The second water system: Xiangjiang River

The Third Water System: Zijiang River

The fourth water system: Lishui

Because Hunan is high in the east, south and west and low in the north. Water flows into Surabaya along the valley, Dongting Lake from south to north, and the Yangtze River. This is the geographical feature of Hunan. Rivers in Hunan belong to rain source rivers. In case of heavy rain, the water level rises and falls sharply. Four waters generally begin to rise in April, and the water level is low after July and August. However, winter floods also occur in some years. Generally, April to September is the flood season, and June 10 is the non-flood season. Hunan is rich in surface water resources, and the average runoff depth in the province is generally between 500 ~ 1500mm. However, the distribution of water resources in Hunan is uneven, and the combination of water and soil resources is not suitable. 35% of water resources belong to flood runoff, which is difficult to make good use of and easy to cause floods. The sediment load of rivers in Hunan is small, and the annual average sediment load is 0. 1 ~ 0.5 kg/m3. In winter, the river is crystal clear and won't freeze.

I. Xiangjiang River

Xiangjiang River originated in Haiyangping, Haiyangwei, Lingui County, Guangxi, and was called Haiyang River in ancient times. It flows northward into Hunan, passing through Xiao Na Water in Lingling, Nayong Lingshui in Jiaohe, Zhenghui Water and Leishui in Hengyang, Na Wei Water in Hengshan, Lushui in Lukou, Lianshui in Xiangtan, Liuyang River in Changsha, and Naimi in Xinkang. Xiangjiang River system is located in the south of the Yangtze River and north of Nanling Mountains, with Luo Xiao and Ganjiang River systems in the east and Hengshan Mountain adjacent to Zishui in the west. The main tributaries of Xiangjiang River, Xiao Shui, Ling Ling Shui, Lei Shui, Mi Mi Shui, Wei Shui and Liuyang River, flow into the main stream from the right bank, while the tributaries Qi Shui, Steamed Water, Trickling Water, Lianshui and Wei Shui flow into the main stream from the left bank. Xiangjiang river basin is mostly undulating hills, valley plains and basins. The alluvial plain below Changsha has a wide range and is connected with Ziyuan, Yuanyuan and Lihekou Plain, which is the largest lakeside plain in the province. There is little difference in elevation between the upstream and downstream of Xiangjiang River Basin, but it is uneven, which accelerates rainwater collection. The upstream of each tributary winds in the mountains, showing the characteristics of mountain streams and rivers. Xiangjiang river is called the upper reaches above Lingling, and the water is swift. Sometimes, rivers pass through cut rocks and form canyons. Limestone is widely distributed in the basin, with many karst caves and large groundwater recharge river flow. Xiangjiang River is the middle reaches between Lingling and Hengyang, with undulating mountains along the coast and scattered basins and canyons. Xiangjiang River flows into the lower reaches of Hengyang and Hengshan. The terrain is flat, the river is stable, and sandbars along the river can be seen intermittently. There are lakes of different sizes scattered at the mouth of Xiangjiang River, most of which are the remains of Dongting Lake in the past. There are 3 1 navigable rivers in Xiangjiang River system. The main stream of Xiangjiang River is 660 kilometers long. Xiangjiang river basin is abundant in rainfall. Precipitation is concentrated in spring and summer, and April-June is the rainy season. The water level of Xiangjiang River rises in rainy season, and the highest water level appears from April to July. Most of Xiangjiang River and its tributaries were flooded. The floodplain is higher than the water surface in the dry season and flooded in the flood season. When the flood came, the river surged. Wastewater from iron and steel, metallurgy, chemicals, pesticides and other factories along the Xiangjiang River is discharged into the Xiangjiang River, and the water quality is polluted. According to the book "Overall Assessment of Surface Water Pollution in China" by Institute of Geography of China Academy of Sciences 1978, "among the two major rivers in China 12, the degree of water pollution in Hunan ranks first".

