the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Sep 2024
The dynamics of peak head responses at Dutch canal dikes and the impact of climate change
Abstract. The management of water and flood risk levels in low-lying polder regions depends on the performance of canal dikes. Heavy rainfall can lead to peak hydraulic heads within the dikes affecting their stability, which can induce dike breaches. Variations in head responses and head statistics are both relevant for regional flood risk analysis of canal dike systems. This study examined the dynamics of peak heads in canal dikes on a national scale using time series models calibrated on observed heads. Various model structures are evaluated and a nonlinear model performed the best. These models were used to simulate long-term head time series. Subsequently, dike clusters were identified based on the coincidence of peak heads, allowing for the identification of dikes where peaks are caused by (dis)similar types of rainfall events. The differences and similarities in peak head response were related to physical dike characteristics. While no single significant relationship emerged, the soil type combined with the width of the dike appears to be important factors influencing the variation in head responses. However, the presence of the same soil type and dike widths in multiple clusters indicates that these characteristics do not yield a definitive outcome for the head response. Moreover, peak head statistics across various dikes were derived and indicated that extreme and yearly load conditions are relatively close to each other, with a median decimation height of only 15 centimeters. The head statistics are affected by climate change, characterized by increasing winter precipitation and summer evaporation. By 2100, extreme peak heads are expected to occur between 3 times less and 8 times more frequently, depending on the climate scenario and the type of canal dike.
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RC1: 'Comment on egusphere-2024-1495', Anonymous Referee #1, 02 Dec 2024
The paper reports on a comprehensive analysis of dike strength and failure for a large number of polder dikes across the Netherlands. Using a model for dike 'ground'water head calculation and time series of precipitation and evapotranspiration, the model produces time series of water heads in dikes. Results are statistically analysed, including grouping of dike types across the area.
The subject fits well to the scope of NHESS, and addresses a field that has received increasing attention, both in water management and (applied) research into dike stability and flood risk.
Still the manuscript requires revision before final publication. My main points are:
- I miss a spatial component in the discussions of clusters and 'correlation': how would a map indicating cluster member of dike sections look - is there any spatial correlation, or not?
- The meaning of the clusters determined from the statistical analyses remains a unclear - what do they tell us, and how do these contribute to the overall objective, i.e. predicting dike stability over large areas, under conditions of extreme precipitation. I got the impression that a different type of clustering would have added more insight.
- The discussion section should me restructured and complemented with thoughts about climate change impacts, and implications for the dikes, and their management.
- The conclusions are too much a summary: rewrite these in 'conclusive' style, not a story of what you did.
- At several points the text is wordy, or unclear - see specific comments.
In the attached pdf I have put my detailed comments.
- AC1: 'Reply on RC1', Bart Strijker, 07 Feb 2025
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RC2: 'Comment on egusphere-2024-1495', Anonymous Referee #2, 20 Jan 2025
This manuscript outlines an application of time series models using impulse response functions to model the hydraulic heads observed with dike systems in the Netherlands. Different model structures are tested to simulate the heads, with a nonlinear-threshold model (TARSO) found to perform the best. This is an interesting result, that could teach us something about how the heads in dike systems respond to precipitation and potential evaporation. The study attempts to relate model characteristics to various physical characteristics of the dike systems, with moderate success. I generally found the manuscript well written and the figure quality appropriate. The topic fits the scope of the journal. I have a couple of major comments that should be addressed, and some minor technical comments at the bottom.
- One thing I was missing in the manuscript is an explanation and interpretation of why the threshold nonlinear model structure (TARSO) works best for the hydraulic heads in Dikes in the Netherlands. This is a surprising outcome to me, that deserves more thought and might be informative for future attempts to model the heads in dikes. This model was designed for a different type of system (groundwater levels in polders, influenced by ditches falling dry and being activated). Perhaps there is topping-off of the heads in dikes. These types of models are commonly used to gain understanding of how groundwater systems function, and why. A discussion of this type is currently missing from the manuscript but would be a welcome addition.
- Looking at Figure 6, I was very surprised by the simulated behavior of the FlexModel given that all models share the same input and not be that far off from each other. I made a quick script to model the data using the Pastas default values to better understand the result but got an average of R2=0.68 for the FlexModel, much higher than the reported value of 0.32. I suspect some suboptimal choices were made for that model. Perhaps the Authors can revisit the scripts and double-check this, or explain this result in more detail.
- I assessed the manuscript for its reproducibility. I appreciate the authors providing the original head, precipitation, and evaporation data is provided. This data provides a unique dataset on head measurement in dike systems, which might be worth highlighting in the manuscript. I note here that none of the data underlying the results shown in the figures and tables are shared, nor are the scripts that lead to the results. This makes it difficult to verify the results and/or build upon this work. I would recommend the authors to share the scripts and output data on a FAIR repository to improve the reproducibility of this study.
Minor technical suggestions:
- L84: Potential evaporation
- L195: Figure 4 and 5 appear to be the same. I am not sure if another figure is meant to be here. Otherwise Figure 5 can be removed.
- L192: How well does GeoTop actually work for dikes? I can imagine that these are not related at all, given that dikes are built by humans with specific materials. This may influence the results later on relating outcomes to the soil types, i.e., would the relationship with the soil type improve if the GeoTop data is left out? Some consideration about this would be good here.
- L238: I think Sm is substituted by R, not the other way around.
- L276: simulate “the heads”.
- L288: How was this threshold of 0.7 determined? How sensitive are the result to changing this threshold.
- L302: Analyses
- L303: every “…”?
