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« Paterson stands by science | Main | Met bashes Cameron »
Thursday
Jan092014

Flooding risk

A reader sent me this. Take a look at the Environment Agency flood risk map. Zoom in on a bit of coastline of your choice. My reader points out that the areas between a the high and low tide marks appear to be flagged up as being at risk of flooding.

True, but misleading?

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Reader Comments (21)

Six Thousand Environmental Agency Civil Servants are getting sacked so they have to find a way of someway of talking themselves up to keep their jobs.

Jan 9, 2014 at 8:46 PM | Unregistered Commenterjamspid

I checked the map for Porthcothan Bay, and it looks correct: the main beach is marked as prone to flooding, which it is because the river overflows to cover most or all of the beach after very heavy rain, while the small beach to the south (locally known as Golden Burn) is not marked as flooding.

Jan 9, 2014 at 8:47 PM | Registered CommenterJonathan Jones

I had a look at our bit of coast and the towns either side of our estuary. The map is 100 percent correct which is why we now have a flood defence scheme on either side of the estuary.

Tonyb

Jan 9, 2014 at 8:48 PM | Unregistered CommenterTonyb

In Snowdonia the"high risk" areas do include the actual existing lakes - eg the entire area of Llyn Trawsfynydd, Llyn Dinas and Llyn Gwynant - as well as many lowland areas in eg the Glaslyn and Dwyryd estuaries that have always flooded after heavy rains, specially when spring tides are combined with westerly winds.

Jan 9, 2014 at 8:58 PM | Unregistered CommenterRoger Hird

Cardiff Bay makes for interesting viewing... Since the creation of the Cardiff Bay Barrage I am not aware of any flooding - having said that, prior to its creation, that particular area of shoreline did face the second highest tides in the world.

I have checked http://penarthnews.wordpress.com/ and there seems to be no reported flooding this year....

I have an excuse - I grew up there and still like to check the news on the site...

Jan 9, 2014 at 9:24 PM | Registered CommenterKnockJohn

@Roger Hird - Hello Roger, as I'm sure you're aware that whole area of Gwynedd is prone to flooding due to it being at or below sea level. The sea used to reach as far north as Nantmor until the whole valley was reclaimed only 200 years ago. The bridge just south of Beddgelert on the A498 marks the spot. In fact, Nantmor is an old fishing village (the name means 'seastream').

There is not much risk of flooding here in Holyhead. Because we are hard b***ards. :)

Jan 9, 2014 at 9:37 PM | Unregistered CommenterPeter Crawford

Ahem. I think the point was that the areas of coastline between high and low water are marked as being at risk of flooding. They are not at risk, they will flood as the tide rises but will drain as it falls. They are tidal areas (owned by the Crown) not land.

Jan 9, 2014 at 10:20 PM | Unregistered Commenterssat

Rubbish

First I looked for the areas which I know are at flood risk near Kirkintilloch on the Kelvin valley - I know they are at risk because last weekend they were flooded. They are not there.

So, next I looked at the Gadloch ... a loch which .... mmm ... floods ... because it is several feet below the natural water level (it's complicated but true).

But the key is that it is currently flooded.

Jan 9, 2014 at 10:24 PM | Unregistered CommenterMikeHaseler

It's true, if you are thinking of building at the foot of the white cliffs of Dover beneath the South Foreland lighthouse, its a flood prone beach, look-

http://en.wikipedia.org/wiki/File:Douvres_(6).JPG

With the added risk of hundreds of tons of Chalk on your head. But just think of all the solar panels you could deploy.

Jan 9, 2014 at 10:33 PM | Registered CommenterPharos

ssat,

That may be the point of the original comment, but it happens not to be true. Only certain areas between high and low water are so marked, and at least in the area I have checked they are chosen correctly.

Jan 9, 2014 at 10:46 PM | Registered CommenterJonathan Jones

I'm corresponding with the EA at the moment who have listed my house, or at least the part halfway up to my back garden, as a flood risk. There has never been any flooding even to the part of the river which lies 500 yards away from my house. It's increased my house insurance premium. Even during these latest floods the river stayed at the same level despite the downpours.
Wouldn't trust them with a bargepole.

Jan 9, 2014 at 11:12 PM | Unregistered CommenterPaul

Looking at our house on the map, I realise now why our house insurer desperately tried to sell us a 'Flood Policy'.

There is absolutely no risk, so our premium would be all profit!

Jan 9, 2014 at 11:17 PM | Unregistered CommenterJoe Public

These are simplistic maps produced by overlaying a digital elevation map on top of an OS map. There is no local knowledge whatsoever embodied in the resultant map. In some cases this means that areas depicted as at risk of flooding have never flooded and never will.

