Weihe River is the largest tributary of the Yellow River.

The biggest tributary of the Yellow River is the Weihe River. Next, I will enjoy its majestic momentum with you.

Weihe River, formerly known as Weishui, is the largest tributary of the Yellow River. Originated in Bird and Rat Mountain in Weiyuan County, Dingxi City, Gansu Province, it mainly flows through Tianshui in Gansu Province, Baoji, xianyang, Xi and Weinan in Guanzhong Plain of Shaanxi Province, and joins the Yellow River in Tongguan County, Weinan City. There is an east-west Qinling Mountains on both sides of the Weihe River, and a Liupanshan barrier in the north. Weihe river basin can be divided into loess hilly and gully region in the west and Guanzhong plain region in the east.

Water system composition

The main stream of Weihe River spans eastern Gansu and central Shaanxi. The total length is 8 18km, and the total drainage area is 134766km2.

Gansu section: It flows through the central and southeastern parts of Gansu Province and the central part of Shaanxi Province. Generally, the west source is the positive source, that is, the Weihe River originated from Bird and Mouse Mountain. There are two sources: Qingyuan River in Nanyuan County, which originated in Huohuo in the southwest of Weiyuan County and gathered many tributaries in the mountainous area. It is a perennial river with a length of more than 30 kilometers, which flows to Qingyuan Town and Xiyuan River in Weiyuan County in the northeast. Xiyuan, named Yu He River, originated from Xiniaoshu Mountain in Weiyuan County. The river is short and intermittent, and it is called Weihe River only after it flows eastward with Xiyuan. Longxi county flows east. Then it flows into Wushan County in the southeast, with Bangsha River, Shandan River and Danan River on the south bank, Gangu County on the east bank, Sandu River on the north bank, Hulu River in Tianshui City on the north bank, Jinghe River in the west and Niutou River in the east. Cross Xiaolongshan and enter Shaanxi Province. Among them, in Dingxi City, Gansu Province, it originated from the north side of Bird and Mouse Mountain, which is 3,495 meters southwest of Weiyuan County, Dingxi City, with the source elevation of 1.383 meters [1]. The main stream flows from west to east through Weiyuan County and Longxi County, and flows into Tianshui in Yalxia. The domestic catchment area is 1024 1.78 km2, accounting for 7.6% of the total area of Weihe River, with an annual sediment transport of 50.44 million tons and a domestic erosion modulus of 5100t. [3] In Tianshui City, the main stream of Weihe River flows through Wushan County, Gangu County and Maiji District, with a total length of 270 kilometers.

Central Shaanxi: The main stream of Weihe River is in Shaanxi, with a flow 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 average annual runoff of the whole river is 65.438+0.037 billion cubic meters, of which Shaanxi runoff is 6.266 billion cubic meters; More than 580 million tons of sediment is imported into the Yellow River every year, accounting for about 1/3 of the total sediment in the Yellow River. The main stream of Weihe River leaves Gansu from Tianshui and flows eastward into Tianshui, bordering Baoji, passing through Chencang, Weibin, Jintai, Qishan, Meixian and Fufeng in Baoji, Yangling, Wugong, Xingping, Qindou and Weicheng in Xianyang, Zhouzhi, Huxian, Chang 'an, Weiyang, Baqiao, Gaoling, Lintong and Weinan in Xi.

Hydrological characteristics

The average annual runoff of Weihe River is 7.57 billion cubic meters, and that of Shaanxi is 5.38 billion cubic meters. The distribution of runoff area is uneven, and the general trend is decreasing from south to north, which is higher in Qinling and Guanshan areas and lower in the original and valley areas. The west is bigger than the east, and the middle reaches are richer than the downstream. The runoff modulus on the northern slope of Qinling Mountains is relatively high, ranging from 9 to 15 liter/s? Square kilometers, while the runoff modulus in the original loess area is only 0.8 ~ 2.2 liters/second? Square kilometers, only He Qian has a higher runoff modulus, and Qianyang Station is 4.66 liters/second? Square kilometers. Weihe River runoff modulus is 2.5 ~ 3.7L/s? Square kilometers, of which Weijiabao and Xianyang stations are higher, which is caused by the addition of tributaries.