- L327: r2 was previously referred to as R2, check throughout
- L329: The FlexModel is a nonlinear recharge model, the other three models are not. I think the TARSO model is meant here, which still computes recharge using a linear equation.
- L342: replace by “in the summer of 2019”
- L343: disturbances
- L345: scatter plot in Figure XX.
- L366: I don’t understand what “peak block” is, please clarify.
- L496: Apparently, the head time series were filtered using some reliability criteria in this study. This should be mentioned in the section describing the data. What reliability criteria were used?
- L501: Remove “explicitly”. Uncertainty was not considered, as I understood from the manuscript.
Citation: https://doi.org/10.5194/egusphere-2024-1495-RC2 - AC2: 'Reply on RC2', Bart Strijker, 07 Feb 2025
Status: closed
-
RC1: 'Comment on egusphere-2024-1495', Anonymous Referee #1, 02 Dec 2024
The paper reports on a comprehensive analysis of dike strength and failure for a large number of polder dikes across the Netherlands. Using a model for dike 'ground'water head calculation and time series of precipitation and evapotranspiration, the model produces time series of water heads in dikes. Results are statistically analysed, including grouping of dike types across the area.
The subject fits well to the scope of NHESS, and addresses a field that has received increasing attention, both in water management and (applied) research into dike stability and flood risk.
Still the manuscript requires revision before final publication. My main points are:
- I miss a spatial component in the discussions of clusters and 'correlation': how would a map indicating cluster member of dike sections look - is there any spatial correlation, or not?
- The meaning of the clusters determined from the statistical analyses remains a unclear - what do they tell us, and how do these contribute to the overall objective, i.e. predicting dike stability over large areas, under conditions of extreme precipitation. I got the impression that a different type of clustering would have added more insight.
- The discussion section should me restructured and complemented with thoughts about climate change impacts, and implications for the dikes, and their management.
- The conclusions are too much a summary: rewrite these in 'conclusive' style, not a story of what you did.
- At several points the text is wordy, or unclear - see specific comments.
In the attached pdf I have put my detailed comments.
- AC1: 'Reply on RC1', Bart Strijker, 07 Feb 2025
-
RC2: 'Comment on egusphere-2024-1495', Anonymous Referee #2, 20 Jan 2025
This manuscript outlines an application of time series models using impulse response functions to model the hydraulic heads observed with dike systems in the Netherlands. Different model structures are tested to simulate the heads, with a nonlinear-threshold model (TARSO) found to perform the best. This is an interesting result, that could teach us something about how the heads in dike systems respond to precipitation and potential evaporation. The study attempts to relate model characteristics to various physical characteristics of the dike systems, with moderate success. I generally found the manuscript well written and the figure quality appropriate. The topic fits the scope of the journal. I have a couple of major comments that should be addressed, and some minor technical comments at the bottom.
- One thing I was missing in the manuscript is an explanation and interpretation of why the threshold nonlinear model structure (TARSO) works best for the hydraulic heads in Dikes in the Netherlands. This is a surprising outcome to me, that deserves more thought and might be informative for future attempts to model the heads in dikes. This model was designed for a different type of system (groundwater levels in polders, influenced by ditches falling dry and being activated). Perhaps there is topping-off of the heads in dikes. These types of models are commonly used to gain understanding of how groundwater systems function, and why. A discussion of this type is currently missing from the manuscript but would be a welcome addition.
- Looking at Figure 6, I was very surprised by the simulated behavior of the FlexModel given that all models share the same input and not be that far off from each other. I made a quick script to model the data using the Pastas default values to better understand the result but got an average of R2=0.68 for the FlexModel, much higher than the reported value of 0.32. I suspect some suboptimal choices were made for that model. Perhaps the Authors can revisit the scripts and double-check this, or explain this result in more detail.
- I assessed the manuscript for its reproducibility. I appreciate the authors providing the original head, precipitation, and evaporation data is provided. This data provides a unique dataset on head measurement in dike systems, which might be worth highlighting in the manuscript. I note here that none of the data underlying the results shown in the figures and tables are shared, nor are the scripts that lead to the results. This makes it difficult to verify the results and/or build upon this work. I would recommend the authors to share the scripts and output data on a FAIR repository to improve the reproducibility of this study.
Minor technical suggestions:
- L84: Potential evaporation
- L195: Figure 4 and 5 appear to be the same. I am not sure if another figure is meant to be here. Otherwise Figure 5 can be removed.
- L192: How well does GeoTop actually work for dikes? I can imagine that these are not related at all, given that dikes are built by humans with specific materials. This may influence the results later on relating outcomes to the soil types, i.e., would the relationship with the soil type improve if the GeoTop data is left out? Some consideration about this would be good here.
- L238: I think Sm is substituted by R, not the other way around.
- L276: simulate “the heads”.
- L288: How was this threshold of 0.7 determined? How sensitive are the result to changing this threshold.
- L302: Analyses
- L303: every “…”?
- L327: r2 was previously referred to as R2, check throughout
- L329: The FlexModel is a nonlinear recharge model, the other three models are not. I think the TARSO model is meant here, which still computes recharge using a linear equation.
- L342: replace by “in the summer of 2019”
- L343: disturbances
- L345: scatter plot in Figure XX.
- L366: I don’t understand what “peak block” is, please clarify.
- L496: Apparently, the head time series were filtered using some reliability criteria in this study. This should be mentioned in the section describing the data. What reliability criteria were used?
- L501: Remove “explicitly”. Uncertainty was not considered, as I understood from the manuscript.
Citation: https://doi.org/10.5194/egusphere-2024-1495-RC2 - AC2: 'Reply on RC2', Bart Strijker, 07 Feb 2025
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