The Great Barrier Relief – Inside London's heavy metal and concrete defence act
Waves against the machine
Posted in Geek's Guide, 14th July 2015 11:31 GMT
Geek's Guide to Britain Last time London flooded was 1953. Three hundred lives were lost, 30,000 evacuated and the damage totalled a considerable £5bn in today’s money.
Given how London has expanded since then, the record-breaking wet winter of 2014 would have been worse had it not been for the presence of 51,000 tonnes of metal and 210,000 cubic meters of concrete – called the Thames Barrier.
The barrier has been raised 174 times in the 35 years of its life: and 50 of those took place during that three-month period of 2014.
That year saw one of the wettest winters since records began in 1766 – 435mm of rain, beating incumbent 1915 (423mm) – with the flood walls of 1953 that breached still in place. The barrier added a crucial extra three meters to their height.
Without that, a 125-square-kilometres-area of London was at risk: historical landmarks, commercial and residential buildings, and underground lines and stations in a city that contributes £250bn to the UK's economy.
The Thames is not unique in having a flood defence system – other big cities and waterways have them, too, with at least six in Northern Europe: in Venice, Holland and St Petersburg all of various systems. There’s a further eight systems on the Thames across tributaries that – with the Thames Barrier – are links in London's flood-defence chain.
London shelters behind the Thames Barrier, photo: Gavin Clarke
Where the Thames Barrier stands out is in the fact it married forward-thinking design with innovative, yet practical, engineering. It's not the biggest flood barrier in the world, but it is the largest moveable barrier.
The secret was a new floodgate design – the rising-sector gate conceived by those designing the barrier – that's both powerful enough to withstand nearly ten thousand tons of water pressure yet wide enough for commercial and leisure craft to pass through into, and out of, London.
The barrier's gates rely on a simple system of industrial plant with multiple levels of redundancy. In a nightmare scenario of lost power and computers, it is possible to operate the gates manually out on the barrier.
Then there's that look. Bigger barriers in St Petersberg and Holland are testament to their municipal roots or practical purpose: squat concrete cubes or guillotine gates serving as bulwarks against angry Mother Nature.
The Thames Barrier's signature are a set of seven, silver-coloured domes on boat-shaped piers that straddle the river and resemble a fleet of yachts with the wind behind them, in flight into the center of London.
These domes and piers might well serve a practical purpose by housing the barrier's machinery from the elements, but they have also earned iconic status. Any picture of the London skyline that includes Nelson's Column, Tower Bridge and St Paul's is incomplete without the Thames Barrier.
I survey this sight from my vantage point high in the barrier's control room. I'm clutching a blue hard hat as I’ll be out there in a few minutes, descending walkways, and squeezing past gears and pistons on a journey through this water-control machine and under the Thames to pier number seven.
It’s a brisk and breezy December afternoon when I visit. Daylight is waning with Canary Wharf and the O2 receding in purple gloom and a banshee wind screeching around the piers. I feel like Ripley and the Colonial Marines in the terraformer on LV-426.
Compounding this, is the secure feel of this facility. The control room on the south bank tops a tower in the middle of a small complex containing a power station and workshops and protected by stout walls, heavy gates and a very taking-no-chances pillbox-like entry point. It's testament to the barrier's status as a piece of critical national infrastructure.
Inside the control room, however, all is calm (mundane even) with barely a handful of staff visible. The presence of flat-screen monitors, workstations and carpet makes it feel rather office like, albeit an office with a commanding view. There's glass on three sides: to the left the City, ahead the north bank's tower blocks, and east Woolwich Ferry and beyond.
But don’t be fooled. Everything is arranged with purpose like the bridge of a ship, like the USS Enterprise, even. This bridge is split into distinct ares of activity: on one side weather monitoring, opposite are systems that raise and lower the gates, across the back run desks and phones where supervisors filter incoming data and assess whether to close the gates. In the far corner is comms who relay to the world any decision to raise or lower the flood control gates spanning the Thames.
Along the back is a schematic of the barrier, showing walkways and power lines.
Thames tidal defence operations manager Andy Batchelor is my guide. Batchelor is one of those who'd sit on that desk at the back, and who's authorized to give the order to open and close the barrier. He’s been working here since 1984, when it was officially opened by HM the Queen and Prince Phillip.
No medals for the wrong decision
Batchelor's position is high pressure: yes, closing the barrier has the potential to save London and her people but getting it wrong would also be a disaster, if of different proportions.
“We’ve got to be certain of what we are doing to minimise the disruption,” Batchelor tells me. “It’s got to be based on the information, and there’s no medals for getting this wrong.”
