The deformable body of Guobu slope is on the right bank of Laxiwa hydropower station, 0.9~1.7 km upstream the dam. It is an ultra-large granitic rock slope with a volume of 102 million m 3 , affected by various deformation mechanism, mainly toppling deformation, and is classified as Class B Grade I. After the reservoir impoundment in March 2009, obvious deformation of Guobu slope is observed. Hence, scientific research, safety monitoring and risk control measures are carried out, including geological exploration, deformation monitoring, numerical calculations using various methods, and stability analysis. Due to the high deformation rate of Guobu slope in the early stage of reservoir impoundment, the deformable body of Guobu slope was assessed as a major hazard of Grade Ⅱ. In 2018, based on study results, Guobu slope was reclassified as a safety risk of Grade Ⅱ (acceptable risk of Grade Ⅱ). In October 2015, the reservoir water level reached the normal impoundment level of 2 452 m. Long-term monitoring data since then show that the deformation of Guobu slope has slowed down after the reservoir water level stabilized between 2 450 m and 2 452 m. The daily deformation rate by the monitoring point at the maximum deformation decreased to less than 2 mm/d. Currently, the deformable body of Guobu slope is generally stable, and the risk is controllable. This paper introduces the specific measures and achievements in the treatment of the deformable body of Guobu slope of Laxiwa hydropower station, for reference.

This paper presents a compilation of data summaries on dam failures and the life safety consequences from the flooding caused by failures that have occurred in the United States. It has been prepared by the National Performance of Dams Program (NPDP) at the Department of Civil and Environmental Engineering at Stanford University.

Earthquakes, especially strong earthquakes, may easily cause dam accidents. The actual damage of the dam is determined by the earthquake intensity, which is related to the earthquake magnitude, hypocenter depth, geological structure and the distance between the dam and the hypocenter. To realize the graded warning for dams under the condition of earthquake, it is necessary to use the statistical model to quickly calculate the earthquake magnitude at the dam site and compare it with the design standard. By computer programming, the above-mentioned functions can be realized, which can quickly locate the dam that may be damaged by the earthquake and realize rapid early warning for the dam.

This paper provides a systematic summary of the current status and development direction of the standards system, regulatory system, management mode and technology for dam safety of China′s hy⁃ dropower stations. Responsibility shared among power enterprises, government departments and Large Dam Safety Supervision Center is established as the dam safety management mode of China′s hydropow⁃ er stations. China has released 101 effective standards and formulated a system table for dam safety stan⁃ dards. China has established a regulatory system centered around Regulations on the Supervision and Management of Operation Safety of Hydropower Dams. In the future, China will revise regulations, im⁃ prove standards and develop technologies to enhance the emergency response capability, informatiza⁃ tion, intelligence and internationalization level of dam safety, and promote the stable and far- reaching development of dam safety management.

With the development of information technology, the traditional paper-based hydraulic patrol inspection work is gradually transformed into a patrol inspection management system (module). At present, the patrol inspection system still has some problems. For example, the patrol inspection objects are not abstractly classified, the defects are not objectified, and the functions of patrol inspection App are simple. Aiming at the above-mentioned problems, the optimization design scheme is proposed and applied to the patrol inspection module in the dam safety information management system for Yalong river basin. Web terminal and mobile terminal (App) are mainly included in this module and functions such as viewing tasks, patrol inspection, result recording and query, defect tracking and query are available. With the help of information management means, this system can optimize the information management mode of hydraulic patrol inspection and further improve the level of dam safety information management.

