신비한사전

There are over 10,000 dams that don't hold water hidden in mountain valleys across the country. These dams let water flow through smoothly, only filtering out rocks and logs that come down during heavy rain. The structure is designed so that rocks carried by debris flows act as plugs themselves. What's even more amazing is that they are completed only when filled with soil. The accumulated soil gradually slopes down the valley, making the mountain itself safer. They are the last line of defense protecting villages during the rainy season.

There's a power plant that devours electricity all night long. It uses surplus electricity to pump water up to a mountaintop reservoir, and then when electricity is scarce, it lets the water fall back down to convert it into electricity again. The entire mountain is essentially a giant water battery. What's truly terrifying is during a blackout. When other power plants can't start up due to a lack of initial electricity, pumped-storage power can come online in just 3 minutes, becoming the first spark to revive the nation. Tonight, they're pumping water up again.

There's a bridge in the middle of Seoul that gets submerged every time it rains. Instead of building it high to escape floods, they chose to build it low, letting it go underwater. An underwater bridge has no target for the floodwaters to hit. However, the problem is that you can't cross it when it's submerged, so they built another bridge on top of it. That's how Banpo Bridge, Korea's first two-tiered bridge, was born. Even now, if the Han River's water level reaches 6.2 meters, the Jam수gyo (underwater bridge) quietly hides beneath the water.

The 500-meter wide river that runs through Tokyo is actually an artificial canal dug by humans. After Tokyo's east side was completely submerged by a great flood in the 1910s, they decided to create an additional channel for water drainage. It's 22 kilometers long. The project was led by an engineer who was the only Japanese person to participate in the Panama Canal construction. It took 20 years of digging with shovels and pickaxes, involving a total of 3.1 million person-days. Even though they experienced the Great Kanto Earthquake midway, the floodgates he built reportedly remained intact.

In the Netherlands, there's a 9-kilometer dam with 62 gates that are kept open year-round. Initially, they were building a concrete dam that would completely block the entrance. However, the tidal flats inside began to die off. Fishermen protested by sailing their boats out, and eventually, they halted the construction of the dam. The solution they came up with was gates that are normally open and only close during storm surges. Although it cost significantly more than a complete blockage, both the tidal flats and the oyster farms survived.

Ten steel gates lie flat at the bottom of the River Thames in London. Normally, ships pass over them without any issue. But when a tidal surge comes in from the sea, these gates turn 90 degrees and completely block the river. There was an option to raise the riverbanks, but the riverside in central London was already packed with buildings and docks, making it impossible to work on. So, they decided to install gates in the river itself. Since they've been activated over 220 times since 1982, London has managed to stay dry thanks to these gates.

Ever wonder how a building made entirely of glass survived the height of summer? The Crystal Palace in London, built in 1851, didn't cool the air; instead, it twisted the angle of sunlight hitting the glass. They dug triangular grooves into the roof, angling the glass panes. What's even more interesting is that the person who came up with this method wasn't an architect but a gardener, bringing over technology used in greenhouses. Still, they couldn't fully beat the summer heat, so they ended up removing some glass panes, and the Royal Engineers had to open and close them based on thermometer readings. It's quite impressive.

After the Normandy landings in 1944, to continue resupplying, they needed to transfer cargo from large ships to the beach. However, securing a large port immediately was difficult. Continuously docking ships on a wave-battered sandy shore meant unloading could be halted by weather and tides. So, instead of waiting for a port to be built, Allied engineers decided to assemble and bring one. Massive concrete caissons, floating roadways, and adjustable piers were constructed separately across Britain and then towed across the channel. Old ships and caissons were sunk to reduce outer waves, the piers were designed to rise and fall with the tides on four legs reaching the seabed, and the roads were divided into sections on floating structures to absorb wave motion. Although the American Mulberry A was severely damaged in a June storm, the British Mulberry B held up until November 19th of that year.

The road deck, weighing a total of 36,000 tons, slowly extends from the edges of both cliffs into the void. This is the Millau Viaduct in France, measuring 2,460 meters in length, and the point where the two deck sections had to meet was about 270 meters above the River Tarn. Assembling the deck suspended in mid-air at this height would have posed extreme risks due to working at great heights and strong winds. Therefore, engineers assembled the deck sections not over the valley, but in workshops behind the plateaus on either side. They then used hydraulic launching devices installed on the piers and temporary steel supports to gradually push them out. The challenge was that the long steel plates could sag under their own weight before the end of the deck reached the next support. To counter this, they preemptively attached a steel tower with cables to the extending end to pull it forward. It's like attaching a giant fishing line to the end of a road stretching into the sky.

About 2,500 years ago, two tunnels dug from opposite sides of a mountain met in the darkness over a kilometer away. This is the Eupalinos tunnel on the Greek island of Samos, with a total length of 1,036 meters. While digging from both sides simultaneously can speed up construction, if the direction deviates by just 1 degree while one side digs 500 meters, the ends can be off by about 9 meters. Researchers believe they precisely set the direction and gradient of the two entrances and continuously re-measured and corrected the course during construction. In reality, the northern tunnel deviated from a straight line, corrected its direction multiple times, and eventually curved back towards the southern tunnel. Furthermore, the main passage for people was almost flat, so they dug a separate deep trench next to the passage, lowered the floor further towards the south, and laid pipes inside to drain water.