Storm-Induced Boulder Displacements: Inferences from Field Surveys and Hydrodynamic Equations
Round 1
Reviewer 1 Report
This study is a great example of field work in the context of boulder displacement.
I ask that you consider the following to strengthen the analysis.
Can you comment on the phase velocity of the waves during the storm? Ryu et al. 2007 [Runup and green water velocities due to breaking wave impinging and overtopping; Exp Fluids (2007) 43:555-567] show some nice results here on the development of the velocity during overtopping events.
In terms of the lift coefficient of 0.178 used, Rovere 2017 (supplementary material) [Giant boulders and Last Interglacial storm intensity in the North Atlantic, PNAS 114 (46)] discusses a re-analysis of a boulder site to determine hydrodynamic coefficients required to made that deposit. A distribution of lift coefficients between 1-4 is determined. This is similar to those determined for a potential flow over boulders fractured from a stepped platform, see Herterich & Dias [Potential flow over a submerged rectangular obstacle: consequences for initiation of boulder motion, European Journal of Applied Mathematics 31.4 (2020): 646-681].
I discuss the above in relation to Table 4. The authors make a note to take caution with the results. However, I ask them to consider making stronger statements. Is a solitary wave of minimum height greater than a few metres realistic? I believe this calculation requires the value to be an onshore value, when it reaches the boulder. It is a realistic height for a wave during a storm in the sea, but near the shore wave breaking will reduced wave heights. I think that reconsidering onshore fluid velocities and the lift coefficient can reduce the wave heights considerably.
Minor:
Please add units to the two y-axes of Figure 6.
Please reword the following (the numbers refer to the manuscript line number, and in one case a figure).
10. "usually have plays"
34. "of the global warming"
39. "where caused"
63. "are close the coastline"
67. "large hundreds of meters"
96. "a through at 500 hPa"
Fig6. "image drown using"
257. "stormy days is increased"
289. " It is remark the"
294. "displaced of 2 m only"
Author Response
Dear reviewer,
we thank you for the appreciation of the paper and are pleased with the accuracy of the research-type definition. Our paper, as a matter of fact, is “field work” oriented, and it regards the effects produced on eleven boulders by one storm. Therefore, we cannot strengthen the analysis beyond a few initial hypotheses. Based on the data collected so far, our conclusions cannot go beyond a preliminary assessment of the minimum wave height required to displace the boulders. The used tools cannot be other than the most used equations. We aim to continue the geomorphological monitoring and perform flow velocity measurements at the study area. Activities that should allow us to do more in-depth analysis.
Comment 1: “I ask that you consider the following to strengthen the analysis. Can you comment on the phase velocity of the waves during the storm?”
Reply: Although a profound analysis is beyond the scope of the paper, some mentions are now reported in the perspective of the development of the research. The relevance of the changes in flow velocity during the overtopping, found in studies on the so-called green water, are now highlighted (line 254-258).
Comment 2: “In terms of the lift coefficient of 0.178 used, Rovere et alii 2017 … discusses a re-analysis of a boulder site to determine hydrodynamic coefficients required to made that deposit. A distribution of lift coefficients between 1-4 is determined. This is similar to those determined for a potential flow over boulders fractured from a stepped platform, see Herterich and Dias 2020”.
Reply: We are quite in agreement with the comment on the relevance to determine the hydrodynamic coefficients from specific study. In the first version of the manuscript we have referenced to Cox et alii 2020 about such an issue (previous version: lines 211-214; current revised version: lines 217-220). Based on your comment, in the revised version, we have further stressed this key datum by referencing to other relevant papers (lines 220-222).
Comment 3: “I discuss the above in relation to Table 4. The authors make a note to take caution with the results. However, I ask them to consider making stronger statements. Is a solitary wave of minimum height greater than a few metres realistic? I believe this calculation requires the value to be an onshore value, when it reaches the boulder. It is a realistic height for a wave during a storm in the sea, but near the shore wave breaking will reduced wave heights. I think that reconsidering onshore fluid velocities and the lift coefficient can reduce the wave heights considerably”.
