.rightmove...y-50892341.html

Ooops. But most of the Daily Wail photo is actually outside the site, and the photo caption is misleading.

I haven't looked at the Planning Apps themselves.

Ferdinand

Edited by ferdinand, 27 December 2015 - 01:03 PM.


#11 ferdinand

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Posted 27 December 2015 - 12:52 PM

PS There appears to be a flood risk report for part of the site here:

https://www.ribbleva..._fra_mar_14.pdf

No more time to dig any more.

Ferdinand

#12 PeterW

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Posted 27 December 2015 - 01:03 PM


There is an existing surface water drain that was laid when the Dale View Development was built running through the site which will be available for use by the purchaser/s the location of which are also shown on plan Gel/454/1571/01.



That will be useful then ..!!

I've looked at sites in flood plains where flooding is known - the biggest issue is insurance as the usual suspects look at a map and the EA data... What they ignore is the fact you've built on a set of piles that means that you've got 800mm of free space under the building even at 1:1000 year flood events ..!

Friends had D!r£Ct L!ne turn them down for their holiday place in the Cotswolds because it had a deck over the lake ... There is a 600mm drop to the water, and the overspll from the lake is 150mm .... So unless they had most of the valley under 3 ft of water (removing a few towns in the process..) they could never be flooded however as the komputa said "within 500m of water" it said no ....

#13 jsharris

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Posted 27 December 2015 - 01:20 PM

We're in just this situation, as our postcode is blacklisted by all the insurance companies as being a high flood risk. The result is that no insurer will quote using any of the more common on-line or telephone services.

The fact that we're perched up on a hillside, well clear and above the flood risk zone, makes no difference to the dumb systems that front up all the insurers that offer quick quotes. The answer is to go to a broker, who will be able to get around the automated systems and agree cover at a reasonable premium. It's tedious, and has (more than once) had me enraged with the morons who use the simplest possible way of filtering out what they think might be an unacceptable risk.

#14 ProDave

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Posted 27 December 2015 - 01:41 PM

We are also in an odd situation.

The flood maps don't include us, not surprising as although we are only half a mile from a river, we are about 100 feet above it.

But we do have a burn running through our garden, so whenever asked I have to answer honestly about the burn. As it doesn't appear on many maps and doesn't appear to even have a name, it seems to stump them, but they have all accepted the fact it has never flooded since we have been here.

#15 joiner

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Posted 27 December 2015 - 01:43 PM

Dave, have you got a direct link to that pic?

#16 ferdinand

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Posted 27 December 2015 - 01:54 PM

View PostProDave, on 27 December 2015 - 01:41 PM, said:

We are also in an odd situation.

The flood maps don't include us, not surprising as although we are only half a mile from a river, we are about 100 feet above it.

But we do have a burn running through our garden, so whenever asked I have to answer honestly about the burn. As it doesn't appear on many maps and doesn't appear to even have a name, it seems to stump them, but they have all accepted the fact it has never flooded since we have been here.

Must be tempting to hive the burn off into a separate adjacent plot that you also own.

Ferdinand

#17 SteamyTea

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Posted 27 December 2015 - 03:17 PM

There seem to be a conflict here.
The EA flood risk maps are too course and seem to include places that have a very low risk of flooding.
Insurance companies use the EA maps to assess risk.
The planning departments and developers don't seem to think that the maps are worth anything so get around any restrictions.

Then we seem to think that building in a flood risk area is silly, but building out of the flood risk area is expensive.

Makes me wonder that it is really all about. All a bit confusing.

#18 jsharris

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Posted 27 December 2015 - 03:38 PM

View PostSteamyTea, on 27 December 2015 - 03:17 PM, said:

There seem to be a conflict here.
The EA flood risk maps are too course and seem to include places that have a very low risk of flooding.
Insurance companies use the EA maps to assess risk.
The planning departments and developers don't seem to think that the maps are worth anything so get around any restrictions.

Then we seem to think that building in a flood risk area is silly, but building out of the flood risk area is expensive.

Makes me wonder that it is really all about. All a bit confusing.

Sums things up reasonably well.

No one really trusts the EA flood data, as it's been shown to be flawed many times now. That includes planners, who tend to take little notice of the EA's responses regarding flood risk. This isn't surprising. The EA wanted conditions to be placed on our build that were ludicrous, like flood damns on all entrances, all electrical outlets/switches high up on walls, no absorbent materials to be used in the construction of the ground floor walls and no soft furnishings or carpets on the ground floor, the provision of a flood alarm system and the provision for flood escape from the first floor. They also demanded that the finished floor level be no lower than 83.45m AOD and that the car parking area and garage floor should be no lower than 83.1m AOD. Their 1 in 1000 year flood level, in the lane at the entrance to our house, is about 81.5m AOD and the lane itself is 81.48m AOD at that point.

