Underground canal, the miracle water conservancy project Karez

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Underground canal, the miracle water conservancy project Karez

On the Gobi Desert in Turpan, you can see piles of round soil bags descending the high slopes like "pearls" strung together, stretching out to the oasis in an orderly manner. It is the soil dug out of a well.

The Turpan area is arid and deserted, and it is extremely hot in China. The high temperature is above 35 degrees for more than 100 days every year, the extreme temperature is nearly 50 degrees, and the surface temperature of the desert can even reach 85 degrees, so Turpan is called "Fire State".

The annual precipitation in Turpan is 16 millimeters, but the evaporation is more than 3000 millimeters. It is one of the extremely arid regions in China. But Turpan is also the hometown of melons and fruits. We all know the grapes in Turpan, so where does the water for irrigation come from? That is Karez.

Turpan means "a rich and fertile place" in Turkic. Bogda Mountain in the north, Klaucheng Mountain in the west, Turpan is in the basin, and Aiding Lake at the bottom of the basin is the lowest place in China. Whenever summer comes, a large amount of mountain snowmelt and rainwater flow to the basin. When the water flows out of the mountain pass, it quickly seeps into the Gobi Desert and becomes an undercurrent. Accumulation over time has thickened the underground aquifer in the Gobi Desert and increased the water reserves, providing a rich source of water for Karez wells.

The soil in Turpan is cemented with gravel and clay, the texture is solid, and the excavated well walls and culverts are not easy to collapse, which provides good geological conditions for excavating a large number of Karez wells. Smart people took advantage of the situation and used the slope of the mountain to ingeniously create Karez wells that guide the underground flow without power to irrigate farmland and build oases. Especially in winter, when the snow-capped mountains freeze and the rivers dry up, Karez water becomes an important domestic water for the local people.

"Kan'er" means "well point", which was called "Jingqu" in ancient times and "Kan'erzi" in Uighur. Pool) consists of four parts. Underground water storage can reduce strong water evaporation and save water resources; avoid surface pollution and ensure water quality; self-flow irrigation does not require power. The local people rely on their hands and simple tools, and the operation techniques are easily mastered by the local people. The excavation passed down from generation to generation makes Karez well worthy of being the soul of life in China.

The well diggers first search for the water source at the undercurrent of the snow water in the mountains, and then start digging from the downstream. The first section of the open channel and the long mouth of the Karez well (exit of the underground channel) should be dug first. Underdrain excavation arranges shafts section by section from downstream to upward. A shaft is drilled every 20 to 30 meters, and the shaft is used for ventilation, excavation, and soil lifting when repairing Karez. The downstream shafts are relatively shallow, generally only a few meters, and the upstream shafts are relatively deep, some up to more than 100 meters. Then, according to the terrain, culverts were built at the bottom of the well to communicate with the wells. The culvert generally has a height of 1.5-1.7 meters and a width of 0.6-0.7 meters. The culvert diverts water downwards, leading the groundwater to the surface open channel to irrigate the mulberry fields. A dam is a reservoir that regulates water volume. A karez is generally about 2 or 3 kilometers long, and several karez can be connected for dozens or even hundreds of kilometers.

Nullah and Longkou

It is very important to run the wells and channels in a straight line to avoid bending and reduce the amount of earthwork in the project. A well rope is hung above the wellhead between the two shafts. The well ropes are tied with a sharpened horizontal wooden stick. The direction of the two stick tips facing each other is the shortest straight line between the two shafts. Then use the same method to orientate the wooden sticks under the shaft, and the underground people can dig in the direction pointed by the wooden sticks.

The excavation of shafts and culverts is carried out by manpower pulleys for shallow wells and animal power for deep wells

stick orientation

Digging a culvert is groping in the dark, only relying on oil lamps for lighting. Two oil lamps are hung in the shaft, and the direction and height of the two lamps can be used to correct the direction and longitudinal slope of the culvert to ensure the water flows freely. It is also possible to use mirrors to reflect sunlight to orientate and serve as lighting. It is using such simple tools and methods to solve the technical problems in the project.

digging underground drains

Regarding the origin of Karez, due to the different records and remains, Chinese and foreign scholars have heated debates about its origin. The points of view can be summarized as the theory of the introduction of Iran (Central Asia), the theory of the introduction of the "well canal" in Guanzhong in the Han Dynasty, and the theory of local self-creation. The country and region with the most Karezes in the world is Iran, followed by Afghanistan, and there are more than 2,000 Karezs in Xinjiang.

Lin Zexu was the most influential person who advocated and promoted Karez in modern times. In the 25th year of Daoguang reign of the Qing Dynasty (1845), Lin Zexu saw Karez well about 40 kilometers away from Turpan on his way to garrison Ili. He was very surprised at that time. He presided over the digging of more than 60 Karez wells in Xinjiang. Another climax of the construction of Karez was after Zuo Zongtang recovered Xinjiang in the 6th year of Guangxu (1883). In the 9th year of Guangxu (1886), the Xinjiang province was established. The Qing government called on the army and the people to promote water conservancy, and built 185 Karez wells in Turpan, as well as in other areas of Xinjiang. After liberation, due to the expansion of cultivated land and the widespread use of motorized wells, and the long-term lack of maintenance and repair of Karez wells, more and more Karez wells are in a state of abandonment.

Lin Zexu

Zuo Zongtang

Karez, the Great Wall and the Beijing-Hangzhou Grand Canal are known as the three major projects in ancient China. When traveling in Xinjiang, when you arrive in Turpan, you must see this great water conservancy project.