Hydrological characteristics of the Luanhe River

According to the statistics of Luanhe River annual runoff data from the 18th year of the Republic of China (1929 AD) to 1984, the total multi-year average annual runoff of the Luanhe River is 4.61 billion cubic meters, and the maximum annual runoff is 12.9 billion cubic meters. , appeared in 1959, the minimum annual runoff was 1.27 billion cubic meters, appeared in 1981, the annual runoff with a frequency of 20% was 6.37 billion cubic meters, and the annual runoff with a prediction rate of 50% was 3.99 billion cubic meters, The annual runoff at 75% frequency is 2.69 billion cubic meters, and the annual runoff at 95% frequency is 1.58 billion cubic meters.

The Luanhe River Basin has a typical temperate, warm temperate, semi-humid and semi-arid continental monsoon climate. In winter, under the control of Mongolian high pressure and the influence of westerly wind troughs at high altitudes, the climate is cold and dry. Precipitation is minimal. Summer is controlled by the North Pacific subtropical high and is hot and rainy. The main weather system that causes rainfall is the polar front, but westerly troughs, shear lines, northwest vortices, southwest vortices, typhoons, etc. can all cause precipitation. If two or more weather systems cooperate with each other and the water vapor is abundant, heavy rains with heavy rainfall, long duration, and wide rain areas can often form. Spring is basically still controlled by the winter circulation system, with less precipitation and more wind and sand. Coupled with the rapid rise in temperature, spring drought often occurs. In autumn, the North Pacific subtropical high retreats quickly. Except for the cloudy and rainy weather during the retreat, autumn weather is generally warm and crisp. Precipitation is mainly concentrated from June to September. Especially in the two months of July and September, precipitation throughout the year is often concentrated in a few heavy rains.

The runoff of the Luanhe River varies greatly between years. The annual runoff variation coefficient is mostly 0.5-0.8, and the ratio of the maximum annual runoff to the minimum annual runoff is about 8 times, and even reaches more than 10 times in some stations. The tributaries of Xingzhou River, Yisun River, Yimatu River, Wulie River, Buhe River, and Xun River are all more than 10 times higher. Only river source tributaries such as the Daluan River, Tuligan River, and Xiaoluan River have smaller interannual changes in runoff. The annual runoff variation coefficient is 0.3-0.5, and the extreme value ratio is 3-5 times. The Luanhe River not only has large fluctuations in water volume, but also often has continuous high or low water levels.

The runoff of the Luanhe River mainly comes from rainfall. Therefore, the annual distribution of runoff is very consistent with the annual distribution of precipitation. The flood season lasts from the end of June to the beginning of September, with the largest flood peak occurring in July and August. There is very little water in winter and spring. From March to April, there are often minor spring floods due to melting ice and snow. In May and June, short-lasting dry spells occur due to early dryness. Although they do not last long, the flow rate is often lower than the dry season in winter and is the minimum in the whole year. Mountainous areas in the Luanhe River Basin account for more than 90%, and most of them are rocky mountains with well-preserved vegetation (vegetation coverage is 30-60%). The sediment content of each river is relatively small among the rivers in Hebei Province. The upper reaches of the trunk and tributaries including the Lightning River, Daluan River, Xiaoluan River and other rivers have a sediment content of 1-2 kg/cubic meter. The tributaries in the middle reaches below Zhangbaiwan, including the Yisun River, Wulie River, Changhe River and other basins, have a large amount of loess distribution. Coupled with unreasonable human reclamation, soil erosion has been aggravated and the sediment content of the rivers has increased. The sediment content at Yison River Weichang Station, Bucheng River Branch Qianqianshan Station and Yimatu Hexiahenan Station, a tributary of the Yisun River, are all above 20 kg/cubic meter, making them one of the main sources of sediment in the Luan River. Other tributaries are old The sediment content in Niu River, Pu River, and Xun River is slightly smaller, generally 3-4 kg/cubic meter, while the sediment content in Qinglong River is only 2-3 kg/cubic meter. The sediment content at Taolinkou Station is 2.88 kg/cubic meter, which is one of the tributaries of the Luanhe River with a small sediment content. The Luanhe River flows out of Yanshan and reaches Luanxian Station with a sediment content of 4.76 kg/cubic meter. Below Luanxian County, it flows into the plain, and the sand settles slowly, and the sand content decreases. However, because the downstream river channel is very short, it quickly reaches the mouth of the sea, and sediment accumulates at the mouth of the river, forming the Luanhe River Delta.

The sediment transport volume of the Luanhe River is smaller than that of the Haihe River. The average annual sediment transport volume of Luanxian County Station for many years is 22.7 million tons. However, the amount of sediment transported varies greatly from year to year. The maximum annual sediment load of Luanxian Station was 87.9 million tons (1959), and the minimum value was 2.35 million tons (1951). The maximum value is 37 times the minimum value.

The amount of sediment transported by each river is very unevenly distributed within the year. About 90% is concentrated in the flood season (June-September), especially in July and August, when the amount of sediment is the largest. The amount of sand is very small in the months outside the flood season, especially in winter and spring during the dry season. Some river sections are close to zero.