The main stream of the Yangtze River runs through the central part of China from west to east, and lies between 90 33 ′ ~122 25 ′ east longitude and 24 30 ′ ~ 35 45 ′ north latitude. Hundreds of tributaries converge north and south, extending to parts of eight provinces, including Guizhou, Gansu, Shaanxi, Henan, Guangxi, Guangdong, Zhejiang and Fujian. The drainage area is 6.5438+0.8 million square kilometers, accounting for 654.38+0/5 of the total land area of China. Most of the water in the Huaihe River also flows into the Yangtze River through the Grand Canal. [2]
Yichang, the main stream of the Yangtze River, is upstream, with a total length of 4,504 kilometers and a drainage area of 6,543.8+0,000 square kilometers. Among them, the branch gate reaches Yibin and is called Jinsha River, with a total length of 3,464 kilometers. Yibin-Yichang section, commonly known as Chuanjiang, is 1040 km long. Yichang to Hukou is the middle reaches, with a total length of 955 kilometers and a drainage area of 680,000 square kilometers. Below Hukou is the downstream, with a length of 938 kilometers and a drainage area of 6.5438+0.2 million square kilometers. [2]
Chinese name
Yangtze river
Foreign name
Yangtze River/Yangtze River
Another name
Yangtze river, natural barrier, nine schools
Total length of river
More than 6,300 kilometers
Important coastal cities
Chongqing, Yichang, Wuhan, Nanjing and Shanghai
quick
navigate by water/air
Hydrological characteristics of segmented drainage system; General situation of river basin; Control and development policy.
historical changes
China Yangtze River
The ancient Yangtze River was formed in ancient times, and most of the Yangtze River basin was submerged by seawater. During the Triassic period 200 million years ago, the Yangtze River basin was still occupied by the ancient Mediterranean Sea (Tethys Sea). At that time, Tibet, Qinghai, western and central Yunnan, and western Guizhou were all Wang Yang Sea. Western Hubei is a huge bay protruding eastward from the ancient Mediterranean, extending to the middle of the Three Gorges of the Yangtze River today. The southern half of the middle and lower reaches of the Yangtze River is also submerged at the bottom of the sea, and the northern part of the middle and lower reaches of North China and Northwest China and the eastern part of Eurasia are relatively high. Indosinian orogeny occurred at the end of Triassic 65.438+0.8 billion years ago. At that time, Kunlun Mountain, Kekexili Mountain, bayan har, Hengduan Mountain and Qinling Mountain began to rise, and the southern half of the middle reaches of the Yangtze River rose to land, and the Yunnan-Guizhou Plateau began to appear. Between Hengduan Mountains, Qinling Mountains and Yunnan-Guizhou Plateau, fault basins and depressions are formed. At the same time, Yunmengze, Xichang Lake and Dianhu Lake are connected in series, flowing from east to west through the Nanjian Strait in western Yunnan and flowing into the Mediterranean Sea, which is opposite to the current direction of the Yangtze River.
Today, the formation of the Yangtze River originated from the Yanshan Movement of Jurassic10.40 billion years ago, and Tanggula Mountain was formed in the Yangtze River. The Qinghai-Tibet Plateau rises slowly, forming many mountains, deep valleys, depressions and rift valleys. Dabie Mountain and Wushan Uplift between Sichuan and Hubei in the middle and lower reaches of the Yangtze River, Sichuan Basin depression, and the ancient Mediterranean further retreated westward. 1 100 million years ago, in Cretaceous, Sichuan basin rose slowly, leveled and continued to develop, and Yunmeng and Dongting basins continued to sink. In Eocene, 30-40 million years ago, there was a strong Himalayan movement, the Qinghai-Tibet Plateau uplifted, the ancient Mediterranean disappeared, and the Yangtze River basin generally rose intermittently. Its rising degree is moderate in the east and severe in the west. The mountains on both sides of Jinsha River are raised, and the Qinghai-Tibet Plateau and Yunnan-Guizhou Plateau are obviously raised, and some fault basins are formed at the same time. Due to the strong downward cut of the river, many deep and steep canyons appeared, and the water systems that originally flowed from north to south merged with each other and flowed eastward. The middle and lower reaches of the Yangtze River are slightly uplifted, forming middle and low hills, and the depressions sink into plains (such as the two lakes plain, Nanxiang plain, Duyang plain, Jiangsu and Anhui plain, etc.). ). By 3 million years ago, the Himalayas rose strongly and the western part of the Yangtze River basin rose further. Under the influence of topography, the ancient Yangtze River, which flowed westward, began to flow eastward, forming the present Yangtze River. [4]
Cultural relics unearthed from Panlongcheng site in Huangpi
Watershed segmentation
The birthplace of the Yangtze River is tuotuo, with high mountains and dangerous shores, and the snow is tens of meters all year round, with a total length of 374 kilometers.
