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Water, Water, Everywhere

Storm Surge Barrier at Maeslantkering near Rotterdam
To tour the Netherlands is to marvel at Dutch ingenuity in water management. With one quarter of Holland below sea level and one half at one metre or less above sea level, the Dutch have lived with the threat of flooding for their entire history. The country boasts over 17,000 kilometres of dikes, along their rivers, intended to protect residents from flooding. 

But one night in 1953, the confluence of an especially high spring tide and a wind storm over the North Sea struck just after midnight and caused water levels to rise more than 5 meters above normal, breaching the protective dikes. Radio was off the air and government agencies were not staffed; there was no warning for the residents of low-lying land and islands. By 3 a.m., more than 1,800 people had lost their lives.

The Netherlands decided to get serious about a new era of flood control water management. They wanted to have defences that would handle once-in-a-thousand years storms. This is a lofty goal, as our guide pointed out, comparing it to the US goal of coping with once-in-a-hundred years storm.

1  Now, the Netherlands has built dikes to keep the water out for centuries. The idea of those dikes is part of their DNA. Here's a photo while we were driving along a road on a dike - note how the houses sit at a lower level than the dike. (Also worth nothing is the fact that there are two bike lanes but only one lane for cars).

To innovate successfully, you have to 'let go of what you know'. And the Dutch did just that. They concluded that they just couldn't build the dikes high enough for full protection. And besides it would be much too expensive. There are still use dunes as a natural barrier along the sea shore. These large dunes needed to be reinforced annually, a significant task to dump the sand all along the coast. But the Dutch are so clever. They observed where sand was distributed naturally by tides and currents and concluded they could simply dump sand in a few strategic places and let nature distribute it where needed.

2 So, they concluded they had to block the water before it got to the rivers. In the first project, they simply built two dams south of Rotterdam. Where once there had been a gradual change from salt water to fresh water, now there are two totally separated ecosystems and the types of fish the fishermen used to fish no longer exist. The Dutch had to build more such protections and dams were clearly not the answer.

3  Further south, at Oosterschelde, a different approach was taken in the 70s: to build gates that
stay in a raised position normally but would be lowered during a storm. This allows the fish - and their predators the fishermen - to pass through freely. An excellent movie at the visitors' centre described how huge piers were placed on the ocean floor, sitting on ‘mattresses’ made of material filled with rocks to form a firm foundation. The mattresses were laid by being uncoiled off huge rollers on the back of special boats. The piers were built on shore on a huge dock, and towed out to sea after the dry dock was submerged. Then each pier was lifted off the dock and precisely placed on the mattress floor. Then, the movable concrete blocks were placed between the piers.  Lastly, road we had driven along was laid on top.

We had seen these barriers as an accident of Lib’s misguided trip planning: after determining that the huge new surge barrier she had read about was created by Delta Works, she used Google maps to locate it and that’s how we ended up here, one of the Delta Works projects, but not the one we were most interested in. We were told the storm barrier we so wanted to see was north of us at the Hook of Holland. Luckily that was just over an hour away and virtually on the way to Delft, our next stop. Whew, disaster averted.

The solution of gates that could be raised and lowered between fairly closely set piers wouldn't work at the mouth of the Rotterdam port. Once the largest ports in the world, Rotterdam is now surpassed by ports in Asia, but it’s still impressive. The day before, we had taken a detour to drive to the end of the series of berths of Rotterdam (numbered from 1 to 9900), that stretched seemingly endlessly off the main road. We drove for miles and miles. The scope of the port is absolutely amazing. We were surprised to see almost no activity anywhere - no loading or unloading, and no stream of trucks on the highway. Perhaps that is because the port is in decline?

So, back to the story of the huge new storm surge barrier. Proposals were invited for techniques to close off the mouth of the river as required in the case of big storms, but leave it open for shipping. The winning proposal involved two huge arms (the size and twice the weight of two Eiffel Towers) which are swung in from either side of the estuary to close it off completely if there is a risk of the water level rising 3 metres in Rotterdam. You can see the scale of the arms that support the barrier from the picture of me standing by them.

These massive blocks of concrete are swung in by equally massive ball bearings, which can move in several directions, like shoulder joints. They have to move sideways to swing the barrier across the channel, an exercise which takes half an hour. Then the ball bearings have to be able to move up and down, as the concrete wall is filled with water and descends to fit on the concrete block on the bottom over an hour and a half. Here's a diagram from the New York Times article showing how everything fits together.

The system is tested once a year, and various disaster scenarios are added to the exercise each year. This bottom block gathers a metre of sediment every year. As the barrier slowly descends, the water is compressed and gathers speed and washes away the sediment. This is the reason for the slow descent. Brilliant.

This amazing piece of engineering was completed in 1997 after 6 years of construction, on time and on budget. Equally amazing. All the pieces were build in Holland, except for the massive ball bearings, which were made by Skoda in Czech Republic. I was told at the Amsterdam conference that the Canadian software firm CGI built the software to control the barrier. 

The risk of flooding is assessed every ten minutes to check water levels and the risk of a big storm. When the system was originally built in 1997, it took ten minutes to complete the calculations! Today they complete in seconds, but they have not felt the need to do the calculation more often. When there is a risk, a warning is sent out to all ships with four hours notice so that they can determine if they have time to get past the barrier before closing. (Tug boats are on standby to haul ships away if there is a risk they’ll get caught as the barrier closes). At two hours, the decision to close becomes irrevocable and the countdown starts.

Having completed all these projects, the Dutch still didn't feel they had enough protection against flooding in an era of climate change and the inexorable rise in sea levels. So they had to overturn all their past thinking again. If you can't keep the water out, then you have to learn to live with it. So you start projects with another approach to the problem and brand them Room for the River. That's another radical change in thinking. They are building catchment areas for when, not if,  there is flooding. Some of these catchment areas are lakes designed to overflow, some are used as recreational areas, some even as parking lots.

The Dutch have consulted on water management for a long time; in fact they helped the English drain the fens. And they are consulting around the world about this approach as well(as described in this wonderful New York Times article). Toronto is also taking this approach to protecting against flooding of the Don River, as described here


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