the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jan 2022
Modelling the compound flood hydrodynamics under mesh convergence and future storm surge events in Brisbane River Estuary, Australia
Abstract. Floods are the most common and destructive disasters around the globe, which becomes more challenging in coastal areas due to higher population density and catchment areas relative to floods in an inland area. For effective coastal flood management to reduce flood adverse impacts it is necessary to investigate the flooding processes and their joint interaction in a coastal area. This paper selected the Brisbane River Estuary, Australia as an example, and the MIKE 21 model is applied to investigate the effects of mesh resolution on the flood discharge and to explores compound flooding by computing variances in coastal flood assessments resulting from a separation of tidal and riverine processes. The statistical results showed that the Nash-Sutcliffe coefficient, E of water level are varied from 0.84 to 0.95 and the model simulated the 2011 flood extent results agreed with 90 % accuracy with the observed flood extent. Five mesh resolutions cases were analyzed and the result found that the finer mesh resolution Case 5 was more appropriate for calculating the peak discharge with 2.7 % with estimated discharge. Compound flood event simulation results emphasized that not considering the interaction of various flooding drivers caused 0.62 m and 0.12 m reduction in the flood levels at Jindalee and Brisbane city gauges, and uncertainties in flood extent. Simulated results of flood at Brisbane city gauge, showed that 2011 and 2013 floods with storm surge scenario 4 demonstrate, the increase in flood level to be 12 % and 34 % respectively. The results recommend flooding assessment by using mesh convergence with joint probability of compound flood under future storm surge for planning and management of coastal projects.
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Status: closed
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RC1: 'Comment on nhess-2021-284', Anonymous Referee #1, 11 Mar 2022
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-284/nhess-2021-284-RC1-supplement.pdf
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AC2: 'Reply on RC1', Usman Khalil, 16 Jun 2022
Reviewer 1 Comments Reply
Criteria:
1) Scientific Significance Does the manuscript represent a substantial contribution to the understanding of natural hazards and their consequences (new concepts, ideas, methods, or data)?
The idea of the manuscript is interesting, and the datasets and methods used are appropriate.
Yes, the study has enough scientific merit for publication. It is not particularly original but is a useful case study.
Response: Thanks for your valuable comment.
2) Scientific Quality: Are the scientific and/or technical approaches and the applied methods valid? Are the results discussed in an appropriate and balanced way (clarity of concepts and discussion, consideration of related work, including appropriate references)?
The abstract is good, although a little editing would make it even better. The logic followed in the abstract and introduction is clear.
However, the methodology is poorly described. It is necessary to establish in Mike 21 model calibration how the different adjustment parameters influence the modeling conditions for each case in order to be able to perform traceability of results (you could add a table for each case). It is also necessary to incorporate the errors of the parameters as they influence the scales of the intervening processes.
The manuscript’s results are presented in a way that allows the reader to draw their own conclusions.
Response: Thanks for your valuable comment. The abstract is reviewed and edited as per the reviewer's advice. We have gone through the whole manuscript again and have added several changes that will help in the clarification and in the understanding of the paper. The track change paper would be helpful to identify changes.
The Figure has illustrated that the refining mesh and changing Manning’s n are two main parameters for refining the results. The following were added in lines 155 and 156 “The manning’s n and mesh convergence were used for the calibration of the model and to study various model scenarios”
3) Presentation Quality: Are the scientific data, results and conclusions presented in a clear, concise, and well-structured way (number and quality of figures/tables, appropriate use of technical and English language, simplicity of the language)?
Possibly – the figures could be clarified and quality too, please standardize font sizes in graphics. The English language is clear…
Response: Thanks for your valuable comment. The figure's font sizes have been standardized and graphics are enhanced.
Citation: https://doi.org/10.5194/nhess-2021-284-AC2
-
AC2: 'Reply on RC1', Usman Khalil, 16 Jun 2022
-
RC2: 'Comment on nhess-2021-284', Anonymous Referee #2, 11 May 2022
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-284/nhess-2021-284-RC2-supplement.pdf
-
AC1: 'Reply on RC2', Usman Khalil, 16 Jun 2022
Reviewer 2 Comments Reply
Title: Is ‘mesh convergence’ a well known term? I understood there are two directions (mesh resolution, and compound events in future) in this manuscript, but I believe there should be a ‘meeting point’, and reflected in title.
