the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 May 2025
Numerical modelling framework for assessing dune effectiveness against coastal inundation
Abstract. Coastal inundation is one of the prominent natural hazards threatening both economic assets and human lives. Precise modeling of these events is vital for comprehensive risk assessment, yet there is a persistent gap in data availability and modelling accuracy for coastal flood mapping. In this study, we expanded the LISFLOOD-FP model's ability to simulate coastal floods by incorporating wave setup and swash, as well as the interaction with protective infrastructures like temporary dunes. This improved approach was applied to the coastline of Cesenatico, Italy, where dunes are built each winter as seasonal coastal defenses. We analyzed two storm events for which observational flood maps are available for validation: the 2015 Saint Agatha Storm, which saw intense waves breaching the dunes and causing extensive inland flooding, and the 2022 Denise Storm, when the dunes withstood the storm and successfully shielded the coast. Our results demonstrate that dunes are highly effective in mitigating inundation, particularly during the 2022 event. However, they also reveal that the failure of even a small portion of the dunes can lead to widespread inundation, emphasizing the need for optimized dune design. These findings represent a significant advancement toward developing a digital twin of coastal regions, providing valuable support for a range of coastal management activities.
Competing interests: Co-author Michalis Vousdoukas is employed by the company MV Coastal and Climate Research Ltd. Co-author Maurilio Milella is employed by the company Environmental Surveys S.r.l. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.- Preprint
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RC1: 'Review of Manuscript: egusphere-2025-1695 Title: Numerical modelling framework for assessing dune effectiveness against coastal inundation', Anonymous Referee #1, 24 Jul 2025
The manuscript presents a work of considerable interest and relevance, addressing the crucial topic of coastal inundation modeling, with a particular focus on the protective role of dunes, including artificial and seasonal structures. The authors propose an extension to the well-known LISFLOOD-FP model by introducing new parametrizations to account for wave contributions (setup and swash) and a dune failure mechanism. The approach has been validated against two real storm events on the coast of Cesenatico, Emilia-Romagna (one with dune failure, one without), demonstrating the model's capability to reproduce highly diverse scenarios and underscoring the critical importance of an accurate representation of coastal defenses.
Overall, the study is well-structured, methodologically sound, and the results are presented in a clear and convincing manner. The work represents a significant step forward toward the creation of more reliable and computationally efficient forecasting tools, which are fundamental for coastal risk management and the development of coastal "digital twins."
However, certain methodological aspects require greater detail and a more robust justification to ensure the full reproducibility and validity of the conclusions. Furthermore, a more in-depth discussion of the approach's limitations would enhance its scientific value. I recommend the manuscript for publication after addressing the following revisions, which I deem to be of a "major" nature due to their importance for the soundness of the conclusions.
Major Comments
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Justification and Sensitivity of Key Parameters (α and FWD)
The core of the methodological novelty lies in the introduction of two critical parameters: the overwash efficiency coefficient α (eq. 2) and the dune Failure Water Depth (FWD). Their determination and impact on the results are of fundamental importance.Overwash Efficiency (α): The authors set α = 0.25 based on "geometrical considerations and approximating the waves as triangular" (lines 189-191). This justification is overly qualitative and requires more rigorous explication. What are these geometrical considerations precisely? It is suggested that the authors add a section or an appendix to illustrate the physical or geometrical reasoning behind this choice. More importantly, the manuscript would benefit immensely from a sensitivity analysis of this parameter. How do the results (inundation extent and dune failure for the 2015 event) change for values of α ranging from 0 (setup only) to 1 (full swash contribution)? Such an analysis would not only strengthen the choice of 0.25 but also provide valuable insights into its role as a potential calibration parameter, as suggested by the authors themselves (lines 375-376).
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Failure Threshold (FWD): The dunes were modeled with a uniform FWD of 1.4 meters (line 186). This is a strong assumption. How was this value determined? Is it based on literature specific to the artificial dunes of the Emilia-Romagna region, on post-event observations, or on engineering criteria? Is its uniformity along the entire coastline realistic? As the success or failure of the dunes is the centerpiece of the analysis, a detailed justification for this value is imperative. Here too, a sensitivity analysis, at least for the 2015 event, showing how the number of failed dune cells varies with the FWD (e.g., 1.3 m, 1.4 m, 1.5 m), would be extremely insightful and would demonstrate the model's robustness (or sensitivity) to this parameter.
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Simplification of the Dune Failure Mechanism
The implemented failure model is binary in nature: when TWL > FWD, the dune is "entirely" and instantaneously removed from the terrain (line 138). While this is an understandable and pragmatic simplification for a non-morphodynamic model like LISFLOOD-FP, its implications must be discussed more thoroughly. Dune erosion is a progressive process in both time and space.-
It is suggested that a paragraph be added to the Discussion (Section 4) that explicitly acknowledges this limitation. Instantaneous failure could, for instance, overestimate the peak water discharge into the hinterland compared to a more gradual erosion process. How might this simplification affect the inundation hydrograph and the maximum flood extent?
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Furthermore, the model removes the entire dune cell. What occurs if TWL only slightly exceeds FWD? Is it realistic for the entire dune (50m wide, according to the model resolution) to be eroded instantaneously? The discussion should contextualize this approach as a first, yet effective, step toward modeling these complex processes, perhaps mentioning potential future developments (e.g., partial or time-parametrized erosion).
