Refined Environmental Flow Management: Integrating Fish Multiple Life‐Stage Requirements Into Fine‐Scale Operation of Cascade Reservoirs

Determination of suitable ecological flow regimes for spawning of four major Chinese carps: A case study of the Hongshui River, China

The input variable selection in multiobjective cascade reservoir operation is an important and difficult task. To address this problem, this study proposes the cascade reservoir input variable selection (CIS) method that searches for the most valuable input variables for decision making in multiple‐objectivity cascade reservoir operations. From a case study of Hanjiang cascade reservoirs in China, we derive reservoir operating rules based on the combination of CIS and Gaussian radial basis functions (RBFs) methods and optimize the rules through Pareto‐archived dynamically dimensioned search (PA‐DDS) with two objectives: to maximize both power generation and water supply. We select the most effective input variables and evaluate their impacts on cascade reservoir operations. From the simulated trajectories of reservoir water level, power generation, and water supply, we analyze the multiobjective operating rules with several input variables. The results demonstrate that the CIS method performs well in the selection of input variables for the cascade reservoir operation, and the RBFs method can fully express the nonlinear operating rules for cascade reservoirs. We conclude that the CIS method is an effective and stable approach to identifying the most valuable information from a large number of candidate input variables. While the reservoir storage state is the most valuable information for the Hanjiang cascade reservoir multiobjective operation, the reservoir inflow is the most effective input variable for the single‐objective operation of Danjiangkou.

Hydrodynamic impact on trace metals in sediments in the cascade reservoirs, North China.

Multi-objective water-sediment optimal operation of cascade reservoirs in the Yellow River Basin

Optimal impoundment operation for cascade reservoirs coupling parallel dynamic programming with importance sampling and successive approximation

The establishment and operation of cascade reservoirs in the mainstream of the upper and middle reaches of the Yangtze River have changed the river’s thermal regimes. This study analyzed the correlation between water temperature and its influencing factors and employed various evaluation indexes—including ∆T (the temperature-increasing index, °C/100 km), IEC (the extreme fluctuation index), IBD (the baseline deviation index), and IPO (the phase offset time index). The aim was to uncover the variation characteristics and influencing factors of water temperature and quantify the impact of cascade reservoir construction on annual and seasonal water temperature rhythms. Our findings show that the construction and operation of cascade reservoirs weaken the synchronization of water temperature and air temperature downstream. The construction and operation of cascade reservoirs in the middle and lower reaches of the Jinsha River led to obvious homogenization, baseline deviation, and lagging effects on water temperature downstream, which intensified with the increase in storage capacity. These effects were more pronounced in colder months compared to warmer months. Additionally, the influence of tributaries and water–air heat exchange on these effects is alleviated to different degrees. These results are significant for assessing river ecological health in the context of cascade hydropower development.

Planning and optimal operation of reservoirs under the paradigm of climate change is one of the most momentous problems in the planning and management of water resources due to the rapid growth of economy and population. In this study, Soil and Water Assessment Tool (SWAT) and reservoir operation optimization (HEC-ResPRM) models have been employed in the three cascade hydropower reservoirs in Tekeze basin, Ethiopia to investigate the impact of planned cascade reservoirs’ operation on the existing reservoir on the face of climate change. Results showed that an increase in rainfall and temperature in the future will be critical to future inflow in cascade hydropower reservoirs, with rainfall variability having a greater impact than temperature variability. HEC-ResPRM was prepared to reproduce optimum hydropower reservoir storage and water levels on the joint cascade operation of Tekeze reservoirs in each mode under climate change effect. Joint optimum operation of cascade reservoirs in different operation modes under climate change in both RCP4.5 and RCP8.5 climate scenarios affects existing reservoir operation in the future. Therefore, it is better to improve existing reservoir operation before investing into new planned cascade reservoirs and incorporate climate change scenarios in the planning, design, and operation of new reservoirs in Tekeze Basin. The results of this study can help the water resources planners and managers to plan and manage the future water resources of Ethiopian Rivers.

