The largest tributary of the Yellow River is undoubtedly the Wei River

The largest tributary of the Yellow River is undoubtedly the Weihe River. Next, I will appreciate its majesty with you.

The Weihe River, known as the Wei River in ancient times, is the largest tributary of the Yellow River. Originating from Niaoshu Mountain in Weiyuan County, Dingxi City, Gansu Province, it mainly flows through Tianshui, Gansu Province, Baoji, Xianyang, Xi'an, Weinan and other places in the Guanzhong Plain of Shaanxi Province, and finally joins the Yellow River in Tongguan County, Weinan City. There is the Qinling Mountains running east-west across the Weihe River in the south, and the Liupan Mountain barrier in the north. The Weihe River Basin can be divided into two parts: the west is the loess hilly and ravine area, and the east is the Guanzhong Plain area.

Water system composition

The main stream of the Weihe River spans eastern Gansu and central Shaanxi. The total length is 818 kilometers and the total drainage area is 134,766 square kilometers.

Gansu Province Section: flows through the central, southeastern part of Gansu Province and the central part of Shaanxi Province. Generally speaking, the west source is the main source, that is, the Wei River originates from Niaoshu Mountain. It has two sources: the Nanyuan Qingyuan River originates from Huohuo Mountain in the southwest of Weiyuan County, and gathers many tributaries in the mountainous area. It is a perennial river with a length of more than 30 kilometers. It flows northeast to Qingyuan Town in Weiyuan County and joins Xiyuan; The name Yu River originates from the Niao Shu Mountain in the west of Weiyuan County. The river is short and intermittent. When the east flow merges with the west source, it is called the Wei River. It flows eastward through Longxi County. Then it flows into Wushan County from the southeast, Bangsha River, Shandan River and Danan River merge into it on the south bank, then flows into Gangu County in the east, Sandu River flows into it from the north bank, and when it reaches Tianshui City, Hulu River flows into it from the north bank, and Jinghe River flows into it from the west. Then it meets the Niutou River in the east. Pass Xiaolongshan and enter Shaanxi Province. Among them: In Dingxi City, Gansu Province, it originates from the north side of Niaoshu Mountain with an altitude of 3495 meters in the southwest of Weiyuan County, Dingxi City. The source elevation is 1383 meters [1]. The main stream flows from west to east through Weiyuan County and Longxi County, and ends at Ya'er Gorge flows into Tianshui. The water collection area within the territory is 10241.78 square kilometers, accounting for 7.6% of the total area of ??the Weihe River of 134767 square kilometers. The annual sand transport volume is 50.44 million tons, and the erosion modulus within the territory is 5100 tons per square kilometer. [3] In Tianshui City, the main stream of the Wei River flows through Wushan County, Gangu County and Maiji District, with a total length of 270 kilometers.

Central Shaanxi: The main stream of the Weihe River is in Shaanxi, with a length of 502.4 kilometers and a drainage area of ??67,108 square kilometers, accounting for 50% of the total area of ??the Yellow River basin in Shaanxi. The annual average runoff of the entire river is 10.37 billion cubic meters, of which 6.266 billion cubic meters are generated in Shaanxi. More than 580 million tons of sediment are input into the Yellow River every year, accounting for about 1/3 of the total sediment in the Yellow River. The main stream of the Wei River leaves Gansu Province from Tianshui, flows east to Tianshui and borders Baoji, passing through Chencang, Weibin, Jintai, Qishan, Meixian and Fufeng in Baoji City, Yangling, Wugong, Xingping, Qindu and Weicheng in Xianyang City. 22 counties (cities and districts) including Zhouzhi, Huxian, Chang'an, Weiyang, Baqiao, Gaoling, and Lintong in Xi'an City, and Linwei, Dali, Huaxian, and Huayin in Weinan City enter the Yellow River from the port of Tongguan.

Hydrological characteristics

The average annual runoff of the Wei River is 7.57 billion cubic meters, and that in Shaanxi is 5.38 billion cubic meters. Runoff is distributed unevenly across regions, with the general trend decreasing from south to north. It is higher in the Qinling and Guanshan Mountains and lower in the original and valley areas. The west is greater than the east, and the midstream has richer runoff than the downstream. The runoff modulus on the northern slope of the Qinling Mountains is relatively high, ranging from 9 to 15 liters per second per square kilometer, while the runoff modulus in the loess plain area is only 0.8 to 2.2 liters per second per square kilometer. Only the Qianhe River has a higher runoff modulus, with the Qianhe River having a higher runoff modulus. Yang station is 4.66 liters/second per square kilometer. The runoff modulus of the main stream of the Weihe River is 2.5 to 3.7 liters per second per square kilometer. The runoff modulus at Weijiabao and Xianyang stations is higher due to the addition of tributaries.