Response: Thanks for your valuable comment. We have changed the title to “Investigating compound flooding by using hydrodynamic modelling under mesh resolution and future storm surge events in Brisbane River Estuary, Australia”
Abstract
L16 , ‘investigate the flooding processes …’ is it from sea side?
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter.
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right?
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12
Response: Thanks for your valuable comment.
L16, ‘investigate the flooding processes …’ is it from sea side? Yes, it is from the seaside.
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter
We have added model details here ‘ The boundary conditions were added in the MIKE 21 model and calibration of the model was performed by changing Manning’s n.” The N-S coefficient is used by many authors to compare the statistical results of the models (Kumbier et al., 2018, Shrestha et al., 2020).
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right? We agreed, we have calculated the error between estimated discharge and simulated discharge and presented in Table 4. Further, we compared the peak discharge comparison with the observed data and presented the peak error.
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12. We have modified it in the abstract “Compound flood event simulation results emphasized that not considering the tidal boundaries caused a 0.62 m and 0.12 m reduction in the flood levels at Jindalee and Brisbane city gauges, and uncertainties in flood extent.” It cant be plus and minus
Introduction
L40, ‘USD’ should be ‘$US’, to be consistent with L38?
L56, I think here could start a separate paragraph for modeling work. The first paragraph is quite long.
L82, ‘The recent flooding’ is the right word to describe such a widespread disaster. L85-86, I believe only events could not ‘specify the needs’. I would more believe, ‘more frequent or more costly events’ is the wording should be specified here.
L92-93, ‘tidal flooding’ is not defined. Is it should be ‘storm surge’ as defined.
Response: Thanks for your valuable comment. All above suggestions are agreed upon and incorporated and changes are made in the paper as suggested by the reviewer.
Methods
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
Fig. 3, very bad quality figures.
L234-243, should be moved to Introduction?
Fig.5, base scenario and scenario4 have very similar blue color.
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Response: Thanks for your valuable comment.
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
We have modified it and added the following “Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig. 3, very bad quality figures.
We have modified the Fig. 3
L234-243, should be moved to Introduction?
We have moved it in the introduction
Fig.5, base scenario and scenario4 have very similar blue color.
The colour is changed as advised
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Yes, we agreed that the wind speed and direction is not considered for the MIKE 21 Modelling. The study of (Yu et al., 2016), illustrates that alongshore movement was mainly driven by the tidal current and wind effects were less significant in the Brisbane estuary. That’s why we ignored the wind effect in this study.
Results
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
Response: Thanks for your valuable comment.
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
The trade-off is the point where further increase in mesh refinement doesn’t improve the result and increases the computational time. As mentioned before ““Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
The sewage system is not relevant to Brisbane Rive. We are not aware of any study that discusses the sewage system for different flood extents in the Brisbane River.
KUMBIER, K., CABRAL CARVALHO, R., VAFEIDIS, A. T. & WOODROFFE, C. D. 2018. Investigating compound flooding in an estuary using hydrodynamic modelling: a case study from the Shoalhaven River, Australia.
SHRESTHA, A., BHATTACHARJEE, L., BARAL, S., THAKUR, B., JOSHI, N., KALRA, A. & GUPTA, R. Understanding Suitability of MIKE 21 and HEC-RAS for 2D Floodplain Modeling. 2020. American Society of Civil Engineers.
YU, Y., ZHANG, H., SPENCER, D., DUNN, R. J. K. & LEMCKERT, C. 2016. An investigation of dispersion characteristics in shallow coastal waters. Estuarine, Coastal and Shelf Science, 180, 21-32.