Second, Zijiang

Zijiang River is divided into two tributaries above Shuangjiangkou in Shaoyang County, with good water on the left and rich water on the right. Fuyi water originated in Ziyuan County, Guangxi, flowed into Xinning County, Hunan Province, and flowed northward into Shuangjiangkou, Shaoyang County. Haoshui originates from Aoshijing, North Mao Ping, Chengbu County, and flows through Wugang and Dongkou, successively connecting Liaoshui and Pingxi, returning to Chen Na Water in Longhui, then connecting Fuyishui from the south in Shuangjiangkou, Shaoyang County, passing through Shaona Water in Shaoyang City, passing through Nashima River, Dayangjiang River and Qujiang River under Xinhua, tributaries of Funa River, Qinyi River and Yixi River under Anhua, and Ganxi River under Yiyang. Zijiang is 653 kilometers long. The Zijiang River Basin is bounded by Xuefeng Mountain and Yuanshui River in the west and Hengshan Xiangjiang River in the east. The basin is hilly, with high mountains in the southwest and low terrain in the northeast. Zijiang winds from southwest to northeast. The valley below Majitang is wide, and the alluvial plain below Yiyang. There is a great difference between the upstream and downstream of Zijiang River Basin. The upper source of Mao Ping depression is more than 500 meters above sea level, reaching Yiyang 23 meters, and the difference between Heyuan and Yiyang is 492 meters. Most of the Zijiang River Basin flows through hills and valleys, and the mountains on both sides of the valley are close, and the rainwater is collected quickly, and the water level of the river fluctuates greatly, which has the characteristics of a mountain stream river. Above Wugang, Zijiang River is the source reach with steep slope and shallow and narrow current. Wugang to Xiaomiaotou is upstream, with a water length of 226 kilometers. On the head of the small temple, the flow has greatly increased. Xiaomiaotou to Majitang is the middle reaches, with a length of 27 1km. Among them, Xiaomiaotou to Zhexi are mostly canyons. After crossing Zhexi, the terrain is open, and then there is the canyon. Below Majitang, it enters the downstream, the valley is open, and there are many beaches in the river. Taojiang River is affected by the backwater of Dongting Lake, and its banks are gentle. Below Yiyang is the alluvial plain. The Zijiang River basin is abundant in precipitation, and the rainstorm is disastrous, and the river surges and falls sharply. Generally, the water rises from April, and the highest water level appears in April-June, and the water level drops after August. The lowest water level generally appears from September to 65438+February or 1 to April. The water supply of Zijiang River mainly depends on rainwater and groundwater recharge. Because the Zijiang River basin is mostly a small tributary, the concentrated area is not large, but the interval runoff is very large. Summer rainfall is concentrated, and runoff is also concentrated. Generally, there is less precipitation in autumn and winter, and rivers are mainly replenished by underground runoff. The vegetation in Zijiang River basin is good, and the river is clear most of the time, only in flood season, the river is turbid. The water quality of Zijiang River Basin is generally good.

Third, Shui Yuan.

Shui Yuan, which originated in southeastern Guizhou, has two sources, the north and the south, with the south as the main source. Nanyuan Longtou River originated in Jiguanling, Wu Yun, Duyun County, Guizhou Province, also known as Mawei River. The source of north and south meets at the mouth of Shangcha River in Lushan County, which is called Qingshui River. This river flows into Zhijiang County, Hunan Province in Luanshan Mountain, Guizhou Province, and flows eastward to meet dancing water in Qiancheng Town, Qianyang County, which is called Shui Yuan. Shui Yuan flows through Zhijiang, Huaihua, Huitong, Qianyang, Xupu, Chenxi and Luxi counties in Hunan, turns northeast in Yuanling, and flows into Dongting Lake via Taoyuan and Changde. Changde Deshan is the mouth of Yuanshui River, and the tail water flowing into Dongting Lake is below Deshan Mountain and in Hanshou. Total length of Shui Yuan1033km. The Yuanshui River Basin is surrounded by mountains, with Xuefeng Mountain and Zijiang River in the east, Miaoling Mountain and Liu Shui in the south, Fanjingshan and Wujiang River in the west and Wuling Mountain and Lishui in the north. Yuanshui River Basin is long from north to south, narrow from east to west, and there are many tributaries on the left bank, mainly dancing water, old water, martial water and unitary water. There are mainly canal water, witch water and falling water on the right bank. There are many mountains, steep slopes, canyons, beaches and fast currents in the Yuanshui River Basin, which are the characteristics of Yuanshui River. Shui Yuan from Heyuan to Qiancheng belongs to the upper reaches, with many mountains and deep valleys. Qiancheng to Yuanling is the middle reaches, and it is a hilly area. Below Yuanling is called the downstream, and below Taoyuan is the alluvial plain. The precipitation in Yuanshui River Basin generally decreases from east to west and increases from upstream to downstream. The lower reaches of Yuanshui River and eastern Guizhou are high rain areas, which are related to the Three Gorges rain area formed by air masses from the eastern Sichuan Basin and the eastern Guizhou rain area formed by marine air masses from the south. The precipitation season generally begins in April, and the rainfall is the highest from April to July. Rainfall is characterized by local rainstorm, which mostly occurs in the middle and lower reaches with heavy rainfall. Shui Yuan is a mountain stream. The distribution of runoff depth in Yuanshui basin varies with the change of topography and rainfall, and it gradually increases from upstream to downstream. Sediment concentration in Shui Yuan: The rivers such as Wushui, Xu Shui, Chenshui, Wushui and Youshui have higher sediment concentration. After these tributaries enter the main stream, the sediment concentration increases with the increase of water volume in the main stream. The water quality in Shui Yuan is basically good.

