Besides the Grand Canal, what other famous engineering historical themes are there?

First, the Great Wall built on the mountain stretches across Wan Li, just like a dragon swimming among mountains, protecting the safety of the Chinese nation. The second is the Beijing-Hangzhou Grand Canal. The Grand Canal Project was built in the Sui Dynasty, which is a huge project. It took millions of people to complete the Grand Canal project. After the completion of the Grand Canal, it not only communicated the North and the South, but also promoted the cultural exchange and integration between the two places. More importantly, the Grand Canal project also promoted the economy of ancient China and greatly promoted the development of the Chinese nation. This is the Karez project in Xinjiang.

Xinjiang Karez Project: Karez Project is a unique water conservancy project in Xinjiang. The main function of Karez is to bring groundwater from Xinjiang as an open channel to irrigate local farmland. Then why can a water diversion project become one of the greatest projects in ancient China? Listen to me slowly, and you will know why. The Karez Project was built in the Han Dynasty. During the reign of Emperor Wu of the Han Dynasty, the northwest region was greatly developed. After a large number of immigrants and border guards enter Xinjiang, it is imperative to build a sound water conservancy project in order to enable immigrants to take root in this barren land of Xinjiang and be self-sufficient.

However, due to the natural conditions in Xinjiang, general water conservancy projects in Xinjiang are useless. Even if the groundwater is pumped out, a large amount of water will not remain and will evaporate in large quantities. During the reign of Emperor Gaozu of the Han Dynasty, 15,000 people, including Jiang, were sent to Dunhuang, the main purpose of which was to solve the agricultural irrigation problem in Xinjiang. Although the weather in Xinjiang is hot and there are few open water surfaces, there are tall snow-capped mountains in Xinjiang, and the water covered with snow all year round flows into the ground. Therefore, Xinjiang is rich in groundwater resources, but these underground rivers are far from the surface, and the farthest is close to 100 meters, so it is extremely difficult to develop. In the end, our ancestors used their extraordinary wisdom to develop the Karez project suitable for Xinjiang.

Karez, also known as well canal, consists of three parts: shaft, culvert and open channel. The shaft is a channel for conveying underground sediment or silt when digging or cleaning the culvert of Karez, and it is also an air supply outlet. The biggest difficulty of this project is vertical operation. In ancient times without machinery, it was very difficult to dig down the shaft, and the height of some shafts could reach more than 90 meters. Culverts flow out of the ground and become open channels. People have built a reservoir with the function of storing water and regulating water quantity in a certain place. These large and small reservoirs are called waterlogging dams. Water accumulates in the waterlogged dam and is sent wherever it is needed.

Culvert, also known as underground passage, is the main body of Karez. Generally, it is dug from low to high according to a certain slope, so that water can automatically flow out of the surface. Culverts are the most difficult part of the whole project, so I will list them separately. First of all, we must determine the direction of underground excavation to avoid digging in the wrong direction in the dark without a sense of direction. Therefore, people invented the oil lamp that can light. The deeper the culvert, the narrower the space. Only one person is allowed to work in the back passage, and the soil in Turpan is hard calcareous cohesive soil. I can't imagine how hard the workers have to work to dig a 25-kilometer-long culvert under the condition of working alone. The most important point is that when digging a culvert, due to space reasons, workers can only kneel in the accumulated water to dig, which not only increases the difficulty of digging, but also makes the accumulated water in the snowy mountain bitter and cold, so the life span of workers who generally engage in culvert digging will not exceed 30 years old.