Citation: https://doi.org/10.5194/nhess-2021-284-AC1 -
AC3: 'Reply on RC2', Usman Khalil, 16 Jun 2022
Reviewer 2 Comments
Title: Is ‘mesh convergence’ a well known term? I understood there are two directions (mesh resolution, and compound events in future) in this manuscript, but I believe there should be a ‘meeting point’, and reflected in title.
Response: Thanks for your valuable comment. We have changed the title to “Investigating compound flooding by using hydrodynamic modelling under mesh resolution and future storm surge events in Brisbane River Estuary, Australia”
Abstract
L16 , ‘investigate the flooding processes …’ is it from sea side?
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter.
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right?
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12
Response: Thanks for your valuable comment.
L16, ‘investigate the flooding processes …’ is it from sea side? Yes, it is from the seaside.
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter
We have added model details here ‘ The boundary conditions were added in the MIKE 21 model and calibration of the model was performed by changing Manning’s n.” The N-S coefficient is used by many authors to compare the statistical results of the models (Kumbier et al., 2018, Shrestha et al., 2020).
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right? We agreed, we have calculated the error between estimated discharge and simulated discharge and presented in Table 4. Further, we compared the peak discharge comparison with the observed data and presented the peak error.
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12. We have modified it in the abstract “Compound flood event simulation results emphasized that not considering the tidal boundaries caused a 0.62 m and 0.12 m reduction in the flood levels at Jindalee and Brisbane city gauges, and uncertainties in flood extent.” It cant be plus and minus
Introduction
L40, ‘USD’ should be ‘$US’, to be consistent with L38?
L56, I think here could start a separate paragraph for modeling work. The first paragraph is quite long.
L82, ‘The recent flooding’ is the right word to describe such a widespread disaster. L85-86, I believe only events could not ‘specify the needs’. I would more believe, ‘more frequent or more costly events’ is the wording should be specified here.
L92-93, ‘tidal flooding’ is not defined. Is it should be ‘storm surge’ as defined.
Response: Thanks for your valuable comment. All above suggestions are agreed upon and incorporated and changes are made in the paper as suggested by the reviewer.
Methods
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
Fig. 3, very bad quality figures.
L234-243, should be moved to Introduction?
Fig.5, base scenario and scenario4 have very similar blue color.
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Response: Thanks for your valuable comment.
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
We have modified it and added the following “Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig. 3, very bad quality figures.
We have modified the Fig. 3
L234-243, should be moved to Introduction?
We have moved it in the introduction
Fig.5, base scenario and scenario4 have very similar blue color.
The colour is changed as advised
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Yes, we agreed that the wind speed and direction is not considered for the MIKE 21 Modelling. The study of (Yu et al., 2016), illustrates that alongshore movement was mainly driven by the tidal current and wind effects were less significant in the Brisbane estuary. That’s why we ignored the wind effect in this study.
Results
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
Response: Thanks for your valuable comment.
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
The trade-off is the point where further increase in mesh refinement doesn’t improve the result and increases the computational time. As mentioned before ““Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
The sewage system is not relevant to Brisbane Rive. We are not aware of any study that discusses the sewage system for different flood extents in the Brisbane River.
KUMBIER, K., CABRAL CARVALHO, R., VAFEIDIS, A. T. & WOODROFFE, C. D. 2018. Investigating compound flooding in an estuary using hydrodynamic modelling: a case study from the Shoalhaven River, Australia.
SHRESTHA, A., BHATTACHARJEE, L., BARAL, S., THAKUR, B., JOSHI, N., KALRA, A. & GUPTA, R. Understanding Suitability of MIKE 21 and HEC-RAS for 2D Floodplain Modeling. 2020. American Society of Civil Engineers.
YU, Y., ZHANG, H., SPENCER, D., DUNN, R. J. K. & LEMCKERT, C. 2016. An investigation of dispersion characteristics in shallow coastal waters. Estuarine, Coastal and Shelf Science, 180, 21-32.