It can be clearly seen from the runoff depth contour map that the runoff depth on the northern slope of the Qinling Mountains increases with the elevation of the mountain, from less than 100 mm to more than 600 mm, with the highest center in Taipei. Baishan Mountain and South Wutai Mountain. The Weihe River alluvial plain is very flat, has a high degree of water conservancy, and is a low runoff area.

Basin Overview

The interannual variation of runoff in the middle and lower reaches of the Weihe River is small in the south and large in the north. That is, the annual runoff in the Qinling Mountains on the south bank of the Weihe River is rich but the interannual variation is small; the loess on the north bank The annual runoff in the area is small but has large inter-annual variability. The coefficient of variation of annual runoff on the northern slope of the Qinling Mountains is generally 0.30 to 0.40. Among them, the Shitou River and Qingjiang River are only 0.30, and the Heihe, Laohe and Fenghe rivers are 0.40. Further east, the Dayu River and Shibianyu River are The river level is reduced to 0.35 again.

The ratio of the maximum year to the minimum year is 3.0 to 4.0, and the distribution on the northern slope of the Qinling Mountains is consistent with the distribution of the coefficient of variation. The loess plateau area has the largest change, with a coefficient of variation of 0.45 to 0.60, and the ratio of the maximum annual runoff to the minimum annual runoff is 4 to 6 times. The main stream of the Weihe River has a large water volume, and the interannual changes in runoff are relatively small, with a coefficient of variation of 0.30 to 0.35. The seasonal changes in the runoff of the Wei River are obvious. The main stream has the largest flow in autumn, accounting for about 38% to 40% of the annual runoff, 32.8% to 34.2% in summer, 17.7% to 19.1% in spring, and 8.3% to 9.9% in winter. The Heihe River, a tributary on the south bank, and the rivers to the west have the largest runoff in summer, followed by autumn; the rivers east of the Heihe River have the largest runoff in autumn, followed by summer, and the proportion of spring runoff is larger, accounting for 21% to 27.3%. The annual runoff distribution of Qianhe River is the most uneven among the north bank tributaries. Autumn runoff accounts for 52.6%, summer runoff only accounts for 23.5%, and spring runoff is also lower, accounting for 14.6%. The runoff of the Qishui River is relatively evenly distributed throughout the year, with spring accounting for 23.2%, which is similar to 25.1% in summer. Winter runoff is as high as 15.8%, which is higher than the spring runoff of Qianshui River. The reason is the influence of underlying surface factors.

The Huaxian Station of the Weihe River transports an average of 492 million tons of sediment to the Yellow River every year. The sediment mainly comes from the loess area on the north bank, especially from the Jinghe River and the upper reaches of the Weihe River. The Jinghe River transports an average of 309 million tons of sediment to the Weihe River every year (Zhangjiashan Station), accounting for 62.8% of the total sediment transport of Huaxian Station, while the drainage area only accounts for 40.6% of Huaxian Station. The amount of sediment from the upper reaches of the Wei River reaches 200 million tons per year at Linjiacun Station, accounting for 40.6% of the annual sediment load at Huaxian Station, while the drainage area only accounts for 28.8% of that at Huaxian Station. The south bank of the Weihe River is in the Qinling Mountains, a mountainous area with good vegetation and little sediment content, generally below 1.0 kg/cubic meter. The average annual sediment transport module is generally several hundred tons per square kilometer. The Bahe River flows through the loess area. The sand content at Maduwang Station is 5.6 kg/cubic meter, and the annual sand transport module is 2110 tons/km2.

The sediment content in the main stream of the Weihe River gradually decreases from Linjiacun (63.7 kg/cubic meter), Weijiabao (43.9 kg/cubic meter) to Xianyang (31.1 kg/cubic meter). The reasons are: first, after the Weihe River leaves Baoji Gorge and enters the Guanzhong Plain, the river valley suddenly opens up, the river bed ratio decreases greatly, and the sand-carrying capacity of the water flow decreases. The sediment brought by the upstream is deposited in the river channel, making the river water have a natural sediment content. Secondly, the sand content of the tributaries on both sides of the river section is small. The Qianhe River and Qishui River, the north bank tributaries with larger sand content, only have 10-11 kg/cubic meter, which reduces the sand content; and It is Baoji Gorge that diverts water from the Wei River to the irrigation area, bringing part of the sediment into the irrigation area to reduce the sand content. The sediment content of rivers below Xianyang has increased sharply, reaching 55 kg/cubic meter at Lintong Station and 49.3 kg/cubic meter at Huaxian Station. The main reason is that the Jinghe River has brought a large amount of sediment. The sediment content at Zhangjiashan Station of the Jinghe River has reached as high as 148 kg/m3. The idiom "Jinghe and Weihe" we often use means that the water in the Jinghe River is clear and the water in the Weihe River is muddy. It has become the water in the Jinghe River is muddy and the water in the Weihe River is clear. The sediment input into the middle and lower reaches of the Wei River and its tributaries is much greater than the sediment transported to the Yellow River through Huaxian Station. That is, a large amount of sediment is still deposited in the middle and lower reaches of the river every year. The main reason is that the Sanmenxia Reservoir increases river erosion. base point.

