| 26 Jan 2026
Hydrological Regime Shifts in River-Connected Lakes under Upstream Dam Regulation: Insights from the Three Gorges Project and Poyang Lake
Abstract. Revealing the impacts of mainstream dams on the hydrological regime of connected river–lake systems is crucial for elucidating river–lake interaction mechanisms and providing a scientific basis for basin-scale water resources regulation and ecological protection. Taking the Three Gorges Project–Poyang Lake system as a representative case, this study integrates the Light Gradient Boosting Machine (LightGBM) model with the SWAT model to analyze the lake’s hydrological responses to dam regulation. Based on long-term runoff, water level, and meteorological series, simulated and observed hydrological events were compared to quantify the influence of the Three Gorges Project on Poyang Lake. Results indicate that backflow events declined significantly in frequency (−11.58 %), duration (−22.6 days), water level (−7.79 %), and discharge (−35.60 %), with the dam contributing 72.19 % of the variation in backflow events discharge. The backwater effect at Hukou weakened markedly (fitted backflow −150.58×10³ m³/s), triggering cascading effects across the lake. Normalflow events were notably prolonged (+25.9 days), whereas flood events decreased in both frequency (−5.18 %) and discharge (−11.03 %), demonstrating a significant flood peak attenuation effect (fitted backflow −10512.89×10³ m³/s). In contrast, a decline in water levels (−7.47 %) and discharge (−12.90 %) during normalflow events, and a 15.18 % increase in drought event frequency, to which the dam contributed 30.03 % of the runoff variation. During drought events, discharge deviated substantially from model predictions (+391.34×10³ m³/s), indicating enhanced hydraulic resistance at Hukou. Moreover, under drought events, the hydrological relationship at Hukou shifted from mainstream water-level dominance to lake-outflow dominance. Overall, the construction of the Three Gorges Dam has made hydrological variations in the Poyang Lake region more stable and secure, but has also increased drought risks, marking a gradual transition from a naturally regulated lake system to a semi-natural, dam-regulated system. Future management should aim to optimize dam operation schedules and enhance river–lake connectivity to promote the coordinated and sustainable development of water resources and ecosystems.
Dear authors,
This work aims to assess the influences of the largest Three Gorges Project on the downstream Lake Poyang. The authors used a SWAT model and a LightGBM tool, however, the scientific background, the innovation and advances of the study seem to be insufficient.
Section Abstract: Backflow should be well addressed when it first occurs, for example, from the lake to river? The river-lake connection should be briefly introduced.
Section Abstract: The model seems to be quantitatively to examine the contribution of the upstream dam on the lake hydrology, however, the author's main results come off as rather trivial. Is presenting model contribution rates to two decimal places really necessary?
Section Introduction: The authors stated that “These processes are difficult to accurately capture using traditional one-dimensional or quasi-two-dimensional models(Wu et al., 2022).” I am profoundly skeptical of this viewpoint. Moreover, the cited literature fails to substantiate the claim.
Section Introduction: paragraph 70-75, this part aims to highlight the importance of combined SWAT model and LightGBM model for the present work, however, this part should be moved elsewhere.
Section Introduction: paragraph 80-85, looking into the literature (e.g., backflow, Three Gorges Dam, Poyang Lake), it seems the author has missed a lot of earlier work, for example,
Zhang, Q., Li, L., Wang, Y. G., Werner, A. D., Xin, P., Jiang, T., & Barry, D. A. (2012). Has the Three‐Gorges Dam made the Poyang Lake wetlands wetter and drier?. Geophysical research letters, 39(20).
Li, Y., Zhang, Q., Werner, A. D., Yao, J., & Ye, X. (2017). The influence of river‐to‐lake backflow on the hydrodynamics of a large floodplain lake system (Poyang Lake, China). Hydrological Processes, 31(1), 117-132.
Section 2.1, Poyang Lake, located on the southern bank of the middle–lower Yangtze River. Perhaps the location is wrong. It locates in the middle steam of the River? Please check it.
Section 2.1, the authors used two hydrological stations Jiujiang and Hukou (Fig.1), however, these two stations are so close to each other. What are their respective purposes, then? I'm not sure if the author has taken into account the possible joint impact from the lake and the upper Yangtze River on the station hydrology.
Section 2.2.2, the authors only used 1970 as the reference year, the reason should be well explained and a one-year timeframe lacks representativeness. In addition, the MK test method is very simple, but it still requires citation of the original literature.
Section 2.2.3, the authors stated that the LightGBM has the ability to reproduce the lake–river confluences exhibiting backflow phenomena. I am uncertain how the authors' understanding of the model's nonlinear capture capability leads to the conclusion that it can accurately represent a specific hydrological phenomenon like backflow.
Section 2.2.3, the model seems to use discharge data from the basin river inflows, but these key stations were not shown in Fig. 1.
Fig. 3 should be moved into the Section “3 Results”. In addition, the unit of the metric RMSE is m3/s. Apparently, the authors may have overlooked this unit issue.
Section 2.2.4, The construction for the SWAT model of the Poyang Lake basin should be very complex, involving the data collection, many hydrological parameters, and basin reservoirs. The model construction process is described inadequately, and a complete presentation of the calibration and validation procedures is lacking. This is an issue that cannot be overlooked. The absence of these critical components significantly undermines my confidence in the subsequent results.