the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Nov 2025
Effects of the Three Gorges Dam Operation on the hydrological interaction between the Yangtze River and downstream aquifers
Abstract. The construction of the Three Gorges Dam (TGD) has profoundly altered the groundwater cycle downstream. The obscure spatiotemporal patterns of exchange fluxes between the Yangtze River and groundwater hinder the resolution of water resources and environmental issues in the watershed. In the Four-Lake Basin, the first river-lake wetland plain downstream of the TGD, this study investigated the spatial extent of the Yangtze River's influence on adjacent groundwater by leveraging multiple groups of monitoring wells installed along the river. A coupled SWAT-MODFLOW model was applied to quantify period-specific SW-GW exchanges. A counterfactual scenario without TGD operation-holding other conditions constant is also simulated for comparison. The results show: (1) The influence range of the Yangtze River on confined groundwater is larger in the ZJ-JLX2 section, whereas it is relatively minor on groundwater near HH1 profile and HH2 profile. The influence distance at the HH1 profile is the smallest, measuring as 1.94 km. (2) River and groundwater exchanges exhibit pronounced seasonal and spatial characteristics: river-to-aquifer recharge dominates during drawdown and flooding periods, while aquifer-to-river discharge dominates during impounding and dry periods. Using JLX2 as a divider, interaction rates are consistently higher in the upper section than in the lower one. (3) Relative to natural conditions, TGD operation dramatically dampens Yangtze River-groundwater interactions overall. The effect is most pronounced during the dry period in the upper section, when the interaction rate decreases by 40.6 %. These research outcomes serve as a vital theoretical foundation for assessing the effects of the Three Gorges Dam's regulation on the regional water cycle.
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Status: final response (author comments only)
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RC1: 'Comment on egusphere-2025-5682', Anonymous Referee #1, 19 Dec 2025
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AC1: 'Reply on RC1', Zhang Wen, 04 Jan 2026
We appreciate the reviewer's positive comments on the innovative aspects of this study. We will implement all suggestions provided. For instance, we will add geographic identifiers—such as specifying that ZJ-JLX2, HH1, and HH2 cross-sections are located in the upper and lower sections below the Three Gorges Dam—to help readers better locate these profiles before the results are presented.
In response to the suggestion that the SWAT-MODFLOW model be discussed in a dedicated paragraph, we will revise the introduction to include a separate paragraph highlighting key SWAT‑MODFLOW applications worldwide. This will also clarify the specific hydrological processes addressed in this study—such as rainfall‑runoff, crop evapotranspiration, irrigation, subsurface discharge, and surface water–groundwater interactions—that the model is well-suited to handle.
Regarding the segmentation approach, we will provide ample justification for including JLX1 in Segment 1 and for categorizing the study area into two segments. Additionally, to explain the anomalous behavior observed at the JLX1 cross-section, we will conduct a focused analysis of the uniqueness of its groundwater level response, with emphasis on the distribution characteristics of the riverine systems and anthropogenic influences.
Finally, as suggested, we will create a figure illustrating the hydraulic head groundwater drivers in each segment to further support the segmentation strategy. All of the reviewer’s wording and grammar recommendations will also be incorporated.
Citation: https://doi.org/10.5194/egusphere-2025-5682-AC1
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AC1: 'Reply on RC1', Zhang Wen, 04 Jan 2026
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RC2: 'Comment on egusphere-2025-5682', Anonymous Referee #2, 05 Jan 2026
This manuscript aims to investigate the effect of the Three Gorges Dam (TGD) on the groundwater cycle downstream. With that in mind, the authors examined the spatial extent of the Yangtze River’s influence on adjacent groundwater. The authors achieve this objective by leveraging monitoring wells and using a coupled SWAT-MODFLOW model to quantify period-specific surface water-groundwater exchanges. Additionally, the authors included a counterfactual scenario without TGD operations for comparison. The findings illustrate (1) the influence range of the Yangtze River on confined groundwater aquifers upstream and downstream, (2) the marked seasonality between the river and groundwater exchanges, and (3) the dampening effect of TGD in the overall interactions between the Yangtze River and groundwater.