Rainfall in the middle and lower reaches of the Weihe River is concentrated in July, August and September, and heavy rains will cause more flood disasters. According to actual measurement data, the main stream of the Weihe River had the largest flood in 1954. The maximum peak flow rate at Linjiacun Hydrological Station was 5030 cubic meters/second (August 17, 1954), and that at Xianyang Station was 7220 cubic meters/second (August 18, 1954). day), Huaxian Station is 7660 cubic meters/second (August 19, 1954). The tributary Qingjiang River once had a flow of 504 cubic meters/second (Yimen Town 1964). The peak flow of Qianhe Fengjiashan at 0:00 on August 17, 1954 was 3960 cubic meters/second. The Shitou River Xieyuguan had 1050 cubic meters/second in 1964. m/s, Heihe Heiyukou had 3040 cubic meters/s in 1980. According to historical records, the Baoji section of the Weihe River suffered from 22 floods from 1200 to 1981, with an average of one every 35.5 years. The major flood years included the second year of Xianfeng in the Qing Dynasty (1852) and the sixth year of Tongzhi (1867). ) and the 10th year of the Republic of China (1921), etc.

Flood disasters in this area are often caused by continuous rain. There were 14 floods from 1700 to 1949, 10 of which had rain records. Five of them (1811, 1933, 1922, 1939, 1949) were like this, and they lasted for a long time. , wide in scope, occurring at the same time as neighboring provinces. Due to the low sill of the Weihe River, general floods can flood the farmland. The riverbed oscillates erratically. According to surveys, the Baoantan river section experienced 7 major changes in the 64 years from 1898 to 1962, with the largest swing amplitude of more than 5 kilometers. In Henan Province in 30 years and Hebei Province in 30 years, the riverbed fluctuated erratically. said. In 1933, floods inundated 497,400 acres of tidal flats and farmland, damaging and destroying 181 villages. In 1954, the flood inundated a total area of ??363,200 acres and destroyed 79 villages.

In August 1981, a catastrophic flood occurred in Baoji City. The Qianhe River, Qingjiang River, Shitou River, Tangyu River, and Tongguan River all exceeded the maximum peak flow in current records. According to statistics, from August 17 to 21, the average flow rate in Weijiapu, the main stream of the Weihe River, was 621 to 2540 cubic meters per second. The maximum one-day flood volume was 219 million cubic meters, which was 0.74 times the maximum one-day flood volume in the past years, and the three-day flood volume was 500 million cubic meters. cubic meters, which is 0.82 times the maximum flood volume in three days in history. The daily flood volume in July was 1 billion cubic meters, which was 1.16 times the maximum flood volume in seven days in history. Qingjiang River Yimen Town Station experienced five flood peaks in seven days from the 15th to the 21st. The maximum one-day flood volume was 18.9 million cubic meters, which was 0.93 times the maximum one-day flood volume in the past years. The maximum three-day flood volume was 51.1 million cubic meters, which was the maximum volume in the past years. The maximum flood volume in three days was 1.33 times, and the maximum flood volume in seven days was 84.8 million cubic meters, which was 1.69 times the maximum flood volume in seven days in the past. Due to the regulating effect of the reservoir, a flood disaster was avoided. The Duanjiaxia Reservoir in the upper reaches of the Qianhe River reduced the peak flow of the Qianhe River from 436 cubic meters/second to 36 cubic meters/second, protecting Longxian County; the Fengjiashan Reservoir and Wangjiaya Reservoir downstream also reduced the peak flow of 1,170 cubic meters/second. The peak flow rate in 2 seconds was reduced to 309 cubic meters/second, and the peak flow was staggered for 58 hours; the peak flow rate of 1360 cubic meters/second at the Shitou River Yinggebii Hydrological Station was reduced by 2/3 by the Shitou River Reservoir under construction; The flood peak of 131 cubic meters per second at Haoweihe Hydrological Station on the Qishui River is captured by the Yangmaowan Reservoir. Without the flood control and peak reduction of these reservoirs, the Weijiabao Station on the main stream of the Weihe River would have a peak flow of 6,480 cubic meters/second, which would exceed the peak flow of the 54-year flood of 5,780 cubic meters/second. However, the actual peak flow was only 4,500 cubic meters/second. Seconds of peak flow.

