vol 7, issue 11

Extreme floods and the need for better monitoring

19 November 2012
By Crispin Andrews
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New York floods with Hurricane Sandy

New York is the latest city to feel the brunt of climate change as it continues to play havoc with weather

New York's yellow cabs caught in flood

New York City’s submerged streets were jammed with floating yellow cabs

Map showing the effects of hurricane Sandy

Impact of 'Superstorm' Sandy

Extreme flooding has become a problem on a global scale, affecting the UK to Australia. Is flood monitoring technology the answer to preventing the devastation experienced in the past?

The UK, like the rest of the world, has experienced heavy flooding over the past decade, which has affected thousands of people and caused millions of pounds worth of damage. Although it is impossible to say this increased flooding is a direct result of climate change, some computer predictions say that we can expect to see further extreme weather events in the future.

In early November of this year, the eastern seaboard of the USA became the latest region to be hit by severe flooding. At least 41 people died in New York at the hands of category 1 Hurricane Sandy, predicted to have caused economic damage on a par with that of Hurricane Irene last year.

International news and social media feeds have been jammed with images of yellow cabs floating down submerged streets, survivors being plucked from rooftops by helicopters and subways swallowed up by the unprecedentedly high levels of flood water.

A prominent casualty has been the capital's transport infrastructure. The initial tidal surge flooded empty subway and highway tunnels, leaving the abandoned subway an out-of-bounds zone for 10 days after the storm hit.

Flooded tracks and tree-felled power lines have stalled New York City's rail infrastructure with similar repercussions in New Jersey and Long Island. Mainland trains running on the New York line were suspended until flooding subsided, leaving evacuees of New York's submerged City Zone A stuck in refugee shelters, unable to return to their homes.

The result of flooding in the tunnels below the Hudson and East rivers has been most catastrophic, leaving rail companies struggling to remove excess water and repair rail, signal and power systems.

"The amount of water intrusion into the tunnels is unprecedented, as was the storm itself," said a statement from New York rail provider Amtrak. "So far, a date for the restoration of Amtrak service directly to or from the New York Penn station, either from the North or the South, is not available."

The city's power network has taken a substantial blow from the hurricane, leaving almost a quarter of residential and commercial properties without power after Sandy flooded electrical networks, sparking an explosion at a Consolidated Edison substation on the East river.

The explosion contributed to New York's power cuts and will significantly delay efforts to fully restore power supplies to the city. Reports of electrified puddles charged by fallen power lines have emerged, with authorities urging pedestrians to keep vigilant after one woman was fatally electrocuted.

Telecommunication services experienced erratic signal failures as major telecoms provider Verizon experienced flooding in its central offices in downtown Manhattan. Internet, mobile networks and landlines all experienced disjointed connection due to water damage to the company's generators and batteries.

Advance flood-risk planning

Complacency is a word that has been recently bandied about in reference to New York City's less-than-proactive long-term flood-risk planning. Despite rising sea levels along the East Coast, existing systems have scarcely been updated, mostly due to the fact that flooding of this magnitude is simply not the norm in New York City.

Due to a lack of flexible and adaptable technology systems, Dutch flood experts have encouraged New York to look to the surge barriers and flood-defence structures employed in Holland for inspiration.

Twenty five per cent of Holland - including 60 per cent of the population and 70 per cent of its economic output - lies below sea level. If the nationwide network of pumping stations ever failed, the entire country would be under 1m of water within a week. Last December, after 152mm of rain, twice the monthly average, 800 people had to be evacuated from Groningen as flood waters reached window height. The country has relied on its complex network of dikes, flood basins and sea defences since the 13th Century, and preventive measures such as inflatable dams, storm surge barriers and emergency flood basins contained the floods.

However, stresses on the dikes are considerable, and the consequences of a collapse would be catastrophic. Because of that, modern Dutch flood prevention technology is getting smarter.

A smart dike can autonomously and continually check whether it is under threat, informing various users accordingly. This September, online data from sensors in specially set up test dikes at IJkdijk, near Groningen, predicted when the structures would start to fail before water started pouring through the breach. Viewed online in real-time, the sensors measured sudden changes in water pressure in the pores as well as soil temperature and movement.

Although systems like these may not protect New York areas such as coast-side Brooklyn, Staten Island or Queens, scaled-up versions of surge barriers could provide some protection for Lower Manhattan or the Red Hook part of Brooklyn.

The Directorate-General for Public Works and Water Management also used European Earth observation satellites to remotely monitor the external integrity of the IJkdijk dikes on a daily basis and to the nearest millimetre. TenCateGeoDetect, marketed as the world's first intelligent geotextile, provided early warning of soil structure deformation. It incorporates optical glass fibres as well as special instrumentation equipment and software. It immediately registers the slightest settlements and changes in temperature and strain in embankments and dikes

In an earlier test in 2008, sensors gave 42 hours warning after detecting premature subsidence in the dike. Another experiment in 2009 showed that a drainage pipe in the correct place can prevent piping. When water levels are high, the pressure can force water to seep through the base of a dike, taking grains of sand with it and creating tubular openings - pipes - under the dike that gradually grow, weakening the dike and, in extreme cases, causing it to collapse.

