Chengdu Plain: Geographical Opportunities for Building a “Land of Abundance”

In 316 BC, the State of Qin began to annex the six states and prepare for war to unify the world. King Huiwen of Qin was hesitant about whether to attack Shu or Han first, so he asked his ministers for advice.

Sima Cuo, a Qin official, and Zhang Yi had a wonderful debate on this issue. Zhang Yi advocated attacking Han first and kidnapping the Zhou emperor to rule the world. Sima Cuo, on the other hand, believed that Shu should be taken first, "the land is enough to expand the country", "the wealth is enough to enrich the people and train the army", and Bashu can be connected to Chu by water, "if Shu is taken, Chu will be taken, and if Chu is destroyed, the world will be united".

King Huiwen of Qin finally adopted Sima Cuo's plan to attack Shu. He first destroyed the Shu Kingdom in the western part of the Sichuan Basin from Shiniu Road, and then destroyed the Ba Kingdom in the eastern part of the basin. He incorporated the entire Sichuan Basin into the territory of Qin and laid the foundation for Qin to unify the world.

▲Qin conquered Bashu and then took over the world. Image from the Internet

"Qin annexed the six kingdoms, starting with Shu." The successful experience of King Huiwen of Qin in "establishing a kingdom by using the land of Shu" was also emulated by later generations.

Liu Bang, who founded the Western Han Dynasty, and Liu Bei in the late Eastern Han Dynasty both used Bashu as their base to achieve their great undertakings. Moreover, Bashu also played the role of a refuge and a rear base during times of national crisis. During the Tang Dynasty, Shu became a refuge for the dynasty twice, and during the Anti-Japanese War, Sichuan and Chongqing became a rear base that was crucial to the survival of the nation.

The reason why Shu achieved the status of "a national treasure that can benefit the world" is naturally due to its prosperity where "floods and droughts are controlled by people, and there is no famine", and its prosperity is the geographical opportunity provided by the Chengdu Plain.

▲In Longzhong, Zhuge Liang offered Yizhou to bring peace to the world. Photo/Still from "Three Kingdoms"

The Chengdu Plain is located in the west of the Sichuan Basin, which is one of the four major basins in my country and the only outflow basin and green basin. Although it is a basin, the bottom of the Sichuan Basin is not flat, with hills and low mountains accounting for more than 90%. Only the Chengdu Plain in the west can be truly considered flat and vast. The total area of ​​the Chengdu Plain only accounts for 9% of the Sichuan Basin, but this 9% of flat land has become the most prosperous place in the Sichuan Basin and the center of the origin and development of the ancient Shu civilization.

Chengdu Plain is located between the Qinghai-Tibet Plateau and Longquan Mountain. It is an irregular strip surrounded by mountains and hills. It covers an area of ​​18,810 square kilometers and is the largest plain in southwest my country. Chengdu Plain is a fan-shaped alluvial plain. Its formation can be traced back to about 2 million years ago. It was initially affected by the Longmen Mountain thrust structure to form a fault basin.

Afterwards, the rivers in the mountains on the northwest side of the basin accelerated their cutting and formed river valleys under the uplift of the Qinghai-Tibet Plateau. The Minjiang River, Xihe River, Xiejiang River, Nanhe River, Chejiang River, Shiting River, and Mianyuan River all cut through the Longmen Mountains and entered the basin. After the rivers entered the basin, a large amount of alluvial materials such as silt, pebbles, etc. were carried from the mountains and deposited to form a series of alluvial fans in front of the mountains. These alluvial fans continued to expand and connect with each other, eventually forming a vast alluvial plain.

▲Topography of Sichuan Basin. Image from the Internet

Due to the different sedimentation rates in the basin, the thickness of the sediments varies from thick in the west to thin in the east, and multiple sedimentation centers are formed. The thickest part is 541 meters, and the thinnest part is only a few meters. The Chengdu urban area is about 15-30 meters.

These sediments have a double-layer structure. The lower layer is composed of gravel, sand, and pebbles, with a thickness of tens to hundreds of meters, and the upper layer is composed of silty clay or sub-clay, with a thickness of several to tens of meters. In particular, the clay or sub-clay in the upper layer is rich in minerals and organic matter, forming fertile soil, which is the basis for the reproduction and survival of the ancient Shu people and the formation of the farming culture of the Chengdu Plain. Therefore, the reputation of "fertile fields for thousands of miles" and "known as land and sea" is known to the world.

The west side of the Chengdu Plain is the famous Longmenshan Fault Zone, which has experienced frequent earthquakes in history. The magnitude 8 Wenchuan earthquake on May 12, 2008 is still chilling. The Longquanshan Fault Zone in the east also occasionally has small-scale earthquakes, such as the 5.5-magnitude earthquake in 1967 and the 5.1-magnitude earthquake in 2020. Although the east and west sides are both "turbulent", the Chengdu Plain is very stable. Even if the Longmenshan Mountains dozens of kilometers away are turned upside down, it is as stable as a rock. Such geological structure is the "safety guarantee" for the Chengdu Plain to become the "Land of Abundance".