Majiabin culture
When Quhekou reaches Bashou Estuary in Yushu County, Qinghai Province, it is called Tongtianhe, with a total length of 8 15 km. The water is gentle, the river valley is wide, but it is swampy, with plenty of sunshine, dense grass beaches, towering peaks, deep snow on both sides and magnificent scenery. It is an important animal husbandry area in the Yangtze River Basin.
The Bakou River flows into the Minjiang Estuary in Yibin, Sichuan, which is called Jinsha River, with a total length of 2,308 kilometers, and is named after gold production. At the end of the Ming Dynasty, Song recorded in his book Heavenly Creations that Jinsha River (formerly Lishui) was more than 500 kilometers long and mined gold for several years. Jinsha River has high mountains and deep valleys, fast-flowing water, and a large slope of the water surface, with a total drop of about 3 kilometers. The steep Tiger Leaping Gorge is only 16 km long, with a water level drop of 200 meters and an average drop of 12.5‰, which shows how rich water resources are.
The Minjiang River from Yibin to Wusongkou is 2803 kilometers long, including Yibin to Yichang in Hubei 1030 kilometers, also known as Chuanjiang, and Zhijiang in Hubei to Chenglingji in Hunan is 340 kilometers long, also known as Jingjiang, which is divided into upper and lower Jingjiang. Shangjing River: the total length from Zhijiang to Ouchikou160km. Xiajing River: The total length from Ouchikou to Chenglingji in Hunan180km.
***9 pieces
Beautiful Yangtze River
The lower reaches of Jiangsu Province are also called the Yangtze River. The river below Jiangyin gradually widens and develops labyrinthine towards the estuary. The water near Jiangyin is only one kilometer wide, but it is 80 kilometers wide when it reaches the estuary. Some scholars believe that 6000 years ago, the Yangtze River entered the sea in Yangzhou and Zhenjiang. Because of the wide river surface and gentle slope, the river meets the tide, and because of the slow flow, the salt in the seawater condenses and a lot of sediment is gathered, and the suspended substances inside and outside the estuary sink to the bottom of the river. Chongming Island at the mouth of the Yangtze River is made up of sediment from the Yangtze River. The island appeared only over a thousand years ago. The Huangpu River at the southern tip of Chongming Island is the last tributary of the Yangtze River. [5]
Topographic map of the Yangtze River Basin (Source: Records of the Yangtze River System)
Water system composition
source
Jacky on the Yangtze River is a vast geographical unit, including the vast area between Kunlun Mountain and Tanggula Mountain. It is about 400 kilometers long from east to west and 300 kilometers wide from north to south, with a total area of over 654.38+ 10,000 square kilometers. The terrain in the area is gentle, with an average elevation of 4,400-4,700 meters, the annual average temperature is below -4℃, the temperature is low, the vegetation is sparse, the frozen soil is widely distributed, and the animal species are simple, most of which are endemic to the plateau, including wild donkeys, white-lipped deer, bison, snow leopards, Tibetan antelopes, brown bears, wolves and green sheep. The source of the Yangtze River consists of Chuma River in the north, Dangqu River in the south and Tuotuo River in Jacky. Chumar River originates from Lake Hoh Xil in the depth of Hoh Xil Nature Reserve, which means "Hongshui River" in Tibetan, with a total length of about 5 15 km and a small flow. The source is often cut off in summer and finally flows into the Tongtian River in the upper reaches of the Yangtze River. [7]
The source of the Yangtze river
main stream
Upstream
Yichang, the main stream of the Yangtze River, is in the upper reaches, with a total length of 4,504 kilometers, accounting for 70.4% of the total length of the Yangtze River, and controlling the basin area of 6,543.8+0,000 square kilometers. Yibin, known as Jinsha River, has a total length of 3,464 kilometers and a drop of about 5 100m, accounting for 95% of the total river drop. The river bed has a steep slope and the beach is fast flowing. The main tributary to join is Yalong River. The total length from Yibin to Yichang is1040km, and the main tributaries are Minjiang River and Jialing River on the north bank and Wujiang River on the south bank. [8]
Three Gorges on the Yangtze
middle reaches
Yichang City to Hukou County is the middle reaches, with a total length of 955 kilometers and a drainage area of 680,000 square kilometers. The main tributaries of this section are four rivers of Qingjiang and Dongting Lake in Hunan, Zi, Yuan and Li, and five rivers of Poyang Lake in Jiangxi, Fu, Xin, Xiu and Rao. There is the Han River on the north bank. This section is the famous Jingjiang Zhicheng to Chenglingji, with Songzi, Taiping, ouchi and Rao on the south bank. [8]
lower reaches
Hukou County is located in the lower reaches of the estuary, with a length of 938 kilometers and an area of 654.38+0.2 million square kilometers. The main tributaries are Qingyi River, Shuiyangjiang River, Taihu Lake and Chaohu Lake. [8]