Citation: https://doi.org/10.5194/nhess-2021-284-AC3
-
AC1: 'Reply on RC2', Usman Khalil, 16 Jun 2022
Status: closed
-
RC1: 'Comment on nhess-2021-284', Anonymous Referee #1, 11 Mar 2022
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-284/nhess-2021-284-RC1-supplement.pdf
-
AC2: 'Reply on RC1', Usman Khalil, 16 Jun 2022
Reviewer 1 Comments Reply
Criteria:
1) Scientific Significance Does the manuscript represent a substantial contribution to the understanding of natural hazards and their consequences (new concepts, ideas, methods, or data)?
The idea of the manuscript is interesting, and the datasets and methods used are appropriate.
Yes, the study has enough scientific merit for publication. It is not particularly original but is a useful case study.
Response: Thanks for your valuable comment.
2) Scientific Quality: Are the scientific and/or technical approaches and the applied methods valid? Are the results discussed in an appropriate and balanced way (clarity of concepts and discussion, consideration of related work, including appropriate references)?
The abstract is good, although a little editing would make it even better. The logic followed in the abstract and introduction is clear.
However, the methodology is poorly described. It is necessary to establish in Mike 21 model calibration how the different adjustment parameters influence the modeling conditions for each case in order to be able to perform traceability of results (you could add a table for each case). It is also necessary to incorporate the errors of the parameters as they influence the scales of the intervening processes.
The manuscript’s results are presented in a way that allows the reader to draw their own conclusions.
Response: Thanks for your valuable comment. The abstract is reviewed and edited as per the reviewer's advice. We have gone through the whole manuscript again and have added several changes that will help in the clarification and in the understanding of the paper. The track change paper would be helpful to identify changes.
The Figure has illustrated that the refining mesh and changing Manning’s n are two main parameters for refining the results. The following were added in lines 155 and 156 “The manning’s n and mesh convergence were used for the calibration of the model and to study various model scenarios”
3) Presentation Quality: Are the scientific data, results and conclusions presented in a clear, concise, and well-structured way (number and quality of figures/tables, appropriate use of technical and English language, simplicity of the language)?
Possibly – the figures could be clarified and quality too, please standardize font sizes in graphics. The English language is clear…
Response: Thanks for your valuable comment. The figure's font sizes have been standardized and graphics are enhanced.
Citation: https://doi.org/10.5194/nhess-2021-284-AC2
-
AC2: 'Reply on RC1', Usman Khalil, 16 Jun 2022
-
RC2: 'Comment on nhess-2021-284', Anonymous Referee #2, 11 May 2022
The comment was uploaded in the form of a supplement: https://nhess.copernicus.org/preprints/nhess-2021-284/nhess-2021-284-RC2-supplement.pdf
-
AC1: 'Reply on RC2', Usman Khalil, 16 Jun 2022
Reviewer 2 Comments Reply
Title: Is ‘mesh convergence’ a well known term? I understood there are two directions (mesh resolution, and compound events in future) in this manuscript, but I believe there should be a ‘meeting point’, and reflected in title.
Response: Thanks for your valuable comment. We have changed the title to “Investigating compound flooding by using hydrodynamic modelling under mesh resolution and future storm surge events in Brisbane River Estuary, Australia”
Abstract
L16 , ‘investigate the flooding processes …’ is it from sea side?
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter.
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right?
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12
Response: Thanks for your valuable comment.
L16, ‘investigate the flooding processes …’ is it from sea side? Yes, it is from the seaside.
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter
We have added model details here ‘ The boundary conditions were added in the MIKE 21 model and calibration of the model was performed by changing Manning’s n.” The N-S coefficient is used by many authors to compare the statistical results of the models (Kumbier et al., 2018, Shrestha et al., 2020).
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right? We agreed, we have calculated the error between estimated discharge and simulated discharge and presented in Table 4. Further, we compared the peak discharge comparison with the observed data and presented the peak error.
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12. We have modified it in the abstract “Compound flood event simulation results emphasized that not considering the tidal boundaries caused a 0.62 m and 0.12 m reduction in the flood levels at Jindalee and Brisbane city gauges, and uncertainties in flood extent.” It cant be plus and minus
Introduction
L40, ‘USD’ should be ‘$US’, to be consistent with L38?
