Specific information of the Yangtze River

The first part is an overview.

I. Physical geography

The Yangtze River originates from the northern foot of Tanggula Mountain on the Qinghai-Tibet Plateau and the southern side of Gladding Winter Snow Mountain. The source of the river is Tuotuo River, and its main stream flows through Qinghai, Tibet, Yunnan, Sichuan, Chongqing, Hubei, Hunan, Jiangxi, Anhui, Jiangsu, Shanghai, etc. 1 1 province (city, district), passes through the three economic zones of Southwest China, Central China and East China, and flows into the East China Sea in Shanghai. The Yangtze River, with a total length of more than 6,300 kilometers, is the largest river in China and one of the largest rivers in the world, with a drainage area of about 6,543.8+0.8 million square kilometers, accounting for 654.38+0.87% of the country's total area. The shape of the Yangtze River basin is long from east to west, short from north to south, high in the northwest and low in the southeast.

Rivers in the main stream of the Yangtze River are divided into upper, middle and lower reaches according to the characteristics of rivers and the topography of river basins. From Jiangyuan to Yichang, Hubei, it is called upstream, with a length of about 4500km and a drainage area of 1 10,000 km2. Yichang to Hukou, Jiangxi Province is called the middle reaches, with a total length of more than 950 kilometers and a drainage area of 680,000 square kilometers. The reach from Zhicheng to Chenglingji, commonly known as Jingjiang River, is about 340 kilometers long. On the south bank, there are four ports, Songzi, Taiping, ouchi and Tiao County (Tiao County was blocked in 1959), which discharge water into Dongting Lake and connect with Hunan, Zi, Yuan and East Lake. After passing Chenglingji, the Yangtze River turns to the northeast. When it reaches Wuhan, the Han River flows into Hukou, where it receives the rivers of Jiangxi, Fuzhou, Guangxi, Rao and Xiu in Poyang Lake. Hukou to the Yangtze estuary is called the downstream, with a length of 938km and a drainage area of about 654.38+200,000 km2. The plain area in the middle and lower reaches of the Yangtze River is the key area for flood control.

See Figure 2- 1 for the distribution map of major rivers and hydrological stations in the Yangtze River Basin.

About 109 large reservoirs have been built in the Yangtze River basin, with a total storage capacity of 86.7 billion m3, including more than 12 in Three Gorges, with a total storage capacity of 818 billion m3. There are 929 medium-sized reservoirs with a total storage capacity of 23.8 billion m3, of which there are over three Gorges 163 reservoirs with a total storage capacity of 3.94 billion m3.

Second, the meteorological and hydrological characteristics

The Yangtze river basin is located in the subtropical region in the eastern part of Eurasia and has a typical monsoon climate. South winds prevail in summer, north winds prevail in winter, and Leng Xia is hot in winter, with four distinct seasons. The average annual precipitation in the basin is 1067mm, and the regional distribution and annual distribution of annual precipitation are very uneven.

The Yangtze River flood is formed by rainstorm, so the flood occurrence time and regional distribution are consistent with rainstorm. From the time of flood occurrence, the downstream is earlier than the upstream, and Jiangnan is earlier than Jiangbei. Dongting Lake and Poyang Lake have the earliest flood season, generally from April to July, and Lishui is from April to August. Wujiang River on the south bank of the upper reaches of the Yangtze River is from May to September; The tributaries of Jiangbei, including Jinsha River and Hanjiang River in the middle reaches, from June to10; The main stream of the middle and lower reaches is affected by the floods in Dongting Lake and Poyang Lake, and the flood season is from May to 10. The main flood season of Xiangjiang River, Zishui River and Poyang Lake is from April to June. May-July in Yuan, Lishui, Qingjiang and Wujiang; The tributaries in Jiangbei and the main stream above Hankou are from July to September; The main flood season of Datong Station is from June to August. In the main flood season of the main tributaries in Jiangbei and the main stream above Hankou, the water volume is the largest in July and August, and the flood peak opportunities are the most. The flood in the Yangtze River is mainly characterized by peak height, and the flood process of each tributary is generally about 10 day. Because the main stream collects tributary floods, especially the middle and lower reaches are regulated by lakes and river troughs, a flood lasts for a long time, with Pingshan and Yichang in the upper reaches about 10 ~ 30 days, and Hankou and Datong in the middle and lower reaches over 50 days.

Three. Types of floods

In general, floods in the middle and lower reaches of the Yangtze River occur earlier than those in the upper reaches, so it is not easy to encounter large-scale floods. Usually, there will be a "regional" rainstorm and flood in the Yangtze River basin in a year. According to the composition of incoming water in different areas, it can be determined as different regional floods, such as 1935, the Lishui and Hanjiang floods in the middle reaches of the Yangtze River; 198 1 year, a catastrophic flood occurred in Sichuan in the upper reaches of the Yangtze River; 1983, the Hanjiang River was flooded. 199 1 year, floods occurred in the middle and lower reaches of the Yangtze River; During 1995, the flood mainly came from Poyang Lake; 1996, a flood mainly from Dongting Lake occurred.

