Tuesday, August 21, 2007


After the flood

[This is the pre-edited version of my Lab Report column for the September issue of Prospect.]

Can there be a pub in the country that has not witnessed some sage shaking his head over his pint and opining “Well, if you will build on a flood plain…”? These bar-room prophets are, as usual, merely parroting the phrases they have heard from Westminster, where flood plains have become the talk of the House. “Gordon Brown has to accept the inconvenient truth that if you build houses on flood plains it increases the likelihood that people will be flooded”, says shadow local government secretary Eric Pickles. But the chief executive of the National Housing Federation counters that “there’s simply no way we can’t build any more new homes because of concerns about flood plains… much of the country is a flood plain.”

But what exactly is a flood plain? Perhaps the most pertinent answer is that it is a reminder that rivers are not, like canals, compelled to respect fixed boundaries. They are, in fact, not things at all, but processes. Surface water flow from rain or snow melt, erosion, and sediment transport combine to produce a river channel that constantly shifts, redefining its own landscape. The meanders gradually push back the surrounding hill slopes and smooth out a broad, flat valley floor, thick with fertile sediment: the perfect setting for agrarian settlements, or so it seems. The catch is that when the river waters rise above the banks, there is nothing to hold them back from washing across this wide plain. Levees may try, but struggle against the fact that a river’s curves are always moving slowly: the Mississippi shifts its tracks by up to 20 m a year. One of the fundamental problems for building near rivers is that buildings stay put, but rivers don’t.

What’s the solution? To judge from recent events, it hasn’t changed much in a hundred years: you pile up sandbags. But some precautions are still little heeded: replacing soil with concrete exacerbates the dangers by increasing runoff, and the inadequacies of Britain’s Victorian drainage system are no secret. There’s nothing particularly sophisticated about flood defence: it’s largely question of installing physical barriers and gates. But permanent walls can create conflicts with access and amenity – no one would tolerate a three-foot wall all along the Thames. And some areas are simply impossible to protect this way. So there’s no real call for new science or technology: it’s more a matter of recognizing that flood threats now have to be considered routine, not once-in-a-lifetime risks.

The UK floods were the worst for 60 years, and claimed at least nine lives. But the tribulations of a soggy summer in Gloucester are put in perspective by the situation in Asia. In China, heavy rainfall in the north brought flooding to the Yangtze, and the combined effects of storms has affected one tenth of the population. In a reversal of the usual situation where the parched north envies the moist south, a heatwave in the southern provinces has left more than a million short of drinking water. Meanwhile, an unusually intense monsoon has devastated parts of India and Bangladesh, killing more than 2000, displacing hundreds of thousands from their homes and affecting millions more. A map of the flooded areas of Bangladesh is almost surreal, showing more than half the country ‘under water’.

There’s little new in this, however. Low-lying Bangladesh floods to some degree most years. The Yellow River is commonly known as China’s Sorrow, which has brought recurrent catastrophe to the country’s Great Plain well over a thousand times in history despite herculean efforts to contain its flow with dikes. A flood in 1887-8 created a lake the size of Lake Ontario and, one way or another, killed an estimated six million.

But perhaps surprisingly, some in China have been more ready than in the West to blame the recent events on global warming. Dong Wenjie, director-general of the Beijing Climate Centre, claims that the frequency and intensity of extreme weather events are increasing, and that this “is closely associated with global warming.” Well, maybe. No single event can itself be interpreted one way or the other. The most one can really say is that it is in line with what global warming predicts, as the hydrological cycle that moves water between the seas and skies intensifies – although that by no means implies more rain everywhere. That regional variation, in fact, was a central component of the recent claim by scientists to have detected evidence of global warming on 20th-century rainfall: computer models predict that this influence has a particular geographical fingerprint that has now been identified in the data. It’s a clear sign that the future predictions of more extreme weather – droughts as well as floods – need to be taken seriously.

One question so far given rather little consideration is what this implies for the major hydraulic engineering projects underway in Asia. Ten years ago, specialists in water-resource management were predicting that the problems evident with existing big projects, such as the Aswan Dam on the Nile, might curtail the era of mega-dams and suchlike. Now that looks unlikely: China’s Three Gorges dam is basically complete, and both China and India seem set on ambitious and controversial schemes to transfer waters between their major rivers. The South-North Water Diversion Project in China is scheduled to deliver water to Beijing in time for the Olympics from over 1,000 km away, while the massive Interlinking Rivers project in India would convert the entire country into a grid of waterways controlled by dams, with the aim of alleviating both flooding and drought.

Both of these schemes are already fraught with economic, environmental, social and scientific questions. The prospect of greater variability and more extremes of rainfall can only make the issues more uncertain, and prompts us to shed the illusion that we understand what rivers can and will do.

