Can We Hold Back the Flood ?

A    LAST winter’s 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 Rhône is south-east France burst its banks, driving 15,000 people from their homes, and worse could be on the way. 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-sides 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 haunt them, from the Mississippi to the Danube. And when the floods come, they seem to be worse than ever.

B    No wonder engineers are turning to Plan B: sap the water’s destructive strength by dispersing it into fields, forgotten lakes, flood plains and aquifers. Back in the days when rivers took a more tortuous path to the sea, floodwaters 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’s flow farther downstream becomes more violent and uncontrollable. Dykes are only as good as their weakest link – and the water will unerringly find it.

C    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’s 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’s second- largest river catchment into the Gulf of Mexico.

D    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’t stop the floods. To do that, say, hydrologists, you need a new approach to engineering, not just Agency – country £1 billion – puts it like this: “The focus is now on working with the forces of nature. Towering concrete walls are out, and new wetlands are in.” to help keep London’s upstream and reflooding 10 square kilometres outside Oxford. Nearer to London it has spent £100 million creating new wetlands and a relief channel across 16 kilometres.

E    The same is taking place on a much grander scale in Austria, in one of Europe’s largest river restorations to date. Engineers are regenerating flood plains along 60 kilometres of the river Drave as it exits the Alps. They are also widening the river bed and channeling 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 floodwaters and slow storm surges coming out of the Alps by more than an hour, protecting towns as far downstream as Slovenia and Croatia.

F    “Rivers have to be allowed to take more space. They have to be turned from flood-chutes into flood-foilers,” 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. But a new breed of “soft engineers” wants out cities to become porous, and Berlin is their governed by tough new rules to prevent its drains from becoming overloaded after heavy rains. Herald Kraft, an architect working in the city, says: “We now see rainwater as giant Potsdamer Platz, a huge new commercial redevelopment by DaimlerChrysler in the heart of the city.

G    Los Angeles has spent billions of dollars digging huge drains and concreting river beds to carry away the water from occasional intense storms. “In LA we receive half the water we need in rainfall, and we throw it away. Then we spend hundreds of millions to import water,” 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’s floodwater. And it’s 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’s 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 – and how bad we are at it.

Multitasking Debate
Can you do them at the same time?

A.            Talking on the phone while driving isn’t the only situation where we’re worse at multitasking than we might like to think we are. New studies have identified a bottleneck in our brains that some say means we are fundamentally incapable of true multitasking. If experimental findings reflect real-world performance, people who think they are multitasking, are probably just underperforming in all – or at best, all but one – of their parallel pursuits. Practice might improve your performance, but you will never be as good as when focusing on one task at a time.

B.            The problem, according to Rene Marois, a psychologist at Vanderbilt University in Nashville, Tennessee, is that there’s a sticking point in the brain. To demonstrate this, Marois devised an experiment to locate it. Volunteers watch a screen and when a particular image appears, a red circle, say, they have to press a key with their index finger. Different coloured circles require presses from different fingers. Typical response time is about half a second, and the volunteers quickly reached their peak performance. Then they learn to listen to different recordings and respond by making a specific sound. For instance, when they hear a bird chirp, they have to say “ba”; an electronic sound should elicit a “ko”, and so on. Again, no problem. A normal person can do that in about half a second, with almost no effort.

C.            The trouble comes when Marois shows the volunteers an image, and then almost immediately plays them a sound. Now they’re flummoxed. “If you show an image and play a sound at the same time, one task is postponed,” he says. In fact, if the second task is introduced within the half-second or so it takes to process and react to the first, it will simply be delayed until the first one is done. The largest dual-task delays occur when the two tasks are presented simultaneously; delays progressively shorten as the interval between presenting the tasks lengthens.

D.            There are at least three points where we seem to get stuck, says Marois. The first is in simply identifying what we’re looking at. This can take a few tenths of a second, during which time we are not able to see and recognize the second item. This limitation is known as the “attentional blink”: experiments have shown that if you’re watching out for a particular event and a second one shows up unexpectedly any time within this crucial window of concentration, it may register in your visual cortex but you will be unable to act upon it. Interestingly, if you don’t expect the first event, you have no trouble responding to the second. What exactly causes the attentional blink is still a matter for debate.

E.            A second limitation is in our short-term visual memory. It’s estimated that we can keep track of about four items at a time, fewer if they are complex. This capacity shortage is thought to explain, in part, our astonishing inability to detect even huge changes in scenes that are otherwise identical, so-called “change blindness”. Show people pairs of near-identical photos – say, aircraft engines in one picture have disappeared in the other – and they will fail to spot the differences. Here again, though, there is disagreement about what the essential limiting factor really is. Does it come down to a dearth of storage capacity, or is it about how much attention a viewer is paying?

F.            A third limitation is that choosing a response to a stimulus – braking when you see a child in the road, for instance, or replying when your mother tells you over the phone that she’ s thinking of leaving your dad –also takes brainpower. Selecting a response to one of these things will delay by some tenths of a second your ability to respond to the other. This is called the “response selection bottleneck” theory, first proposed in 1952.

G.           But David Meyer, a psychologist at the University of Michigan, Ann Arbor, don’t buy the bottleneck idea. He thinks dual-task interference is just evidence of a strategy used by the brain to prioritise multiple activities. Meyer is known as something of an optimist by his peers. He has written papers with titles like “Virtually perfect time-sharing in dual-task performance: Uncorking the central cognitive bottleneck”. His experiments have shown that with enough practice – at least 2000 tries – some people can execute two tasks simultaneously as competently as if they were doing them one after the other. He suggests that there is a central cognitive processor that coordinates all this and, what’s more, he thinks it uses discretion sometimes it chooses to delay one task while completing another.

H.            Marois agrees that practice can sometimes erase interference effects. He has found that with just 1 hour of practice each day for two weeks, volunteers show a huge improvement at managing both his tasks at once. Where he disagrees with Meyer is in what the brain is doing to achieve this. Marois speculates that practice might give us the chance to find less congested circuits to execute a task – rather like finding trusty back streets to avoid heavy traffic on main roads – effectively making our response to the task subconscious. After all, there are plenty of examples of subconscious multitasking that most of us routinely manage: walking and talking, eating and reading, watching TV and folding the laundry.

I.             It probably comes as no surprise that, generally speaking, we get worse at multitasking as we age. According to Art Kramer at the University of Illinois at Urbana- Champaign, who studies how ageing affects our cognitive abilities, we speak in our 20s. Though the decline is slow through our 30s and on into our 50s, it is there; and after 55, it becomes more precipitous. In one study, he and his colleagues had both young and old participants do a simulated driving task while carrying on a conversation. He found that while young drivers tended to miss background changes, older drivers failed to notice things that were highly relevant. Likewise, older subjects had more trouble paying attention to the more important parts of a scene than young drivers.

J.             It’s not all bad news for over- 55s, though. Kramer also found that older people can benefit from the practice. Not only did they learn to perform better, but brain scans also showed that underlying that improvement was a change in the way their brains become active. While it’s clear that practice can often make a difference, especially as we age, the basic facts remain sobering. “We have this impression of an almighty complex brain,” says Marois, “and yet we have very humbling and crippling limits.” For most of our history, we probably never needed to do more than one thing at a time, he says, and so we haven’t evolved to be able to. Perhaps we will in the future, though. We might yet look back one day on people like Debbie and Alun as ancestors of a new breed of a true multitasker.