I have read the manuscript with great interest. It is well-written, but needs minor revisions and clarifications. Below, I have listed comments, hoping they may help improve the manuscript’s quality.
Specific Comments
- In lines 143-144, the authors state that the groundwater in the study area is primarily recharged by precipitation. Is this a result of the study, or something that has been determined in other studies? Do you have a citation?
- This reviewer understands the limitations of the current study. However, have the authors considered the potential role of Mountain Block Recharge (MBR) (Markovich et al., 2019; Wilson & Guan, 2004) in the study area? Have you considered collecting environmental tracers to determine the age of the water in the aquifers you are studying, and to assess the potential role of regional groundwater as a source for the confined aquifers?
- It is not clear to this reviewer how the authors feed MODFLOW back into SWAT in their coupled framework. Did they use a drain boundary at the surface? What happens when the groundwater reaches the surface? Also, did the authors include a river package in the MODFLOW model that contains SWAT-derived information? I suggest including additional clarification on the model specifics to ensure interpretation and reproducibility.
- The authors briefly mention a “wavelet coherence analysis” performed on the water levels (lines 406-409). However, the reviewer is unclear about how this analysis was performed in detail. Figure A5 is pixelated, and the conclusions drawn from this analysis are not clear from the figure. I encourage the authors to provide clarifications and citations in the methods section to ease the interpretation of these results.
- I encourage the authors to include a paragraph discussing potential sources of uncertainty in their study, as well as its limitations and future work.
Technical Corrections
Besides the comments described above, I have a few technical recommendations for the manuscript.
- This is a minor comment. In the abstract (lines 29 and 31), it is not clear what the ZJ-JLX2 section and HH1 and HH2 profiles are without reading the manuscript. I suggest including a descriptive term for the profiles (e.g., upstream or downstream sections) to aid interpretation from the outset.
- In Figure 1, there are two cross-sections (1-1’ and 2-2’). However, these cross-sections are not shown in the figure until later in the text with Figure A4. I suggest referencing this earlier in the text (maybe in the paragraph starting in line 132), as it contains crucial geologic information that aids interpretation.
- Correct “cclassification” in the Figure 2 caption for (d).
- Change “SWAT-MODFLOW mode” to “SWAT-MODFLOW model” in line 421.
- Correct “amd” in line 430.
- In Table A1, the authors describe the Horizontal Hydraulic Conductivity as Kxy. This is misleading, as it makes me believe that the authors are using a different value for the off-diagonal elements of the hydraulic conductivity tensor. I suggest renaming this variable to Kx and Ky.
References
Markovich, K. H., Manning, A. H., Condon, L. E., & McIntosh, J. C. (2019). Mountain-Block Recharge: A Review of Current Understanding. Water Resources Research, 55(11), 8278–8304. https://doi.org/10.1029/2019WR025676
Wilson, J. L., & Guan, H. (2004). Mountain-Block Hydrology and Mountain-Front Recharge. In J. F. Hogan, F. M. Phillips, & B. R. Scanlon (Eds.), Groundwater Recharge in a Desert Environment: The Southwestern United States (pp. 113–137). American Geophysical Union. Retrieved from http://onlinelibrary.wiley.com/doi/10.1029/009WSA08/summary
Citation: https://doi.org/10.5194/egusphere-2025-5682-RC2 -
AC2: 'Reply on RC2', Zhang Wen, 14 Jan 2026
We thank the reviewer for the detailed comments. Regarding the specific comments raised by the reviewer, we will make the following revisions:
In response to the reviewer's points about the insufficient explanation of the groundwater recharge overview related to Mountain Block Recharge (MBR) in the study area and the inquiry into whether we conducted environmental tracer work, we will further clarify the hydrogeological conditions of this region and the degree of relevance between the Yangtze River–groundwater interaction (which is the focus of our study) and MBR. Additionally, we will thoroughly review existing environmental tracer studies in this research area to address the reviewer’s concerns regarding the sources of water in the confined aquifer. Based on our research objectives, we will also analyze the significance of environmental tracer studies for our work.