There are many cracks in the face slab and toe slab of the lower reservoir of a pumped-storage power station during the construction period. The cracks are mainly deep cracks and seepage cracks, with 1.1~13.2 m in length and 0.03~1.12 mm in width. The cracks on the face slab are basically regular transverse, and the cracks on toe slab are perpendicular to the extension direction of toe slab, with a few inclined cracks, X-shape cracks and Y-shape cracks. The preliminary analysis shows that the cracks are mainly caused by the factors such as drying shrinkage of concrete, thermal deformation, foundation constraint and et al. For cracks from class Ⅰ to Ⅳ, different treatment methods are adopted such as surface sealing, close grouting and surface sealing, slotting across cracks and surface sealing, chemical grouting and surface sealing after chute-cutting and crack patching. The results of water pressure test before impoundment show that satisfying effect is obtained from crack treatment, cracks are filled densely and defects are effectively eliminated. There is no obvious leakage after impoundment and the operation condition of the lower reservoir is stable.

Based on design review, the typical problems in design of safety monitoring for small reservoirs were systematically summarized, including inadequate capability of design organization, omission of important design content, incomplete design-related basic information, improper utilization of existing safety monitoring equipment, design divorced from engineering practice, confusing set of important and unimportant monitoring items, and et al. It is proposed that the quality management of safety monitoring needs to be enhanced in aspects such as more attention paid to the design, improvement of guidance and training, strengthening of design inspection, special focus on safety monitoring design of reinforced and newly-built small reservoirs.

Aiming at the problems such as low work efficiency, weak professional level, and poor timeliness existing in the manual analysis, information technology is adopted and a set of dam safety monitoring data diagnosis and analysis system is designed and developed, which has obvious advantages in monitoring data preprocessing, distribution map drawing, engineering analogy, abnormous situation feedback, and et al. As well, it can realize the automatic generation of monthly reports, quarterly reports, annual reports, earthquake express reports and comprehensive monitoring data analysis reports. The application shows that the system can significantly improve the efficiency and quality of dam safety monitoring data diagnosis and analysis work, and it is worthy of promotion in dam safety management industry.

The major dam shell of Xiaolangdi water conservancy project is filled with rockfill materials containing siltstone, clay rock and other soft rocks. After years of operation, the soft rocks on dam surface have weathered into fragments, and part of soft rocks have been eroded into rockfill voids, which will have a certain impact on the physical and mechanical properties of rockfill materials in the dam shell, such as the permeability coefficient and shear strength, and may also affect the stability of upstream and downstream dam slopes. At the same time, Xiaolangdi dam has large dam height, complex and deep overburden, many kinds of dam materials and complex operating conditions, so it is necessary to study the properties of rockfill materials in dam shell. Through in-situ excavation and sampling, relevant tests of the grading, compactness and permeability of rockfill materials and original rock character and strength are carried out to conduct the experimental study on properties of rockfill materials in the major dam shell. The results show that the main character parameters of rockfill materials in the major dam shell slightly changed, and the weathering degree and compressive strength of rockfill materials have limited influence.

Typhoon exerts great impact on the operation safety of dams in China, especially on the dams in typhoon prone areas along the southeast coast. The impact of typhoon wind on the dam is mainly determined by the wind scale. At present, China Meteorological Administration has realized the prediction of typhoon track and different wind grade radius in the four quadrants of typhoon. The geographic coordinate information database of the concerned dams is established, the typhoon prediction information can be obtained in real time and the later influence range of different typhoon wind scale can be calculated. Based on the dam location and the local wind scale, graded warning is realized. The above-mentioned functions are realized through computer programming. It would quickly identify the dams which may be damaged by typhoon and realize rapid early warning for dams encountering typhoon.

After the reinforcement of Longshan reservoir, there is a problem of settlement, which leads to cracks on the dam crest and has unknown impact on the dam operation safety. This study comprehensively uses pit exploration, drilling and geophysical exploration methods to evaluate the dam operation safety, analyze the current situation of dam filling, investigate and analyze the causes of cracks and settlement problems. Meanwhile, the impact of the infiltration line lowering caused by reinforcement is considered to conduct a preliminary evaluation of settlement. The results indicate that the settlement of Longshan reservoir is mainly due to the low filling quality in some areas of dam body and the infiltration line lowering, which leads to the consolidation settlement of filling material. Although the settlement situation still meets requirements, the risk of continued settlement cannot be ruled out. It is necessary to excavate the non- dense soil and rerun the thickening and reinforcement project. The relevant survey methods and analysis can provide reference for similar dam settlement problems.

