Why is the Delhi Metro not completely underground?

technology: Full pipe

Full pipe - side 1

That is not in the travel guide: One of Tokyo's greatest attractions is the underground cathedral. Profane people call them »catchment basins«, but that is not appropriate: We are talking about five huge concrete cylinders, 32 meters in diameter and 65 meters deep (which exceeds the gable height of Cologne Cathedral), connected by over 60 kilometers of tunnels that are 50 meters run beneath the surface of Tokyo. Like the columned forest of Gothic church naves, the pillars of the complex extend into the darkness. The wet metal of pumps and tubes is reminiscent of films like Matrix or Alien.

"The facility also serves as a tourist attraction," says Yukimitsu Watanabe from Saitama Prefecture. "It can be viewed free of charge during the dry season." In the rainy season and during the typhoon season, however, a visit would not be advisable. Then pumps with 14,000 horsepower shovel water through the canal system under the Japanese capital out into the Edogawa River, which flows into the Pacific. The 280 billion yen (around two billion euros) expensive underworld pumping system has been in trial operation for three years. The construction work will be completed in the coming year, after twelve years of underground digging and concreting.

The monstrous structure is called »G-Cans«. Mr. Watanabe provides information: "'G' stands for Gaikaku Housuiro, the river of the outskirts" well, and "Cans", which is supposed to be English in some way, express the confidence that something can be done in this place. G-Cans can therefore be roughly translated as "You can do something on the outskirts of the river," says Mr. Watanabe. What?

Well, remove 200 tons of water per second in an emergency. So that Tokyo doesn't drown.

The horror scenario looks like this: the streets are full of water, gullies overflow, the sewer system is overwhelmed. Gradually, but inexorably, the dirty soup makes its way up stairs and escalators to the subway stations. They run full, their discharges are also insufficient. The result: Tokyo, the world's largest agglomeration, is flooded. From underneath.

Somehow this metropolis is a mistake in settlement. It is located on a Pacific coast threatened by tsunamis. On a narrow clod of land that has been shaken by earthquakes for ages. And torrential downpours continue to pour down on them. Between 1999 and 2001 alone, the natural showers were so strong in 17 cases that it was called "Land under" in Tokyo's subway.

Rain catchers and drains, sewer systems and drainage were not able to cope with such precipitation. Deep beneath the most technologically advanced city in the world, raw nature claimed deaths: people drowned in overflowing railway tubes and stairwells. And these are by no means the only cavities under the capital that can fill up in the event of a rain catastrophe. With supply and disposal facilities, underground garages and basements, Tokyo is increasingly being expanded towards the center of the earth. Underground train stations and shopping centers now merge seamlessly and form a megacity below the megacity. The length of all tunnels, pipes, tubes and shafts in the Tokyo underground is already 33 times the length of the main inner-city streets.

Full pipe - side 2

Big cities are attractive - and prone to the increasing number of storms

Meanwhile, architects are planning even bigger things: Whole blocks of houses are to be driven into the depths as crusts of the earth. Why? Lack of space! It is characteristic of Japan, but not only Japan.

The experts agree that the age of confinement has only just begun. Every second person on earth already lives in a large city or urban agglomeration. By 2025 it could be two thirds of humanity, then around five billion people on earth. Big cities are attractive. But also sensitive to storms, the number and strength of which is increasing. »In 2004 there were four times as many typhoons in Japan as the long-term average. In Germany, too, we have significantly more heavy rain and winter storms, "says Janos Bogardi," in general we have observed an increase in extreme weather phenomena in the past three decades. "The hydraulic engineer is director of the Institute for Environment and Human Security, which is barely a year old and Human Security, EHS) in Bonn, part of the United Nations University (UNU), a global research network of the world community. Threats, risks and vulnerability of the changing world are the research field of the UN scientists in Bonn. You write: "The management of too much or too little water, especially in mega-cities, will challenge the brightest brains of future generations."

The term mega-city is used from a population of eight million people. Ten percent of the world's population now live in such a huge city as New Delhi, Cairo, Tokyo or Mexico City. "Hidden vulnerability of mega-cities" is the name of the EHS research project that is dedicated to the risk of flooding. However, according to Janos Bogardi, the habitats below smaller cities with a million inhabitants and urban agglomerations could also become mass graves in the event of catastrophic rainfall; the mega-cities are just particularly blatant examples. According to UN estimates, 800 million people are exposed to the risk of a flood every year. In other words, Tokyo is everywhere.

A map of the world in Bogardi's Bonn office shows the distribution of the world's population. While large parts of the interior of the continents remain largely white (only moderately to not populated), their edges, i.e. the coasts, are heavily speckled with dark and the more densely populated, the larger the corresponding black circle. India: tightly packed coastline. Japan: black. China: sown over and over along the sea. This pattern from Southeast Asia can also be found in a moderate form on other parts of the world. "Large cities at estuaries, in deltas, and generally in coastal areas, are particularly at risk," says Bogardi. "Unfortunately, people have always liked to settle there and continue to move there."

