Water conservancy and hydrology departments, journals, documents, etc. In addition, the changes are relatively large, see below;
Analysis and calculation of runoff 1. Analysis of runoff Runoff analysis is an important part of studying regional hydrological laws and regional water resources evaluation and calculation. Since the founding of New China, the frequency analysis method has been mainly used to analyze and calculate annual runoff. The "Practical Hydrology Manual of Hebei Province" compiled in 1958 and the "Surface Water Resources of Hebei Province" compiled in 1984 both list important single-station annual runoff characteristic values, and draw the annual runoff depth mean and variation coefficient isolines. picture. The regional distribution pattern of annual runoff depth in Hebei Province is basically consistent with annual precipitation, showing zonal differences. On the windward slopes of Taihang Mountain and Yanshan Mountain, there is a high-value zone with a runoff depth greater than 150 mm that is consistent with the arc of the mountain. There are a series of high-value zones such as Chanfang, Manshan, Dalianggang, Xinli Village, and Zhucaoying. In the center, the annual runoff is 300-350 mm deep. The Manshan area upstream of Cihe Hengshanling Reservoir is the highest. On both sides of the high-value zone, the annual runoff depth gradually decreases toward the northwest and southeast respectively, and the inland river basin of Zhangjiakou is the low-value zone. There are two low-value areas in the plain area, one in Shilipu in the east of Dingxing County, and one around Jizhou and Nangong, with runoff depths below 25 mm. The runoff depth in the remaining areas is mostly between 50 and 150 mm. In mountainous areas with karst development and piedmont alluvial fan areas, abnormal annual runoff often occurs because the watershed is not closed. Fuyang River Linxu Mingguan Station has very little annual runoff due to serious water leakage. The Dongwushi Reservoir Station in the adjacent basin has groundwater recharge from the outer basin, so the annual runoff depth is more than twice the annual precipitation. The characteristics of runoff distribution within the year are very similar to the pattern of precipitation changes within the year. 50-80% of the annual water production is concentrated in the flood season from June to September. However, due to the differences in the recharge form of each river's runoff and the regulation and storage capacity of the basin, the concentration of water in each river is different. The multi-year variation pattern of runoff is not only affected by the multi-year variation pattern of precipitation, but also affected by underlying surface factors. Therefore, the disparity in multi-year changes is more severe than that in precipitation, and there are also large differences between regions. The coefficient of variation of annual runoff depth is about 0.5 in mountainous areas, 0.6-0.8 in mountainous areas, and above 1.0 in plain areas, with a maximum of 1.8. In order to reduce the influence of non-regional factors on runoff in the annual runoff calculation of small rivers, in the "Hydrological Atlas of Hebei Province" compiled in 1961, the underground runoff in the runoff was separated and the multi-year average surface runoff depth contours were drawn. Figure 1 is the first in China to use surface runoff depth to calculate annual seasonal river runoff, and it also provides a way to estimate groundwater resources in mountainous areas. In the atlas, it is also proposed to use empirical formulas to calculate the coefficient of variation, instead of looking at maps to deduce the coefficient of variation of annual runoff, and achieve better results. In the 1976 "Analysis Report on Annual Runoff in Haihe and Luanhe River Basins", the relationship between annual precipitation and runoff in mountainous areas was analyzed, and Hebei Province was divided into three regions: Bashang, Yanshan, and Taihang Mountains. The region was further divided into leeward area, windward area, and mountainous area. In the front area, the relationship between different annual precipitation and annual runoff depth is given. The annual runoff of medium and small rivers can be calculated based on the relationship line, which is more accurate than directly checking the runoff depth contour map. This method will also be introduced in subsequent hydrological manuals. 2. The impact of human activities on annual runoff Since the late 1950s, Hebei Province has built large-scale water conservancy projects and carried out farmland water conservancy infrastructure. The continuous formation of reservoir water storage and water diversion irrigation projects has had a huge impact on the annual runoff of rivers. Due to man-made regulation such as reservoir leakage, reservoir evaporation, reservoir storage capacity, irrigation water, urban and industrial water, cross-basin water diversion, river flood diversion, etc., the annual runoff of rivers decreases or increases, and changes in natural runoff are expected. According to the law, the annual runoff must be restored and calculated. Through water survey, it has been proved that many rivers have changed the natural situation of river runoff, and the measured data of hydrological stations can no longer reflect the natural laws of runoff above the cross-section. For example, the multi-year average restored water volume at Yanghe Xiangshuibao and Sanggan River Shixiali stations accounts for nearly 50% of the measured water volume. In the 1976 "Hai and Luan River Annual Runoff Analysis Report", the annual runoff series data were restored and calculated item by item for the first time, so that the restored annual runoff series remained consistent and consistent with the data basis for statistical analysis. In the early 1980s, when conducting water resource assessments in Hebei Province, itemized reduction calculations were generally performed on measured annual runoff data affected by human activities. By investigating water consumption and performing reduction calculations, we have also accumulated a lot of experience.
In the "Collection of Papers on Water Resources Assessment" published by the Hydrology Department in 1989, the article "Calculation of annual runoff restoration in northern hilly areas" co-written by Wang Huanbang and He Weicheng is listed as a representative one. Two schools of thought debate whether forests can increase runoff. Based on the comparison of hydrological data between Donggou and Xigou in Chongli County, Zhangjiakou, in the leeward area, and the analysis of hydrological observation data before and after the small watershed treatment at the Liujiaping Station of Liulin River, Pingshan County, in the windward area of ??Taihang Mountains, it has been confirmed that small watersheds dominated by rainfall recharge in mid-latitudes, Creation of forests increases evaporation from the land surface, thereby reducing normal annual runoff. From the perspective of Hebei Province, from the perspective of water balance, the general trend of hydrological effects produced by forests is to reduce annual runoff, which is more obvious in small watersheds. In the early 1990s, through the analysis of the relationship between the annual precipitation and the restored annual runoff in the watersheds of Xiaojue Station, Hengshanling Reservoir Station and other stations in the Haihe River Basin in the windward area of ??the Taihang Mountains, it was found that the restored natural runoff was higher than the same amount of precipitation. Under such circumstances, the annual runoff in the 1980s and 1990s was significantly less than that in the 1950s and 1960s, and the degree of reduction varied in different river basins. With the same annual precipitation of 500 mm, the annual runoff depth above Xiaojue Station is reduced by 21 mm; the southern branch of the Daqing River system is reduced by 45 mm; and the annual runoff depth above Hengshanling Reservoir Station is reduced by 95 mm, equivalent to 30% of the runoff depth produced in the 1950s and 1960s. —40%. The reason is that in addition to the influence of climate factors, large-scale and continuous human activities are the main reasons for the decrease in yield. With the increasing impact of human activities, the trend of natural runoff reduction is still developing. At present, due to technical conditions, only annual runoff calculations have been calculated by item restoration. To truly make the data meet the requirements of identity, the problem of restoration of changes in underlying surface conditions should be considered.