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Longpan HPP is located at the upper Tiger Leaping Gorge on the middle reaches of the Jinsha River. The dam site lies 4km downstream of the upper narrow of Tiger Leaping Gorge, with Shangri-la County of Diqing Tibetan Autonomous Prefecture in Yunnan Province on the left bank and Yulong County of Lijiang City on the right bank. The proposed installed capacity of the project is 4200MW.
The purposes for the development are power generation, water supply, flood control, ecological environmental protection, tourism, navigation and other comprehensive utilization benefits, and project would play significant role in water storage, energy storage and water resources regulation.
Longpan HPP would be able to bring about huge comprehensive benefits in power generation, water supply, flood control, and water resources allocation. Its key technical difficulties are mainly in aspects of high earthquake intensity, high slope and high geo-stress that are commonly confronted in the hydropower development in Southwest China. In addition, social concerns such as resettlement and environmental protection need to be addressed properly.
The first is the anti-seismic safety analysis and seismic design of its arch dam. Longpan HPP would be situated in Southeast China featuring in dense active faults and frequent strong earthquakes. As determined by he Institute of Geology under China Earthquake Administration, the basic seismic intensity of the project area is 8, corresponding to bedrock peak horizontal acceleration of 0.408g at exceeding probability of 2% in 100-year design reference period. Seismic effect is the control factor in the dam design because of the high dam, large reservoir and high seismic intensity. The safety of the dam in case of violent earthquake is extremely important and requires in-depth study.
The second is the abutment stability analysis under high seismic intensity. The rock mass stability for abutment of high arch dam is critical to dam safety in areas with high seismic intensity. Moreover, the dynamic coupling of dam body and abutment rock mass is considered to evaluate the anti-sliding stability agreeing better with the reality.
The third is the study of flood discharge and energy dissipation mode. Longpan Project is characterized by high dam, large discharge flow, high head, large flood discharge power, and narrow river course owing to the project location of high-mountain and gorge area, the main technical difficulty in flood discharge and energy dissipation is to selec_t optimum flood discharge structure layout scheme and energy dissipater type so as to lessen the scouring of river bed and high slopes on both banks by outflow and mitigate the impact of atomization of released flood on high slopes and landscape of the gorge.
The fourth is the surrounding rock stability analysis for the underground cavern group in high seismic intensity zone. The basic seismic intensity of the project area is 8, and the powerhouse and main transformer cavern would be huge, so it’s required to study the geological conditions and surrounding rock structural features and quality of the cavern group, analyze the cavern block stability and surrounding rock stability against deformation, evaluate the cavern group surrounding rock stability against earthquake, and propose corresponding countermeasures.
The fifth is the high slope stability analysis. After abutment excavation, a 400m-500m-high slope would be created at the arch dam site, and other high slopes would be created due to the excavation of other structures, so the high slope stability is a key issue in the project development.
The sixth is the study of general construction layout and landscape protection of Tiger Leaping Gorge during the construction period. The dam site is to be located at the entrance of the Upper Tiger Leaping Gorge and would impact the natural landscape of the gorge to a certain extent. In order to minimize the adverse impact of the project development, the general construction layout should meet not only the requirements of construction, but also the requirements of environmental and landscape protection.
The seventh is the analysis of compensation benefit and economic benefit to the lower cascade developments of Longpan backbone reservoir. Longpan HPP would bring about enormous compensation benefit to the lower cascade developments, and the magnitude of benefit directly relates to the reservoir operation mode. The lower cascade power stations are characterized by large scale and extensive distribution, and they belong to various power systems and differ greatly in system characteristics and economic index, so the calculation and analysis of cascade compensation benefit, especially how to reflect this benefit, is a complicated issue with regard to economic index and needs special study.
The eighth is the flood control study for Longpan reservoir. According to the Flood Control Plan for the Yangtze River Basin, the reservoir should have a certain capacity for flood control and play a certain role in flood control.
The ninth is the forestry and fruit industry development plan for Longpan reservoir area. Because of the large absolute quantity of relocatees (most of them are ethnic minorities) and limited local land resources, the resettlement would be difficult. The Long-Acting Compensation Mechanism proposed by Yunnan People’s Government offers a good solution to this problem. To develop the competitive industries in the reservoir area such as forestry and fruit industry is important to resettlement program. Therefore, it’s necessary to carry out study of forestry and fruit industry planning for the reservoir area.
The tenth is the study of impact of climatic effect of Longpan reservoir on glaciers and snow line of Jade Dragon Snow Mountain. Longpan reservoir would extend 265km long and have a total storage of 38.6 billion m3. The impact of its local climatic effect on glaciers and snow line of Jade Dragon Snow Mountain is an environmental issue with high social certain and requires in-depth study.