So the subject of vulnerability researchers is not just theory. But without theory there is no science. Bogardi's people want to develop such a theory. "When it comes to being well prepared for disasters, Tokyo is more of an exemplary city," says Srikantha Herath. "There they try tirelessly to reduce the physical and social vulnerability of the city, whether caused by floods or tectonic activities." Herath, who comes from Sri Lanka and is a member of Bogardi's team, works in the UNU branch in Japan Capital. The flood researchers want to find a method to express the endangerment of such a city in numbers. Tokyo is an example to them of the realization that vulnerability depends on several factors and not just on the original probability of an extreme event; they ask, for example: how good is civil protection? How informed is the population, how pronounced is the solidarity with one another?

What should come out in the end is a comparative value, the »vulnerability indicator«. Finding a simple size for such complex relationships is not that easy, says Bogardi. Even the search for passable maps of underground cavities, pipes and connecting paths is difficult. And finding data that can be compared with one another is even more of a challenge, admits the flood researcher from Bonn.

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It is a bit easier to estimate which natural attacks cities will have to resist in the future. After all, research is certain that the pollution is currently increasing. Bogardi, who did his doctorate on flood protection in Karlsruhe: “For example, the protective devices in Germany must be designed in such a way that they can withstand a flood that occurs on average only every hundred years. The only question is what kind of flood we are talking about. At the time from which this regulation originates, the underlying series of measurements were still stable. There is now a clear upward trend. "

It only becomes unstable underground when cavities are flushed out

That is why the Japanese provided their capital with the underground cathedral. Should other waterfront cities do the same? Bordeaux maybe, or Hamburg? Pure theory. “The price is immeasurable,” says Srikantha Herath, “so it is unlikely that a similar project will be tackled anywhere else.” At most, the Saudis can still afford a facility like the Japanese. Civil engineer Dietrich Stein from the Ruhr University in Bochum, an expert on the urban underworld in Germany, has just returned from the Saudi Arabian capital Riyadh. This city is predicted to grow from 5 to 15 million inhabitants over the next ten years. There, too, gigantic underground basins and drains are currently being built to cope with the cloudbursts that are rare but feared in the desert state, says Stein. »In Germany we have an average annual rainfall of 800 millimeters of water. That can come down in Saudi Arabia in a single day. "

But what advice can be given to others who are not in the money? At least city planners and hydrologists, i.e. water experts, have to get together, but that almost never happens, Herath criticizes. In most metropolises, for example, the construction of subways is inevitable, but then drainage areas would have to be kept free from the outset and retention basins planned. This applies especially to poor countries that cannot afford any other low-tech solution.

For now, the flood researcher suggests: "Dig connections!" Often, subterranean cavities are not connected to one another, although they run over, next to and past one another. But that is fatal in an emergency. If you have to evacuate quickly, there cannot be enough ways up.

Especially since in the worst scenarios of the UNU researchers, the flooding from below is followed by the flooding from above.

Entire blocks above the submerged surface of the earth could become unstable and collapse. "Today, underground structures are planned like simple floors of a high-rise building," explains engineer Bogardi. However, for reasons that are easy to see, they cannot run full. »They are not designed in such a way that, instead of taking normal loads, they would withstand the weight of around 300 kilograms per square meter that would be placed on a crowded basement. Even at half a meter of water, that would be an additional 500 kilograms per square meter. ”With dramatic consequences: If one floor collapses underground, a cascade downwards and from above threatens because broken basements are no longer a foundation for high-rise buildings.

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“That is a pretty extreme assumption,” says Stein, a civil engineering engineer from Bochum, “but no coastal city is immune to this, including Hamburg.” Stein continues in an engineering way: “An underground infrastructure only becomes unstable when cavities are flushed out. The scenario would be realistic if water currents had contact with the ground and could erode the foundations. ”As long as everything is properly built, nothing can actually happen, confirms Bogardi, but adds:“ Unless, of course, an underground structure is built before or during a flood Damaged, for example by an earthquake. «Possible, so one must add such sentences, are therefore causal chains that could come from a catastrophe film.

"There are events that you cannot protect yourself from simply because the effort would be too high," says Stein. "Any precaution would be pointless." For example against floods with unprecedented water levels, storm surges or tsunamis that would exceed the current dyke heights. "We are not concerned with offering protection from every event," says Bogardi, "that would be an illusion. But we want to find out where people are particularly vulnerable, so where we can improve safety with a comparable amount of effort. "

You can call that pragmatism. Aside from the gigantomania of concrete flood cathedrals, Tokyo also has something to offer to illustrate this principle: the Japanese build mini dikes around all entrances to newly built subway stations. "If you want to go down the stairs, you first have to climb two or three steps," says Bogardi. "You don't see anything like this anywhere in Europe."

Two stone steps only. Two steps up before the path to the underworld. Like a ritual sacrifice in passing so that the cathedral can stay dry under the city.