The possible mitigation of floods by dams and the risk to dams from floods are key problems. The People’s Republic of China is now leading world dam construction with great success and efficiency. This paper is devoted to relevant experiences from other countries, with a particular focus on lessons from accidents over the past two centuries and on new solutions. Accidents from floods are analyzed according to the dam’s height, storage, dam material, and spillway data. Most of the huge accidents that have been reported occurred for embankments storing over 10 hm³. New solutions appear promising for both dam safety and flood mitigation.

The earth-rockfill dam is one of the primary dam types in the selection of high dams to be constructed in Western China, since it is characterized by favorable adaptability of the dam foundation; full utilization of local earth, rock, and building-excavated materials; low construction cost; and low cement consumption. Many major technical issues regarding earth-rockfill dams with a height of over 250 m were studied and solved successfully in the construction of the 261.5 m Nuozhadu earth core rockfill dam. This paper describes research achievements and basic conclusions; systematically summarizes the accumulated experiences from the construction of the Nuozhadu Dam and other high earth-rockfill dams; and discusses major technical issues, such as deformation control, seepage control, dam slope stability, safety and control of flood discharging, safety and quality control of dam construction, safety assessments, early warning, and other key technical difficulties. This study also provides a reference and technological support for the future construction of 300 m high earth-rockfill dams.

This study is concerned with the feasibility of power generation using a pico-hydraulic turbine from sewage flowing in pipes. First, the sewage flow rate at two connection points to the Toyogawa River-Basin Sewerage, Japan, was explored for over a year to elucidate the hydraulic energy potential of the sewage. Second, the performance of the pico-hydraulic turbine was investigated via laboratory experiments that supposed the turbine to be installed in the sewage pipe at the connection points. This study indicates that the connection points have hydraulic potential that can be used for power generation throughout the year. It also demonstrates that the pico-hydraulic turbine can be usefully employed for power generation from sewage flowing in the pipe at the connection points.

The first author proposed the concept of the cemented material dam (CMD) in 2009. This concept was aimed at building an environmentally friendly dam in a safer and more economical way for both the dam and the area downstream. The concept covers the cemented sand, gravel, and rock dam (CSGRD), the rockfill concrete (RFC) dam (or the cemented rockfill dam, CRD), and the cemented soil dam (CSD). This paper summarizes the concept and principles of the CMD based on studies and practices in projects around the world. It also introduces new developments in the CSGRD, CRD, and CSD.

Based on systematic experiments on the influence of air entrainment on rock block stability in plunge pools impacted by high-velocity jets, this study presents adaptations of a physically based scour model. The modifications regarding jet aeration are implemented in the Comprehensive Scour Model (CSM), allowing it to reproduce the physical-mechanical processes involved in scour formation concerning the three phases; namely, water, rock, and air. The enhanced method considers the reduction of momentum of an aerated jet as well as the decrease of energy dissipation in the jet diffusive shear layer, both resulting from the entrainment of air bubbles. Block ejection from the rock mass depends on a combination of the aerated time-averaged pressure coefficient and the modified maximum dynamic impulsion coefficient, which was found to be a constant value of 0.2 for high-velocity jets in deep pools. The modified model is applied to the case of the observed scour hole at the Kariba Dam, with good agreement.

Starting with the Ertan arch dam (240 m high, 3300 MW) in 2000, China successfully built a total of seven ultra-high arch dams over 200 m tall by the end of 2014. Among these, the Jinping I (305 m), Xiaowan (294.5m), and Xiluodu (285.5 m) arch dams have reached the 300 m height level (i.e., near or over 300 m), making them the tallest arch dams in the world. The design and construction of these 300 m ultra-high arch dams posed significant challenges, due to high water pressures, high seismic design criteria, and complex geological conditions. The engineering team successfully tackled these challenges and made critical breakthroughs, especially in the area of safety control. In this paper, the author summarizes various key technological aspects involved in the design and construction of 300?m ultra-high arch dams, including the strength and stability of foundation rock, excavation of the dam base and surface treatment, dam shape optimization, safety design guidelines, seismic analysis and design, treatment of a complex foundation, concrete temperature control, and crack prevention. The experience gained from these projects should be valuable for future practitioners.

The concrete-faced rockfill dam (CFRD) is an important dam type in the selection of high dams to be constructed in Western China, owing to its direct utilization of local materials, good adaptability, and distinct economic advantages. Over the past decades, China has gained successful experience in the construction of 200?m CFRDs, providing the necessary technical accumulation for the development of 250–300?m ultra-high CFRDs. This paper summarizes these successful experiences and analyzes the problems of a number of major 200?m CFRDs around the world. In addition, it discusses the key technologies and latest research progress regarding safety in the construction of 250–300?m ultra-high CFRDs, and suggests focuses and general ideas for future research.

