Hydrological characteristics of Haihe River
The Haihe River Basin is located in the warm temperate continental monsoon zone, with cold and dry winters and hot and rainy summers. Most precipitation falls in the form of heavy rains. The annual precipitation is often the result of several heavy rains. The water volume of the main branches of the Haihe River is mainly based on rainfall recharge (the water volume recharged by rainfall accounts for more than 80% of the annual runoff), so the spatiotemporal changes in annual runoff are basically consistent with the annual precipitation change trend.
Rivers in the northern region, such as the Chaobai River and Yongding River, are also supplied with seasonal snowmelt water, causing less obvious spring floods.
In addition to being recharged by rainfall and melting snow, the Haihe River is also recharged by groundwater. Rivers flowing through Taihang Mountains and Yanshan Districts. Groundwater mostly recharges rivers in the form of spring water. For example, the Jianghutuo River, Fuyang River, Zhangwei River, etc. all receive spring water recharge. The amount of groundwater recharge generally accounts for about 8 to 10%, but some river sections have abundant underground runoff, which can reach 40%. Only 5 to 6% have low underground runoff. Rivers flowing through plain areas, such as the main stream of the Hai River and the middle and lower reaches of the five major tributaries, most of the river channels have not been cut down to the water level. During flood periods, the water level is often higher than the ground on both banks, or there are very few rivers that feed the river (accounting for less than 6% of the annual runoff), or The river cannot be recharged. The Haihe River basin spans four provinces (Hebei, Shanxi, Shandong, and Henan), the first region (Inner Mongolia), and the second city (Beijing, Tianjin), with a total drainage area of 263,600 square kilometers. The annual runoff is 22.8 billion cubic meters. The basin area is 125,700 square kilometers in Hebei Province. The annual runoff is 10.63 billion cubic meters, including 7.66 billion cubic meters in mountainous areas and 2.97 billion cubic meters in plain areas.
Regional distribution of runoff
The regional distribution of annual runoff in the Haihe River is basically consistent with annual precipitation. On the windward slopes of Taihang Mountain and Yanshan Mountain, there is a high-value zone with runoff depth greater than 150 mm consistent with the arc-shaped trend of the mountains. The distribution range of the high-value area is basically consistent with the rainy belt with an isohyet line of average annual precipitation of 600 mm for many years. In the high-value runoff area, several high-value centers are formed due to the influence of local landforms and water vapor transport direction. For example, Dalianggang in Yi County, Manshan in Lingshou County and Chanfang in Shahe County are all high-value centers.
The annual precipitation in these high-value centers is 750 to 800 mm, and the average multi-year runoff depth is 300 to 350 mm. Among them, the Manshan area upstream of Cihe Hengshanling Reservoir is the highest, with annual runoff as deep as 400 mm. It gradually decreases from both sides of the high value zone to the northwest and southeast respectively. To the northwest, the annual runoff depth drops to less than 50 mm in the upper reaches of Sanggan River and Yanghe River, with the minimum being only 25 mm. To the southeast is the Hebei Plain, with two low-value centers, one in Shilipu in the east of Dingxing County, and one around Jixian, Nangong, Hengshui, and Shulu. The annual runoff depth is below 25 mm, with the minimum being only 10 mm. The annual runoff depth in the remaining areas is mostly between 50 and 150 mm.
The rivers flowing through the Taihang Mountains and piedmont alluvial fans have developed karst landforms due to the abundance of Ordovician limestone in the basin. When the watershed is not closed (that is, the above-ground and underground water lines are inconsistent), the distribution of annual runoff often appears abnormal. For example, the Linmingguan and Hancun stations of the Fuyang River have serious water leaks, with annual runoff of only 59.1 mm. However, the Dongwushi Reservoir Station in the adjacent basin has a large amount of groundwater recharge from the outer basin, and the annual runoff depth is as high as 1225.7 mm. It is more than double the annual average precipitation, and the recharge water from the outer basin accounts for 9 times the self-produced water.
Interannual changes in runoff
For tributaries with a small catchment area in the Haihe River Basin, the interannual changes in runoff are similar to the interannual changes in precipitation. The difference is the change in specific precipitation. are more severe and the differences between regions are greater. For tributaries with larger catchment areas, the interannual changes in runoff are more complicated due to the influence of the climate zone, underlying surface and catchment area.