It can be clearly seen from the contour map of runoff depth that the runoff depth on the northern slope of Qinling increases with the elevation, from below 100 mm to above 600 mm, with the highest center in Taibai Mountain and South Wutai Mountain. Weihe River alluvial plain is very flat and has a high degree of water conservancy, belonging to a low-yield flow area.

River basin survey

The annual variation of runoff in the middle and lower reaches of Weihe River is smaller in the south than in the north, that is, the annual runoff in Qinling Mountain on the south bank of Weihe River is rich and the annual variation is small; The annual runoff in the loess area on the north bank is small and the interannual variation is great. The variation coefficient of annual runoff on the northern slope of Qinling Mountains is generally 0.30 ~ 0.40, of which Shitou River and Qingjiang River are only 0.30, Heihe River, Laohe River and Fenghe River are 0.40, and further east, Dayu River and Shibianyu River decrease to 0.35. The ratio of the maximum year to the minimum year is 3.0 ~ 4.0, and the distribution of the northern slope of Qinling Mountain is suitable for the distribution of coefficient of variation. The loess plateau has the largest change, with a coefficient of variation of 0.45 ~ 0.60, and the ratio of maximum annual runoff to minimum annual runoff is 4 ~ 6 times. The main stream of Weihe River has a large amount of water, and the runoff changes relatively little during the year, with a coefficient of variation of 0.30 ~ 0.35. The seasonal variation of Weihe River runoff is obvious. The runoff of the main stream is the largest in autumn, accounting for about 38% ~ 40% of the annual runoff, 32.8% ~ 34.2% in summer, 65,438+07.7% ~ 65,438+09.65,438+0% in spring and 8.3% ~ 9.9% in winter. Heihe River, a tributary of the south bank, and the rivers to the west, have large runoff in summer, followed by autumn; The river east of Heihe River is the largest in autumn, followed by summer, and the proportion of spring runoff is large, which is 2 1% ~ 27.3%. The runoff of Heqian River is the most uneven in the north bank, accounting for 52.6% in autumn, 23.5% in summer and 14.6% in spring. The runoff of Qishui River is evenly distributed during the year, accounting for 23.2% in spring, approaching 25. 1% in summer and reaching 15.8% in winter, which is higher than that of He Qian in spring. The reason lies in the influence of underlying surface factors.

Weihe hua county Station transports 492 million tons of sediment to the Yellow River every year. Sediment mainly comes from the loess area on the north bank, especially the upper reaches of Jinghe River and Weihe River. Jinghe River transports 309 million tons of sediment to Weihe River every year (Zhangjiashan Station), accounting for 62.8% of the total sediment transport at hua county Station, while the basin area only accounts for 40.6% of hua county Station. The sediment from the upper reaches of Weihe River is 200 million tons per year at Linjiacun Station, accounting for 40.6% of the annual sediment discharge at hua county Station, while the basin area only accounts for 28.8% of that at hua county Station. The south bank of Weihe River is a rocky mountain area in Qinling Mountains, with good vegetation and little river sediment concentration, generally below 1.0 kg/m3. The average annual sediment transport modulus is generally several hundred tons per square kilometer. Bahe River crosses the loess area. The sediment concentration at Maduwang Station is 5.6 kg/m3, and the annual sediment transport modulus is 2 1 10 ton /km2.