From July to October 1983, continuous rainfall occurred in the Guanzhong Basin, resulting in large-scale waterlogging. The affected area was 11.448 million acres, nearly 580,000 houses (kilns) collapsed and damaged, and more than 600 people died. 174 kilometers of various channels and 735 buildings of various types were destroyed. Due to the poor drainage system in urban Xi'an, the Beicheng River overflowed, and the cement pavement on Dongxi Street sank and cracked, resulting in the collapse of power poles, water outages, power outages, and production suspension losses in some areas.

The exposure of open water, which is the most serious cause of waterlogging hazards, is very widespread. According to incomplete statistics, the open water area reaches 1,635,900 acres. There are two centers for the distribution of large areas of open water, one is Zhouzhi, Huxian, and Xingping; the other is Erhuacao (Huaxian, Huayin). In terms of hazards, waterlogging is more serious in the irrigation areas of Baojixia, Fengjiashan, Jinghui, Luohui, Jiaokou and Weibei in Weibei, with an area of ??345,000 acres of open water, accounting for 21% of the open water area in Guanzhong. The Luohui Irrigation District accounts for 22.12% of the waterlogged area with a groundwater depth of more than 2 meters, the Jiaokou Drainage District accounts for 48.25%, and the Jinghui Irrigation District accounts for 4.66%. The causes of waterlogging in the Guanzhong Basin are relatively complex. Geology and landforms are the topographic basis for waterlogging. Precipitation and irrigation are the main sources of groundwater recharge. The thick terrestrial sediments provide conditions for rivers and precipitation to infiltrate. In rainy years, groundwater The level rises, forming a large area of ??waterlogged area.

The upper reaches from the Shaanxi border to Linjiacun, the river is 123.4 kilometers long, with a drop of 791 meters, and an average drop of 1.81?. The upper section is mainly the gully area of ??the Loess Plateau, with alternating sections of rivers and gorges; the lower section is mainly Qin In Longshan District, the river cuts about 200 meters into the granodiorite bedrock, forming a stone gorge with a width of only 50 to 60 meters and steep stone walls standing like arches, and the Baoji Gorge with towering peaks and steep mountains that are 100 to 200 meters wide.

The middle reaches from Linjiacun to Xianyang are 171 kilometers long, with a basin area of ??46,856 square kilometers, a drop of 224.4 meters, and an average drop of 1.24 degrees. The water flow is slow and scattered, with many sandbanks and shoals. The river width is 1,500 to 2,000 meters, and it can reach up to 1,500 meters including the beach. 4000 meters to 5000 meters. More than 110 kilometers below the Weijiabao Weihui Canal Dam, the river swings from north to south and changes frequently. People also have a folk proverb of "Thirty Years in Henan, Thirty Years in Hebei". The downstream section from Xianyang to the port is 208 kilometers long, with a drop of 56 meters, and an average relative drop of 0.28°. The section from Xianyang to the mouth of the Jinghe River is a wandering branch river, and the main channel is relatively stable; the section from the mouth of the Jinghe River to the mouth of the Luohe River has a relatively stable right bank. The left bank collapsed seriously. In the Tang Dynasty, the "Sanjue Stele" was 7.5 kilometers away from the Weihe River, and now it is only more than 100 meters away from the river bank. The river width below the mouth of the Beiluo River is 3,000 meters to 15,000 meters. Due to the support of the Yellow River, backflow is prone to occur. After the completion of the Sanmenxia Reservoir, The riverbed above the mouth of the Weihe River is silted up and raised by more than 5 meters. Barrier sand is formed at the Tongguan checkpoint, which has become a thorn in the side of flood control.

The Guanzhong Weihe River was formed in the Early Pleistocene, about 2 million years ago. Human activities in the basin have been traced for more than 800,000 to 1 million years ago. There are Lantian ape-man sites 800,000 years ago and 150,000 years ago. The ruins of the Dali people, the Banpo ruins of the matrilineal clan commune community six to seven thousand years ago, as well as a large number of Yangshao Culture and Longshan Culture ruins, etc. Guanzhong is also the foundation for the Chinese nation to realize the great reunification of the country. Emperors Yan and Huang, the first humanistic ancestors, unified the people here, fought farming and weaving; more than 10 dynasties such as Zhou, Qin, Han and Tang Dynasties relied on the Wei, Jing, Chan, Ba, Feng, Shen, The capital was built here for more than a thousand years due to the floods and floods, making China one of the four ancient civilizations in the world.