The Port of London, with offices on the opposite bank, annually contributes £3.4bn to the national economy. Ships passing through the Barrier to the Port of London handle 50 million tonnes of goods, 70 independent wharfs and terminals along 95 miles of water. When the barrier goes up, that lot comes to a halt. That network of other barriers along the Thames would close, too.
If the gates close, Batchelor's team must get on the phone to the Port of London Authority, London Transport, emergency services, local authorities, the Woolwich ferry, plus 36 other floodgates and 400 smaller structures that comprise a flood-defense ring with the barrier including the Dartford Barrier and Tilbury Dock.
View from the bridge: view of the Thames Barrier from inside the control tower
The barrier gets the attention but it couldn't work on its own. “People get confused – they think it’s just the Thames Barrier that’s doing the job – it’s the complete system, it’s like a chain. Take out one of the links and you will have flooding,” Batchelor said.
Any decision to operate the thousands of tonnes of machinery sitting out there in the river is based on an expert reading of incoming data from weather forecasts and situations on the ground. Data read outs are displayed on a bank of flat monitors currently wiggly displaying coloured lines.
Some of the feeds come from five-day ensemble forecasts crunched by Met Office’s supercomputers in Exeter. Ensemble forecasts give you not one but a variety of results based on different factors. Forecasts are run for three days, to give greater detail.
The results are mapped against knowns, such as scheduled sea tides and fluvial flow up the river. Forecasts are supplemented with data from monitors ranging from up in the North Sea to Teddington Weir in West London, the last tidal point on the Thames.
The team sifts for signs of surges mixed with a high tide and low-pressure in the North Sea – the fatal mix of 1953. They look, too, for any excess rain running off land into the river, as occurred in 2014.
Closure is triggered when a combination of high tide forecasts in the North Sea and high-river flows Teddington Weir – 22 miles from here – indicate water levels would exceed 4.87m in central London.
In winter 2014, the barrier closed nine times because of tidal surges and 41 because of high river flow, essentially water running off into the Thames.
The strategy was to raise the barrier's gates after low tide to stop water coming back upstream from the North Sea and thereby creating an empty reservoir behind the gates. Run off from the land would fill this reservoir so that, rather than hit a wall of tidal inflow from the North Sea, it could be released in a controlled way after the next high tide.
Coming back to the now, Batchelor points to a bulge of coloured lines on one screen: it represents a tidal surge as recorded by various tidal markers at different points along the North East coast.
Things are quiet today but in Winter 2014 it was different: 38 cubic metres of water a second were flowing over that Teddington tidal outpost. The weekend before my trip was wet, 100 cubic metres a second. January to March 2014 hit 535 cubic metres per second, although history records even bigger numbers, up to 800 in 1894. However, these lasted for just a few days.
Directly opposite us on this bridge are the systems responsible for the remote control of those gates down in the river. When it unofficially opened in 1982, the operations centre resembled the control room of a power station that used levers and knobs and was full of dials.
Instructions to the barriers gates were sent via thousands of relays. The only computers were a VAX machine running PDP-11 code for forecasting, and a Commodore Pet with a five-and-a-quarter-inch floppy drive that ran planned maintenance.
The Bakelite and white-coat era systems were phased out in the 1990s, for the first PC-based systems controlled via custom keyboards.
Today, it’s Windows 7 PCs and Windows Server 2008 R2 systems that talk to the industrial plan on the barrier's piers to raise and lower the gates. The network and servers are mirrored and a RAID 6 blade server with several terabytes of storage records every piece of data generated.
These computers control a system of moving gates that are unique.
Command and control closure
Prince Philip inspects the Barrier's state-of-the art control room in 1982, photo: the Environment Agency
The Eastern Scheldt, South-west Netherlands, and the St. Petersburg flood use concrete piers, sluices and dams while the barrier in Venice is tripped automatically. Permanent defences couldn’t have worked on the Thames because of the river's importance to all that commerce going in and out of the Port of London, it would have blocked ships. A system tripped by tidal pressure was impossible because of the variance of rainfall that the UK receives and the fact the Thames has a tidal range of seven metres.
The systems up here control six rising sector gates in the centre of the river and a further four falling radial gates sitting on the shallow north and south banks. Instructions are relayed to a plant that does the lifting on nine concrete piers, seven of which are topped by those silver-cloured shells.
A single engineer could in theory operate all the Barrier’s gates but in practice there’s always two on duty, as operating the gates isn’t as simple as clicking “OK” on a screen dialogue. You need to step through a series of sequenced and connected moves beginning with turning on power packs that control a series of arms and levers out on those islands responsible for raising and lowering the gates. This is done gate by gate.