Take a look at Portsmouth; almost 50% of which is at risk of flooding. I doubt very much whether this risk takes account of the complex tidal effects of the presence of the Isle of Wight and the very narrow entrance to the harbour which severely throttles flow into the harbour.

I am sure there are many more examples around the country where local factors make a mockery of the map. I'm also sure the insurance industry salivates over it however.

It is amusing to note that risk of flooding is not a continuous function but comes in little squares. If you are making a fake graphic it is better to make it look more plausible by smoothing (as any number of climatologists will tell you).

Jan 10, 2014 at 12:24 AM | Unregistered CommenterBilly Liar

"Looking at our house on the map, I realise now why our house insurer desperately tried to sell us a 'Flood Policy'."

As from 2015 all householders will be paying an extra £10.50 as a result of an agreement between the government and insurers to provide cover to otherwise uninsurable houses in flood risk areas.
http://www.economist.com/news/britain/21591597-if-you-have-expensive-house-near-sea-its-time-sell-sea-change

Jan 10, 2014 at 12:46 AM | Unregistered Commenterteven Whalley

Well my house is correctly shown just above the flood line for my river, but I wouldn't trust the accuracy to that level of detail.

Jan 10, 2014 at 6:33 AM | Registered CommenterPhillip Bratby

The whole of the Welsh coastline is at High Risk of flooding. The whole lot. Including the high cliffs of Holy Island, Holyhead and the Great Orme, Llandudno, The Lleyn Peninsula around Trefor/Nefyn and the Pembrokeshire coast. All of these have a thick strip of High Risk slapped on them. Also, the various estuaries and sand flats such as Lavan Sands, Llanfairfechan and Conway sands. These sands, exposed at Low Tide are at a High Risk of flooding. Well, they do. Twice a day.

According to the site High Risk means
"High means that each year, this area has a chance of flooding of greater than 1 in 30 (3.3%).
This takes into account the effect of any flood defences that may be in this area. Flood defences reduce, but do not completely stop the chance of flooding as they can be overtopped or fail."

So, every year, there is a 1 in 30 chance that Lavan sands, who are covered twice every 24 hours, will flood. Every year there is a 1 in 30 chance that 300 foot high cliffs of Great Orme will flood.

The effect of all this is that when looked at from 'a height' the first thing that strikes you is that there is a huge problem, far worse than the actuality, and 'Something Must Be Done'

Jan 10, 2014 at 8:28 AM | Unregistered CommenterMike

Mike Haseler
The Environment Agency's remit stops at the Border. I don't know whether or not SEPA produce a similar map. If they do it might be interesting to do a comparison to see if they're as bent as their colleagues in England and Wales.
Just south of the Border is a site I know well and anyone who thinks that Andrew's contact has got it wrong should look at Holy Island!
To describe this map as "misleading" would be to commit GBH on the English language.

Jan 10, 2014 at 10:10 AM | Registered CommenterMike Jackson

I had a look at NW Cumbria - the bit I'm familiar with. The bits marked as being at high risk of flooding are the bits that do in fact occassioanly flood - including upper beaches and salt marshes.

Jan 10, 2014 at 2:48 PM | Unregistered CommenterSleepalot

Sleepalot

Going north from Maryport to Silloth.The B5330 virtually hugs the coastline.

There is a thick slice of HIGH RISK along Croscanonby, Allonby, Dubmill Point and Beckfoot. None of it though, apart from an ocassional river, covers this B 5330. And the road, according to Google maps and google streets is within yards of the high tide mark. Looking at the map enviroment agency map at 5mile/10Km level you'd think the whole lot was High Risk such is the thickness of the High Risk marking.

Jan 10, 2014 at 3:52 PM | Unregistered CommenterMike

It's the output from a model...

Jan 10, 2014 at 4:20 PM | Unregistered CommenterNW

In Selsey, on the coast (think Selsey Bill) south of Chichester, the EA's map shows no risk of flooding in the area just to the east of the junction of Manor Road and the B2145. Up until a few years ago this area ( the square outlined in blue, under the B2145 tag on the EA's map) was shown as being at medium risk of being flooded.
Then Pye Homes applied for planning permission to build 150+ homes in that area and amazingly the flooding risk abated.
It was a miracle!
Fortunately for those opposed to the planning application, one very thoughtful person had saved copies of the EA's "Flood Maps" over the previous years and was able to produce them to the Planning Committee. The application to build was refused.

Jan 10, 2014 at 7:13 PM | Unregistered CommenterStephen Brown

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