The Jundu Mountains, Taihang Mountains and piedmont slopes are areas with high interannual variability in annual precipitation and runoff in the Haihe River Basin. The coefficient of variation of annual precipitation is 0.40~0.50, while the coefficient of variation of annual runoff is 0.80~1.00. The ratio of the maximum annual runoff value to the minimum value is 10~25. The area north of Jundu Mountain and west of Taihang Mountain is an area with low interannual changes in annual precipitation and annual runoff. The coefficient of variation of annual precipitation is 0.25~0.35, and the coefficient of variation of annual runoff is 0.40~0.60. The ratio of the maximum and minimum annual runoff is 3 to 5. The vast plain area south of Yanshan Mountain and east of Taihang Mountain is the area with the second highest interannual variation in rainfall
in the Haihe River Basin, but the interannual variation in runoff is the highest in the Haihe River Basin, with the annual precipitation variation coefficient is 0.35~0.45, and the annual runoff variation coefficient is 1.0~1.5.
The reason for this phenomenon is that the plains are low and flat and the soil is deep. In normal and dry years, there is a lot of evaporation and leakage, making it difficult to generate runoff, but in wet years, the water production is large.
In the southern section of the Dahang Mountains, karst is developed, and there are two abnormal situations in the interannual changes in runoff. One is a leaky area. The coefficient of variation is as high as 1.50~1.75, and the ratio between the maximum and minimum annual runoff can be 70~80 times. Such as Cuiyang River Linmingguan Station. The other type is a river fed by spring water. The interannual variation in runoff is very small, with a coefficient of variation of only 0.20~0.30. The ratio between the maximum and minimum annual runoff is generally only 3 times, such as at Fuyang Hedong Wushi and Yehe Didu stations.
The flood years appear in different years for each tributary of the Haihe River. The chance of simultaneous floods in the entire basin is small. Generally, when the southern tributaries are in wet years, the northern tributaries are in normal water years. On the contrary, when the northern river systems are in wet years, the southern tributaries are in normal years. For example, in 1963, there was a flood in the southern system, while in the northern system, except for the Beiyun River, it was a normal year.
The dry years of each tributary occur in relatively consistent years. Since the 6th year of the Republic of China (1917 AD), the Haihe River Basin has experienced 11 special dry years with a variability of less than 0.4 and dry years with a variability of 0.4 to 0.6. Among them, the 9th and 19th years of the Republic of China (1920 AD) , 1930), the entire basin was extremely dry. In the 20th and 25th years of the Republic of China (1931 and 1936 AD), the entire basin was dry. In 1965 and 1968, the entire basin was dry. In the 30th year of the Republic of China (1941 AD), the southern system was extremely dry. The northern system is dry. In the 34th year of the Republic of China (1945 AD), 1972, and the 16th year of the Republic of China (1927 AD), the entire river basin was dry, and only 1 to 2 river systems were estimated to be extremely dry. In 1951, the northern system was dry, the southern system was dry, and 1 to 2 tributaries were extremely dry.
Runoff distribution within the year
The distribution of runoff within the Haihe River trunk and tributaries within the year is mainly restricted by the distribution of precipitation within the year. The general feature is that the distribution of runoff within the year is relatively concentrated, with 50-80% of the annual water volume concentrated. Within four months from July to October (flood season), the concentration of runoff in each river during the year is different due to differences in runoff recharge forms, basin regulation and storage capabilities, and climate zones.
The Jiyun, Daqing, and Fuyang rivers originating from the southern foothills of Yanshan Mountain and the eastern foothills of Taihang Mountain have relatively small watershed regulation and storage capacity. The water volume is highly concentrated, with the water volume in the flood season accounting for approximately 70% to 80% of the annual water volume.
Rivers originating from the Loess Plateau and basin areas, with their middle reaches passing through mountains, with large drainage areas and a considerable proportion of spring water supply, such as Yongding River, Hutuo River, Zhang River, Wei River, etc. The water volume during the flood season generally accounts for 50% to 60% of the annual water volume.
Most of the rivers in plain areas and areas with serious water leakage in the piedmont are intermittent rivers. There is water in the flood season and dry up in the non-flood season. The amount of water is often several times (even one or two) throughout the year. The result of heavy rain.