Parameters must be satisfied, such as packs running, the correct selections made, direction (open or closed) selection of the correct gate, and so on.
On my trip I met one of those whose jobs it is to operate the gates, control-room shift engineer Tony Davies. “Tony has the intellect to know what to do if we need to run down that series of circumstances,” Batchelor tells me.
There’s different ways to close the gates; using the main control and local, using duty and stand-by power pack, or manually on the barrier should systems up here fail and should there be a major power outage. There are monthly test closures, with gates operated once a fortnight.
“On those, we go through all those options. If we didn’t, well, we are all creatures of habit and would do it one way. It’s my way of doing QA,” Batchelor said.
Tidal defenses operations manager Batchelor, inside the Barrier and beneath the waterline, photo: Gavin Clarke
“We need Tony as an engineer to know what it is he’s pressing, so he’s not just following a script. We need to have his intelligence to know that when, say, we come to step number five what number five does rather than moving onto number six,” Batchelor told us.
The flight desk Tony pilots is sacrosanct: there's no internet connection and – sorry codeheads – no upgrades or fiddling on live systems in case bugs are introduced. This system hasn’t been touched in four years with changes only made when there’s a systems upgrade or a need for a re-think.
Arguably the biggest change was the switch to computers in the 1990s with the move away from Bakelite and thousands of relays. A computerised system based on those used in oil exploration in the North Sea was constructed using custom keyboards and controls that evolved into a supervisory control and data acquisition (SCADA) system of standard mouse and keyboard UI.
Today it's a custom-built point and click interface. Opening the gate involves satisfying a series of logical sequences, from getting power packs running through to moving the gates, one at a time, gate by gate. Closing one gate takes 15 minutes and shutting the lot takes an hour and a half.
Change is in the wind for this lot: the plant out in the piers is being replaced while the aging control-room software is ready for an update. A pilot is underway looking at "tighter integration" and use of Windows Server 2012.
The juice for this lot, meanwhile, comes courtesy of the National Grid: two sources on the north and the south bank for redundancy plus there's a trio of 1.5MW generators on site and a rotary flywheel that serves as a UPS in the event of a blackout and ensures uninterrupted supply during any outages.
The flywheel replaced hundreds of batteries and ensures uninterrupted supply during a total loss of mains power. There’s been six blackouts in the south east of England during the barrier’s history.
Doors to manual
But, hey, I'm not holding a hard hat for the fun of it: it’s time to get out on the barrier.
I leave the control room with Batchelor and we descend to ground level via an aluminium lift, pause for a reading of the health and safety rules before Batchelor pushes the bar on what looks like a fire-escape and next thing I can barely hear myself think for the wind ripping past my ears.
We traverse a walkway over the first falling sector gate, over a muddy bank and enter a door in the side of a the first of those silver-coloured domes, before descending the first of a series of glossy grey metal gantries and stairways en route to our destination: pier number seven.
The Thames Barrier looks big enough from outside, spanning half a kilometre of water with each concrete pier eight times longer, five times wider and four times higher than a traditional London double-decker bus. Each silver roofs peaks at six times the height of a modern two-storey house.
But this is an iceberg and it's only inside you grasp the enormity of things: we clank across gantries and down stairways heading 18 metres below water level into the muddy bed of the river and the barrier's base.
Fire suppressant systems left, comms cables right: inside one of two 500-metre access tunnels, photo: Gavin Clarke
Each pier comprises 168,000m3 of concrete while the sill is made of a further 33,000m3. Two service tunnels run through the sill; these let you traverse the barrier and connect each of the piers.
Remarkably, while the concrete was poured during the 1970s things look fresh and you’d never guess you’re underwater: there’s no dripping pools of water gathering on the floor and no mineral excretion squeezing through walls. Rather, the concrete walls and floor have an eggshell glaze, rows of orange cables hurry along walls and high-viz signs point their way to the various decks and walkways. It even smells clean, apart from one area on the tunnel dominated by a damp dish-cloth smell as we pass through, the result of engineers flushing old oil through the system.
We hit the bottom, and we're in one of two service tunnels. The sill contains a concave recess to house the rising sector gates when open, thereby allowing shipping to continue to pass unobstructed overhead. This sill is 18 metres deep and sits 8.5 metres deep in the riverbed; there’s two metres of concrete above my head. Beneath my feet, 27 metres of foundation.
Along one wall run pipes carrying oil and the fire suppression system while on the other power lines, carrying up to 1,100 volts, and data cables, with copper being replaced by fibre. In the floor, drains run beneath metal covers.
