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LAST winter鈥檚 floods on the rivers of central Europe were among the worst since the Middle Ages, and as winter storms return, the spectre of floods is returning too. Just weeks ago, the river Rh么ne in south-east France burst its banks, driving 15,000 people from their homes, and worse could be on the way. So now that the dams and dykes have been found wanting yet again, what next for the crowded flood plains of Europe? And what lessons does its plight hold for the rest of the world?

Perhaps it is time for a new response to flooding. Traditionally, river engineers have gone for Plan A: get rid of the water fast, draining it off the land and down to the sea in tall-sided rivers re-engineered as high-performance drains. But however big they dig city drains, however wide and straight they make the rivers, and however high they build the banks, the floods keep coming back to taunt them, from the Mississippi to the Danube. And when the floods come, they seem to be worse than ever.

No wonder engineers are turning to Plan B: sap the water鈥檚 destructive strength by dispersing it into fields, forgotten lakes, flood plains and aquifers. Progressive planners are tearing down banks, dykes and levees to return the rivers to their flood plains. They are putting back meanders and marshes to slow the flow, and even plugging city drains to encourage the flood waters to percolate underground. Rivers need room to flood, they say. And cities need to become more porous.

鈥淭he recent floods have provoked a completely new way of thinking,鈥� says hydrologist Piet Nienhuis of the University of Nijmegen in the Netherlands. Back in the days when rivers took a more tortuous path to the sea, flood waters lost impetus and volume while meandering across flood plains and idling through wetlands and inland deltas. But today the water tends to have an unimpeded journey to the sea. And this means that when it rains in the uplands, the water comes down all at once.

Worse, whenever we close off more flood plain, the river鈥檚 flow farther downstream becomes more violent and uncontrollable. Dykes are only as good as their weakest link 鈥� and the water will unerringly find it. By trying to turn the complex hydrology of rivers into the simple mechanics of a water pipe, engineers have often created danger where they promised safety, and intensified the floods they meant to end.

Take the Rhine, Europe most engineered river. For two centuries German engineers have erased its backwaters and cut it off from its flood plain. The aim was partly to improve navigation, and partly to speed flood waters out of the Alps and down to the North Sea. Today, the river has lost 7 per cent of its original length and runs up to a third faster. When it rains hard in the Alps, the peak flows from several tributaries coincide in the main river, where once they arrived separately. And with four-fifths of the lower Rhine鈥檚 flood plain barricaded off, the waters rise ever higher. The result is more frequent flooding that does ever-greater damage to the homes, offices and roads that sit on the flood plain.

Much the same has happened in the US on the mighty Mississippi, which drains the world鈥檚 second largest river catchment into the Gulf of Mexico. Despite some $7 billion spent over the past century on levees, Ol鈥� Man River is proving the truth of Mark Twain鈥檚 words: 鈥淭en thousand river commissions, with the mines of the world at their back, cannot tame the lawless stream, cannot say to it Go here or Go there and make it obey.鈥�

The recent floods along the Rh么ne were just the latest in a long series of damaging floods in mainland Europe that in the past six years have cost more than 鈧�30 billion. Memories of the severe floods of 2002 are still vivid, when dykes failed engulfing Prague and Dresden in what the European research commissioner Philippe Busquin described as 鈥渙ne of the worst flood catastrophes in central Europe since the Middle Ages鈥�. The European Union is trying to improve rain forecasts and more accurately model how intense rains swell rivers. That may help cities prepare, but it won鈥檛 stop the floods.

To do that, say hydrologists, you need a new approach to engineering not just rivers, but the whole landscape. The UK鈥檚 Environment Agency 鈥� which has been granted an extra 拢150 million a year to spend in the wake of floods in 2000 that cost the country 拢1 billion 鈥� puts it like this: 鈥淭he focus is now on working with the forces of nature. Towering concrete walls are out, and new wetlands are in.鈥�

To help keep London鈥檚 feet dry, the agency is breaking the Thames鈥檚 banks upstream and reflooding 10 square kilometres of ancient flood plain at Otmoor outside Oxford. Nearer to London it has spent 拢100 million creating new wetlands and a relief channel across 16 kilometres of flood plain to protect the town of Maidenhead, as well as the ancient playing fields of Eton College. And near the south coast the agency is digging out channels to reconnect old meanders on the river Cuckmere in East Sussex that were cut off by flood banks 150 years ago.

The same is taking place on a much grander scale in Austria, in one of Europe鈥檚 largest river restorations to date. Engineers are regenerating flood plains along 60 kilometres of the river Drava as it exits the Alps. They are also widening the river bed and channelling it back into abandoned meanders, oxbow lakes and backwaters overhung with willows. The engineers calculate that the restored flood plain can now store up to 10 million cubic metres of flood waters and slow storm surges coming out of the Alps by more than an hour, protecting towns as far downstream as Slovenia and Croatia. 鈥淩ivers have to be allowed to take more space. They have to be turned from flood-chutes into flood-foilers,鈥� says Nienhuis.

