Three Gorges Dam

Stand still for a moment and listen. Under the wind there is a low, steady hum. It is not quite a sound you hear with your ears. It is more a pressure, a feeling of enormous water held in place. In front of you, a pale grey wall of concrete runs across the valley, so long that its far end fades into the haze. This is the Three Gorges Dam, on the Yangtze River, upstream from the city of Yichang.

The Yangtze is the longest river in Asia. It begins on the high Tibetan Plateau and runs across China to the sea near Shanghai. For thousands of years it fed farms, carried boats, and drowned towns. Here, just above Yichang, the river leaves its mountain gorges and spreads into the open plains. That made this stretch the natural place to try to control it. The dam sits near a village called Sandouping, where the valley floor is solid granite, a firm base for a structure this heavy.

The idea is older than most visitors expect. Here is the first surprise. Sun Yat-sen, the revolutionary often called the father of modern China, proposed damming the Yangtze in the early twentieth century, around 1919. Engineers studied the gorges again in the 1940s and the 1950s. Mao Zedong even wrote a poem in 1956 that imagined a calm lake rising between the narrow cliffs. But wars, politics, and fierce debate delayed everything for decades.

Construction finally began in 1994. The main wall was completed in 2006, and the last of the main turbines came online around 2012. Tens of thousands of workers took part over those years. The finished dam stands about 181 metres high and runs more than two kilometres from bank to bank. The concrete inside it is counted in the tens of millions of cubic metres. Numbers like that are hard to picture, so look at the trucks and buses on the crest. From here, they look like grains of rice.

The dam has three main jobs. The first is flood control. The Yangtze has a long record of disastrous summer floods, and a severe one in 1998 killed thousands of people downstream. The reservoir behind the wall can absorb part of a flood surge and release it slowly. The second job is electricity. The third is shipping, because the deep reservoir lets larger vessels travel far inland, all the way toward the city of Chongqing.

The electricity is the part that set records. By installed capacity, this is the largest hydroelectric power station in the world. Turbine halls on both sides of the river hold more than thirty giant generator units. Water drops through steel pipes, spins the turbines, and leaves at the base of the dam. Power from here travels by high-voltage lines to cities hundreds of kilometres away, including the crowded east coast.

Now look upstream, to the reservoir. That calm, wide surface did not exist before this century. The water now stretches roughly six hundred kilometres back through the mountains. It covers the river's old channel, its rapids, and the floors of the three famous gorges, called Qutang, Wu, and Xiling. The cliffs are still there, but the water sits much higher against them. Old boat pilots used to fear the rapids of Xiling Gorge. Today, those rapids lie deep under the surface.

This is where the story becomes harder. Here is the second surprise. The rising water forced more than one million people to leave their homes. Whole towns and cities were rebuilt higher up the slopes. Farmland, temples, and archaeological sites went under the water. Some monuments were moved stone by stone, such as the Zhang Fei Temple, which honours a general from China's Three Kingdoms period. Ancient stone inscriptions that recorded river levels were protected in an underwater museum upstream, in the city of Fuling.

Scientists and critics have raised other concerns too. The dam traps sediment that once flowed downstream to build up the river's delta. The reservoir has been linked to landslides along its steep banks. River wildlife has also suffered. The Chinese sturgeon, a large fish that has lived in the Yangtze for millions of years, has struggled to reach its old spawning grounds. These debates are part of the place. To understand the dam honestly, it helps to hold both its achievements and its costs in mind.

Turn your attention to the north side of the dam, if you can see it. That stepped staircase of concrete chambers is the ship lock. It has two parallel lanes, each with five stages. A ship enters one chamber, the gates close, and the water level changes to lift or lower it to the next step. The full passage takes several hours. Next to the locks stands a newer ship lift, opened in the mid-2010s. It works like a huge elevator, raising an entire vessel in a tank of water.

Most visitors see all this from Tanziling, a hill above the north bank that serves as the main viewing area. Shuttle buses bring people up from the visitor centre after a security check. At the top there is a large model of the whole project. It helps to study it first, because the real dam is too long to take in at once. Other terraces lower down bring you closer to the crest and the spillway gates.

If you visit in summer, you may see the spillways open. White water then bursts from the face of the dam with a deep roar, and a fine mist drifts across the viewing points. In drier months the gates stay closed, and the scene is quieter. The reservoir level also changes through the year. It is kept lower in the flood season to leave room for storm water, and it rises again in autumn and winter.

After your visit, you might travel down to Yichang itself. On the way, the river passes another, older barrier, the Gezhouba Dam, which was built in the 1970s and 1980s. Yichang grew in part because of these two projects. Many river cruises through the gorges begin or end here, so the city has long been a gateway between the mountains of the west and the plains of the east.

Before you leave, look once more at the wall in front of you. Notice how flat and still the water is on one side, and how lively it is on the other. Behind that concrete lies a lake that covers old villages, old roads, and old rapids. In front of it, the river keeps moving toward the sea, as it always has. Listen for that low hum again as you walk away.