▲Aerial panoramic view of Huanglongxi Ancient Town in Chengdu, photo by Xianren Banban (TuChong Creative)

The rivers flowing from the Qinghai-Tibet Plateau into the Chengdu Plain not only bring flood disasters to the Chengdu Plain, but also nourish the prosperity here. The prosperity of the Chengdu Plain is largely due to the nourishment of the Min and Tuo Rivers and the management and scientific utilization of the Min and Tuo Rivers by the Dujiangyan Project.

The success of Dujiangyan water control is due to the perseverance and wisdom of our ancestors and the unique geographical conditions of the slightly inclined Chengdu Plain. The Chengdu Plain is in the shape of an inclined fan, which slopes slightly from northwest to southeast. The fan slope is between 3-5‰. From Dujiangyan to the main urban area of ​​Chengdu, the straight-line distance is about 50 kilometers, and the altitude drops from 730 meters to 500 meters, with a natural drop of about 230 meters.

▲Diagram of the water system of Chengdu Plain. Image/Results of the Chengdu Water Cultural Heritage Survey

Such a natural slope laid the geographical foundation for the formation of the grand water control system and gravity irrigation system of the Min and Tuo rivers. From Dayu's "Min Mountain guides the river and the east is Tuo River" to the ancient Shu Bie Ling's "breaking the Yulei Mountain to eliminate water disasters", to Li Bing, the prefect of Qin Shu County, all the water control experts of all dynasties made full use of this advantage and guided the Minjiang and Tuojiang rivers accordingly, thus creating the land of abundance where "floods and droughts are controlled by people, and famine is unknown".

Sima Qian praised Li Bing's achievements in flood control in "Records of the Grand Historian: Book of Rivers and Canals". He wrote, "Bing dug the Lidu to avoid the harm of foamy water and dug two rivers in the middle of Chengdu. These canals are all navigable, and the surplus water is used for irrigation, and the people benefit from it. As for where he passed, he often diverted water for better use. There are tens of millions of canals for irrigating fields, but they are too numerous to count."

After Li Bing, Wen Weng in the Western Han Dynasty, Zhuge Liang in the Three Kingdoms period, Gao Jian and Zhang Chou Jianqiong in the Tang Dynasty, Lu Yi in the Ming Dynasty, and countless water conservancy experts in modern times continued to expand and improve, and finally formed the grand irrigation system of Minjiang River and Tuojiang River that we see today. Today, the Chengdu Plain has countless main canals, trunk canals, branch canals, tributaries, and countless dikes, weirs, and gates, like a big network, and every detail and every subtle place can be nourished by the river water.

▲Dujiangyan on the Minjiang River. Photo by Wang Hong

To summarize, the formation of the "Land of Abundance" is due to the four conditions of the Chengdu Plain. First, the earth's crust is stable and it is rarely attacked by disasters such as earthquakes. Second, the terrain is flat, the soil is deep, and the land is fertile, making it suitable for living and farming. Third, there is abundant rainfall, a humid climate, and no natural disasters. Fourth, the Min and Tuo Rivers were effectively managed and scientifically utilized by water conservancy experts throughout the dynasties.

The "climate factor" is somewhat accidental and lucky. The credit should be attributed to the Qinghai-Tibet Plateau. The 30th parallel north latitude where the Chengdu Plain is located belongs to the subtropical tropical high pressure zone, which should be dry, hot and rainy. Along this line, there are almost deserts or semi-desert areas, with the exception of the section of mainland China in the east of the Qinghai-Tibet Plateau. This is because the uplift of the Qinghai-Tibet Plateau not only blocked the cold current from the north, but also prompted the warm and humid air currents from the Indian Ocean in the south to bypass and form a monsoon circulation, destroying the control of the planetary wind system over the Chinese mainland, thus changing the water and heat pattern of the Chinese mainland, and the arid area across the mainland retreated to the northwest. The eastern part of the mainland, including the Chengdu Plain, also changed from arid to humid and rainy, becoming the most suitable paradise for human habitation.

Among the four major basins in my country, except for the Sichuan Basin, all are located in the arid northwest region, with dry climate, desolate and cold weather. Many places are forbidden areas for life. Only the Sichuan Basin has a humid climate and rich resources, which is an exception. How lucky are the people living here!

The land of abundance not only benefits from the right time and place, but also from human wisdom.

▲The golden rice fields of the "Tianfu Granary" rice planting base in Yongfeng Village, Meishan City. Photo by Xianren Banban (TuChong Creative)

Source: Xiake Geography