Reply: Due to the type of the study (geological field investigation) the use of solitary wave formulas is a first approach to the general problem of the boulder displacement. The question of the wave height reduction near the shore is clearly shareable. However, for the study case, wave amplification processes, such as shoaling can happen. All this will be the subject of further analysis in next notes. Furthermore, we still confirm the importance of determining the lift coefficient taking into account the physical characteristics of the site. We look forward to doing this in the continuation of our activities. A side note: we checked the results of Table 4 and found a data transcription error; Hm for SI19g is 2.03 (not 1.2 as previously written). This obviously does not change the substance of the results.
Minor comment 1: “Please add units to the two y-axes of Figure 6”
Reply: “The units have added to the two y-axes”.
Minor comment 2: “Please reword the following (the numbers refer to the manuscript line number, and in one case a figure). 10. "usually have plays"; 34. "of the global warming"; 39. "where caused"; 63. "are close the coastline"; 67. "large hundreds of meters"; 96. "a through at 500 hPa"; Fig6. "image drown using"; 257. "stormy days is increased", 289. " It is remark the"; 294. "displaced of 2 m only".
Reply: “the phrases have been reworded. Thanks”.
Reviewer 2 Report
I found the paper by Delle ROse et al. well structured, interesting and properly written. It deals with a problem of an increasing importance that is the effect of climate change on coastal areas. So it has a significant interest for the general audience as well as for those particularly studying the interested area.
It surely deserves publication.
May be the authors could considet to cite the followiong paper which also referes to the effect of catastophic waves in the same area:
Sansò, P.; Calcagnile, L.; Fago, P.; Mazzotta, S.; Negri, S.; Quarta, G.; Romagnoli, C.; Vitale, A.; Mastronuzzi, G. Sand Ridges on Rocky Coastal Platforms as Markers of Tsunami Impact: A Multi-Disciplinary Analysis along the Ionian Coast of Southern Apulia (Italy). Geosciences 2020, 10, 204.
Author Response
Dear reviewer,
we thank for your flattering comments.
Comment: the reviewer kindly suggests to consider a paper referencing the effect of catastrophic waves in the study area.
Reply: The suggestion was accepted (lines 62-64).
Reviewer 3 Report
The paper outlines the initiation of a longterm project aiming at identifying the nature and magnitude of storm wave impacts on the selected shoreline. It presents a report on the impact of the first major storm event experienced during the project. The storm itself is evaluated from available meteorological information. Direct field observations were made of the impact of the event in respect of boulder movements caused by storm wave run-up, and evaluated using a range of existing models. This creates a benchmark against which to evaluate future events.
The recognition of potential tsunami signatures has come to the fore in the past two decades, especially around the Mediterranean. Very large boulders on shorelines are indicative of high- powered events, such as major storm or tsunami, both of which are capable of inflicting damage to both coastal life, business and property. A key question is the relative capabilities of the two types of event and, in particular, the potential limits of storm wave activity. This paper addresses that specific question. It is, therefore, most timely and also novel as it is one of very few papers thus far to address that question.
- Specific comments referring to line numbers, tables or figures. Reviewers need not comment on formatting issues that do not obscure the meaning of the paper, as these will be addressed by editors.
Section 3.
(General)
Includes synoptic conditions, storm damage, met data records, wave models. There is a mixture of background, method, wave modelling, and storm consequences. There needs to be a narrative which flows in a consequential order. Perhaps subheadings to signpost the way; maybe (in order) as synoptic (cause), met data (available), wave modelling (consequences) and impact (outcome). Sources of models need citation.
(Specifics)
The weather maps: Figs. 2a,b are potentially outstanding, if only the coastlines were visible to enable the reader to identify their locations. Could they be made visible?
The storm is described with reference to synoptic conditions. Could the authors explain why and how the chosen meteorological parameters link into the nature of coastal wave impact?
Coastal hazard concerns both magnitude and frequency of events. The reported storm event would carry much greater significance in a magnitude and frequency framework. Was it a 1 in 20 yr storm, or 50 or 100 or 500 years? Is there a backlog of data which would enable such analysis to be made?
Alternatively, what does the Crotone buoy say about magnitude and frequency of storm waves on the day of IonicS19?
Section 4.
(Boulder Displacements). Basic data on the boulders and their movements are presented, together with descriptions of the inferred types of movement. The authors are correct in recognising the irregularly rough surface of the shore platform and that that must be a major factor in influencing the difficulty of boulder movement, and its interpretation
It would be helpful also to see a summary analysis of boulder movement thus – the origin and destination data supply information to show boulder movement distance and direction of travel. That could easily be shown as a table or even a map. What patterns would then appear to show of boulder movement trajectories, and their boundary limits of distance and elevation?