Fourth, Lishui

Lishui is located in the northwest of Hunan, across Hunan and Hubei provinces, in the south of the Yangtze River, separated from the Qingjiang River system in Hubei by the northern branch of Wuling Mountain in the north, separated from Shui Yuan by the southern branch of Wuling Mountain in the south, starting from Chongshan Mountain in Hunan in the west and facing the end of Dongting Lake in the east. The terrain is high in the west, low in the south and low in the east. The main stream and tributaries flow from northwest to southeast. The source of Lishui is located in Nancha, Sangzhi County, which is divided into three sources: north, middle and south, with the north source of Chinese fir as the main source. After the confluence of the three sources in Nancha, they flow southward through Sangzhi and Yongshun, then eastward into Maoxi, pass through Dayong to Cili, receive the water from Loulai, pass through Shimen to Naishui, pass through Linli to Lixian to receive the water from Naishui, and then flow to Tianjin Xiaodukou for injection into Dongting Lake. Lishui is 388 kilometers long. Lishui from the source to Sangzhi County is called upstream, in the mountains. The middle reaches from Sangzhi to Shimen are hilly areas. Downstream from Shimen to Tianjin, through Linli and Lixian, the terrain is open and flat. Lishui is the shortest of the four major rivers in Hunan. The distribution characteristics of precipitation in Lishui River basin are more upstream and less downstream, and more plains in hilly areas. The average annual precipitation in the upper reaches of the Lishui River is 1600 ~ 1800 mm, and the lower reaches of the Lishui River are low and flat, and the rain air mass passes by, but the precipitation is less. Generally speaking, the rainfall in Lishui River Basin only increased significantly from April, with the largest rainfall in April-August, the most concentrated in summer and the least rainfall in winter. During the rainy season or rainstorm, flash floods occur every time. In some years, there is still a lot of rain in September and June, and the water level is still rising in 65438+1October, but from the perspective of the whole year, it is already a trend of falling into the water. Generally, it enters the dry season from September to March of the following year, and rivers dry in some years. Lishui is a mountain stream river, and the runoff distribution changes with the rainfall distribution. There is abundant rainfall in the upper reaches, and the runoff depth above Dashong is more than 1000mm, and that above Liangshuikou is more than 1500mm, which is the highest in the province. The downstream rainfall is less, and the runoff depth is below 600 mm, which is one of the low-value areas in the province. The sediment concentration of Lishui River is higher than that of Hunan, Zi and Yuan rivers. Due to the deep valleys in Lishui Mountain, the river is swift and the soil erosion is serious. In non-flood season, the river is clear and the sediment concentration is very small. The pollution level in Lishui is not great.

Dongting Lake

Dongting Lake is located on the south bank of Jingjiang River, in the north of Hunan Province, between Hunan and Hubei provinces. It is one of the five largest freshwater lakes in China. Dongting Lake has three ports connected with the Yangtze River, and Hunan, Guizhou, Yuanshui and Lijiang River flow into it in the south. This is the third geographical feature of Hunan. Dongting Lake is like a huge reservoir, which contains the water of four rivers in Hunan and plays a role in dealing with the Yangtze River flood. Dongting Lake area in Hunan is used to include all areas protected by dikes in Hunan, Tibet, Yuan and Li. Therefore, as far as the administrative scope is concerned, it includes all or part of 19 counties, 7 cities and 15 state-owned farms, among which the pure lake area includes Changde, Hanshou and Huarong. According to the statistics of 1985, Dongting Lake area accounts for114, population accounts for19, cultivated land accounts for16, grain output accounts for16, and cotton production accounts for 4/6. Dongting Lake area is a commodity grain production base in Hunan and occupies an important position in Hunan's national economy.