The Thames Barrier seen mid-construction, photo: the Environment Agency
It's as good a place as any to take stock, in the gloom and artificial light.
Floods are a feature of life on the Thames going back the full 1,500 years of human settlement around the river, but 1953 was the worst recorded in terms of sheer losses. However, things only kicked off following a 1967 review in the wake of yet more flooding, this time in the German city of Hamburg, and the Thames Barrier Act was passed by Parliament in 1972.
For a while, the barrier’s iconic designers hung in the balance but fortunately the government set a high bar, ruling a barrier must be reliable, compatible with tidal flows, navigable and appealing to the eye.
Designers Rendel, Palmer & Tritton (today HPR) had proposed a guillotine-like drop-gate with two large openings in 1958 but this was rejected as were a pair of 150-metre wide openings favoured by Port of London.
Rendel, Palmer & Tritton evaluated 10 sites and 41 different plans with various options rejected either for not being navigable or for being visually offensive. The break through came in 1969 when he company's engineer, Charles Draper, conceived the rising sector gate, reputedly inspired by the domestic gas valve. The design ticked all the government’s boxes and construction started in 1974.
The rising sector gates looks in profile like a semicircle and when not in use they lie flat side up in the concrete sills making the route between the piers navigable for shipping of most commercial and military size.
The gates rotate on a trunnion shaft attached to a concrete pier on either side lifted by an jointed arm and powered by the industrial plant inside each pier and sheltered beneath those silver-coloured domes.
As for the site, Woolwich Reach, this was selected for its narrow width and firm foundations, being of solid chalk.
Construction spanned 18-plus contractors and eight years, and involved digging and dredging channels and the sinking of coffer dams driven to depths of up to 24 meters into the river bed. The concrete piers, the base of those silver roofs, were sunk first; the sills were built using a mix of concrete re-enforced with steel.
They were built in a specially constructed dry dock on the north bank that was flooded so they could be floated out and lowered into position. It was a finely choreographed ballet that involved tugs and specially designed heavy-duty beams and synchronized winches from Sparrows Contract Services.
Precision was paramount: the biggest sills are 60 meters long by 27 meters wide, and 8.5 meters high — oh yeah, and weighs 9,000 tones. Units had to be moved in a confined space in fast-flowing water and positioned on the river bed 16 meters below with an accuracy of within 10mm.
Apart from the metal gates, which were unique construction, every piece of machinery that was used to power the raising and closing of the gates had already been proved in the field elsewhere, according to Batchelor
But the barrier didn't just challenge the engineering brains, it shook up labor relations and financing, too.
The project initially used 12-hour shifts of workers – a common practice in civil engineering, but alien to a local labor force more accustomed to a 40-hour week. A switch to three eight-hour shifts produced resentment, caused by loss of overtime pay.
The length of the project combined with the uncertain economic climate of the 1970s and early 1980s (up to 24 per cent inflation) meant contractors wouldn’t agree to a fixed-price contact. Funding was finally split between the government, 75 per cent, and the customer, the Greater London Council (GLC) who covered 25 per cent of the bill that landed at £535m (roughly £1.8bn in today’s money.)
Nearling completion: the Thames Barrier acquires its distinctive look, photo: the Environment Agency
After a brief stop to consider this and stroll down the service tunnel we reach a sign to pier seven – time to ascend. Clattering upwards and crossing anterooms we break onto the daylight, and that screaming wind. Each central pier is 50 meters tall, penetrating the riverbed to 15 meters, is 11 meters wide and 65 meters long.
It’s a minimalistic business out here: the pier is boat shaped, with a yellow crane stationed in the middle, like a sail boom. At one end of this pier, a large equipment room at the other a smaller local control room where engineers can operate a shift and latch system to move the gate should they have to.
These cranes are used to lift the equipment inside and below up and out for repair – there’s one on each pier.
Tucked away just to one side is what looks like a yellow elbow joint: it’s one of a pair of hydraulic-powered arms 24 meters in diameter attached to the rising sector gate. Mostly one arm is used but in exceptional circumstances two could.
These gates were built in the North of England and barged down the coast to London. The largest sector gate has a navigable width of 61 meters (equivalent to the aperture at Tower Bridge up stream) and the smallest rising sector and radial gates that are not navigable.
Shopping trollies don't stand a chance
The 61-meter gates weigh 3,300 tonnes of which 50 is paint and another 20 are anodes applied to prevent corrosion to the metal. Each gate is hollow, made of plates 40mm thick and capable of holding back 9,000 tones of water during a tidal surge.