This paper summarizes the development of hydro-projects in China, blended with an international perspective. It expounds major technical progress toward ensuring the safe construction of high dams and river harnessing, and covers the theorization of uneven non-equilibrium sediment transport, inter-basin water diversion, giant hydro-generator units, pumped storage power stations, underground caverns, ecological protection, and so on.

The basic element in any sustainable dam project is safety, which includes the following safety elements: ① structural safety, ② dam safety monitoring, ③ operational safety and maintenance, and ④ emergency planning. Long-term safety primarily includes the analysis of all hazards affecting the project; that is, hazards from the natural environment, hazards from the man-made environment, and project-specific and site-specific hazards. The special features of the seismic safety of dams are discussed. Large dams were the first structures to be systematically designed against earthquakes, starting in the 1930s. However, the seismic safety of older dams is unknown, as most were designed using seismic design criteria and methods of dynamic analysis that are considered obsolete today. Therefore, we need to reevaluate the seismic safety of existing dams based on current state-of-the-art practices and rehabilitate deficient dams. For large dams, a site-specific seismic hazard analysis is usually recommended. Today, large dams and the safety-relevant elements used for controlling the reservoir after a strong earthquake must be able to withstand the ground motions of a safety evaluation earthquake. The ground motion parameters can be determined either by a probabilistic or a deterministic seismic hazard analysis. During strong earthquakes, inelastic deformations may occur in a dam; therefore, the seismic analysis has to be carried out in the time domain. Furthermore, earthquakes create multiple seismic hazards for dams such as ground shaking, fault movements, mass movements, and others. The ground motions needed by the dam engineer are not real earthquake ground motions but models of the ground motion, which allow the safe design of dams. It must also be kept in mind that dam safety evaluations must be carried out several times during the long life of large storage dams. These features are discussed in this paper.

To date, the Three Gorges Project is the largest hydro junction in the world. It is the key project for the integrated water resource management and development of the Changjiang River. The technology of the project, with its huge scale and comprehensive benefits, is extremely complicated, and the design difficulty is greater than that of any other hydro project in the world. A series of new design theories and methods have been proposed and applied in the design and research process. Many key technological problems regarding hydraulic structures have been overcome, such as a gravity dam with multi-layer large discharge orifices, a hydropower station of giant generating units, and a giant continual multi-step ship lock with a high water head.

In recent years, risk analysis techniques have proved to be a useful tool to inform dam safety management. This paper summarizes the outcomes of three themes related to dam risk analysis discussed in the Benchmark Workshops organized by the International Commission on Large Dams Technical Committee on “Computational Aspects of Analysis and Design of Dams.” In the 2011 Benchmark Workshop, estimation of the probability of failure of a gravity dam for the sliding failure mode was discussed. Next, in 2013, the discussion focused on the computational challenges of the estimation of consequences in dam risk analysis. Finally, in 2015, the probability of sliding and overtopping in an embankment was analyzed. These Benchmark Workshops have allowed a complete review of numerical aspects for dam risk analysis, showing that risk analysis methods are a very useful tool to analyze the risk of dam systems, including downstream consequence assessments and the uncertainty of structural models.

Hydropower is a clean, renewable, and environmentally friendly source of energy. It produces 3930?(TW•h)•a^–1, and yields 16% of the world’s generated electricity and about 78% of renewable electricity generation (in 2015). Hydropower and climate change show a double relationship. On the one hand, as an important renewable energy resource, hydropower contributes significantly to the avoidance of greenhouse gas (GHG) emissions and to the mitigation of global warming. On the other hand, climate change is likely to alter river discharge, impacting water availability and hydropower generation. Hydropower contributes significantly to the reduction of GHG emissions and to energy supply security. Compared with conventional coal power plants, hydropower prevents the emission of about 3?GT CO₂ per year, which represents about 9% of global annual CO₂ emissions. Hydropower projects may also have an enabling role beyond the electricity sector, as a financing instrument for multipurpose reservoirs and as an adaptive measure regarding the impacts of climate change on water resources, because regulated basins with large reservoir capacities are more resilient to water resource changes, less vulnerable to climate change, and act as a storage buffer against climate change. At the global level, the overall impact of climate change on existing hydropower generation may be expected to be small, or even slightly positive. However, there is the possibility of substantial variations across regions and even within countries. In conclusion, the general verdict on hydropower is that it is a cheap and mature technology that contributes significantly to climate change mitigation, and could play an important role in the climate change adaptation of water resource availability. However, careful attention is necessary to mitigate the substantial environmental and social costs. Roughly more than a terawatt of capacity could be added in upcoming decades.