The middle and lower reaches of the Yangtze River in China's four major plains

The banded plain in the middle and lower reaches east of the Three Gorges of the Yangtze River in China. From Wushan to the seaside in the east, Huaiyang Mountain in the north and Jiangnan hills in the south, it is alluvial by the Yangtze River and its tributaries. The area is about 6.5438+0.6 million square kilometers. The terrain is low and flat, and the ground height is mostly below 50 meters. In some places, the altitude is less than 5 meters, and there are many rivers and lakes, so it is known as "Water Town Zeguo". The middle reaches include Jianghan Plain in Hubei, Dongting Lake Plain in Hunan and Poyang Lake Plain in Jiangxi. The downstream plain includes the Yangtze River Delta along the Yangtze River in Anhui, Chaohu Plain and between Jiangsu, Zhejiang and Shanghai, in which the ground height of the Yangtze River Delta is below 10 meter. Rivers, branches and lakes are criss-crossed on the plain. Dongting Lake, Poyang Lake, Taihu Lake, gaoyou lake, Chaohu Lake, Hongze Lake and other famous freshwater lakes are all distributed in this narrow strip. Guanzhong Plain is located in the middle of Shaanxi Province, also known as Eight Hundred Li Qinchuan, which refers to the Weihe River alluvial plain at the northern foot of the Qinling Mountains, so it is also called Weihe Plain. Qinling Mountains in the south, Baoji Gorge in the west and Tongguan in the east. It is about 360 kilometers long from east to west, accounting for 19% of the total land area of the province. Since ancient times, it has been a civilized country of Qin with pleasant climate, fertile land and developed agriculture. History Last week, thirteen dynasties including Qin, Han, Sui and Tang established their capitals here, and Qin Zhou has been the capital of emperors since ancient times.

"Huang Jincheng is thousands of miles away" means that the Guanzhong Plain is surrounded by mountains and rivers, just like a huge natural castle. There are Qinling Mountains in the south-central, Longshan Mountain in the west, Loess Plateau in the north, and Yellow River natural moats in the north and northwest. There is a natural terrain barrier in the east, which is easy to defend but difficult to attack. Since the Warring States period, there has been a saying of "a country with four blockades". Therefore, in the Han Dynasty, Sean used the advantage of "a golden city of thousands of miles" to persuade Liu Bang to make Guanzhong his capital.

People are familiar with Sichuan Basin, which is customarily called "Land of Abundance", that is to say, it is rich in products, just like a land of abundance. In fact, Guan Zhong was the first to be called "Feng". During the Warring States Period, Su Qin told Qin Chen about the plan of "Lian Heng", praising Guanzhong's "fertile land, rich people, numerous chariots, tackling difficulties in all fields, fertile fields and abundant products", and said that "this so-called rich land is also a hero in the world", more than 500 years earlier than Chengdu Plain was awarded the title of "Land of Abundance". This is because Guanzhong has become a treasure trove of geomantic omen and the capital of emperors since Zheng Guoqu was restored in the Warring States Period. Guanzhong Plain connects Qinling Mountains in the south and Beishan Mountains in the north. Between the northern Shaanxi Plateau and the Qinling Mountains. From Baoji Gorge in the west to Tongguan Port in the east, it is about 360 kilometers long from east to west, narrow in the west and wide in the east, with a total area of 39,064.5 square kilometers. Guanzhong plain is formed by river alluvial and loess accumulation, with flat terrain, fertile soil, rich water resources and good mechanical farming and irrigation conditions. It is the best natural area in Shaanxi. The Weihe River flows into the Yellow River across the basin, and the river is low and flat, with an altitude of 326 ~ 600 meters. From the Weihe River to the south, north and south, the terrain is asymmetrical and stepped, from the alluvial terrace of the first and second rivers to the first or second loess plateau 200 ~ 500 meters higher than the Weihe River. Terraces are distributed continuously on the north bank and incomplete on the south bank. The main tributaries of Weihe River also have corresponding multilevel terraces. The broad terrace plain is the most fertile area in Guanzhong. Between the second terrace on the north bank of Weihe River and the northern Shaanxi Plateau, there is a loess tableland in Weibei extending from east to west. The plateau is wide, with an altitude of 460 ~ 800 meters, and it is the main grain-producing area in Guanzhong. The loess tableland on the south side of Weihe River is intermittently distributed, about 250 ~ 400 meters higher than Weihe River, and it is stepped or inclined shield-shaped. They gently incline from the northern foot of Qinling Mountains to the Weihe Plain, such as Wuzhangyuan in Qishan, Shenheyuan, Shaolingyuan and Bailuyuan in the south of Xi, Yangguoyuan in Weinan, Gao Yuanyuan in hua county and Yuyuan Garden in Huayin. , has developed into a comprehensive agricultural area dominated by forests and gardens.