Some river sections that are mainly supplied by spring water, such as Sanggan River Mayi, Mianhe Didu, and Fuyang Hedong Wushi Reservoir, have a relatively even distribution of runoff throughout the year. The water volume in the flood season generally accounts for 40% of the annual water volume. % or less. The sediment content of the main branches of the Haihe River is second only to the Yellow River among the major rivers in the country. Due to the different natural and geographical conditions of the areas where each tributary flows, the sediment content varies.
The tributaries originating from the Shanxi Plateau, such as the Yongding River, Hutuo River, Zhang River, etc., have widespread loess distribution in the basin. In addition, the vegetation coverage is small, soil erosion is serious, and the river sediment content is high. The Yongding River is the river with the largest sediment content among the tributaries of the Hai River. The multi-year average sediment content at the Guanting Station of the Yongding River is 52.2 kg/cubic meter, the upper source Sanggan River Shixiali Station is 25.0 kg/cubic meter, and the Yanghe Xiangshuibao Station Station is 21.0 kg/m3, and the erosion modulus of the upper reaches of the Yongding River is 1000~2000 tons/km2·year.
Most of the main branches and tributaries of the Hutuo River flow through the Loess Plateau and Taihang Mountains. The sand content is second only to the Yongding River. The average sand content at Xiaojue Station for many years is 13.9 kg/cubic meter, and the erosion modulus is 900~1000 tons. /km²·year.
Once again, it is the Zhanghe River that originates from the South Canal. The multi-year average sand content at Guantai Station is 9.07 kg/m3, and the erosion modulus is 700~800 tons/km²·year.
Rivers originating from the Yanshan and Taihang Mountains have rocky mountains in the basin, less loess material, and lighter water and soil erosion than the Loess Plateau. The multi-year average sand content at the Zijinguan Station of the Juma River, a tributary of the Daqing River, is 2.92 kg/m3.
Daqing River Xingaifang Station is 1.4 kg/cubic meter, Chaobai River Suzhuang Station is 4.14 kg/cubic meter, and Beiyun Yun Qujia Station is 2.54 kg/cubic meter. The sand content in the Haihe River Basin is relatively small.
The distribution of sediment in each tributary of the Haihe River within the year is highly concentrated. The sediment transport volume of each river from June to September accounts for more than 94% of the annual sediment transport volume, and the sediment transport volume in other months is very small. The interannual variation of sediment is great. The ratio of the maximum annual average sediment content to the minimum annual average sediment content of each river is generally more than 10 to 20 times, and the highest can be more than 45 times. The multi-year average water temperature in the main branches and tributaries of the Haihe River is mostly 11~15℃. Because the basin spans large latitudes, the water temperature of the rivers in the north and south is different. The upper reaches of the Chaobai River and Yongding River flowing through the mountainous area in the northern part of the basin are 11~12℃, and the Nanyun River flowing in the south of the basin is 14~15℃. The water temperature is the lowest in January at 0.1~2.5℃ throughout the year. Chaobai River and Yongding River are 0.1~0.9%℃, and Nanyun River is 2.0~2.5℃. The water temperature is the highest in July, ranging from 42 to 27°C. The northern rivers are 24 to 26°C, and the southern rivers are 25 to 27°C. Only a few rivers are lower than 24°C. The highest water temperature in the past years can reach 31~36℃, and the lowest water temperature in the past years is 0℃.
All tributaries of Haihe River are generally frozen in winter. The average first ice date is from late November to mid-December, and the last ice date is mid-to-late March. Only Ziya River and Nanyun River can be earlier than late February. The ice age lasts from three months to three and a half months. The average freezing date is mostly in mid-to-late December, the thawing date is in mid-to-early March, and the average freezing days are 50 to 80 days. In 2002, the wastewater discharge in the entire basin was 5.36 billion tons, of which industrial sewage discharge accounted for 60% and urban domestic sewage discharge accounted for 40%. The water quality evaluation results of the 7151 kilometers of rivers in the entire basin are as follows: 21% of the river lengths are in Class I and II water quality, 22% are in Class III water quality, 10% are in Class IV and V water quality, and 10% are in Class IV and beyond Class V water quality. Accounted for 47%. The length of polluted rivers in the entire basin (water quality worse than Class III water) reaches 4,083 kilometers, accounting for 57% of the evaluated river lengths, and the water bodies are seriously polluted.