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Why Flood Defence Is A Myth

December 9, 2015
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By Paul Homewood   

 

 

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https://theconversation.com/total-flood-defence-is-a-myth-we-must-learn-to-live-with-the-water-22670

 

In the light of recent flooding, there was a highly relevant, and thoughtful, article in The Conversation, just after the Somerset floods in 2014, by Professor Keith Beven of Lancaster University:

 

Floods happen. Rivers have always inundated their floodplains and the sea has always tried to reclaim land that has been taken from it.

This is certainly true in Somerset, whose name derives from the Old English word for “land of the summer people”; so called because it was too wet in winter. In 1607 a major storm caused floods that killed about 2,000 people and swept away whole villages in Somerset and down the Bristol Channel. This was probably the greatest ever loss of life from British weather.

In the great flood of 1872, more than 100 square miles of land were flooded between October and the following March, and again in 1919. So while this month’s rainfall figures record that parts of England have had the wettest January on record, in the south-west it is only the fifth wettest. However, the previous winter of 2012-2103 also saw parts of the Somerset Levels similarly underwater for more than 100 days.

So the floodwaters are not unprecedented – and this raises two questions: could the damage have been reduced and can we expect more frequent flooding in the future? Undoubtedly damage can be reduced, but at a cost – politically and financially. For example, the standards of coastal and river flood defences in the Netherlands are much higher,and much more costly. With much of the population living below sea level, the reasons for this willingness to spend so much to avoid catastrophic damages is readily apparent. When flood defences failed during the great storm of 1953 it led to 350 deaths in Britain, and 1,800 in the Netherlands.

During the storms in December 2013, the highest storm surge since 1953, there were 26 breaches of the sea defences in East Anglia. But forward warning saw timely evacuations, properties protected and the Thames Barrier raised to counter the highest water level since it was built. Because there had been the will to protect and money to do so, nobody died. How much are we prepared to spend now, especially if as climate models suggest flooding will increase in the future?

Flood protection in London is much higher, justified by the huge cost were central London to be flooded. But protection is not total, and defences could be overcome by a sufficiently strong flood, albeit rare. While this indicates how flooding can be devastating even without causing deaths, the investment in flood defences must be warranted, particularly if losses can be met by insurance. The balance that must be made depends on our estimates of risk, probability and damages, and each is uncertain since we have barely 100 years of data on which to base our estimates, and often much less. Models of the impacts of future change cannot yet provide robust estimates of how flood frequencies might be changing.

 

 

The great flood of 1607, Britain’s worst natural disaster.

 

The flood that gets through

In a sense it does not matter, because floods happen anyway. There were major floods on the Thames and Severn in 1924, 1947 and 1960, and in 2000, 2007 and 2013. The decision that needs to be made is how far people living in flood-risk areas should expect to be protected.

Low-lying areas at risk were avoided as sites for permanent habitation in the past. Flood plains were left as water meadows, and crops were planted in spring time to avoid winter flooding. With nothing to be damaged, the impact was minor. In 1954, the UK’s record highest annual rainfall was recorded at Sprinkling Tarn in the Lake District. The total that year was over 6,500 mm, the equivalent of 21 Cockermouth floods falling in a single year. Yet a trawl through the Cumberland and Westmoreland Gazette for 1954 reveals discussion of the fact that it did not stop raining, but little in the way of reports of damages – because there was little on the flood plains to be damaged.

Flood defences change that approach, bringing an unwarranted air of invincibility. Defences lower the risk of damage from moderate flooding, but this year, or the next, or within 10 years, at some point a flood that exceeds their capacity will arrive. The aim should be to reduce the impact of a flood when it does happen by limiting the amount of people and property at risk behind the defences. Instead, building defences tends to encourage development behind the embankments or walls. In this way, even if overtopping floods occur rarely, the damages from those that do occur rapidly increase, even with major investment in flood defences.

 

Damage is inevitable, try to reduce it

Where’s the sense in spending more on defences if the damages will increase in the long term anyway? The most fundamental question is why society as a whole should pay to protect the one in six households in flood risk areas, many built in the last decade, and some such as at Kendal in Cumbria and Ruthin in Wales flooded within months of their occupants moving in. Under the government’s new flood insurance plans, from 2015 all household insurance policy holders will pay a levy to do so, alongside hundreds of millions of pounds allocated every year to flood management from taxation.

Since the floods in 2000 there has in fact been a policy shift towards mitigating damage rather than trying to build hard defences aimed at protection. Strategies that provide storage for flood waters in areas where damage will be minimised, land management to reduce runoff, restoration of natural river channels, and sustainable urban drainage schemes are being implemented as ways of coping with the impact of a risk that cannot be entirely eliminated.

These are more “natural” ways of dealing with excess water, but may leave some properties and land less well protected or dependent on costly flood proofing. Perhaps if people who wish to live in flood risk areas were required to install flood proofing measures before moving in, it might focus attention to the areas’ vulnerability.

 

The future for Somerset

The emabattled Environment Agency has been accused of neglecting drainage and defences in the Somerset Levels for years, and it does seem that this rural area has not been a priority for expenditure – something exacerbated by the current budget cuts. Without a sudden change in priorities, this government will have cut channel maintenance spending by 45% by 2015. Groups such as the Floods on the Levels Action Group and National Farmers Union have suggested that such cuts represent a false economy when the costs of emergency pumping, disruption to the local population, and need to produce food are taken into account.

Results of studies commissioned by the Environment Agency after the 2012 winter floods, presented in an open letter by the Somerset Drainage Board, suggest that dredging would have significantly reduced the period of flooding in parts of the levels from months to days (although having seen only results I cannot comment on the assumptions made). But dredging is not always the right solution, and in some places might increase the risk to bridges or to areas downstream, and can allow the tides to move faster and reach further upstream, backing up flood waters in the rivers. This was one reason why London’s flood defences have had to be raised in the 20th century following dredging in the Thames estuary.

