Since the first impoundment of Three Gorges Dam in 2003, algal blooms occur frequently in the near-dam tributaries. It is widely recognized that the impoundment-induced change in hydrodynamic condition with the lower current velocity will make the eutrophication problem even more severe when an excessive amount of nutrients is already loaded into a reservoir and/or its tributaries. Operation tests carried out by Three Gorges Corporation in 2010 point to some feasible reservoir operation schemes that may have positive impacts on reducing the algal bloom level. In our study, an attempt is made to obtain, through a numerical hydrodynamic and water quality modeling and analysis, the reservoir operation rules that would reduce the level of algal blooms in the Xiangxi River (XXR), a near-dam tributary. Water movements and algal blooms in XXR are simulated and analyzed under different scenarios of one-day water discharge fluctuation or two-week water level variation. The model results demonstrate that the reservoir operations can further increase the water exchange between the mainstream of the Three Gorges Reservoir (TGR) and the XXR tributary and thus move a larger amount of algae into the deep water where it will die. Analysis of the model results indicate that the water discharge fluctuation constituted of a lower valley-load flow and a larger flow difference for the short-term operation (within a day), the rise in water level for the medium-term operation (e.g., over weeks), and the combination of the above two for the long-term operation (e.g., over months) can be the feasible reservoir operation rules in the non-flood season for TGR.

This paper comprehensively summarizes and discusses the latest research progress in the underwater concrete structure damage repair technology of infrastructures. The prompt application of underwater concrete structure repair technology can effectively deal with the damaged parts of underwater concrete structures, and it can ensure the safe and stable operation of infrastructure and extend its service life. Firstly, this study uses bibliometric methods to analyze the characteristics of the literature on research into underwater concrete repair in the past 30 years (1993–2023), and expounds the research status and hotspots of this field. Then, we conduct a comprehensive classification and discussion of the underwater concrete structure damage repair technologies at the current stage. This technology can be divided into two major types: direct underwater type and dry environment type. Further, the development history of these technologies is systematically sorted out and, combined with practical engineering application cases, the operation processes, applicability, limitations, and economy of these technologies are analyzed. Finally, the challenges and future development trends of the current underwater concrete structure damage repair technology are pointed out, which provides a direction for future research on the intelligent maintenance of underwater concrete structures.

The impoundment and power generation of dams cause the temperature of released water much lower than the original rivers in the thermal stratified reservoirs. In addition, the released low-temperature water would damage the downstream habitats of fish and other biological groups seriously. Available facilities, such as stop log gate intakes and multi-level intakes, are built to alleviate the problem. For overcoming the limitations of traditional facilities on construction conditions and the improved effect of water temperature, a new facility of the temperature control curtain (TCC), with the advantages of convenient regulation and no hydropower loss, has been proposed recently. However, to the author’s knowledge, the theory of TCC is not abundant, with incomplete experimental tests and few numerical simulations. In this paper, a rectangular tank is designed specifically to conduct experimental tests to verify the effects of TCC and explore its potential impacts on released water temperature (RWT) under four major influencing factors. The study results show that TCC has significant effects on improving RWT, with a maximum increase of 8.3 °C. In addition, a three-dimensional hydrodynamic model with the same size of experimental model is established for further research. The results show that RWT is mainly related to the temperature distribution of a reservoir and the water-retaining proportion of the curtain. Finally, a basic principle for TCC construction is proposed and all these laid an important theory foundation for its application in engineering practice.

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