tributary
The Yangtze River system is developed, consisting of thousands of tributaries, of which 437 have a drainage area exceeding 1000 square kilometers, 49 have a drainage area exceeding 1000 square kilometers, and 8 have a drainage area exceeding 80,000 square kilometers. Among them, the areas of Yalong River, Minjiang River, Jialing River and Hanjiang River all exceed 654.38+ 10,000 square kilometers. The tributary basin of Jialing River has the largest area, the annual runoff and average annual discharge of Minjiang River are the largest, and the length of Hanjiang River is the longest. [8]
Provinces and regions where the Yangtze River flows
Yalongjiang
The Yalong River originates in the southern foothills of Bayan Kara and joins the Jinsha River in Panzhihua City. The drainage area is about 1.3 million km2, the length of the main stream is 1.637km, and the average annual discharge of the estuary is 1.9 1.4 m3/s. The theoretical reserve of hydropower in the whole basin is 33.72 million kilowatts, and the exploitable installed capacity of hydropower generation is 2494 1 10,000 kilowatts. Ganzi is called the upper reaches, with a length of about 6 10/0km, a drop of 1.330m and an average gradient of 2. 18‰. Ganzi to Dahewan is the middle reaches, about 600 kilometers long, with a drop of 1790m and an average gradient of 2.98‰. Below the big river bend is the downstream, about 360 kilometers long, with a drop of 750 meters, with an average gradient of 2.08‰. The whole basin can develop hydropower resources of 24.94 million kilowatts, with an average annual power generation of 654.38+052.5 billion kWh. [8]
Yangtze river
the Minjiang River
The Minjiang River originates from the southern foot of Minshan Mountain, flows through the western Sichuan Basin, crosses the Chengdu Plain, accepts the Dadu River in Leshan and joins the Yangtze River in Yibin. The total length of the main stream is 735km, which is called upstream in guanxian, with a length of 340km and a drop of about 3000m, with an average gradient of 8.82 ‰. Guanxian to Leshan is called the middle reaches, with a length of about 232km and a drop of 372m, with an average gradient of 1.6 ‰. Leshan to Yibin is the downstream, about 163km long, with a drop of 97m and an average gradient of 0.59‰. The basin covers an area of 6,543.8+0.33 million square kilometers, with an average annual flow of 2,850 meters per second and a total drop of 3,560 meters. The hydropower reserve is 48.866 million kilowatts, and the exploitable capacity is 30.56 million kilowatts. The average power generation for many years is 65.438+0672 billion kWh. Dadu River is the largest tributary of Minjiang River, which originates from the southern foot of Guoluo Mountain in Qinghai Province and joins Minjiang River in Leshan. The drainage area is 9 10000 square kilometers [8], the total length of the main stream is 1062 kilometers, and the average flow for many years is 1570 meters per second. Hydropower resources are mainly stored in Shuangjiangkou to Tongjiezi reach, with a total length of 600 kilometers, a natural drop of about 1800m, and hydropower resources reserves of17.48 million kilowatts. Qingyi River flows into the estuary. [8]
Yangtze river
Tuojiang River
Tuojiang River originates from the southern foot of Jiuding Mountain in Minshan Mountain System and flows into Chuanjiang River in Luzhou City. The basin covers an area of 27,800 square kilometers, with a total length of 702 kilometers, with an average annual flow of 5 19 cubic meters per second. The theoretical reserve of hydropower is 6.5438+0.52 million kilowatts, and the exploitable capacity is 260,000 kilowatts. Jintang, the main stream, is called the upstream, with a length of about 200 kilometers, a drop of 2 10m and an average gradient of 1.07‰. Jintang to Neijiang is the middle reaches, about 300 kilometers long, with a drop of 147m and an average gradient of 0.49 ‰. Below Neijiang is the downstream, about 202 kilometers long, with a drop of 67 meters, with an average gradient of 0.33‰. [8]
Jialing river
Jialing River originates from the southern foot of the western Qinling Mountains, and after receiving Fujiang River and Qujiang River in Hechuan District, it joins the Yangtze River in Chongqing. The drainage area is160,000 square kilometers, the total length of the main stream is 1 120 kilometers, the annual average flow is 2 120m3/s, and the total drop is 2300m. The theoretical reserve of hydropower is15.22 million kilowatts, and 8.7 million kilowatts of hydropower resources can be developed. Zhao Hua, the main stream, is called the upper stream, with a length of about 394 kilometers and an average gradient of about 3.8 ‰. Showa-Hechuan is the middle reaches, about 633 kilometers long, with a natural drop of 189.9m and an average gradient of 0.30‰. Hechuan to Chongqing is the downstream, about 93 kilometers long, with a natural drop of 23 meters and an average gradient of 0.25‰. [8]
Wujiang river