During this year's test, the dikes collapsed after water forced its way into the body over the clay core. An independent commission will report in early 2013 on how well the sensor systems predicted the time, the type of failure mechanism, and the point of collapse.

Water level monitoring

New York's suffering is one that Queensland residents in Australia are all too familiar with. Last year catastrophic flooding affected 70 towns and over 200,000 people. Grantham, 100km west of Brisbane in the Lockyer Valley, was one of the worst affected when the area was hit by flash floods as a result of a sudden rise in the water levels at nearby Murphy's Creek.

David Hill, chief executive of Moreton Bay Systems, an Australian company that makes battery-powered video surveillance equipment, explains that by the time the water rose to dangerous levels it had washed away the water level monitoring equipment. "The equipment was situated too close to the ground," Hill says. "The river was being monitored on a data screen, which displayed only graphs and figures, and when the operators saw the sudden spike they thought the equipment must be faulty. If they'd have had a real-time photograph, they could have seen what was going on."

When the Fitzroy River flooded Rockhampton, locals saw snakes and <'crocodiles in the city centre. A bull shark was spotted swimming down the street in the Ipswich suburb of Goodna. "The authorities thought that Queensland's dams removed all flood risk," Sydney-based hydrologist Mark Babister says. "Truth is, dams only significantly reduce risk. Queensland has too much development too close to rivers."

After the Queensland floods, the state government commissioned Moreton Bay Systems to install a new solar-powered camera near Spring Bluff in the Lockyer Valley. Hill explains that the imaging system is mounted on top of a 5m pole, safely above the highest flood levels. It uses the 3G wireless network to relay real-time data, with accompanying images, to emergency services and councils. Another system is set to go in near Grantham, while Hill is in discussions with six more Queensland councils and hopes to have them stationed on every major bridge in Queensland over the next few years.

"When there's a sharp rise in water levels, the software can alert monitoring staff, send SMS's to key disaster management personnel, and even activate 'road closed' signs to warn motorists," Hill says. He goes on to explain that the contactless radar technology measures water levels accurately. The system transmits short radar pulses and times the returned signal to determine the distance to the water. It takes 20 seconds to read the water level and average out the waves and fluctuations.

"We can measure the water level to within 3mm from 35m high and take the water level measurement data every ten minutes," he says. "We can then attach the data to a photograph which we send every hour. If the 'rate of rise' or the pre-set water levels are exceeded, the imaging system immediately sends alarm images with the water level data to the monitoring control room."

Online flood alerts

Moreton Bay's battery-powered cameras monitor flood prone waterways throughout the UK, but there are also other defences. During last summer's torrential rain, a live, online, flood-warning system, FloodAlerts, went national after being launched as a Facebook app in April 2011.

The system overlays Environment Agency data onto Microsoft Bing maps, making use of the Microsoft Azure cloud computer system to store server capacity online. "Nobody's interested in flood mapping until there's a flood," says Rod Plummer, managing director of Shoothill, the Shrewsbury-based firm that designed the system. "We needed server capacity that can cope with rapid increases from almost no use to high use."

Users can zoom in on any point of a map of England and Wales to see current flood alerts and flood warning statuses, issued by the Environmental Agency. You can also do a postcode search and get Facebook or email alerts if there's a flood warning nearby.

In 2010/2011, 95 per cent of the '664m Defra spent on flood prevention went on protecting the 5.2 million homes deemed to be at risk of flooding. Nottingham, where current flood defence was built in 1947 after flooding affected 28 miles of road, 3,000 properties and 86 factories in the city centre, is one such area. An Environment Agency report commissioned after more floods in 2000 showed existing defences to be insufficient.

Twelve years and '45m later, the Nottingham Left Bank flood scheme, unveiled in September of this year, protects 16,000 homes on the river's north bank on a 27km stretch of the River Trent, from Sawley to Colwick.

At Sawley and Trent Meadows, contractors raised and rebuilt 1.8km of flood embankment, constructed about 250m of new flood wall, raised the B6540 at Sawley to cross over the defences, and replaced the flood gate across the Erewash canal. New defences surround Attenborough village, and there's 2.5km of new flood wall between the railway line and the Attenborough Nature Reserve. The reserve is a Site of Special Scientific Interest though, and required special care.

Sympathetic defences

Trenchmix, which looks like a gigantic chainsaw attached to a bulldozer, is normally used for the installation of land drains. In Attenborough, however, where the ground is highly permeable, it was used to stop water seeping beneath flood defences. Trenchmix breaks up and mixes the soil with a cement grout, so there's no need to excavate the soil and remove it. The resulting mix of soil and grout solidifies to form a continuous underground barrier.

"It means using less land to build the defence, and that any earth excavated can be recycled on site for landscaping work, so there's less traffic on local roads," says the UK Environment Agency's area flood risk manager Innes Thomson. "Lower noise and vibration levels reduced disturbance to wildlife, visitors and local residents."

