Water quality response to hydropeaking regulation of the Three Gorges Dam and Gezhouba Dam, China

Hydropeaking as the most prominent feature of flow alterations resulting from hydropower plants has received attention worldwide. Ramifications of hydropower on the downstream river systems mainly focus on hydrological regimes or long-term water quality changes. Exceptional knowledge is expected on the sub-daily changes of water qualities in the downstream river reach that is affected by the hydropeaking. In this study, we investigate the dynamics of hydropeaking and thermopeaking at the outlet of the Three Gorges Dam TGD using a high temporal resolution dataset, and inspect its association with water chemistry indices. Hourly measurements are analysed for the downstream station Yunchi , and compared with the upstream station Nanjinguan. The results show that along with water temperature, water quality indices such as dissolved oxygen, total Phosphorus, total nitrogen, PH, and electricity conductivity all show evident ‘peaking’ phenomenon in a short time. These divergent variations, however, are not valid for non-hydropeaking affected indicators including turbidity, permanganate index, and ammonia nitrogen. These hydropeaking-induced perturbations are mitigated by the flood control operation from July to September. This study demonstrates that water quality indices are sensitive to hydropeaking and thermopeaking with respect to the magnitude of change and the seasonal component during a year. The results provide additional evidence for the environmental impacts of hydropower regulation on the receiving river reach, and bridge the gap between hydropeaking studies and thermopeaking, and study water qualities variations that were seldom connected from the same temporal perspective in river research.

Hybrid simulation model for navigation performance evaluation of the Three Gorges–Gezhouba Dams under novel regulations

As an important project on the golden waterway of the Yangtze River in China, the Three Gorges–Gezhouba Dams (TGGD) plays a pivotal role in the construction of the Yangtze River Economic Belt. To improve the efficiency and safety of ship traffic, some novel navigation regulations have been implemented that change the TGGD operation obviously. For example, a piecewise control strategy proposed in the regulations is applied to control the traffic flow of ships under a sectional manner. With the implementation of these regulations, how to understand the dynamic effects of new changes on TGGD has been an important problem. The purpose of this work is to evaluate the navigation performance of the TGGD via a data- and event-driven hybrid simulation model developed by multi-agent and discrete-event modeling theories. The model simulates the three significant navigable scenarios inherent in the actual operating environment: dry season, wet season, and flood season, reflecting the real situations. The input data come from the statistical analysis of the actual navigation data provided by the Three Gorges Navigation Administration. The validity and reliability of the model are verified by comparing the output results with actual data. Moreover, a set of test experiments are designed to explore the TGGD navigation limit and analyze the key factors that restrict the navigation capacity of the TGGD system. The work is expected to provide a certain decision support for the future cooperative scheduling optimization of the TGGD.

Multivariate Dam-Site Flood Frequency Analysis of the Three Gorges Reservoir Considering Future Reservoir Regulation and Precipitation

Under a changing environment, the current hydrological design values derived from historical flood data for the Three Gorges Reservoir (TGR) might be no longer applicable due to the newly-built reservoirs upstream from the TGR and the changes in climatic conditions. In this study, we perform a multivariate dam-site flood frequency analysis for the TGR considering future reservoir regulation and summer precipitation. The Xinanjiang model and Muskingum routing method are used to reconstruct the dam-site flood variables during the operation period of the TGR. Then the distributions of the dam-site flood peak and flood volumes with durations of 3, 7, 15, and 30 days are built by Pearson type III (PIII) distribution with time-varying parameters, which are expressed as functions of both reservoir index and summer precipitation anomaly (SPA). The multivariate joint distribution of the dam-site flood variables is constructed by a 5-D C-vine copula. Finally, by using the criteria of annual average reliability (AAR) associated with the exceedance probabilities of OR, AND and Kendall, we derive the multivariate dam-site design floods for the TGR from the predicted flood distributions during the future operation period of the reservoir. The results indicate that the mean values of all flood variables are positively linked to SPA and negatively linked to RI. In the future, the flood mean values are predicted to present a dramatic decrease due to the regulation of the reservoirs upstream from the TGR. As the result, the design dam-site floods in the future will be smaller than those derived from historical flood distributions. This finding indicates that the TGR would have smaller flood risk in the future.