Wujiang River originates from the eastern foot of Wumeng Mountain and is divided into two sources: Sancha River in the south and Liuchong River in the north, which is later called Wujiang River. It flows through the middle and northeast of Guizhou Province, passes through the southeast edge of Sichuan Basin, and joins the Yangtze River in Fuling. The basin covers an area of 87,920 square kilometers, the total length of the main stream is 1.037 kilometers, the annual average flow is 1.650 meters per second, and the total drop is 2 1.24 meters. The theoretical reserve of hydropower is/kloc-0.0426 million kilowatts, and the exploitable capacity is 8.8 million kilowatts. Mainstream refers to the upper reaches above the roof, the middle reaches from the roof to Sinan, and the lower reaches below Sinan. [8]
Qingjiang river
Qingjiang River originates in Longdonggou, Qiyue Mountain, lichuan county, western Hubei, and joins the Yangtze River in Yidu City. The drainage area is 16700 square kilometers, the total length of the main stream is 423 kilometers, the annual average flow is 4 14 meters per second, and the total drop is 1430 meters. The theoretical reserve of hydropower is 2.504 million kilowatts. Above Enshi is the upper reaches, from Enshi to Qiu Zi is the middle reaches, and below Qiu Zi is the lower reaches. [8]
Yangtze river
Han River
The Hanjiang River originates in the southern foot of Qinling Mountains and flows into the Yangtze River in Wuhan. The drainage area is159,000 square kilometers [8], the total length of the main stream is 1577 kilometers, the average annual runoff for many years is 17 10 m/s, and the total drop is 639m m. The theoretical hydropower reserve is 654.38+009,300 kilowatts, which can be exploited. The mainstream Danjiangkou is called upstream, with a length of about 925 kilometers and a drop of 555m, with an average gradient of 0.60 ‰; Danjiangkou to Zhongxiang is the middle reaches, about 270 kilometers long, with a drop of 50 meters, with an average gradient of 0. 19 ‰. Below Zhongxiang is the downstream, with a length of 382 kilometers and a drop of 34 meters, with an average gradient of 0.09‰. The total theoretical reserve of hydropower is 6.5438+0.006 million kilowatts, and the exploitable hydropower resources are 6 million kilowatts, with an average power generation of 24.39 billion kWh for many years. [8]
Xiang Jiang River
Xiangjiang River is the largest river in Dongting Lake system, which originates from Haiyang Mountain in lingchuan county, Guangxi, and flows into Dongting Lake at Haohekou, Xiangyin County, Hunan Province. The basin covers an area of 94,660 square kilometers [8] with a total length of 844 kilometers, with an annual average flow of 2,370 meters per second and a total drop of 756 meters. Above the old wharf in Lingling is the upstream, about 240 kilometers long, with a drop of 1 10 ~ 220 m and a gradient of 0.9 ‰ ~ 0.45 ‰. The length from Laobutou to the middle reaches of Hengyang is about 284 kilometers, with a gradient of 0.29 ‰ ~ 0. 18 ‰. Hengyang to Haohekou is the downstream, about 320 kilometers long, with a gradient of 0.083 ‰ ~ 0.045 ‰. [8]
Purple water
Zishui, which originated at the northern foot of Yuechengling in Ziyuan County, Guangxi, was injected into Dongting Lake in Ganxi Port, Yiyang, Hunan Province. The drainage area is 2810.42 million kilometers, the total length of the main stream is 710.3 kilometers, the average flow for many years is 759 meters per second, and the total drop is 972 meters. The theoretical reserve of hydropower is 2.24 million kilowatts, which can be exploited by 6.5438+0.49 million kilowatts. Shaoyang City is upstream above Xiaomiaotou, middle reaches from Xiaomiaotou to Majitang, and downstream below Majitang. The lengths of upstream, middle and downstream are 250,276 and 187 km respectively. [8]
Yuanjiang
Mawei River, the main source of Yuanjiang River, originated in Wu Yun at the junction of Hunan and Guizhou, and flowed into Dongting Lake in Hanshou County of Changde City. The drainage area is 891.6000 square kilometers [8], the total length of the main stream is 1.022 kilometers, the average flow for many years is 2 1.70 meters per second, the total drop is 1.462 meters, the theoretical hydropower reserve is 7.94 million kilowatts, and 5.938 million kilowatts can be developed. The main stream above hongjiang city is upstream, with a length of 537 kilometers. Jin Ling Beach in the upper reaches is the middle reaches from hongjiang city to Taoyuan County, with a total length of 389 kilometers. The tour from Lingjintan to Deshan is 96 kilometers long. [8]
Lishui river
Lishui originates from Cunninghamia lanceolata (Nanyuan) in Sangzhi County, Hunan Province, and flows into Dongting Lake at Xiaodukou in Tianjin. The drainage area is 18496 square kilometers, the total length of the main stream is 390 kilometers, and the average flow for many years is 574 meters per second. The theoretical reserve of hydropower is 2.052 million kilowatts, and the exploitable capacity is 1.4 1.000 kilowatts. Above the mulberry planting, the main stream is upstream, and the upstream reach is about 94.2 kilometers long. Sangzhi to Shimen is the middle reaches, 226.8 kilometers long. Below Shimen is the downstream, and the downstream reach is about 69 kilometers long.