If the weather is abnormal, the upstream flood is advanced, or the downstream flood is delayed, and the bottom water of rivers and lakes is too high, the upstream flood will follow, the flood process will overlap, and the main tributaries will encounter floods repeatedly, which will cause "basin-wide" floods with high peak heights, such as 193 1, 1954,1.

Section 2 Characteristics of Rainstorm and Flood

I. Characteristics of rainstorm

1998 The rainfall in flood season has the following characteristics.

1. Rainstorms occur frequently.

Since June 1 1 entered the rainy season in the Yangtze river basin, heavy rains have occurred frequently in various places. The frequency of rainstorm, heavy rainstorm and extremely heavy rainstorm is the highest in July, and only one day in July is intermittent 1 1. During the flood season of 1998, there were 74 days of heavy rain in the Yangtze River basin, including 64 days of heavy rain, accounting for 86% of the total days of heavy rain, and 18 days of extremely heavy rain, accounting for 24% of the total days of heavy rain.

2. The rainstorm covers a large area and a wide range.

On June 23rd, heavy rain occurred in Poyang Lake and Dongting Lake, covering an area of156,000 km2, with rainfall greater than 50mm, spanning nine rivers. Secondly, on July 22nd, the water system of the two lakes and the land water basin was an east-west heavy rainfall belt, with the rainfall level ranging from heavy rain to heavy rain, covering an area of 132800 km2, spanning Jiangxi, Hunan and Hubei provinces. On June 18, heavy rain occurred again in Poyang Lake system, with an area of 122400 km2.

The maximum covering area with daily rainfall exceeding 100mm is the rainstorm that occurred in the two lakes on June 13, covering an area of 50600 km2. On July 2 1 day, heavy rain occurred in Wujiang, Dongting Lake and northeastern Hubei, with an area of 34 1 10,000 km2, ranking second, spanning Guizhou, Hunan and Hubei provinces.

3. Is the rainstorm center stable and has little movement?

On June 1 1 ~ 26, the heavy rainfall area remained stable in the Dongting Lake and Poyang Lake water systems, and the detention time was as long as 16 days. From July 4th to16th, the heavy rainfall belt moved to the upper reaches of the Yangtze River and lasted for 13 days. On July 20 ~ 3 1 day, the heavy rainfall belt returned to the water system of the two lakes for 15 days. On August 1 ~ 29, another persistent heavy precipitation occurred in the upper reaches of the Yangtze River. Heavy rain and heavy rain enveloped the upper reaches of the Yangtze River and the Hanjiang River basin for a long time, lasting for 29 days.

4. The intensity of rainstorm is high and the rainfall is concentrated.

1998 The strongest precipitation process occurred on July 19 ~ 25, especially on July 20 ~ 22. The daily rainfall of the rainstorm center in Longshan County, Yuanjiang, Hunan Province exceeded 100mm, which were 2 14mm, 339mm and1000 mm respectively. At the same time, during the 48 hours from 20: 00 on July 20th to 20: 00 on July 22nd, the rainfall in Wuhan reached 457mm, of which the maximum rainfall of 1 hour reached 95 mm (6 from 6: 05 to 7: 05 on June 2nd1day), which caused serious waterlogging in three towns in Wuhan.

5. The rain belt is seesaw from north to south, and the upstream and downstream swing obviously.

In the main flood season, there are obvious phenomena of north-south sawing and upstream-downstream swinging in the rain belt. The rain belt in the middle and late June is mainly in the middle and lower reaches, especially in Poyang Lake and Dongting Lake. In the first half of July, the rain belt moved upstream; In the second half of July, the rain belt returned to the middle and lower reaches again; In August, the rain belt was pushed upstream and stabilized to August15; From August 16 to August 18, the rain belt pushed to the middle and lower reaches and the south of the Yangtze River; From August19 to 25, he returned to Jia Min River Basin and Hanjiang River. From August 26th to 29th, the rain belt was pushed to the middle and lower reaches and the south of the Yangtze River again.

Second, the flood characteristics

1. The flood affects a wide range.

During the period of 1998, the main stream in the middle and upper reaches of the Yangtze River, the five rivers in Poyang Lake and the four waters in Dongting Lake were flooded, and the floods at several main stations and tributaries exceeded the historical highest water level and maximum flow in the middle reaches of the Yangtze River, covering a wide range, which was another basin-wide flood after 1954.