The sediment concentration in the main stream of Weihe River gradually decreased from Linjiacun (63.7 kg/m3) and Weijiabao (43.9 kg/m3) to Xianyang (3 1. 1kg/m3). The reasons are as follows: firstly, after Weihe River left Baoji Gorge and entered Guanzhong Plain, the river valley suddenly widened, the river bed gradient was greatly reduced, the sediment carrying capacity of water flow was reduced, and the sediment brought by the upstream was deposited in the river course, which naturally reduced the river sediment concentration; Secondly, the tributaries on both sides of the river have small sediment concentration, while the tributaries on the north bank, Heqian River and Qishui River, with large sediment concentration are only10 ~1kg/m3, which reduces the sediment concentration. There is also Baojixia irrigation area, which brings some sediment into the irrigation area to reduce the sediment concentration. The sediment concentration of rivers below Xianyang increased sharply, reaching 55 kg/m3 at Lintong Station and 49.3 kg/m3 at hua county Station, mainly due to the large amount of sediment brought by Jinghe River, and the sediment concentration at Zhangjiashan Station of Jinghe River was as high as 148kg/m3. We often use distinct idioms, meaning that the Jinghe River is clear and the Weihe River is turbid, but it has become turbid and the Weihe River is clear. The sediment input into the middle and lower reaches of Weihe River and its tributaries is much larger than that transported to the Yellow River through hua county Station, that is, a large amount of sediment is still deposited in the middle and lower reaches of the river every year, mainly because Sanmenxia Reservoir has increased the base point of river erosion.

The rainfall in the middle and lower reaches of Weihe River is concentrated in July, August and September, with more storms and floods. According to the measured data, the maximum flood of Weihe River is at 1954, the maximum flood peak discharge of Linjiacun Hydrological Station is 5030m3/s (1954 August 17) and the maximum flood peak discharge of Xianyang Station is 7220m3/s (1954 August/kloc). The tributary Qingjiang River once had a flood peak flow of 504 m3/s (Yimen Town 1964), He Qian Fengjiashan1954 August 17, with a flood peak flow of 3960 m3/s, Stone River Xieyuguan 1964, Heihe Black. According to historical records, there were 22 floods in Baoji section of Weihe River from 1200 to 198 1 * *, with an average return period of 35.5 years. The flood years include two years of Qing Xianfeng (1852) and six years of Tongzhi (18). Flood disasters in this area are often caused by continuous rainfall. 1949 has 1700 ~ 14 floods, and there are 10 floods with rainfall conditions, including 5 floods (18 1 1,/kloc-0) Because the banks of Weihe River are low, ordinary floods can flood farmland. The riverbed fluctuates. According to the survey, during the 64 years from 1898 to 1962, there have been seven major changes, with the maximum fluctuation exceeding 5 kilometers. Thirty years in Henan and thirty years in Hebei? Said. 1933,497,400 mu of beaches and fertile fields were flooded, and 18 1 village was damaged. 1954, the flood flooded a total area of 363,200 mu and washed away 79 villages.

198 1 in August, Baoji city suffered a severe flood, and He Qian, Qingjiang, Shitou, Tangyu and Tongguan rivers all exceeded the maximum flood peak discharge recorded. According to statistics, the average flow of Weijiabao, the main stream of Weihe River, since August is 6217 ~ 21~ 2,540m3/s, and the maximum daily flood volume is 2190,000m3, which is 0.74 times of the maximum daily flood volume, and the maximum daily flood volume is 500 million m3. There were five flood peaks in Yimen Town Station of Qingjiang River 15 ~ 2 1 7 days. The maximum flood volume per day was189,000 cubic meters, which was 0.93 times of the maximum flood volume per day over the years, and the maximum flood volume on three days was 51100,000 cubic meters, which was the highest on three days over the years. Due to the regulation of the reservoir, a flood disaster was avoided. Duanjiaxia Reservoir in the upper reaches of He Qian reduced the peak flow of Heqian River from 436 cubic meters per second to 36 cubic meters per second, thus protecting Longxian County. The downstream Fengjiashan Reservoir and Wangjiaya Reservoir reduced the peak discharge from 1 170 m3/s to 309 m3/s, and the peak was staggered for 58 hours. The peak flow of Yinggezui Hydrological Station 1360 m3/s in Shitouhe River has been reduced by 2/3 by Shitouhe Reservoir under construction. The flood peak 13 1 m3/s of Qi Hao Station of Qishui River was impounded by Maomaowan Reservoir. Without the flood interception and peak clipping of these reservoirs, the peak flow of Weijiabao Station in the main stream of Weihe River will be 6480 m3/s, which will exceed the peak flow of 5780 m3/s in 54 years, but only 4500 m3/s actually appears.