the Ganjiang River
Ganjiang River is the mother river of Jiangxi Province, the largest river in Jiangxi Province and the largest river in Poyang Lake system. Originated in Yuanyangdi Township, Ganjiangyuan Town, Shicheng County, Jiangxi Province, at the junction of Jiangxi and Fujian, it flows into Poyang Lake in four branches near Nanchang City. The basin covers an area of 83,500 square kilometers, with a total length of 766 kilometers and an average annual flow of 2 1.30 m/s. The theoretical reserve of hydropower is 3.64 million kilowatts. The upstream of Ganzhou is 255 kilometers long. Ganzhou to Xingan is the middle reaches, with a total length of 303 kilometers. Below Xingan is the downstream, and the downstream reach is about 208 kilometers long. [8]
Fuhe
Fuhe River originated in Wuyishan at the junction of Jiangxi and Fujian provinces and flowed into Poyang Lake through Qinglan Lake. The drainage area is 1.58 1 1 10,000 square kilometers [8], the total length of the main stream is 349 kilometers, and the average flow for many years is 480 meters per second. The main stream is upstream above Cheng Nan, middle from Chengnan to Fuzhou, and downstream below Fuzhou. The lengths of upstream, middle and downstream are 158, 77, 1 14km respectively. [8]
Xinjiang
Xinjiang originated in Huaiyu Mountain at the junction of Zhejiang and Jiangxi provinces, and flowed into Poyang Lake in yugan county. The drainage area is 1.594 1 10,000 square kilometers [8], the total length of the main stream is 329 kilometers, and the average flow for many years is 579 meters per second. [8]
Raohe
Raohe River is the general name of the Yangtze River and Le 'an River, with Le 'an River as the main source. The two rivers meet at Yaogongdu, Poyang County, and join Poyang Lake at Longkou. The drainage area is 1.5428 million square kilometers, the total length of the main stream is 309 kilometers, and the average flow for many years is 489 meters per second. [8]
He xiu
Hexiu is the largest river in Jiujiang, which originates from the Shogun Mountain at the junction of Hunan and Hubei, and flows into Poyang Lake in Wucheng. The basin covers an area of 65438+4793 thousand square kilometers, the main stream is 357 kilometers long, and the average flow for many years is 390 meters per second. [8]
lake
There are 760 lakes with a total basin area greater than 1 km2, with a total area of17093.8km2.. Among them, the total area of lakes in Jiangyuan area is 758.4km2, that in Yunnan-Guizhou Plateau area is 540.8km2, and the largest lake is Dianchi Lake with an area of 297km2. There are 642 lakes in the middle and lower reaches, with a total area of1579.6km2. These lakes are not only irrigation water sources, but also natural reservoirs for drainage and flood storage. Due to siltation, reclamation and other reasons, their area is shrinking day by day. [8]
Dongting Lake
Dongting Lake, one of the five largest freshwater lakes in China, is an important throughput lake in the middle reaches of the Yangtze River. The name of Dongting Lake began in the Spring and Autumn Period and the Warring States Period. It was named after Dongting Mountain (now Junshan Mountain) in the lake and has been in use ever since. [9]
Poyang Lake (in Jiangxi Province)
Poyang Lake is the largest freshwater lake in China, located at 28 22 ′ to 29 45 ′ north latitude and115 47 ′ to1/kloc-6 45 ′ east longitude. Located in the north of Jiangxi Province, on the south bank of the middle and lower reaches of the Yangtze River. Poyang Lake is bounded by Songmen Mountain and divided into north and south parts. The north is the estuary, which is 40 kilometers long, 3 to 5 kilometers wide, and the narrowest part is about 2.8 kilometers. The main lake is in the south, with a length of 133 km and a widest point of 74 km. [ 10]
Taihu Lake
Taihu Lake is one of the five largest freshwater lakes in China, located in the south of Jiangsu Province and the south of the Yangtze River Delta. All waters are in Jiangsu Province, and the south of the lake is connected with Zhejiang Province. It is the largest lake in East China and the third largest freshwater lake in China. [ 1 1]
Chaohu lake
Chaohu Lake in the middle of Jianghuai hilly area is one of the five largest freshwater lakes in China. It is 54.5km long from east to west, with an average width of 15. 1 km from north to south, and around the lake172km. According to the situation of Chaoxian, Lujiang, Feidong, Feixi and Hefei, the area is 753 square kilometers. Chaohu Lake is absorbed by criss-crossing rivers and ditches. It has a long history as Britain and Mount Hall, and there are Fengle River and Hangzhou in the lake.