Among large and medium-sized hydropower stations in China, some of the older hydropower units that have been in operation for a long time have experienced a decline in performance and an increase in failure rates. It is of significance to take necessary technical measures to increase the capacity of the old units. Therefore, investigations and studies on the issue of hydropower unit capacity upgrading and renovation are carried out. Based on the survey, the existing problems and difficulties in the current implementation of hydropower unit capacity upgrading and renovation are analyzed and summarized, and suggestions are given for reference.

Combined with the operation management of reservoir dams, this paper first analyses the main contents of current research on engineering ethics in the field of hydraulic engineering. And then, based on social and natural dimensions, from the aspects of reservoir resettlement, reservoir degradation and decommision, public education, reservoir big data, reservoir management scope, reservoir aquaculture, biodiversity of reservoir area, etc., this paper discusses how engineers should correctly handle the interpersonal relationship as well as the relationship between mankind and nature in accordance with the code of engineering ethics.

Taking the spillway reinforcement project of a hazardous reservoir as an example, the main problems of the spillway are analyzed, and the discharge capacity of the wide crest weir of the spillway, the height of the side wall, the anti-erosion capacity of the bottom plate and the stability of the side wall are checked. Based on the main problems, the specific reinforcement design scheme is proposed, which provides technical basis for spillway reinforcement and reference for similar projects.

With the continuous development of basin-level clean energy bases, integrated regulation of hydro-wind-solar power has become an important direction for the development of existing hydropower stations, which presents challenges for the traditional regulation of cascade hydropower centralized con⁃ trol centers, and the introduction of systematic and integrated regulation theory and methods is required. In response to this, a multi-time scale sequential nested regulation architecture for integrated hydrowind-solar system is constructed based on the actual needs of the lower reach of Jinsha river basin. The core business model is analyzed, and an integrated regulation process is established to provide a system⁃ atic solution for promoting the new energy consumption and ensuring the safe and efficient operation of hydropower stations in the clean energy bases.

By analyzing the problems existed in current dam safety monitoring system, this paper puts forward the necessity of building an online dam safety monitoring system based on software as a service. Based on demand analysis, the system function design and R&D were carried out. The system was popularized and applied to many hydropower stations, which created a new service mode based on safety big data, and improved the level of safety management of reservoir dams.

During operation, the defects of hydraulic structures would gradually occur in complex water environment, especially the second stage concrete of the gate slot. The defects repair and treatment would affect the operation income of the station, as well as the safety of the station itself and downstream structures. There are few successful underwater repair cases without water discharge during operation at home and abroad. The repair of the second stage concrete of trash rack gate slot of Xiushan hydropower station in Hunan province is introduced as an example. The counter-force frame of trash rack gate is used as the template support system, fine stone self-compacting non-diffusible concrete is poured based on the groove depth, and underwater epoxy mortar plastering method is adopted to repair the second stage concrete of trash rack gate slot. The repair technology is also successfully applied to second stage entrance gate slot of Anjiang hydropower station in Hunan province, which can provide reference for other similar projects.

To eliminate the malfunction of the air-release valve in the gate chamber not being able to close or close early when filling the tail water unit section of Changlongshan pumped storage power station, this article briefly analyzes the structure and weight of the floating bucket, as well as calculates the release area and the average release speed of key parts in the valve. By doing so, a transformation method is proposed under existing conditions, which is to increase the diameter of the floating bucket and release hole, and cancel the floating bucket counterweight. After multiple on-site tests, the optimized parameters of the air-release valve have been obtained. Since then, the water filling and air release process of the tailrace gate chamber have become safe and reliable.