From July 1983 to July 10, there was continuous rainfall in Guanzhong basin, and a large area of waterlogging occurred. The affected area114.48 million mu, nearly 580,000 houses (kilns) collapsed and more than 600 people died. Destroy all kinds of channels 174 km, and 735 buildings of all kinds. In Xi 'an City, the drainage system is not smooth, the river in the north city overflows, and the cement pavements in the east and west streets sink and break, which leads to the falling of poles, water cut, power cut and production stop in some areas.

According to incomplete statistics, the open water area with the most serious waterlogging disaster is 1635900 mu. Mingshui has two centers in a large area, one is Zhouzhi, Huxian and Xingping; Second, second flower clip groove (flower thread, Hua Yin). As far as its harm is concerned, there are serious waterlogging in Baoji Gorge, Fengjiashan, Jinghui, Luo Hui and Jiaokou pumping irrigation areas in Weibei, with 345,000 mu of open water, accounting for 2 1% of the open water area in Guanzhong area. The waterlogged area with groundwater depth greater than 2m is 22. 12% in Luo Hui irrigation area, 48.25% in Jiaokou drainage area and 4.66% in Jinghui irrigation area. The causes of waterlogging in Guanzhong basin are complex. Geological landform is the topographic basis of waterlogging. Precipitation and irrigation are the main sources of groundwater recharge. Huge continental sediments provide conditions for the infiltration of rivers and precipitation. In rainy years, the groundwater level rises, forming a large area of waterlogging area.

Shaanxi to Linjiacun is the upper reaches, with a river length of 123.4km, a drop of 79 1m and an average gradient of 1.8 1? The upper part of it is mainly the gully region of the loess plateau and the interlaced zone of rivers and canyons; The lower segment is mainly the Qinling Mountains. The river cuts into the bedrock of granodiorite about 200 meters, forming a stone gorge with a width of only 50 to 60 meters. The steep stone wall stands like an arch, and there is Baoji Gorge with a steep mountain slope and a width of 120 meters. Linjiacun to Xianyang is the middle reaches, with a river length of 1, 7 1km, a drainage area of 46,856 km2, a drop of 224.4m, and an average gradient of 1.24? The current is slow and scattered, and there are many shoals in the sandbar. River width 1500m ~ 2000m, including the beach, it can reach 4000m ~ 5000m m. Weijiabao Weihui Quba is more than kilometers below 1 10. The river swings from north to south and changes frequently, and so do the people. Thirty years in Henan and thirty years in Hebei? Folk proverbs. Xianyang to the port is downstream, with a river length of 208 kilometers and a drop of 56 meters, with an average gradient of 0.28? Xianyang-Jinghekou section is a wandering tributary, and the main channel is relatively stable. From Jinghekou to Luohe estuary, the right bank is relatively fixed and the left bank collapses seriously. The Three Wonders Monument in Tang Dynasty is 7.5 kilometers away from Weihe River, and now it is only 100 meters away from the river bank. The width of the river below Beiluo estuary is 3000 ~15000m. Because of the top support of the Yellow River, it is easy to flow backwards. After the completion of Sanmenxia Reservoir, the riverbed siltation above the Weihe River estuary rose by more than 5 meters, and the Tongguan River estuary formed bar sand, which became a worry of flood control.

The Weihe River in Guanzhong was formed in the early Pleistocene, about 2 million years ago. Traces of human activities in the basin have reached more than 800- 1 10,000 years, including Lantian ape-man site 800,000 years ago, Dali ape-man site 0/50,000 years ago, Banpo site of matriarchal clan commune 67,000 years ago, and a large number of Yangshao culture and Longshan culture sites. Guanzhong is also the foundation of the national unity of the Chinese nation, and it is the place where the ancestor of mankind, Emperor Yanhuang, led his ancestors to fight in farming and textile. More than 10 dynasties, including Zhou, Qin, Han and Tang dynasties, established their capitals here for more than 1,000 years, making China one of the four ancient civilizations in the world.