L56, I think here could start a separate paragraph for modeling work. The first paragraph is quite long.
L82, ‘The recent flooding’ is the right word to describe such a widespread disaster. L85-86, I believe only events could not ‘specify the needs’. I would more believe, ‘more frequent or more costly events’ is the wording should be specified here.
L92-93, ‘tidal flooding’ is not defined. Is it should be ‘storm surge’ as defined.
Response: Thanks for your valuable comment. All above suggestions are agreed upon and incorporated and changes are made in the paper as suggested by the reviewer.
Methods
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
Fig. 3, very bad quality figures.
L234-243, should be moved to Introduction?
Fig.5, base scenario and scenario4 have very similar blue color.
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Response: Thanks for your valuable comment.
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
We have modified it and added the following “Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig. 3, very bad quality figures.
We have modified the Fig. 3
L234-243, should be moved to Introduction?
We have moved it in the introduction
Fig.5, base scenario and scenario4 have very similar blue color.
The colour is changed as advised
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Yes, we agreed that the wind speed and direction is not considered for the MIKE 21 Modelling. The study of (Yu et al., 2016), illustrates that alongshore movement was mainly driven by the tidal current and wind effects were less significant in the Brisbane estuary. That’s why we ignored the wind effect in this study.
Results
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
Response: Thanks for your valuable comment.
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
The trade-off is the point where further increase in mesh refinement doesn’t improve the result and increases the computational time. As mentioned before ““Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
The sewage system is not relevant to Brisbane Rive. We are not aware of any study that discusses the sewage system for different flood extents in the Brisbane River.
KUMBIER, K., CABRAL CARVALHO, R., VAFEIDIS, A. T. & WOODROFFE, C. D. 2018. Investigating compound flooding in an estuary using hydrodynamic modelling: a case study from the Shoalhaven River, Australia.
SHRESTHA, A., BHATTACHARJEE, L., BARAL, S., THAKUR, B., JOSHI, N., KALRA, A. & GUPTA, R. Understanding Suitability of MIKE 21 and HEC-RAS for 2D Floodplain Modeling. 2020. American Society of Civil Engineers.
YU, Y., ZHANG, H., SPENCER, D., DUNN, R. J. K. & LEMCKERT, C. 2016. An investigation of dispersion characteristics in shallow coastal waters. Estuarine, Coastal and Shelf Science, 180, 21-32.
Citation: https://doi.org/10.5194/nhess-2021-284-AC1 -
AC3: 'Reply on RC2', Usman Khalil, 16 Jun 2022
Reviewer 2 Comments
Title: Is ‘mesh convergence’ a well known term? I understood there are two directions (mesh resolution, and compound events in future) in this manuscript, but I believe there should be a ‘meeting point’, and reflected in title.
Response: Thanks for your valuable comment. We have changed the title to “Investigating compound flooding by using hydrodynamic modelling under mesh resolution and future storm surge events in Brisbane River Estuary, Australia”
Abstract
L16 , ‘investigate the flooding processes …’ is it from sea side?
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter.
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right?
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12
Response: Thanks for your valuable comment.
L16, ‘investigate the flooding processes …’ is it from sea side? Yes, it is from the seaside.
L20, There is a ‘jump’ here. I do not believe N-S coefficient is well known parameter
We have added model details here ‘ The boundary conditions were added in the MIKE 21 model and calibration of the model was performed by changing Manning’s n.” The N-S coefficient is used by many authors to compare the statistical results of the models (Kumbier et al., 2018, Shrestha et al., 2020).
L23, ‘with 2.7% with estimated discharge’? It sounds like the error is between peak discharge and estimated discharge. It should be the error between simulated and estimated discharge during peak discharge time, right? We agreed, we have calculated the error between estimated discharge and simulated discharge and presented in Table 4. Further, we compared the peak discharge comparison with the observed data and presented the peak error.