So, the one in 1000 year flood level is about 20mm above the lane (we get more water than that running down there after heavy rain) and the 1 in 1000 flood level is around 1.95m below the house finished floor level. Needless to say the planners ignored 90% of the EA recommendations and left us with the minimum floor and car parking levels as a condition (both of which are completely OTT - they could have been dropped half a metre and made life a lot easier with no realistic increase in flood risk).

If we had decent flood risk maps, that had been created by comparing the models the EA use with real flood events, then we'd be in a better position, as at least what the EA say might then be viewed as being more credible. If we divorced the flood risk map from post codes things would be even better, as the granularity of post code areas is such as to cover zero risk and very high risk properties within the same code, particularly in rural areas or areas where the terrain isn't very flat.

Edited by jsharris, 27 December 2015 - 03:40 PM.


#19 SteamyTea

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Posted 27 December 2015 - 04:03 PM

Not really up to the EA to say how houses are built. That should be down to Building Control (who may or may not take advice from the EA).

Does the EA use rainfall or river flow as their main indicator. Or are they a bit more sophisticated and use known ground conditions, known changes etc.

With weather patterns seeming to be changing because of climate change (most projections for the UK was more rainfall in the winter and more rainfall overall, though this can be very regional and seasonal), using historic data is limiting the probability (though I can't believe they only use historic data). It is a bit like playing cards where you are allowed to keep some of the cards after a shuffle, but you don't know what those cards are.

When I did my Masters in Climate Change my mate was looking at storm events globally, we found a general shift to higher latitudes. There were many reasons for this though and we were not looking at weather events. But the physics suggested that more water should be transported higher into the atmosphere, which can then travel further North Eastwards (warming poles and those strange Hadley Cells).

I may have to have a look at rainfall figures and river gauges and wee what the time delay is, then compare that to development/farming maps if I can get the data.

#20 jsharris

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Posted 27 December 2015 - 04:48 PM

My understanding is that the EA model is extremely simplistic (this is based on a long conversation with a hydrologist who produced his own local flood risk map, using far more detailed data). His view was that the EA couldn't afford to do proper modelling, so got a bunch of students to come up with a model. The main problem seems to be that the model is essentially just a topographic one that only accounts for surface flow, both from existing watercourses and from new or changed watercourses that arise from increased water levels. They use 100m square blocks to define the terrain, and assume that the whole of each 100m block is dead flat. The model takes no account of soil retention or absorption capability, nor does it account for sub-surface drainage. It assumes that the ground is uniformly absorbent at a fixed level for the whole of the UK.

They take the rain fall water volume falling on a given area and then model where it flows, allowing a small fixed loss and a corresponding pre-saturation release delay. They then compute the flow rates in each 100m grid square based on the depth of water over it and the gradient to the down flow grid squares.

To the best of my knowledge the model wasn't properly validated against known flood events, and this is largely why it is viewed with suspicion by many. A commonly heard comment in our village is that areas marked as high flood risk haven't flooded in living memory, yet areas marked as low flood risk are subject to regular flood events. A large part of the local error is that the stream through our village (where we are now, not the new house) is a winterbourne and so disappears and reappears along its length, depending on the height of the water table in the chalk downland that surrounds us. The impact of the chalk downland to store water in heavy rain events, or not if the aquifer is already fully charged, isn't taken into account, yet that is the dominating factor when it comes to local flooding.

The other major flaw in the EA model is that it seems to ignore watercourse vertical restrictions (mainly bridges). Two years ago we saw the impact of this flaw when a small bridge was over-topped, but caused a large obstruction to flow and increased flooding upstream, both because of much increased turbulence (there was a hydraulic jump in front of the bridge where the flow became highly turbulent) and because attempts had been made to stop the lane flooding by placing sand bags along the bridge parapet.

I'm pretty sure that the EA are aware of the major flaws in their model, but they are extremely reluctant to admit to them. Their budget for producing the flood risk map was tiny, when to do the job properly it would have needed funding for the same sort of computational modelling as the Met Office use, something that was way beyond the means of the EA.

Edited by jsharris, 27 December 2015 - 04:50 PM.