Nevertheless, the government has promised the Somerset rivers will be dredged as soon as possible. Just as the flood defences in Carlisle were redesigned after the floods in 2005, this must be considered a political decision in response to the misery of those affected – and the resulting media coverage. After all, when flood defences succeed it’s not nearly so newsworthy as when they fail.

But more spending on protection still poses the question as to whether this will lead to more flood plain development and more potential damage in the future. It does not appear as if we are managing the potential for future flooding that well, particularly in communicating to people in flood risk areas that they cannot be completely protected and that – even with flood defences in place – they should expect floodwaters, and prepare for them.

14 Comments leave one →
  1. Gordon W. Triggs permalink
    December 9, 2015 12:13 pm

    I believe Professor Keith Beven is refering to the 1607 ‘Tsunami’ which came up the Bristol Channel from the Atlantic. But this was caused by a Tectonic Plate Slip. Nothing to do with rain fall. Please correct me if I am wrong.

    • johnmarshall permalink
      December 9, 2015 1:33 pm

      Quite correct. Though could have been edifice collapse on the Canarie Islands. These have caused tsunamies many times in the past. They are very unstable.

    • December 9, 2015 1:34 pm

      That is one theory.

  2. December 9, 2015 12:15 pm

    True story from across the pond. This city built a “Flood Wall”. Designed to be shut (massive gates and all) in the event of a flood of the James River (named after one of your kings), it has never really been used (it was built after Agnes and Camille dumped feet of rain and raised the level by 20+ feet back in the late 60s early 70s). Until 2005.

    In 2005, a little nothing of a storm (never was a hurricane, just a Tropical Storm) named Gaston came onshore down in South Carolina, spread its beneficial rains over a path up to Richmond, Virginia, and stopped. It dropped 14 inches of rain (over a very small area – 20 miles outside of the city they got less than an inch) in 7 hours. Panicked, the City Engineers shut the flood gates! And all that water had no place to go, so it flooded the city bottom!

    Floods – they will not be denied.

  3. December 9, 2015 12:20 pm

    A rare good article in The Conversation, notorious for being even more dark-green than The Guardian, maybe Prof Bevan could be persuaded to contribute here.

  4. balloon permalink
    December 9, 2015 12:41 pm

    Anecdote 73: I live a literal stone’s throw from the Thames. There are two ways we can be flooded. Firstly, the rain can fall from the sky so fast that it cannot get past us quickly enough to get into the river and away, it gets backed up and comes into the house. This has happened to me twice – trivial carpet-wetting compared to what happens to some but horrible nonetheless. I installed a simple defence against it happening a third time, and that has yet to be overwhelmed. When the rain falls hard and the water flows past down from the town, I open the door and watch it go by. (Yes, I have got a stash of sandbags just in case. They’ve not been deployed this century.)

    The other way disaster happens is that the river fills up with water from somewhere else’s rain and the river rises. Every house between me and the river has been flooded like that – in my 25 years here, three times at least, and the last house with its river frontage many times more than that. My house, built several hundred years ago, has never flooded from the river rising. Because? Because the long dead people who built it knew how high the river can get – generally speaking, in a bad year. Maybe I will get flooded by a once in a lifetime flood but I will not get flooded by the incidental weather and geography of the everyday.

    So, yes, we need to learn to live with the water and the river, and I think people who live near water know that.

    • Bloke down the pub permalink
      December 11, 2015 12:16 pm

      A few years back, when there was serious flooding around Tewkesbury, it was interesting to see aerial images of the affected region. There, on an island surrounded by the floodwater, stood the abbey. I wonder what computer model the builders used to know how to avoid the inundation?

  5. December 9, 2015 1:16 pm

    Nature happens. The “wizards of smart” are unable to predict it even with their pathetically flawed computer models. Just when you plan for one direction, boom, it comes from the other side. Common sense helps a lot, but cannot protect in all situations.

    This June, when at Runnymede for Magna Carta, I kept hearing it referred to as a “water meadow.” Finally, I asked what that was and found it to be what we called a “floodplain.” Wise, from a standpoint of history and development, to leave it the beautiful meadow it is. Odd, there was not a computer model in 1215 to tell them that.

  6. johnmarshall permalink
    December 9, 2015 1:36 pm

    Flood defences can make the flooding worse. Water gets behind the walls and cannot escape. Dredging is the answer.

  7. A C Osborn permalink
    December 9, 2015 5:26 pm

    Flood defenses are about a lot more than just “walls”, they are about “managing” the water, it’s distribution and flow and has worked quite well to not stop flooding but reduce it’s impact.
    So the EA brags about it’s spending of £28M on defenses in the area of the worst flooding, compare the trivial £28M they spent with the cost of the damage & cleanup of £500M.
    Perhaps they should have invested a bit more with some real Engineering soultions as in the past and not just “raising the height of a few walls”.

    • A C Osborn permalink
      December 9, 2015 5:27 pm

      Sorry should be solutions.

  8. Kelvin Vaughan permalink
    December 9, 2015 6:47 pm

    http://phys.org/news/2015-12-unprecedented-storms-common.html

    Unprecedented storms and floods more common than we think.

  9. December 9, 2015 9:01 pm

    Water is one of the greatest forces of nature and floods are destructive and many times they end up by causing great damages and mny deaths. Sometimes I think that it would be better to use some of the many that are used for useless conferences of for expensive “green” energy for improving our techniques and ways of protection against floods, fire, volcanoes, tornadoes and other forces of nature…..

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