5 comments:

JimmyGiro said...

If the great volcano eruptions of the past have caused global cooling due to the SO2 they launch into the stratosphere, then maybe global warming can be mollified by issuing sulphur hoppers to all high altitude aircraft engines. To deploy albedo enhancing cloud formation whenever the aircraft sees sunlight whilst flying in the thermosphere.

If the idea takes off, I expect 10% :))

Philip Ball said...

You're quite right Jim - seeding the atmosphere with sulphur to create more aerosol scattering is one of the geo-engineering solutions htat has been proposed as an emergency measure, in this case by Nobel laureate Paul Crutzen. It would be a very drastic move - let's hope it doesn't come to that.

I'm glad my suspicions were correct - nice to hear from you after so many years. By the way, I think I usually used to win at table tennis.

JimmyGiro said...

Damn those Nobel Laureates, coming over here and pre-empting our ideas!

By the way, the cleaner ladies told me to let you win, so you wouldn't break so much furniture.
:P

uhfdf said...

歐美a免費線上看,熊貓貼圖區,ec成人,聊天室080,aaa片免費看短片,dodo豆豆聊天室,一對一電話視訊聊天,自拍圖片集,走光露點,123456免費電影,本土自拍,美女裸體寫真,影片轉檔程式,成人視訊聊天,貼圖俱樂部,辣妹自拍影片,自拍電影免費下載,電話辣妹視訊,情色自拍貼圖,卡通做愛影片下載,日本辣妹自拍全裸,美女裸體模特兒,showlive影音聊天網,日本美女寫真,色情網,台灣自拍貼圖,情色貼圖貼片,百分百成人圖片 ,情色網站,a片網站,ukiss聊天室,卡通成人網,3級女星寫真,080 苗栗人聊天室,成人情色小說,免費成人片觀賞,

傑克論壇,維納斯成人用品,免費漫畫,內衣廣告美女,免費成人影城,a漫,國中女孩寫真自拍照片,ut男同志聊天室,女優,網友自拍,aa片免費看影片,玩美女人短片試看片,草莓論壇,kiss911貼圖片區,免費電影,免費成人,歐美 性感 美女 桌布,視訊交友高雄網,工藤靜香寫真集,金瓶梅免費影片,成人圖片 ,女明星裸體寫真,台灣處女貼圖貼片區,成人小遊戲,布蘭妮貼圖片區,美女視訊聊天,免費情色卡通短片,免費av18禁影片,小高聊天室,小老鼠論壇,免費a長片線上看,真愛love777聊天室,聊天ukiss,情色自拍貼圖,寵物女孩自拍網,免費a片下載,日本情色寫真,美女內衣秀,色情網,

liwo said...

av自拍,臺灣18歲成人免費,avon,正妹強力牆,免費線上成人影片,免費遊戲,a片貼圖,正妹圖片,3d美女圖,杜蕾斯免費a片,蓬萊仙山寫真集,a片網站,哈拉網路成人區,sex女優王國,性感美女,自拍密錄館,18禁卡通,爽翻天成人網,go2av,網拍模特兒應徵,台灣18成人,制服美女,小老鼠成人,成人光碟,金瓶影片交流區,85cc免費影城,成人交友,蓬萊仙山寫真集,無碼,正妹強力牆,嘟嘟情色網,影片轉檔程式,免費成人片觀賞,拓網交友,松島楓免費影片,色美眉部落格,18成人avooo,美腿論壇,辣媽辣妹,露點寫真,哈雷聊天室,18禁影片,看a片,美女工廠,影音城論壇,美女影片,免費遊戲,免費算,小魔女貼影片,a片貼圖,美腿褲襪高跟鞋,av女優王國,觀月雛乃影片,性感美女,

女優王國,免費無碼a片,0800a片區,免費線上遊戲,無名正妹牆,成人圖片,寫真美女,av1688影音娛樂網,dodo豆豆聊天室,網拍模特兒,成人文學,免費試看a片,a片免費看,成人情色小說,美腿絲襪,影片下載,美女a片,人體寫真模特兒,熊貓成人貼,kiss情色,美女遊戲區,104 貼圖區,線上看,aaa片免費看影片,天堂情色,躺伯虎聊天室,洪爺情色網,kiss情色網,貼影區,雄貓貼圖,080苗栗人聊天室,都都成人站,尋夢園聊天室,a片線上觀看,無碼影片,情慾自拍,免費成人片,影音城論壇,情色成人,最新免費線上遊戲,a383影音城,美腿,色情寫真,xxx383成人視訊,視訊交友90739,av女優影片,