Section 5. The sources of the models should (again) be cited. And the choice of coefficient values explained.
Section 6. It is not easy to identify a rational developmental narrative sequence here. I suggest that authors clearly identify the purpose of each section – what issue/ question they are addressing in each paragraph, and then create a subheading for each.
Author Response
Dear reviewer,
we thank you for the comments that allowed us to improve the narrative quality of the paper as well as to specify some aspects.
Comment 1: “Section 3: Includes synoptic conditions, storm damage, met data records, wave models. There is a mixture of background, method, wave modelling, and storm consequences. There needs to be a narrative which flows in a consequential order. Perhaps subheadings to signpost the way; maybe (in order) as synoptic (cause), met data (available), wave modelling (consequences) and impact (outcome). Sources of models need citation”.
Reply: We have fully implemented the comment and changed the structure of Section 3 which now consists of three sub-sections.
Comment 2: “The weather maps: Figs. 2a,b are potentially outstanding, if only the coastlines were visible to enable the reader to identify their locations. Could they be made visible?”
Reply: We are sorry for the difficulty to identify the coastline in Figure 2. The images downloaded from the ISAC web site are rasters (improvable with difficulty). However, we have realized our best performance and coastline is now more visible.
Comment 3: “The storm is described with reference to synoptic conditions. Could the authors explain why and how the chosen meteorological parameters link into the nature of coastal wave impact?”
Reply: The choice of the meteorological parameters to describe the conditions driving the coastal waves impact is explained as a follows. Boulder displacements are identified in a portion of the coast of some kilometres, where there are no direct measurements of the sea state. Due to this fact, information about the sea state and the wave height is inferred combining the available measurements on the closest measurement stations (A02TLE for continuous data of wind speed and LIBY for semi diurnal data of wind speed and sea state), with synoptic information. Thus the synoptic view is useful for a validation of the sea state in the observed part of the coastline, and in particular the fetch, intensity and direction of the wind at 10 m over the sea, and the duration of the these storm characteristics, allow the calculation of the peak wave height expected on the whole portion of the coast by equation 2. The reasonable agreement of this result with observed data from table 1 allows a better justification of the comparison with the wave heights calculated in table 4. In addition, even if out of the purpose of this work and only marginally mentioned in the conclusions (figure 11), the identification of the synoptic characteristics of the storm in relation to its damaging effect over the coastline can help in identify possible future trends.
Comment 4: “Coastal hazard concerns both magnitude and frequency of events. The reported storm event would carry much greater significance in a magnitude and frequency framework. Was it a 1 in 20 yr storm, or 50 or 100 or 500 years? Is there a backlog of data which would enable such analysis to be made? Alternatively, what does the Crotone buoy say about magnitude and frequency of storm waves on the day of IonicS19?”
Reply: thanks very much for the comment about the possible return period of the described storm event. Unfortunately, the 2019 records at the Crotone buoy is not currently available. For a first evaluation, considering Figure 11, the return period appears to be greater than at least 10-years.
Comment 5 (Section 4): “It would be helpful also to see a summary analysis of boulder movement thus – the origin and destination data supply information to show boulder movement distance and direction of travel. That could easily be shown as a table or even a map. What patterns would then appear to show of boulder movement trajectories, and their boundary limits of distance and elevation?”
Reply: The main data are reported in Tables 2 and 3. The map showing the pattern of the boulder displacements is under construction (it needs further field observations) and will be shared in a next note.
Comment 6 (Section 5): “The sources of the models should (again) be cited. And the choice of coefficient values explained.”
Reply: the sources of each equation are cited. About the choice of coefficient values, lacking specific studies on the site, we have used the values as inferred from the available literature, however highlighting the limitations of this approach (lines 211-214 of the first version; lines 217-222 of the revised version). In any case, a detailed hydrodynamic analysis is beyond the scope of this field-oriented study. We hope that such an issue will be face in a development of the researches.
Comment 7 (Section 6): “It is not easy to identify a rational developmental narrative sequence here. I suggest that authors clearly identify the purpose of each section – what issue/ question they are addressing in each paragraph, and then create a subheading for each”.
Reply: Section 6 of the revised version is made by to subsections, each of them are clearly titled. Thank for the comment.
