## 2 Study Area  
### Project Overview  
Shaanxi province in China straddles the Yellow River and the Yangtze River. The North of Qinling Mountains is the Yellow River and the South is the Yangtze River. The Hanjiang River, the largest tributary of the Yangtze River, originates from the south of Qinling Mountains in Shaanxi Province, flows through Shaanxi and Hubei provinces and flows into the Yangtze River in Wuhan City, with a total length of 1577 km and a drainage area of 159,000 km\({}^{2}\). The annual average rainfall of the basin is 600-1300 mm, the annual average runoff is about 60 billion m\({}^{3}\) and the total water resources are abundant. The Weihe River, the largest tributary of the Yellow River, originates in Weiyuan County, Gansu province, flowing through Gansu, Ningxia and Shaanxi provinces, and flows into the Yellow River in Tongguan. The total length of the Weihe River is 818 km, of which the length in Shaanxi is 502 km. The total area of the basin is 135,000 km\({}^{2}\), of which the area in Shaanxi is 67,100 km\({}^{2}\). The Weihe River is located in arid and semi-arid areas of China, the total amount of water resources is scarce. However, the population of the region is dense, and the economy is developed. To meet the water demand for life and production, the water diversion along the Weihe River is increasing, resulting in the contradiction between supply and demand of water resources.  
The Hanjiang-to-Weihe River water diversion project is a cross-basin water diversion project in Shaanxi province. The water quantity of Hanjiang River is transferred to the Weihe River in Guanzhong area through the super-long water-conveyance tunnel through Qinling Mountains, which is an important engineering measure to alleviate the water shortage problems in cities and industries along the Weihe River in Guanzhong area. The Hanjiang-to-Weihe River water diversion project includes the Huangjinxia Reservoir and the Sanhekou reservoir. The Huangjinxia Reservoir is the main water source of the water diversion project, which is responsible for alleviating the water shortage in the Weihe River, improving the ecological environment in the middle and lower reaches of the Weihe River, and supporting the economic and social development of the Guanzhong Plain.  
This paper took the Huangjinxia Reservoir as the research object. The reservoir is located in the upper reaches of the Hanjiang River, as shown in Figure 1. The main characteristic parameters are shown in Table 1. After the impoundment of the HuangjinxiaReservoir, the water is extracted from the reservoir by the Huangjinxia pump station to supply water for the Weihe River. The Huangjinxia Reservoir is a typical multi-objective reservoir, which not only undertakes the water diversion task, but also takes into account the power generation and the ecological water demand of the downstream river. The operation period of the reservoir is from July to June the next year. According to the water diversion plan, the short-term water diversion in 2025 is 1 billion m\({}^{3}\) and the long-term water diversion in 2030 is 1.5 billion m\({}^{3}\). This paper only discusses the scenario of water diversion of 1.5 billion m\({}^{3}\) in 2030.