Role of Hungry Water on Sediment Dynamics: Assessment of Valley Degradation, Bed Material Changes and Flood Inundation in Pamba River During Kerala Flood, 2018

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Title: Role of hungry water on sediment dynamics: An assessment of valley degradation, bed material changes and flood in Pamba river during Kerala Flood, 2018

 

Summary

This study investigates the role of sediment-starved (“hungry water”) dam releases in exacerbating flood dynamics during the 2018 Kerala Flood, focusing on the Pamba River basin. The authors combine hydrological data, remote sensing, field surveys, sediment characterization (grain size, SEM-EDS), and geochemical indices to demonstrate how reservoir operations amplified erosion, sediment transport, and flood impacts. The work highlights the importance of integrating sediment management into reservoir operations for flood mitigation. While the study addresses a critical gap in flood research, several methodological and contextual issues require clarification to strengthen its conclusions.

Major Concerns and Recommendations

1.Causality and Confounding Factors:

(1) While the study attributes flood amplification to the “hungry water effect,” the relative contributions of sediment-starved releases versus extreme rainfall remain unclear. A sensitivity analysis (e.g., modeling scenarios with/without dam releases) would help isolate the reservoir’s impact.

 

2.Data and Model Limitations:

(1) Streamflow data for Stations 2 and 3 are modeled (MIKE software), but validation against observed data is absent. The accuracy of these models must be demonstrated, especially given their influence on flood extent calculations.

(2) The sediment volume estimation (Rapid Reserve Estimation method) lacks methodological detail. Clarify assumptions, error margins, and validation techniques (e.g., ground-truthing via cores or LiDAR).

(3) Introducing the details of the 2018 flood monitoring

3.Spatial and Temporal Scope:

The study focuses on a single flood event (August 2018). Including historical flood data (e.g., pre-dam conditions or earlier floods) would strengthen the argument for long-term geomorphic impacts of hungry water.

 

4.Interpretation of Results:

(1) The distinction between “first-generation” and weathered sediments in Kakki Ar vs. Pamba Ar relies heavily on visual and textural observations. Quantitative metrics (e.g., roundness indices, mineralogical ratios) would add robustness.

5.Clarity and Presentation:

(1) Figures 4 and 5 (sediment distribution maps) lack scale bars and georeferenced coordinates, limiting reproducibility.

(2) The schematic model (Fig. 8) oversimplifies the hungry water process. Annotating key mechanisms (e.g., energy dissipation zones, sediment entrainment thresholds) would improve clarity.

 

Minor Issues

• Terminology: Define “hungry water” explicitly in the Introduction, citing foundational works.
• Statistical Analysis: Provide statistical tests (e.g., t-tests, ANOVA) to support claims about differences in sediment characteristics between tributaries.
• References: Update citations to include recent studies on sediment dynamics and dam impacts (e.g., post-2020 literature).

(4) Some diagrams need to be modified, such as the units of the vertical axis in Figure 2(b), and the meaning of Figure 2(c)(d)(e)

Additional Comments:

• The authors should consider collaborating with hydrologists or dam operators to obtain reservoir release records (timing, volume) for a more direct linkage to flood impacts.
• A discussion on the socio-economic implications of hungry water (e.g., damage to infrastructure, agricultural losses) would broaden the manuscript’s relevance.

 

Conclusion

This study makes a valuable contribution to understanding the interplay between reservoir operations, sediment dynamics, and flood hazards. However, addressing the major concerns—particularly regarding causality, model validation, and spatial-temporal scope—is essential to solidify the conclusions. With revisions, this work has the potential to inform both academic discourse and practical sediment management strategies.

 

Recommendation: Minor Revision

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The investigations presented in this article are very localized and focus on a single event. It is more of a case study description than a research article. If someone considers this paper a relatively precise description of a particular event, it could be of interest.

Some parts of the text are not directly related to the research but rather provide a general description of the phenomenon, based on books. For example, the text before Chapter 5.1 in Chapter 5 is a general description and is not necessary, as it does not contribute to the discussion of the investigation results.

Figure 8 is also not connected to the research; instead, it provides a general representation of the phenomenon and would be more suitable for inclusion in a book rather than a research article. I believe that both this section of the text and Figure 8 are unnecessary.

In summary, the article is quite average and can be considered a case study.

Figure 2: Why is streamflow measured in cubic meters instead of cubic meters per second?

 

 

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors, 
Find my comments in the attachment, please.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx