Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The study presents a detailed analysis of the effects of the Dubai Creek extension on its hydrodynamics and water quality. Good findings reported, but study need major revision before it is considered for publication.

a)     The study appears to focus on a specific snapshot of conditions, either before or after the creek extension, but does not mention the duration over which data were collected or how seasonal variations might affect hydrodynamic and flushing patterns. Water quality and hydrodynamics can change significantly over time, depending on factors such as temperature, rainfall, tides, and seasonal urban activity. Long-term monitoring would provide a more robust understanding of the extension's impact.

b)    The study mentions the calibration and validation of the hydrodynamic models with "correlation values close to 1" and small RMSE and Bias, which indicates good model performance. However, there is no mention of a sensitivity analysis to identify the key parameters that have the most significant impact on model outputs. This analysis would help understand the uncertainty in the results and the robustness of conclusions based on different assumptions or input variations.

c)     While the study focuses on hydrodynamics and water flushing, it does not seem to explicitly account for anthropogenic influences such as wastewater discharge, industrial activities, or maritime traffic. These factors are likely to play a crucial role in the water quality of Dubai Creek. Ignoring such variables may lead to an incomplete understanding of the overall water quality improvement and the potential impact on the local aquatic ecosystem.

d)    Flushing models are typically sensitive to assumptions regarding flow patterns, pollutant types, and environmental conditions. The study does not discuss the simplifications or assumptions made in the flushing models. For example, it is unclear whether the model considers the full range of pollutants (e.g., heavy metals, nutrients, oils) or assumes a homogenous pollutant distribution across the creek. A more detailed pollutant characterization and more complex models that account for varying pollutant dynamics would provide a more accurate picture.

e)     The paper mentions that the hydrodynamic models are calibrated to replicate conditions before the extension. However, it does not clarify how well the pre-extension data represents the natural conditions of the creek before rapid urbanization. Given the high degree of urbanization in Dubai, the natural hydrodynamics and flushing patterns of the creek may have been significantly altered even before the extension project. More comprehensive historical data or baseline conditions would strengthen the analysis.

f)     While numerical models are powerful tools, their results depend heavily on assumptions and input data. The study might place too much emphasis on the model outcomes without adequate real-world verification. Comparing model results with real-time field measurements (e.g., actual water quality samples and current measurements) could provide validation and ensure the reliability of the conclusions drawn from the modelling effort.

Author Response

Comment (a): The study appears to focus on a specific snapshot of conditions, either before or after the creek extension, but does not mention the duration over which data were collected or how seasonal variations might affect hydrodynamic and flushing patterns. Water quality and hydrodynamics can change significantly over time, depending on factors such as temperature, rainfall, tides, and seasonal urban activity. Long-term monitoring would provide a more robust understanding of the extension's impact.

Response: Thank you for emphasizing the importance of long-term monitoring. The primary objective of this study was to specifically examine the flushing and water circulation characteristics in Dubai Creek as a direct result of the creek extension. While Authors acknowledge that hydrodynamics and water quality can be influenced by factors such as temperature, rainfall, and seasonal urban activities, our study was deliberately focused on isolating the impact of the creek extension itself. Expanding the scope to include long-term seasonal variations would have diverted attention from our primary goal of understanding the direct effects of the extension. Authors propose that a comprehensive, long-term study examining seasonal and interannual variations would be a valuable direction for future research.

Reviewer Comment (b): The study mentions the calibration and validation of the hydrodynamic models with "correlation values close to 1" and small RMSE and Bias, which indicates good model performance. However, there is no mention of a sensitivity analysis to identify the key parameters that have the most significant impact on model outputs. This analysis would help understand the uncertainty in the results and the robustness of conclusions based on different assumptions or input variations.

Response: The authors appreciate the suggestion regarding the importance of sensitivity analysis in understanding model uncertainties. The primary aim of this study was to evaluate the model's ability to reproduce observed hydrodynamic conditions rather than to conduct a comprehensive uncertainty analysis. While we recognize that sensitivity analysis is valuable, the calibration and validation results, showing high correlation and low error metrics, were considered sufficient to demonstrate model accuracy for the specific objectives of our study. The authors agree that performing a sensitivity analysis would enhance the model's robustness; however, it was beyond the scope of this investigation. We recommend this as a potential focus for future studies aimed at exploring the impacts of parameter variability on long-term hydrodynamic predictions.

Reviewer Comment (c): While the study focuses on hydrodynamics and water flushing, it does not seem to explicitly account for anthropogenic influences such as wastewater discharge, industrial activities, or maritime traffic. These factors are likely to play a crucial role in the water quality of Dubai Creek. Ignoring such variables may lead to an incomplete understanding of the overall water quality improvement and the potential impact on the local aquatic ecosystem.

Response: Thank you for your comment. The primary objective of this research was to isolate the impact of the creek extension on hydrodynamic patterns, independent of external anthropogenic influences. Including variables such as wastewater discharge, industrial activities, and maritime traffic would introduce complexities that are outside the scope of this study. The exclusion of these factors was intentional to focus solely on the structural modification of the creek and its direct effect on the flushing and water renewal of the water system. Future studies could build upon this work by incorporating these anthropogenic influences to provide a more comprehensive assessment of the creek's water quality and ecosystem dynamics.

Reviewer Comment (d): Flushing models are typically sensitive to assumptions regarding flow patterns, pollutant types, and environmental conditions. The study does not discuss the simplifications or assumptions made in the flushing models. For example, it is unclear whether the model considers the full range of pollutants (e.g., heavy metals, nutrients, oils) or assumes a homogenous pollutant distribution across the creek. A more detailed pollutant characterization and more complex models that account for varying pollutant dynamics would provide a more accurate picture.

Response: Thank you for raising this point. The flushing analysis in our study utilized a simplified model that assumes a homogeneous distribution of pollutants, which is a common approach for initial hydrodynamic assessments. The focus was on the overall flushing capacity rather than detailed pollutant dynamics. A more complex model considering specific pollutant types and their interactions would indeed provide a deeper understanding. However, this approach requires additional data on pollutant sources and distribution, which is not readily available. Authors suggest that future research could incorporate pollutant characterization, provided the necessary data is accessible, for a more detailed assessment.

Reviewer Comment (e): The paper mentions that the hydrodynamic models are calibrated to replicate conditions before the extension. However, it does not clarify how well the pre-extension data represents the natural conditions of the creek before rapid urbanization. Given the high degree of urbanization in Dubai, the natural hydrodynamics and flushing patterns of the creek may have been significantly altered even before the extension project. More comprehensive historical data or baseline conditions would strengthen the analysis.

Response: Thank you for your comment. Authors acknowledge the concern regarding the representativeness of pre-extension conditions. The available pre-extension data reflect the hydrodynamic state of the creek just before the extension, but within an already urbanized context. Historical data extending before significant urbanization were not accessible for this study. Therefore, our analysis was based on the best available dataset, acknowledging the limitations imposed by existing urban modifications. Future research could explore historical datasets, if available, to reconstruct baseline conditions prior to extensive urban development.

Reviewer Comment (f): While numerical models are powerful tools, their results depend heavily on assumptions and input data. The study might place too much emphasis on the model outcomes without adequate real-world verification. Comparing model results with real-time field measurements (e.g., actual water quality samples and current measurements) could provide validation and ensure the reliability of the conclusions drawn from the modelling effort.

Response: Thank you for your valuable comment. Authors appreciate the emphasis on real-world verification. Our study relied on historical datasets of tidal levels for calibration and validation. The strong correlation and low error metrics between model predictions and observed data indicate satisfactory performance of the hydrodynamic model. It is important to note that the current model focuses on hydrodynamic processes rather than specific water quality parameters. As such, it provides insights into flushing dynamics without simulating individual water quality constituents. In future work, the model could be expanded to incorporate parameter-specific water quality simulations. At that stage, real-time field measurements, such as water quality sampling and in-situ current measurements, would be critical for robust validation to ensure the reliability of the extended model in practical applications.

 

Reviewer 2 Report

Comments and Suggestions for Authors

I suggest the authors to make the following addition and correction of the manuscript

 

1. Line 143 -145: Explain how specific data values ​​are for model development that include bathymetry, current speed and direction, and water level data.

2. Line 208 -209: What statistical parameters were used to compare observed and modeled water levels and instantaneous speed and direction?

3. Line 271: duration from 09/12/2013 to 03/01/2013

4. Line 375 – 379: What hydraulic features along the stream further contribute to water retention?

5. Line 386 – 388: Explain in more detail how hydrodynamic models are created, calibrated and validated

6. Extend the conclusion by applying the research results to other coastal cities in the world with an emphasis on the necessary restrictions.

Author Response

1. Line 143 -145: Explain how specific data values are for model development that include bathymetry, current speed and direction, and water level data.

Response: Authors appreciate this suggestion and have added a detailed explanation regarding the role of bathymetry, current speed and direction, and water level data in the model development.

2. Line 208 -209: What statistical parameters were used to compare observed and modeled water levels and instantaneous speed and direction?

Response: The statistical parameters used for comparison are reported in the next paragraph and are Root Mean Square Error (RMSE), bias, and the correlation coefficient (r) as could be seen in line 217 – 218.

3. Line 271: duration from 09/12/2013 to 03/01/2013

Response: Thank you for identifying this error. Author shave corrected the time period to reflect the intended range.

4. Line 375 – 379: What hydraulic features along the stream further contribute to water retention?

Response: Authors agree that more detail would improve clarity. Additional explanations about specific hydraulic features have been added in line 380 - 381.

5. Line 386 – 388: Explain in more detail how hydrodynamic models are created, calibrated and validated

Response: Authors have expanded the discussion on the creation, calibration, and validation processes of the hydrodynamic models.

6. Extend the conclusion by applying the research results to other coastal cities in the world with an emphasis on the necessary restrictions.

Response: This is a good point, and Authors have extended the conclusion to discuss how the findings can inform strategies for other coastal cities, emphasizing context-specific limitations.

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Authors response is satisfactory.