Cascade reservoir operation can ensure the optimal use of water and hydro-energy resources and improve the overall efficiency of hydropower stations. A large number of studies have used meta-heuristic algorithms to optimize reservoir operation, but there are still problems such as the inability to find a global optimal solution and slow convergence speed. Lightning search algorithm (LSA) is a new meta-heuristic algorithm, which has the advantages such as high convergence speed and few parameters to be adjusted. However, there is no study on the application of LSA in reservoir operation. In this paper, LSA is used to solve the problem of reservoir operation optimization to verify its feasibility. We also propose an improved LSA algorithm, the frog-leaping–particle swarm optimization–LSA (FPLSA), which was improved by using multiple strategies, and we address the shortcomings of LSA such as low solution accuracy and the tendency to fall into local optima. After preliminary verification of ten test functions, the effect is significantly enhanced. Using the lower Jinsha River–Three Gorges cascade reservoirs as an example, the calculation is carried out and compared with other algorithms. The results show that the FPLSA performed better than the other algorithms in all of the indices measured which means it has stronger optimization ability. Under the premise of satisfying the constraints of cascade reservoirs, an approximate optimal solution could be found to provide an effective output strategy for cascade reservoir scheduling.

Considering water propagation impact in short-term optimal operation of cascade reservoirs using Nested Progressive Optimality Algorithm

Refined operation of cascade reservoirs considering fish ecological demand

The reservoirs (hydro plants) along the upper Yellow River are typical cascade reservoirs, with multiple objectives regarding flood control, ice control, water supply, power generation, and ecological security. The competition among these multiple objectives reflects the competition among various agencies with different interests. There has been a certain degree of conflict between ‘power scheduling’, which aims at obtaining greater power generation from the cascade reservoirs, and ‘water regulation’, which is currently being implemented. Questions of how to reasonably use the comprehensive regulation capacity of the cascade reservoirs, in order to relieve the conflicts among multiple objectives, and understand the nature of the competition between ‘power scheduling’ and ‘water regulation’, require urgent research and solutions. Based on an analysis of the current situation regarding water supply, electricity demand, flood control, ice control, and ecology, a multi-objective optimal operation model for the cascade reservoirs in the upper and middle reaches of the Yellow River has been constructed to reveal the relationships between power generation and other objectives. This study provides theoretical evidence for the informed operation of the cascade reservoirs and will be of great significance for coordinating the relationship between power generation and water regulation.

The reasonable utilization of river water resources requires the joint operation of cascade reservoirs. Aiming at power generation and ecological environment protection, taking the Qingjiang cascade reservoir group as the research object, a multi-objective optimization model for maximum power generation considering ecological base flow and minimum ecological flow changed is established. The results of the multi group cooperation operation particle swarm optimization (MGCL-PSO) model based on population cooperation show that the multi-objective of power generation and ecology can achieve a better balance by slightly reducing the power generation. Several schemes with good convergence are obtained from the calculation results, which provide a reference for the operation of cascade reservoirs.

To mitigate the negative effects of hydropower operation on fish reproduction in the downstream river and maximize reservoir ecological benefits, the Xiluodu-Xiangjiaba joint ecological scheduling has been implemented since 2017. Based on early resource survey data from the Jiangjin section of the upper Yangtze River from 2017 to 2022, this study evaluates the effects of cascade reservoir joint ecological scheduling on the natural spawning of the four major Chinese carps in the downstream river section and identifies key hydrological indicators that affect the natural spawning of the four major Chinese carps. The results showed that the total egg production of four major Chinese carps in the Jiangjin section ranged from 42 to 401 million from 2017 to 2022, exhibiting a general fluctuating trend with a peak of approximately 401 million in 2022. Over the six-year period, 25 spawning peaks were observed, mainly concentrated from early June to early July. During ecological scheduling periods, the egg runoff volumes ranged from 0.001 to 108.8 million, accounting for 0.06% to 34.47% of annual totals-exceeding 30% in 2022 and 10% in 2018. In terms of ecological scheduling effectiveness, the breeding peak period that coincided with ecological scheduling accounted for 16% of the total breeding peak period, indicating that ecological scheduling effectively promoted the natural breeding activities in the downstream Jiangjin section. Hydrological demand analysis showed that the suitable flow range for spawning of the four major Chinese carps in the Jiangjin section was 6000—15000 m³/s, with a suitable water temperature of 21—23℃. Correlation analysis further demonstrated that spawning amount had a significant positive correlation with the peak flow, flow increment, and flow increase rate (<italic>P</italic>&lt;0.05). Based on these results, the study recommends conducting 2—3 ecological scheduling events in mid-late May and early June, maintaining rising water conditions in the Jiangjin section for more than 3d, and ensuring a daily fiow increase rate of at least 900 m³/s to facilitate the large-scale reproduction. The results provide a scientific basis for formulating scheduling strategies for the Jinsha River cascade reservoir system.

Risk analysis of water supply-hydropower generation-environment nexus in the cascade reservoir operation

Nexus of water, energy and ecosystems in the upper Mekong River: A system analysis of phosphorus transport through cascade reservoirs