Water System Map of the Yangtze River Basin (Source: Records of the Yangtze River System)
Hydrological characteristics
Volume of water
The Yangtze River is the most abundant river in China, with a total water resource of 961600 million cubic meters, accounting for about 36% of the total river runoff in China and 20 times that of the Yellow River. The Amazon River and the Congo River (Zaire River) are second only to the equatorial rainforest, ranking third in the world. The parana river-La Plata River in South America and the Mississippi River in North America, which are similar in latitude to the Yangtze River basin, have a basin area larger than that of the Yangtze River, but their water consumption is far less than that of the Yangtze River. The former accounts for about 70% of the Yangtze River, while the latter accounts for about 60% of the Yangtze River. [2]
Due to the large population in the basin, the per capita water consumption is 2760 cubic meters, which is only 1/4 of the world's per capita water consumption. The characteristics of water resources in the Yangtze River are mainly reflected in the temporal and spatial distribution of river runoff, and the surface water resources in the basin account for 99% of the total water resources. In surface water resources, river runoff accounts for more than 96%. River runoff in flood season generally accounts for 70% ~ 75% of the annual runoff. The distribution of runoff area is also very uneven. The water yield per unit area is the least in Jinsha River and Hanjiang River systems, and the largest in Poyang Lake and Dongting Lake systems. [8]
Drought and flood disaster
The historical records of droughts and floods in various areas of the Yangtze River Basin have a long history. The earliest drought was recorded in the fifth year of Emperor Hui of the Han Dynasty (BC 190), and "Summer was a great drought, rivers were scarce, and the valley was extinct" (Records of Five Elements of Han Dynasty). In the third year of Gao Hou (BC 185), "In summer, rivers and rivers flooded with Han water, and there were more than 4,000 refugees" ("Han Gao Hou Ji"). Typical dry years in historical periods with detailed records and good comparability are 167 1, 1679, 1778 and 1835. Typical flood years are 1586, 1663, 1788, 183 1, 1853, 1867 and1. The above-mentioned typical drought and flood years are mostly concentrated in the Qing Dynasty, which is mainly because the Qing Dynasty is the closest and the historical documents are well preserved and described in detail, which does not mean that the drought and flood disasters in the Qing Dynasty are the most frequent. Some serious events in drought and flood years before the Qing Dynasty were either described briefly or incompletely in the literature, and most of them were never selected. In the past hundred years, there have also been typical years of severe drought and flood disasters in the Yangtze River basin, and there are a lot of measured data and analytical research documents for reference, so I won't repeat them here. The selected 1 1 typical drought and flood years are divided into three grades according to the disaster severity recorded in historical documents, namely, drought, severe drought, severe drought and flood, severe flood and severe flood.
The geographical distribution of drought and flood disasters in the Yangtze River basin is very strong, and the drought and flood disasters in different regions vary greatly. According to the data of central weather bureau (now the Atlas of Drought and Flood Distribution in China in Recent 500 Years edited by the Institute of Meteorological Science of China Meteorological Bureau), the series of drought and flood can be divided into five grades: grade I-flood, grade II-local flood, grade III-normal, grade IV-local drought and grade V. There are 37 stations in the east of the Yangtze River Basin 100E, and the frequency distribution map of historical drought and flood in the Yangtze River Basin (Grade V) is obtained. The average frequency of severe drought in the flow field is 5.55%, and the probability of drought in the middle and lower reaches is higher than that in the upper reaches. The drought frequency in the Yangtze River Delta, the middle and lower reaches of the main stream and Dongting Lake is as high as 9.0%, which is the highest in the whole flow field. Followed by the upper reaches of Jialing River, the highest drought frequency in the middle is above 7.0%. The average frequency of flood disasters in the basin is 7.97%, which is obviously higher than that of drought. The regional distribution of flood disasters is basically consistent with drought, that is, the middle and lower reaches are generally higher than the upper reaches. There is an east-west high-frequency flood disaster zone in the main stream and the middle and lower reaches of the two lakes, in which the northern part of Poyang Lake and the middle reaches of Yuanjiang River and Lijiang River to Dongting Lake are two high-frequency central areas of flood disaster, and the central frequency is as high as 12.0%. Jialing River and Hanjiang River in the upper reaches of the Yangtze River are the third largest high-frequency flood areas. The above-mentioned flood high-frequency zones and centers are basically consistent with the Meiyu zone in the middle and lower reaches of early summer, the concentrated rain zone in the upper reaches of midsummer and the main rainstorm centers in the basin.