At present, Dongting Lake starts from Jingjiang in the north, reaches Lixian and Changde in the west, reaches Yuanjiang, Hanshou and Yiyang in the south, and reaches Xiangyin, Guluo and Yueyang in the east, covering an area of about 18780 square kilometers. The terrain is high in the north and low in the south, and the natural lake area is about 269 1 km2 (from Yuan Dynasty to the middle of Qing Dynasty, the area was 6270km2 and 6,550 km2). According to the natural form, it is divided into East Dongting Lake, South Dongting Lake, Muping Lake and other small lakes. Dongting Lake area is connected to the Yangtze River in the north, and there are "four waters" inside. Lakes are dotted, rivers and canals crisscross, and branches and tributaries are connected, which has become the center of water transport in Hunan Province. The supply of Dongting Lake water system is mainly rainwater. The water from the Yangtze River flows into the lake through three points; Hunan, Zi, Yuan and Li rivers are rich in water resources, which also provide a large number of water sources for lakes. The characteristics of its water balance are: the proportion of inflow runoff and outflow runoff is very large, which account for more than 90% of the total water revenue and expenditure respectively, and the proportion of precipitation and evaporation on the lake surface is relatively small. Another feature is that the quantity of the two is almost the same, that is, the water output and inflow are 1.04: 1. 15 respectively, indicating that the lake throughput is close.

Dongting Lake takes Chenglingji as the outlet, and the outlet water volume of Chenglingji is the largest in July, and the minimum in June is 65438+ 10. In the five months from May to September every year, there are a lot of water from four rivers and three mouths in the lake, and the inflow is mainly outflow, which is the high-incidence period of the lake, and the outflow is more than the inflow 10 to March next year, which is the low-incidence period of the lake. From June 10 to February 12 and June 10 to March of the following year, the effluent was about 1. 15 times that of the influent, and the lake slowly declined.

Three mouths and four waters flow into Dongting Lake, and the sediment is also imported, which slowly accumulates in the lake, leading to the rise of the lake bottom, the shrinking of the lake surface, and the relative decline of the life and storage function of the lake. Sediment changes, sediment concentration changes along the way. The average sediment concentration in Dongting Lake has been decreasing for many years, and the sediment concentration in the three estuaries has decreased after siltation in the lake area. A large amount of sediment was deposited in the lake. The distribution of sediment transport in Dongting Lake mainly comes from the Yangtze River. Therefore, the sediment transport in the Three Rivers is directly related to the evolution and development of Dongting Lake, and its maximum sediment transport is concentrated in the flood season.

Causes of frequent flood disasters

Hunan is located on the south bank of the middle reaches of the Yangtze River, surrounded by mountains in the east, south and west, with rolling hills in the middle and Dongting Lake Plain in the north.

The whole province covers an area of 2 1. 1.8 million square kilometers and has a population of 64.28 million. The annual average temperature 16℃ and the annual average rainfall1430mm. With mild climate and abundant rainfall, China is a major agricultural province and a major grain, cotton and oil base.

Dongting Lake spans Hunan and Hubei provinces, with an area of 15200k m2 in Hunan, accounting for 80.9%.

Dongting Lake has four waters, which flow into and out of the Yangtze River. There are three ports in the north, Songzi, Taiping and Dani, which discharge the flood of the Yangtze River, and there are four waters in the south, namely Hunan, Zi, Yuan and Li, which form a complex water system in Dongting Lake area and then discharge into the Yangtze River from Yueyang.

Frequent floods in Dongting Lake area: 1954 Yangtze River flood, more than 30,000 people drowned; In the 47 years since 1949, there have been floods in 37 years. 1996 145, resulting in tens of billions of direct economic losses,1000000 people were forced to live on the narrow flood dike for several months.