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Details on Dune and DTM Mapping
The reproducibility of the study is critically dependent on the quality of the input data, particularly the topography. The authors state that they mapped the seasonal dunes from "satellite imagery" (line 185) and incorporated them into the DTM. More details are required:What were the source and resolution of the satellite imagery?
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What methodology was used to extract the dune geometry (height, width, exact position) from the images? Was this a manual or semi-automated process?
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What are the resolution and acquisition date of the base DTM provided by the "Geological, Seismic and Soil Service of the ER region"? Its age relative to the studied events could be relevant.
These details are fundamental, as the uncertainty analysis (Section 3.3) excellently demonstrates how sensitive the results are to small variations in the DTM (±7 cm).
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Presence of Placeholder Text
On page 18, at the beginning of section 3.2, there is an entire paragraph of Latin placeholder text ("Suspendisse a elit ut leo pharetra cursus..."). cancel please.
Minor Comments
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Lines 72-74 (Digital Twin): The introduction mentions the "digital twin" concept. While pertinent, the connection could be made more explicit. The proposed framework is a component of a potential digital twin, not a complete one (which would imply a continuous data stream and assimilation). It might be more accurate to frame it as a "fundamental step toward the development of a digital twin for coastal management."
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Figure 1 (Schematics): The figure is very clear and effective. An excellent choice for explaining the different water level components.
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Figure 4 (Storm Surge Comparison): The validation of the forcing data is a strong point. The agreement is good, especially for 2015. The mention of Adriatic seiches as a possible cause for the residual signal is pertinent and correct.
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Lines 190-191 (Beach-face slope): The value of βf = 0.05% appears extremely low (1:2000). The reference to Ciavola et al. (2006) should be double-checked, as such a gentle slope is atypical for the foreshore. Was 5% or 0.05 (dimensionless) intended? Please check and clarify.
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Lines 354-355 (Backflow): In the discussion, it is hypothesized that the remaining dunes may obstruct the backflow of water. This is an excellent and physically plausible observation. Did the model actually exhibit this behavior? If so, it would be useful to mention this explicitly, perhaps by indicating areas of "ponding" behind the non-failed dunes on the depth maps. If it is only a hypothesis not directly supported by the results, it should be phrased as such.
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Figures 11 and 12 (Uncertainty maps): These figures are an excellent complement to the analysis and effectively visualize where the main uncertainties are concentrated. The conclusion that uncertainty is dominated by the dynamics of failure (2015) or by the very presence of the dunes (2022) is a key strength of the paper.
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Section 2.4 (Table 2): The definition of uncertainties via the difference between simulations is clear and well-presented. The analysis is robust.
Review Conclusion
In summary, the manuscript by Lopes et al. is a high-quality scientific contribution that presents an innovative and pragmatic modeling framework for a complex and relevant problem. Its strengths lie in the clear identification of a research gap, the elegant extension of an existing model, the convincing validation against real case studies, and a thorough uncertainty analysis.
The requested major revisions focus on the need to strengthen the scientific justification for key parameters and assumptions, which are central to the study's conclusions. Addressing these points, along with correcting the minor issues (including the placeholder text), will significantly increase the robustness, reproducibility, and impact of the work.
Therefore, my recommendation is to Accept with Major Revisions.
Citation: https://doi.org/10.5194/egusphere-2025-1695-RC1 -
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RC2: 'Comment on egusphere-2025-1695', Giovanni Scardino, 03 Sep 2025
This manuscript takes into account an important topic for the dune effects in response to coastal inundation. Authors reported a modeling approach using LISFLOOD-FP to simulate coastal floods by incorporating wave setup and swash in Cesenatico coast (Italy). The manuscript is well written and can be considered for publication after minor corrections.
Here, I reported line-by-line my comments that could improve the readability of the manuscript.
Line 32. Hereinafter, you have to report “Sea-Level Rise”.
Line 33. Add also the reference for IPCC 2021.
Line 60. Change form in landform.
Line 61. Change beach interface in backshore.
Lines 61-62. Here, you refer to storm surge and wave overwash as causes of dune erosion. However, you also reported dune breaching in the abstract, which is one of the most evident effects of dune erosion during a storm. Please revise the list of storm-related effects to include dune breaching.
Line 67. Substitute “are erected” with “have been built”.
Lines 97-98. Revise the definition of wave runup, which is not a contribution to the TWL. The wave runup is defined as the maximum vertical extent to which a high-energy wave reaches the coastal landforms above the instantaneous water level (e.g. Villarroel-Lamb and Williams, 2022).
Line 135. Change in “The approach proposed in this study is based on the work of …..”
Line 160. Insert some toponyms in Figure 3 and a scale bar.
Line 180. When you describe the DTM features, provide also some info about the Reference System, in particular about the orthometric elevations (which is the datum?). This is very important if you are applying a simulation based on tide gauge and buoy data.
Line 205. Maybe Figure 6 and Figure 7 can be merged into a unique figure, because boundary conditions for the two storm events are reported in a similar way.
Lines 289-291. There are some unreadable sentences.
Line 365. Several important factors influencing dune erosion are not addressed in the Discussion section, namely sediment mineralogy, grain size, and biological factors. In particular, it is necessary to cite references stating that dune nourishment requires compatible sediments. If the nourishment sediments are incompatible with the native material in terms of mineralogy, grain size, and biological components, the dune will fail to act as an effective barrier against storm impacts and will be more susceptible to erosion.
Many thanks and kind regards.
Citation: https://doi.org/10.5194/egusphere-2025-1695-RC2
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