Hydrological characteristics of Beiluo River

The average annual runoff of Beiluo River is 943 million cubic meters, and that of Shaanxi Province is 873 million cubic meters. The bamboo shoot forest in the middle reaches and tributaries of Hulu River has good vegetation and low annual runoff coefficient. The runoff depth is less than 30 mm (Jiaokou River is 29.6 mm, Zhang Cun Gang is 23.5 mm), and the runoff depth and runoff coefficient are both smaller than the upstream and downstream of Beiluo River. The runoff of Beiluohe River basin changes greatly during the year. According to the variation coefficient of annual runoff, it can be divided into three areas: Luochuan plain and its southern main stream and downstream plain areas, with flat ground and small annual runoff variation, with variation coefficient of 0.40 ~ 0.42; In the middle and upper reaches of the loess hilly and gully region above Fuxian County, the annual runoff changes greatly, and the coefficient of variation is 0.46 ~ 0.47. The annual runoff variation in Ziwuling forest areas such as Hulu River and Zhoushui River Basin is the largest, with the coefficient of variation as high as 0.64 ~ 0.65.

The annual runoff distribution in Beiluohe River basin is very uneven, and the degree of unevenness decreases from upstream to downstream. In Jinfoping in the upper reaches of the river, the runoff is the largest in summer, accounting for 66.8% of the annual runoff from June to August, the smallest in winter (accounting for 3.8%), and slightly larger in spring (16. 1%) than in autumn (13.3%). The maximum monthly runoff (29.5%) is equal to the sum of spring and autumn runoff, while the minimum monthly runoff is only 0.7%. From upstream to downstream, the proportion of runoff in summer gradually decreases, and runoff in spring, autumn and winter gradually increases; The maximum monthly runoff gradually decreases and the minimum monthly runoff gradually increases; The maximum monthly runoff occurs in August, and the minimum monthly runoff occurs in 65438+ 10. The tributaries Hulu River and Qushui River, due to the role of forests, reduce the flood runoff, increase the low-flow runoff, and distribute the runoff fairly evenly during the year. For example, the runoff of Zhang Cun Station is the largest in autumn, accounting for 37. 1%, slightly larger in summer, and as high as 12.5% in winter, which is close to the spring runoff of Jinfoping Station in the upstream, equivalent to more than three times the winter runoff of Jinfoping Station. The maximum monthly runoff (16.2%) is more than twice that of the upstream tributary Zhoushui Zhidan Station (39.7%), and it is also smaller than the main stream, and its occurrence time is delayed until September. The proportion of the minimum monthly runoff is larger than that of the main stream, which is 7 times that of Zhidan Station, a tributary, and occurs in 65438+ 10. Beiluohe River is a river with heavy sediment, with an annual sediment transport capacity of 95.9 million tons, accounting for 12. 1% of the annual sediment transport capacity of the Yellow River in Shaanxi Province, and 1.5 times of the annual sediment transport capacity of the Yangtze River. Among them, the annual sediment discharge of Liu Jiahe Hydrological Station is 8,765,438+10,000 tons, accounting for 90. 1% of the total sediment discharge in the whole basin. River sediment concentration is generally above 100kg/m3, with a maximum of 440 kg/m3 and an annual sediment transport modulus of 17600 tons /km2. The sediment concentration and sediment transport modulus decrease from upstream to downstream, indicating that the basin above Liu Jiahe River and its surrounding basins are the main sources of sediment in Beiluo River.

The distribution of sediment discharge is extremely uneven during the year, and it is highly concentrated in rainy season and flood season. June, July and August account for 93% ~ 97% of the annual sediment discharge. The soil erosion of Hulu River is slight, and the sediment concentration of the river is very small. Zhang Cun station is only 15.9kg/m3, and the sediment transport modulus is 40 1 ton /km2. The annual distribution of sediment is not as concentrated as the main stream, accounting for only 72.8% in June, July and August, because the vegetation is better.

There are many flood disasters in Beiluo River Basin. Due to the deep gully in the upper reaches, the river bed gradient is large, the flood hydrograph is sharp and the peak height is large. For example, the measured maximum peak discharge of Jinfoping is 5920 cubic meters per second, and that of Liu Jiahe is 6430 cubic meters per second. The valley in the middle and lower reaches is relatively wide, the river slope is gentler than that in the upper reaches, the flood fluctuation intensity is reduced, and the peak flow is also reduced. The peak flow of Jiaokouhe Station is 3880 cubic meters per second. The first stop is 4420 cubic meters per second. The area of Hulu River Zhang Cun Station in the upper reaches of Luohe River is more than 900 square kilometers larger than that of Jinfoping, but the measured peak discharge is much smaller than that of Jinfoping. 1On July 6th, 977, a big flood occurred in Beiluo River Basin, and the flood peak discharge at Zhang Cun Station (466 m3/s) was more than ten times smaller than that at Liu Jiahe Station (6430 m3/s), which was also related to the good vegetation in Hulu River Basin. According to the historical flood investigation data, a serious flood occurred in Beiluo River on 1855, and its peak discharge was much larger than the measured flood, and the first station was 2.4 times larger than the measured maximum flood.