The main reasons for frequent floods:

1, the amount of water entering the lake is large, but the amount of water leaving the lake is small. The annual inflow of the lake is as high as 31800 million m3, which is three times that of Poyang Lake, five times that of the Yellow River and 10 times that of Taihu Lake. Because there is only one outlet, the flood discharge capacity is limited. In case of rainstorm, pressure will be formed on the roof and roof, resulting in tens of billions of m3 of redundant flood stranded in the lake, resulting in flood disaster.

2. Sediment deposition reduces the capacity of the lake. A large number of floods bring a lot of sediment, which is deposited in Dongting Lake, with an average annual deposition of 654.38+0 billion m3. Since 1949, the average sedimentation height of the whole lake has been1.7m.

3. The flood control standard is low and the disaster resistance is weak. After the first phase of regulation, the flood control standard is raised from once every 3-5 years to once every 5- 10 years. However, this standard is far from being able to adapt to the severe flood control situation in Dongting Lake area, and it is far below the 20- 100-year standard that has been reached by seven major rivers in China.

Due to the special geographical environment, the floods in Dongting Lake mainly occur in the west Dongting Lake, Shui Yuan and the lower reaches of Lishui, especially in the lower reaches of Lishui. Therefore, it is necessary to control the Lishui River in Dongting Lake.

Lishui is the most serious flood disaster in the Yangtze River system, but it has not been completely rectified.

The main stream of Lishui originates from Sangzhi County, Zhangjiajie City, with a total length of 390km, a drop of 1.439m, an average annual rainfall of 1.542mm, a cultivated land area of 26 1.000 ha and a population of 3.55 million.

The main stream of Lishui and its main tributaries, Loushui and Xishui, belong to the famous Hefeng and Wufeng rainstorm areas in the middle reaches of the Yangtze River. The flood concentrated quickly and the peak height was fierce. We often meet the main and tributary floods, and meet the Yangtze River flood from Songzi River at the tail. In addition, the spillway is blocked and the flood discharge is not smooth, which leads to the increasingly serious flood hazard. 1935 There was a catastrophic flood in history, which drowned more than 33,000 people. Since 1949, there have been floods every year, including a major flood in 14, with a total of167,000 hectares of cultivated land and a population of 2 10/00,000.

Lishui is also a river rich in resources. The famous Zhangjiajie National Forest Park is located in the Lishui River Basin.

1992, the State Council authorized the State Planning Commission to approve the Lishui River Basin Planning Report, which outlined a grand blueprint for the comprehensive management and development of Lishui. According to the Planning Report, 26 cascade projects can be built in the main and tributaries of the whole basin. The total installed capacity of power generation is 22 13MW, and the annual power generation is 6.9 billion kw h. In addition, there are comprehensive benefits such as irrigation, water supply, shipping and soil and water conservation. According to the plan, the flood control capacity of Lishui has been improved from the current once every 4-7 years to once every 50 years, protecting the safety of122,000 hectares of cultivated land and 15 1000 people in the downstream and Song Li area, with a navigation mileage of 66 1000 km and an annual traffic volume of 40,000. Through reservoir operation, the guarantee rate of downstream water use has been greatly improved, which has guaranteed 47,000 hectares of farmland spring irrigation water and 430,000 people and 90,000 large livestock drinking water in Song Li area, and controlled soil erosion area of 4366k m2, which fundamentally improved the ecological environment of Lishui River Basin and West Dongting Lake and promoted regional economic development.

The primary task of harnessing Lishui and promoting profits is to prevent and control floods. According to the Lishui River Basin Planning, reservoirs will be built in the upper reaches and tributaries of the Lishui River, spillway will be dredged in the lower reaches, dikes will be reinforced, and flood discharge capacity will be increased. At the same time, a complete flood control system will be formed in cooperation with non-engineering flood control measures, so that the flood control standard below Shimen and at the end of the Lishui River will be raised from the current once every 4-7 years to once every 20 years in the near future. After the completion of the long-term sluice, it is urgent to build Jiangya Reservoir, Zaoshi Reservoir and Yichongqiao Reservoir in the near future. * * * will undertake the task of flood storage, and reserve the flood control storage capacity of 65.438+77 million m3. Control the flow of the three reservoirs, and ensure that the safe flow of the stone gate does not exceed12000m3/s. ..