Moreton Bay's UK cameras operated for more than six months before an Environment Agency operative has to swap and recharge them. The same technology is used in the Flood Early Warning Systems in Australia but these are solar-powered cameras and the battery is just a backup. At night, the colour megapixel camera activates a high-intensity white LED spotlight over the target area so pictures can be fed back 24/7. This white spotlight also means the camera can take pictures through driving rain. The light from typical Infra-red spotlights is reflected back during heavy rain.

The company are also developing a satellite-based backup system. At the moment they have their own secure network to get the images back to the authorities should main systems go down. Hill says: "If the cameras can't get through the local network, they'll find their own way back to our server in the UK and get the images back here within a fraction of a second."

Origin of the flood

Flood prediction strategies tend to focus on the main stems of large rivers. Unfortunately, many floods start in extensive tributary networks where flash floods threaten lives and property. The University of Texas at Austin Centre for Research in Water Resources researchers have developed technology that can simulate tens of thousands of river branches at a time.

"With the right mix of technology and expertise, engineers could have a snapshot of how a river and its tributaries will behave during floods," says UAT's Ben Hodges. "This would allow them to prioritise levee restoration efforts according to which areas are at highest risk of flooding, and when that's likely to happen."

Hodges explains that new technology, developed for IBM, could, theoretically, be scaled further to predict the behaviour of millions of branches, simultaneously.

"It's a variant of what engineers have been doing, monitoring rivers for 100 years," Hodges says. "We have a set of equations that tell us how a single river might behave, but the roadblock has always been how to upscale this equation to serve an entire river. With the Mississippi you've got a million miles."

The UTA team applied their knowledge of what happens in complex electric circuits to the old river-monitoring equations. The UTA team has applied the model to predict how the 230-mile-long Guadalupe River and its 9,000 miles of tributaries might behave. In a single hour the system generates up to 100 hours worth of predicted river behaviour.

According to Hodges, flood prediction strategies rely too heavily on past rainfall statistics. "Often floods are missed when there's a new rainfall pattern," he says. The new system, Hodges explains, looks at mechanistic equations relating to river behaviour, not historical statistics. "It has been done with major rivers before, but not with the smaller tributaries and a whole river network."

At the moment, the IBM software produces a wholly simulated representation of what might happen in a river. But it could do more. Hodges explains that that electrical behaviour in a circuit is predictable while river behaviour, with many more unknown variables, is less so. "For instance, we won't know what the bottom of a particular part of the river looks like," he says.

However, most rivers have sensors of some sort collecting some kind of data. Hodges says that the IBM software could potentially link into these sensors to add more information to the river behaviour picture. "You'd be able to predict more accurately what was going on," he says. "There might also be an incentive to develop new sensors that can provide even more information about what is happening in a river."

Mark Babister thinks that future planning is the key to dealing with floods. "Future developments must be kept away from at-risk areas," he says. Inland, this means the part of the river system that carries the water and the part of the flood plain that stores it. "Building roads or bridges interferes with the water system, and in areas of risk we need two or three storey buildings with brick or block work downstairs which are strong enough to withstand floods and easy to clear up afterwards."

Often, however, the most effective protection against the natural world comes from within the natural world itself. Sometimes, though, it needs a little help from the engineers.

American flood alert systems

In 1927, the US Army Corps of Engineers built the Bonnet Carre spillway to divert flood water away from New Orleans. Last year, during high floodwaters on the Mississippi, the Corps opened it. However, while only 10 to 15 per cent of the top water went into the spillway, around 36 to 41 per cent of the river's sand deposited there

Before modern civilisation reached the US's south coast, floods would deposit sediment in the wetlands and replace ground'lost to wave erosion. However, New Orleans's levee system has separated the river from the wetlands. The levee systems now take water and sediment straight to the Gulf of Mexico.

"Coastal wetlands act as a natural buffer against storm surges," says Jeff Nittrouer, a geologist from the University of Illinois. "But during stormy weather, under wave attack, these wetlands can disappear into the sea."

Nittrouer continues: "We're disconnecting the river from the surrounding environment and preventing these natural exchange processes." He explains that as the spillway is on the inside of a bend and adjacent to a sandbar it's sediment-enriched water that flows out.

The University of Illinois researchers are now exploring how other local river conditions might also move sediment from the river into the neighbouring wetland spillway. They hope to design other spillways that could help rebuild lost wetlands, without flooding residential areas.

It is clear then. Global warming increases the odds of extreme weather events, and extreme weather events make floods a bigger threat than ever.

In 2010, an Oxford University study found that extreme weather is twice as likely in the'UK. This September, Massachusetts Institute for Technology researchers announced that a 1 per cent increase in temperature would see 10 per cent heavier rainfall extremes in tropical areas.

People have had to deal with floods as long as they've built towns, villages and civilisations by rivers, lakes and the coast. To protect themselves, they've built levees, dams and underground canals, reservoirs to siphon off excess water, and even used islands as a buffer against encroaching sea waters.

But Babister says that what happened in Queensland is a warning against complacency, one from which New York should have perhaps taken heed. "There will always be a flood bigger than the one you've planned for," he says.

"Plan new developments away from high-risk areas and get more effective early-warning systems."

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