The source of the Yangtze River: Tuotuo
The historical droughts and floods in the Yangtze River are also unevenly distributed in time. According to the 1000-year-old "drought and flood chronology" data published in Climate, the fifth issue of China Blue Book of Science and Technology, the historical dry and wet climate and the periodic change law of drought and flood in the Yangtze River Basin are obtained through supplementary analysis. In recent 1000 years, the Yangtze River basin has experienced three large dry and wet climate cycles, the shortest wet season and dry season is 120 years, and the longest is 220 years, including 3-5 small drought and flood periods respectively. Since 1980s, the Yangtze River has entered a new humid climate.
River basin survey
topography
From Heyuan to Hekou, the whole terrain is high in the west and low in the east, forming three huge steps. The first step consists of the plateau and Hengduan Mountain in southern Qinghai and western Sichuan, with an elevation of 3500 ~ 5000 m generally. The second step consists of Qinba Mountain, Sichuan Basin and Hubei-Guizhou Mountain in Yunnan-Guizhou Plateau, with an elevation of 500 ~ 2000 m generally ... The third step consists of Huaiyang Mountain, hills in the south of the Yangtze River and plains in the middle and lower reaches of the Yangtze River, with an elevation of less than 500 m generally ... There are various types of landforms in the basin, including mountains, hills and basins.
Jiangyuan is located in the Qinghai-Tibet Plateau, the "roof of the world", with many peaks above 6000 meters above sea level and snow all year round. The rivers in Jinsha River are strongly cut, forming an alpine canyon about 2000 kilometers long. The river bed gradient is large, the beaches are full of rapids, and the hydraulic resources are very rich. Among them, the famous Tiger Leaping Gorge is 17km long and has a drop of 2 10m. Jinsha River is above the new city in Sichuan Province, and only some sections of it can be navigable seasonally. Enter the Sichuan basin below the new city. The two banks are low mountains and hills, the river valley is widened, and the water flow is gentle, which can be navigable all year round.
Jinsha River has a tributary Yalong River on the left bank of Panzhihua City. The upper reaches of Yalong River are more than 4000 meters above sea level, with plateau landform and wide valley, and runoff is mainly supplemented by snow water. In the middle and lower reaches of the alpine valley, the mountains on both sides are as high as 1000 ~ 1500m, and the river width is 100 ~ 150m.
The Chuanjiang section from Yibin to Chongqing accepts Minjiang River, Tuojiang River and Jialing River. The source areas of these rivers are relatively high, some of which are 3000 ~ 4000 m above sea level, and suddenly drop to 200 ~ 600 m at the edge of Sichuan Basin. The upper reaches of Minjiang River belong to alpine valleys, and the rivers are mostly V-shaped, with a width of 50 ~ 100 m ... The middle reaches from Jiangkou Town to Leshan enter hilly areas, with gentle water flow and developed floodplains. Some river valleys are several kilometers wide, the river surface is wide 155 ~ 500 m, the beach is dense and the water flow is bifurcated. The lower reaches are low mountains and wide valleys with a river width of 400 ~1000 m. Dadu River, a tributary of Minjiang River, is a typical canyon river except that its source area is a wide plateau valley and its downstream is a wide hilly valley below Tongjiezi. Gongga Mountain in the southwest of Luding, Dadu River is 7566 meters above sea level, which is the highest peak in the Yangtze River basin. It is less than 30 kilometers away from the Dadu River Valley in a straight line, and the relative height difference is more than 6500 meters. There are many shoals in the upper reaches of Tuojiang River. When flowing through the Chengdu Plain, the water network is vertical and horizontal, the rivers in the middle and low mountains are curved, and the beaches and tuo alternate with each other, and the water flow is gentle. The upper reaches of Jialing River have deep mountains and narrow valleys, fast-flowing water and many reefs. From Guangyuan to Hechuan, the river gradually widens, first flowing through the deep hills in the northern part of the basin, and then transitioning to the shallow hills. The meanders and terraces are well developed and the slope is gentle. From Hechuan to Chongqing, the river passes through the parallel ridge and valley areas in the east of the basin, forming a canyon reach with a valley width of about 400 ~ 600 m and a water surface width of 150 ~ 400 m, among which there are "Little Three Gorges" (Liyingxia, Wentang Gorge and Guanyin Gorge) formed by crossing the Huaying Mountain Range.
