How Can the Morphometric Characteristics and Failure Conditions of a Historic Gully Caused by Intense Rainfall Be Reconstructed?

Round 1

Reviewer 1 Report

An interesting and important topic was investigated by the authors. It has a sufficient impact and it represents an advance in the subject matter, thus it is constituting a remarkable contribution to knowledge about this subject. It falls within the thematic scope of the earth journal, well carried out, and with results that may be of interest to other scientists, hence, I recommend minor revision of the paper. In addition, there are some questions and advice for the authors.

• How you choose your GCPs, or where you choose, is just a brief description in line 177. Because your time span is long(1978-1984), The fixed control point is difficult to determine, but it is very important for calculating the volume of gully.
• Add the process of calculating gully volume in lines 191-196.
• As mentioned in Line 255, when Fos is less than 1, how to calculate the headward retreat distance of gully.
• line 389 without a full stop.
• The paper mainly discusses the headward retreat of gully, and there is less concern about the extension of gully bank（ 8）. It is suggested to revise the subtitle of the discussion accordingly.
• In the current manuscript version, what is the role of Section 4.1 in the Discussion? It is suggested to discuss the effect of the SFM on reconstructing the gully development historical process.
• In section 4.2, further explain how groundwater rise affects gully development, such as the relationship between changes in pore water pressure, water content, etc. and landslide or gully development.

Author Response

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Reviewer 2 Report

Line 88 – what do you mean by the term

Embankment

(was called “scarp” at fig 3)

Figure 2 is informative, but needs for description in the text. For example, slope morphology was not described – altitudes, inclination, topography??

Line 308

The DoD appears before Fig 3 with explanation of abbreviates

 

Figure 6 – black thin lines at Fig 6a – their meaning was not explained? Better to change the colour of these lines

 

It seems to me that some gullies in New Zealand are of the same type

See 10.1029/2002WR001342, 2003

Author Response

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Reviewer 3 Report

The paper is a good example of multi-model combination, including 3D point cloud model, hydrological model and gully process model, to test the author’s hypothesis. For a particular and large gully, the study collected detailed data as the full evidence for the analysis. These all have the certain theories innovation and actual leading meanings. While there are also some suggestions as following:

1. There is nearly none review about the methodology, hypothesis or gully erosion in the region as the supporting materials to understand the novelty of this paper. So it is suggested to add the review on the relevant research progress.
2. In the line 157-158 “We select the 60 pictures of 1978 and 79 of 1980 that cover the cirque of Salazie”, the year is 1980 or 1984? In the Figure 1, the author mentioned the photography was taken in January 1980.
3. The vegetation cover in the study area should be considered, because the vegetation cover is a main and direct factor of the accuracy of 3D model and hydrological model. But the paper did not mention the status of vegetation cover and how to process it.
4. There are many grammatical mistakes should be revised, and the usage of grammatical tense is confusing, such as in the title “an historic gully”, in the line 68 “does not required extensive……”, in the line 152 “To retrieved characteristics……”, Figure 4b. “Distance form the gully center”, …… . So the English of the whole paper should be improved.

Author Response

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Reviewer 4 Report

Dear Editor and Authors,

I have read the manuscript earth-1561132, entitled "How to reconstruct morphometric characteristics and failure conditions of an historic gully caused by intense rainfall in La Réunion Island?" The paper addresses a well suited topic for the mentioned journal: the reconstruction of the pre- and post-failure topographies using SFM (structure from motion) applied on archive aerial photographs. While the approach is not a novel one, the results and their interpretation could improve the knowledge  on this type of geomorphic phenomena. The manuscript can deserve publication but before accept the manuscript some additional information should be provided.

 

My first issue is related to the Introduction section, because it is not exhaustive, therefore some information should be add regards to methodologies applied. In addition, the my opinion is that the references reported are not exhaustive, therefore I suggest to add some other references:

-Walstra, J.; Dixon, N.; Chandler, J.H. Historical aerial photographs for landslide assessment: Two case histories. Q. J. Eng. Geol. Hydrogeol. 2007, 40, 315–332.

-Borrelli L, Conforti M, Mercuri M. 2019. LiDAR and UAV system data to analyse recent morphological changes of a small drainage basin. Int J Geo-Inf. 8:536.

-Fernández, T.; Pérez, J.; Colomo, C.; Cardenal, J.; Delgado, J.; Palenzuela, J.; Irigaray, C.; Chacón, J. Assessment of the Evolution of a Landslide Using Digital Photogrammetry and LiDAR Techniques in the Alpujarras Region (Granada, Southeastern Spain). Geosciences 2017, 7, 32.

-Conforti M, Mercuri M, Borrelli L. 2021. Morphological changes detection of a large earthflow using archived images, LiDAR-derived DTM, and UAV-based remote sensing. Remote Sens. 13(1):120.

-Turner, D.; Lucieer, A.; de Jong, S. Time Series Analysis of Landslide Dynamics Using an Unmanned Aerial Vehicle (UAV). Remote Sens. 2015, 7, 1736–1757.

-Giordan, D.; Allasia, P.; Manconi, A.; Baldo, M.; Santangelo, M.; Cardinali, M.; Corazza, A.; Albanese, V.; Lollino, G.; Guzzetti, F. Morphological and kinematic evolution of a large earthflow: The Montaguto landslide, southern Italy. Geomorphology 2013, 187, 61–79.

 

. The authors should be add in the text some information about landslide movement, according to their types (for more see: Cruden DM, Varnes DJ (1996) Landslide types and processes. In: Turner AK, Schuster RL (eds) Landslides investigation and mitigation. Transportation research board, US National Council, Special Report 247, Washington, DC, Chapter 3:36-75, and Hungr O, Leroueil S, Picarelli L (2014) The Varnes classification of landslide types, an update.Landslides 11:167-194).

The error analysis of the DSMs should be discuss more in detail.

The authors must emphasize that their work can be successfully used in other regions and settings, because this justify the publication in an international journal.

Best regards

Author Response

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Round 2

Reviewer 3 Report

the authors revised the manuscript carefully.