Regarding the reviewer's comment that the coupling mechanism of our SWAT-MODFLOW model was not clearly explained, we will clarify this mechanism, including whether a drain boundary at the surface was used and whether a river package in the MODFLOW model containing SWAT-derived information was applied. Here, we will focus on elaborating two key points: First, our model is actually a one-way coupling, meaning that only the transmission from SWAT to MODFLOW was implemented, while feedback from MODFLOW to SWAT was not included. The rationale for this approach lies in the fact that the connectivity of the surface water system in this region is extremely high, and the influence of groundwater processes on surface water is often overshadowed by the inherent dynamics of surface hydrology. In other words, the impact of surface hydrology on groundwater far exceeds the influence of groundwater processes on surface water, which justifies the sufficiency of a one-way coupling in our study. Second, our study area, the Four-Lake Basin, is located on the north side of the Yangtze River and does not include the Yangtze River itself within the basin boundaries. To incorporate the Yangtze River into the SWAT model framework, the model would need to be extended to the south bank of the Yangtze, which lies outside our study area. Such an extension would introduce additional uncertainties and potentially increase model errors. Given that long-term water level data for the Yangtze River are readily available, we directly used these water level data as boundary conditions in MODFLOW, rather than embedding the Yangtze River into SWAT to calculate water levels for subsequent use in MODFLOW.
Regarding the reviewer’s comment on the insufficient description of the foundational information in our wavelet coherence analysis, we will add a dedicated paragraph to clarify how the wavelet coherence results—specifically presented in Figure 4a—were obtained.
Regarding the reviewer's encouragement to add a paragraph discussing potential sources of uncertainty as well as limitations and future work, we will proactively respond by incorporating the corresponding content.
For the Technical Corrections mentioned by the reviewer, we sincerely appreciate the thorough review and will address each comment point by point.
Citation: https://doi.org/10.5194/egusphere-2025-5682-AC2
- In lines 143-144, the authors state that the groundwater in the study area is primarily recharged by precipitation. Is this a result of the study, or something that has been determined in other studies? Do you have a citation?
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RC3: 'Comment on egusphere-2025-5682', Anonymous Referee #3, 07 Jan 2026
The paper presents a combination of analysis and modeling approached to understand the impacts of the Three Gorges Dam at the hydrological and groundwater systems of the Yangtze river. I find the presented methodology interesting and well-fitting for the presented problem. The developed model can also be used as a starting point to evaluate different future management and climate scenarios for the river.
The paper is well written, illustrated with very nice figures. I found the number of abbreviations in the text sometimes a bit too much and confusing. I have a few comments and recommendations that in my opinion can improve the manuscript, I have listed them below.General comments:
- I found the investigation period a bit too narrow. For the first data-driven analysis looking at a multiyear period would be neccessary to have reliable results to handle any short-term impacts.
- Could you provide some validation for the first approach? Also a few words about validating the non-TGD modeling results would be helpful.
- While I see the value in both approaches, I don't see how the two presented methodologies are connected with each other. Was the spatial influence analysis used in any way to inform or interpret the modeling?Specific comments:
L27 - Please avoid using abbreviations in the abstract. These references to the specific sections are too specific for the abstract.
L63 - It is unclear which effects are you referring to here.
L159 - is there a reason for this specific, and relatively short time period? A reasoning for this should be provided.L220 - For me the use of the letter K for this parameter is a bit problematic as it can be confused with the hydraulic conductivity which is normally signed as K in hydrogeology. I found this a bit confusing, but I understand if the authors just followed the terminology introduced in past papers.
At the same time I find this methodology really interesting and useful, and it is great to have it done before the actual modeling. I was wondering however, whether this is a completely separate step, or are the results of this step involved in some way to the SWAT+MODFLOW modeling?
Fig 3. - this is a very nice visualization! Is there a reason that the influence is only tested on the left side of the river?L276 - does this mean that the relationship is dynamic over the year? It would be interesting if you could elaborate further, what is behind this dynamic. Also, extending the analysis to another year would be interesting to see whether the same periods behave similarly then (this could be a validation strategy).