2. The flood came early.

From June to March, 5438, the highest water level occurred in the middle and lower reaches of the Yangtze River in the same period in history, and the peak discharge of Xiangjiang River in Dongting Lake system and Ganjiang River in Poyang Lake system was the largest in mid-March.

3. There are many flood peaks with large flood magnitude.

The flood peak discharge of Yichang Hydrological Station in the upper reaches of the Yangtze River has occurred eight times, and the maximum 30-day flood discharge is about once in a hundred years. From June to August, the total flood volume and the maximum 60-day flood volume both exceeded 1.954, and Hankou Station in the middle and lower reaches was close to 1.954.

4. The flood peak water level is high and the high water level lasts for a long time.

The water levels of Shashi-Luoshan and Wuxue-Jiujiang hydrological stations in the middle and lower reaches of the Yangtze River all exceeded the historical maximum water level by 0.55 ~ 1.25m, exceeded the historical maximum water level by more than 40 days and exceeded the warning water level by 57 ~ 94 days. Most areas of Dongting Lake and Poyang Lake water systems also generally exceeded the historical maximum water level, and the two lake control stations Chenglingji and Hukou Hydrological Station both exceeded the historical maximum water level for 29 days.

5. Floods are rampant

Floods in the upper, middle and lower reaches of the Yangtze River and floods in Dongting Lake and Poyang Lake occurred on 1998. From mid-June to late July, the floods in the two lakes were superimposed, and the water level in the middle and lower reaches of the Yangtze River continued to be high. In August, there were many floods in the upper reaches of the Yangtze River. In particular, the sixth flood first met with the floods in the Three Gorges area and Qingjiang River, and then with the floods in Yuanjiang River and Lishui River in Dongting Lake. When passing through the Wuhan section, it met with the Hanjiang River flood that came at the same time. The situation is particularly bad. The floods in the main and tributaries have been encountered many times, and combined into a multi-peak flood process with high peak and large volume, resulting in an extremely severe flood control situation in the middle and lower reaches.

Section 3 Development Process of Rainstorm and Flood

I. Rainfall development process

1998 during the main flood season (June-August), the rainfall in the Yangtze River basin is mostly basin-wide. As shown in Figure 2-2, the rainfall in Poyang Lake, Qingjiang River, Lishui River, Zishui River, Yuanjiang River and Yalong River in Dongting Lake from June to August is 1000 mm, which is more than 60% in the middle and upper reaches of the Yangtze River and 40-50% in Jinsha River, Wujiang River, Dongting Lake and Poyang Lake compared with the historical average.

According to the change of weather situation and the distribution characteristics of rain belt, the rainfall development process in the main flood season of the Yangtze River 1998 can be divided into the following four stages.

1.6 June11~ July 3 (the first stage of meiyu period in the middle and lower reaches)

Rainfall is concentrated in the Yangtze River, Le 'an River, Xinjiang River, Ganjiang River, Fuhe River, Jinjiang River, Liaohe River, Xiushui River and Lake District below Ji 'an in Poyang Lake system, and Xiangtan, Zishui River, Yuanjiang River and Xiangjiang River below Lake District in Dongting Lake system, with rainfall over 300mm ... The coverage area with rainfall over 500mm is nearly 90,000m2, and the local areas such as Shangqing, Yiyang and Tieluping Station in Xinjiang are/kloc-0 respectively. In addition, the lower section of the Three Gorges, Qingjiang and Lishui also have areas larger than 300mm, with the largest being 440mm at Qingjiang Jianshi Station. From June 1 1 to July 3, the coverage area over 300mm was 264,000 km2. See Figure 2-3 for details.

2.7.4 ~ 15 (first stage of upstream concentrated rainfall)

At present, the main rainfall is concentrated in the upper reaches of the Yangtze River and the Han River, and there is basically no rain in the middle and lower reaches of the Yangtze River. See Figure 2-4 for details.

3.7. 16 ~ 3 1 (the second stage of meiyu period in the middle and lower reaches)

From July of 16, the rain belt returned to the middle and lower reaches of the Yangtze River and the main stream of the south of the Yangtze River until July of March1year, which was the second meiyu period of 1998. From July 16 to July 3 1 day, heavy rains occurred in Wujiang, Yuanjiang, Lishui, Wuhan, northeastern Hubei, Xinjiang, Le 'an, Fuhe and Xiushui of Poyang Lake system. During the period, the accumulated rainfall exceeded 300mm, with the range of170,000km2, exceeding 400mm and exceeding 60,000km2. The centers of the three zones are Shuitian Station 100 1mm in Longshan County, Yuanjiang County, Hunan Province, Sandu Station 88 1mm in Wuyuan County, Le 'an River, Jiangxi Province, and Yejia Station 6 18mm in Liaohe River, Jing 'an.