There’s a 200mm gap between gate and sill in the riverbed, shrinking to 75mm. The gap between each gate and the sill means that any obstruction would get jet washed though – when closed, the water velocity under the gate reaches 13 m/s. The obvious question: what about other possible blockages, like supermarket trollies? Faced with the combined power of hydraulics and gate, such a trolley would be mince meat, Batchelor assures me.
Pier decks are spartan affairs, cranes and little else, photo: Gavin Clarke
We retreat from the wind-blasted deck to the larger of the pier’s two silver structures. Inside is not what you’d expect: equipment, yes, but big equipment; those electric pumps that pull 190 horsepower, operating cylinders, power packs, hooks and chains, some painted in the same juicy yellow as the plant outside.
Gear in here is duplicated, so each gate can be closed by any one of its two duty and stand-by power packs. The machinery is capable of producing a total of 8,000 tonnes of thrust to move the gates.
Everything is ensconced snugly beneath a delicate high-arched roof built using Iroko beams and European pine planks that help comprise a three-layer skin. The look and resin smell lends things a Scandinavian touch. The barrier's signature stainless-steel tiles are on the outside.
The whole forms more than just an iconic statement – it's practical: the tiles haven’t been cleaned in 30 years nor have the been replaced.
This was a real break through: the piers could easy have ended up flat, like the stumps of the Eastern Scheldt barrier, with a road across the top.
“At the time stainless steel, as today, was very expensive, but we’ve never had to clean it or renew it” Batchelor said. “I’m a civil engineer, and if I’d put a flat roof on it, I’d probably have had to change that couple of times... it might have taken a little more outlay at the front, but over the term it’s saved on cost.”
One last thing to see: down and into a narrow side chamber housing a single piece of gear that looks like a piece of massive drill: an 11-foot screw shaft black with grease and with a series of levers at one end. This is a giant hand brake that grabs the gate and lets you hold it in position while decompressing the hydraulics. In the event of a total hydraulic failure, operators could also use this to lift the gate from the water.
Having squeezed down the side of this giant screw with controls it’s time to leave: exit is quicker thanks to sleek elevator taking us 17 meters back up and out into the fresh and powerfully battering air whipping around outside. On our way Batchelor makes a small confession – he used to get lost down there, in that kilometer of tunnel and among those walk ways. “There was no signage or anything,” he says.
There’s a big fish we haven’t gutted: climate change. Or, rather, how can a flood defense more than 40-years old stand up to today’s realities of rising sea levels and human development that were, arguably, neither existent nor anticipated at the time? The barrier's end of life was pegged at 2030.
Batchelor cites a report of the Environment Agency, which runs the barrier and called Thames Estuary 2100 plan that gives the facility a role until at least, 2070 based on current assumptions about rising sea levels.
TE2100 recommends the flood defense chain of which the barrier is a large part be actively maintained and improved at a cost of £1.2bn, but advocates need for a long-term decision in 2050 on what comes after 2070. One option on the table a new barrier at Long Reach in Dartford, six miles away.
TE2100 was the product of six years' research into how flood risk in the tidal Thames floodplain that runs from Teddington to Sheerness and Shoeburyness would change as the result of human development and climate change. This floodplain spans an area of 350 square kilometers and encompasses 1.25m residents, 500,000 homes and 40,000 businesses.
“On current levels will we still be OK,” Batchelor said. “Tony will have to keep doing his computer upgrades, the maintenance will keep carrying on, but on current climate predications and forecasts we should be OK to then.”
I return my hard hat, shake hands with Batchelor and find myself once more beyond the stone and steel defenses. There’s time for a look back at the span and wander the short distance to the Thames Barrier Information Center and Café.
Heavy metal. One of the arms responsible for exerting 8,000 tonnes of thrust, photo: Gavin Clarke
You can’t pass through the guts of the beast, but you can marvel from the outside walking down that bank. The Thames Barrier is a landmark on at least two walks – the 180-mile Thames Path and the shorter Green Chain Walk – and it can viewed from the water from a number of tourist and regular riverboats, too.
Surrounding is a mix of commercial and residential, but head south on the Green Chain Walk and you pass through woods once popular with highwaymen leading up to Charlton House and Park. Or, you can go north via the Woolwich foot tunnel or ferry, four miles east is Woolwich Royal Arsenal while to the West is Greenwich and all its attractions.
Further out the towers and bright lights of central London, receding into the purple winter dusk with their lights twinkling. Sites that owe their very viability and dry feet to the machinery I've just seen. ®
Car: A206, then on Eastmoor Street. Car parking available on site. Undergound: North Greenwich, plus two-mile walk. Rail: Charlton or Woolwich Dockyard, plus a short walk.