Visualization on the changes of influence over the year would be also useful on the map.L328: a reference and a short introduction of SWAT-CUP would be needed.
Fig4. - why is the peak in 2016/6 so better captured than the one in 2015/3?
L342: the groundwater level fits are much better then the discharge - why?
Fig 6. - is the dam location at the dashed line? (This is a very good discussion figure)
L388 - refer directly to fig6b
L389 - this sentence sounds weird, please simplify it
L416 - This section is really interesting. Would it be possible with your model to simulate different dam management scenarios too (in a future work)?
Citation: https://doi.org/10.5194/egusphere-2025-5682-RC3 -
AC3: 'Reply on RC3', Zhang Wen, 14 Jan 2026
We sincerely thank the reviewer for their valuable and constructive comments. Our responses to the points raised are as follows:
Regarding the reviewer's suggestion on the necessity of basing the data-driven analysis on data from multiple years, we fully agree with the importance of this perspective. In fact, we have also conducted analyses for the years following 2021, such as 2022, 2023, and 2024. The results indicate that the interannual variation in the lateral influence range of the Yangtze River on groundwater is not significant. This is primarily because the overall rainfall fluctuations in the Yangtze River basin during these years were relatively stable, the operational scheduling of the Three Gorges Reservoir remained consistent, and localized anthropogenic extraction had minimal impact on the entire basin. Consequently, we selected 2021 as a representative year for presenting the results.
We thank the reviewer for their interest in the validation of the data-driven method and the no-TGD scenario simulations. Regarding the former (the data-driven method), we will further explore available data and integrate multiple lines of evidence to validate the robustness of the results. Regarding the latter (the no-TGD scenario), since a true non-regulated condition does not exist in reality, direct validation against field observations is inherently not feasible. Therefore, we will strengthen the rationale by emphasizing the consistency of our findings with existing physical understanding and the internal consistency of our modeling framework.
Regarding the reviewer's question about the connection between the two methods, we will provide a supplementary explanation. In fact, the purpose of conducting the data-driven analysis was to clarify the influence of the Yangtze River on lateral groundwater, specifically to demonstrate that the interaction zone between the river and groundwater is extensive and encompasses numerous surface water bodies. This finding is crucial, as it substantiates the necessity for the subsequent SWAT-MODFLOW coupled modeling study.
Regarding the Specific Comments raised by the reviewer, we will also revise the manuscript accordingly, point by point.
Citation: https://doi.org/10.5194/egusphere-2025-5682-AC3
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AC3: 'Reply on RC3', Zhang Wen, 14 Jan 2026
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This research demonstrated the impact that the TGD has the SW-GW interaction. Overall, the authors produced very interesting and valuable results. The manuscript was well written and the visualizations were designed well. I have a few minor comments below:
Line 30 - Abstract: Since the ZJ-JLX2 and HH1, HH2 is not previously described before the results – can you add in parenthesis a profile /geographic identifier (e.g. upper, lower, middle section below TGD, etc.).
Line 98 – Introduction – I recommend that you make a new paragraph for the SWAT-MODFLOW model and 1. Provide additional explanation about how and where its been used in previous research and 2. Explain and justify briefly how you will use it for this research.
Line 145: Rainfalland typo
Line 294-298: From Table 2 and 3 – It is not clear why you chose only 2 segments – the JLX1 seems like an anomaly in the segments based on Table 3– is there some justification why this is included in segment 1? I see your explanations in line 299-417 – but I’m specifically wondering why only 2 segments. Could you perhaps add a few sentences explaining this choice - or perhaps explaining the JLX1 anomaly?
Line 296: I think it would be clearer if you named the segments ZJ-JLX2 and HH1-HH2, especially since HH1-HH2 are explained this way in line 317.
Line 303-309 – These three features are the explanation for the segments – can you create a figure or visualization to show the hydraulic head groundwater drivers in each segment to justify this decision?
Section 4.3 – 4.4 – I thought the results provided here were very insightful and visualized well. The narrative was clear and you drew important connections and support from the literature.