L26, ‘and uncertainties in flood extent’ could be add as a plus-minus sign to 0.62 and 0.12. We have modified it in the abstract “Compound flood event simulation results emphasized that not considering the tidal boundaries caused a 0.62 m and 0.12 m reduction in the flood levels at Jindalee and Brisbane city gauges, and uncertainties in flood extent.” It cant be plus and minus
Introduction
L40, ‘USD’ should be ‘$US’, to be consistent with L38?
L56, I think here could start a separate paragraph for modeling work. The first paragraph is quite long.
L82, ‘The recent flooding’ is the right word to describe such a widespread disaster. L85-86, I believe only events could not ‘specify the needs’. I would more believe, ‘more frequent or more costly events’ is the wording should be specified here.
L92-93, ‘tidal flooding’ is not defined. Is it should be ‘storm surge’ as defined.
Response: Thanks for your valuable comment. All above suggestions are agreed upon and incorporated and changes are made in the paper as suggested by the reviewer.
Methods
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
Fig. 3, very bad quality figures.
L234-243, should be moved to Introduction?
Fig.5, base scenario and scenario4 have very similar blue color.
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Response: Thanks for your valuable comment.
L221-223, this key part of the ‘mesh convergence’ is not introduced clearly. As a concept of ‘convergence’, one needs to present an asymptotic line and define a threshold. Furthermore, convergence is not only related to the error of the water levels, it should be combined with the computation time together (in L218).
We have modified it and added the following “Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig. 3, very bad quality figures.
We have modified the Fig. 3
L234-243, should be moved to Introduction?
We have moved it in the introduction
Fig.5, base scenario and scenario4 have very similar blue color.
The colour is changed as advised
L262, if MIKE 21 has not considered wind and pressure, the application of this model in a real storm surge case is very limited. In principle, it can be only used for some numerical experiments as what authors did. So, some discussion on the direction is needed.
Yes, we agreed that the wind speed and direction is not considered for the MIKE 21 Modelling. The study of (Yu et al., 2016), illustrates that alongshore movement was mainly driven by the tidal current and wind effects were less significant in the Brisbane estuary. That’s why we ignored the wind effect in this study.
Results
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
Response: Thanks for your valuable comment.
L316-318, I can understand this statement. For sure, better resolution gives better results. However, there is no quantification in the increase in computational time. I could not see how authors considered the trade-off between resolution and computational costs. Therefore, a bit more details (maybe on why errors of flood extents in these areas are rather acceptable) would be very helpful for the similar applications.
The trade-off is the point where further increase in mesh refinement doesn’t improve the result and increases the computational time. As mentioned before ““Computational mesh grid size was reduced in an iteration to observe the effect on simulated water levels and computational time. The mesh grid size was modified until the increase or decree of size make a considerable effect on water levels and computational time. When there was no considerable change in the simulated water levels and computational time was increased substantially, we then stopped the mesh changing and adopted the mesh resolution with confidence, as it was optimum size with computational time and simulated water levels”.
Fig.12 I have not seen sewage system is mentioned. I have seen some papers discussed the impact on sewage system when considering different flood extents scenarios. Is it relevant to Brisbane?
The sewage system is not relevant to Brisbane Rive. We are not aware of any study that discusses the sewage system for different flood extents in the Brisbane River.
KUMBIER, K., CABRAL CARVALHO, R., VAFEIDIS, A. T. & WOODROFFE, C. D. 2018. Investigating compound flooding in an estuary using hydrodynamic modelling: a case study from the Shoalhaven River, Australia.
SHRESTHA, A., BHATTACHARJEE, L., BARAL, S., THAKUR, B., JOSHI, N., KALRA, A. & GUPTA, R. Understanding Suitability of MIKE 21 and HEC-RAS for 2D Floodplain Modeling. 2020. American Society of Civil Engineers.
YU, Y., ZHANG, H., SPENCER, D., DUNN, R. J. K. & LEMCKERT, C. 2016. An investigation of dispersion characteristics in shallow coastal waters. Estuarine, Coastal and Shelf Science, 180, 21-32.
Citation: https://doi.org/10.5194/nhess-2021-284-AC3
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AC1: 'Reply on RC2', Usman Khalil, 16 Jun 2022
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