The Chuanjiang River flows through the southern edge of Sichuan Basin from Yibin to Jiangjin, with gently undulating hills composed of red sand shale on both sides. The river valley is wide, generally reaching 2000 ~ 5000 m ... The river is 500 ~ 800 m wide, and terraces develop along the river. The reach below Jiangjin enters the parallel ridge and valley area in eastern Sichuan, which consists of more than 20 belt anticline mountains and syncline wide valleys from northeast to southwest. When Chuanjiang crossed the anticline, Maoer Gorge, Tongluo Gorge and Huangcao Gorge were formed. The narrowest part of the Huangcaoxia Xiakou River is only 250 meters wide. When Chuanjiang crosses syncline, it forms a wide valley with the widest river surface 1500m. Nearly 200 kilometers from Fengjie Baidicheng to Yichang Nanjinguan, it is the world-famous Three Gorges of the Yangtze River, namely Qutang Gorge, Wuxia Gorge and Xiling Gorge. The mountain peak on the south bank of the canyon is1000 ~1500m above sea level.
Wujiang River flows into the south bank below Chongqing. Wujiang River Basin is located in the eastern part of Yunnan-Guizhou Plateau, which is dominated by limestone strata, with undulating mountains, developed karst landforms, many karst caves and many underground rivers.
After the Yangtze River leaves the Three Gorges and passes Yichang, the Qingjiang River flows into the right bank. The Qingjiang River basin is mountainous except for Lichuan, Enshi and Jianshi, which have hills near the big basin and the estuary. Most of the riverbank is limestone, and a small part is seasonal sandstone, with karst development, which is an alpine canyon river.
The Yangtze River passes through the hilly transition and enters the Jingjiang reach, with Jianghan Plain on the north bank and Dongting Lake Plain on the south bank. There are three ports (four in the past, but now one is blocked) connected with Dongting Lake. The Yangtze River flood is diverted to Dongting Lake through three outlets, which is a natural flood regulation reservoir. However, due to years of sediment deposition, Dongting Lake is shrinking and its flood storage function is obviously weakened. Jingjiang River twists and turns, and the water flow is gentle. It belongs to a winding river, which often bends naturally, leaving many oxbow lakes. The banks of Jingjiang River are seriously threatened by floods, and both banks are protected by dikes. The north bank is the famous Jingjiang levee.
The Yangtze River flows into the Yangtze River on the north bank, and the four waters of Hunan, Guizhou, Yuan and Li flow into the Yangtze River on the south bank via Dongting Lake. The upper reaches of the Hanjiang River run through the Qinling Mountains and Daba Mountains, and there is a basin with a wide valley between the mountains and valleys. The middle reaches flow through hills and basins, and the riverbed is wide and shallow, belonging to wandering bifurcated reach, and the lower reaches meander on alluvial plain. The upper reaches of the four major rivers are generally high mountains, with mountain height 1000 ~ 2000 m and narrow valleys. The middle reaches are hilly areas with basins in the middle, and the lower reaches enter Dongting Lake Plain, which is an alluvial river. Among them, Yuanling-Wuqiangxi Canyon, the longest in Shui Yuan, is 90 kilometers long.
The Yangtze River flows through Jiujiang City, with Poyang Lake on the right bank, and flows into the Yangtze River after passing through Nagan River, Fuhe River, Xinjiang River, Poyang Lake and Xiushui. The upper reaches of Ganjiang River are alpine canyons, and the mountain heights on both banks are 1000 ~ 1500m. The river valley in the middle reaches is narrow, forming eighteen beaches of Ganjiang River. Below Wan 'an, there are wide valleys in mountainous areas, and lakes and swamps in lakeside plain are downstream.
From Chenglingji to Jiangyin 1 168 km, most of the Yangtze River flows through the flat alluvial plain, with dense rivers and lakes. Some rivers cross mountains and mountains, with wide valleys and developed terraces. The river is lotus-shaped, with some gathering and some scattering, and many continents and beaches branch.
Below Jiangyin is the Yangtze River estuary, which is about 200 kilometers long and trumpet-shaped. Tides in the Changjiang Estuary belong to the irregular shallow sea half-day cycle, with an average period of 12 hours and 25 minutes and an average tidal range of 4.62 meters ... The average total tidal inflow in flood season is 5.3 billion m, and the dry season is 654.38+0.3 billion m.. The tidal dividing line of the Yangtze River reaches Jiangyin in flood season and Zhenjiang in dry season. Tidal boundary reaches Datong in flood season and Anqing in dry season. The total annual sediment transport of the Yangtze River is 486 million tons. The average sediment concentration is 0.54k8/m3, and part of the sediment comes from outside the mouth, so the whole tide is gentle.