And the Dutch, for whom preventing floods is a matter of survival, have gone furthest. A nation built largely on drained marshes and seabed had the fright of its life in 1993 when the Rhine almost overwhelmed it. The same happened again in 1995, when a quarter of a million people were evacuated from the Netherlands. Nienhuis says the subsequent inquest concluded that 鈥渢he rivers had been straightened and the land had been built on so much that there was nowhere for the water to go鈥�. Since then, the Dutch have resorted to Plan A by reinforcing dykes. But they have also broken one of the most enduring national stereotypes by giving engineers the go-ahead to punch holes in dykes, making plans to return up to a sixth of the country to soggy nature in order to better protect the rest.

Similarly, after the 1995 floods, Germany set about finding ways to lower the Rhine鈥檚 peak flood levels by 70 centimetres by 2020. Nobody knows if this is possible, but the authorities plan to reinstate some of the 1500 square kilometres of flood plain lost on the lower Rhine. Drained fields will be replaced by reed beds, and water meadows set aside for flooding every winter. And after surveying the wreckage in Dresden, the German environment minister, J眉rgen Trittin, last autumn announced legislation that will 鈥済ive our rivers more room again; otherwise they will take it themselves鈥�.

But giving land back to the rivers is easier said than done in a crowded continent like Europe. A tenth of Europeans live or work on flood plains, says John Handmer of the Flood Hazard Research Centre at Middlesex University in the UK. That includes 5 million Britons and a quarter of all Hungarians. Pressure is growing to ban all new developments on flood plains. But for those already living there, the best tactic is to find ways to slow water before it reaches the rivers. That might involve discouraging farmers from 鈥渋mproving鈥� their field drains, for example. Even more radically, it may mean redesigning Europe鈥檚 cities.

Cities could hardly be better designed to create floods. They are concreted and paved and asphalted and culverted so that rains flow quickly into rivers. But a new breed of 鈥渟oft engineers鈥� wants our cities to become porous, and Berlin is their shining example. Since reunification, the city鈥檚 massive redevelopment has been governed by tough new rules to prevent its drains becoming overloaded after heavy rains. Harald Kraft, an architect working in the city, says: 鈥淲e now see rainwater as a resource to be kept rather than got rid of at great cost.鈥�

A good illustration is the giant Potsdamer Platz, a huge new commercial redevelopment by DaimlerChrysler in the heart of the city. The local authority has set a limit for drainage from the site of 3 litres a second for each hectare. That is just 1 per cent of the potential run-off during a big storm. If the project doesn鈥檛 meet the target, the drains will back up. Simple as that. So architects have designed the buildings to divert rainwater from the roofs to flush toilets and irrigate roof gardens, while water falling onto the ground helps fill an artificial lake or percolates underground through porous paving. This high-tech urban development can store a sixth of its annual rainfall, and reuse most of the rest.

New housing estates across the city are adopting similar technology. In the Zehlendorf suburb, rain from the roofs, gardens and drives of 160 houses is collected to irrigate local parkland. Not a drop of water leaves the development. In Harzahn, there is a drain-free estate of 1800 homes packed onto just 30 hectares that features cobble roads to allow rainwater to percolate through the gaps into the soil beneath.

Could this be scaled up to a whole city? The test case could be Los Angeles, one of the world鈥檚 largest urban areas. With impervious surfaces covering 70 per cent of the metropolis, drainage is a huge challenge. LA has spent billions of dollars digging huge drains and concreting river beds to carry away the water from occasional intense storms. The latest plan is to spend a cool $280 million raising the concrete walls on the Los Angeles river by another 2 metres. Yet many communities still flood regularly.

Meanwhile this desert city is shipping in water from hundreds of kilometres away in northern California and from the Colorado river in Arizona to fill its taps and swimming pools, and irrigate its green spaces. It all sounds like bad planning. 鈥淚n LA we receive half the water we need in rainfall, and we throw it away. Then we spend hundreds of millions to import water,鈥� says Andy Lipkis, an LA environmentalist who kick-started the idea of the porous city by showing it could work on one house.

Lipkis, along with citizens groups like Friends of the Los Angeles River and Unpaved LA, want to beat the urban flood hazard and fill the taps by holding onto the city鈥檚 flood water. And it鈥檚 not just a pipe dream. The authorities this year launched a $100 million scheme to road-test the porous city in one flood-hit community in Sun Valley. The plan is to catch the rain that falls on thousands of driveways, parking lots and rooftops in the valley. Trees will soak up water from parking lots. Homes and public buildings will capture roof water to irrigate gardens and parks. And road drains will empty into old gravel pits and other leaky places that should recharge the city鈥檚 underground water reserves. Result: less flooding and more water for the city.

Plan B says every city should be porous, every river should have room to flood naturally and every coastline should be left to build its own defences. It sounds expensive and utopian, until you realise how much we spend trying to drain cities and protect our watery margins 鈥� and how bad we are at it.