the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Dune belt restoration effectiveness assessed by UAV topographic surveys (Northern Adriatic coast, Italy)
Regine Anne Faelga
Luigi Cantelli
Sonia Silvestri
Beatrice Maria Sole Giambastiani
Abstract. Unmanned Aerial Vehicle (UAV) monitoring surveys are used to assess a dune restoration project in the protected natural area of the Bevano River mouth in the Northern Adriatic coast (Ravenna, Italy). UAV is among the most utilized tools in coastal geomorphology studies as high-spatial and temporal resolution surveys can be carried out in an efficient and cost-effective manner. The impact of the installed fences to dune development are assessed in terms of sand volume and vegetation cover changes over time by using a systematic data processing workflow based on Structure from Motion (SfM) photogrammetry and Geomorphic Change Detection (GCD) toolset. Accuracy assessment is performed using statistical analysis between GPS profiles and the elevation models. Results show that the dune fence proves to be effective to prevent dune erosion since significant sand accumulation is observed along the dune foot and front. Progradation of around 3–5 m of the foredune, development of embryo dunes, decrease in stoss slope and blowout features due to increase in vegetation colonization were observed. Erosion is evident at the northern portion of the structure, which could be accounted for by the aerodynamic and morphodynamic conditions around the dune fence, the efficiency of the fence and its configuration to trap sediments. Dune fencing and limiting debris cleaning along the protected coast has been proven to be very effective against dune degradation. The GCD toolset can be a valuable tool if sources of uncertainties are well accounted for. The proposed workflow can also aid in creating transferable guidelines to stakeholders in ICZM implementation in the Mediterranean low-lying sandy coasts.
Regine Anne Faelga et al.
Status: open (extended)
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CC1: 'Comment on egusphere-2023-474', Eduardo Barboza, 27 Mar 2023
reply
The summary presents a study of the recovery of foredunes through the fence installation method.
The methodology used is adequate and the results show recovery in a large sector of the project area.
Citation: https://doi.org/10.5194/egusphere-2023-474-CC1 -
RC1: 'Comment on egusphere-2023-474', Anonymous Referee #1, 15 Apr 2023
reply
GENERAL COMMENT: In this manuscript, drones and GPS were used in two surveys (2016 and 2021) to assess the efficiency of using fences to restore the Bevano dune ridge (Ravenna, Italy). The DEMs and orthomosaics obtained were used to compute a DEM of difference and to classify the area in 3 classes, respectively. The previous allowed the analysis of dune geomorphic and vegetation changes over time. At its present form the manuscript is not ready to be published, and I suggest the authors to perform major changes. The intention of this review is to help them to improve the manuscript, and I hope they find the comments constructive. The different sections are not well connected, as the authors do not introduce properly some aspects (e.g. blowouts, dune slopes) neither in the introduction nor the methodology, but then discuss about those all of a sudden. In addition, important aspects of the methodology (e.g. drone flight elevation, number of control points and configuration used, or image classification accuracy assessment) were not performed, or at least not explained in the text. In addition, the result and discussion sections are a bit vague (see specific comments below). On the other hand, figures should be carefully revised and improved, mainly increasing the size of the font used as they are hard to read, adding the correct units, and adequate size bars and scales. I also recommend the authors to re-phrase some paragraphs and make them easier to read and follow, avoid repetitions, and to review the English, as there are typos throughout the text.
SPECIFIC COMMENTS:
Abstract:
- Lines 8-10: remove that phrase since it would be better placed at the introduction, it does not say much at the abstract.
- Line 11: what’s the temporal scale of your study? It is not mentioned but it is important to indicate it, as you later on talk about dune progradation of 3-5 metres. Also, how many drone surveys were performed?
- Line 14: Do the fences really prevent dune erosion? Or instead they promote dune recovery and growth?
- Lines 14-16: I suggest the authors to include numbers when mentioning the results: how much sand accumulation was measured and how the vegetation cover changed, instead of mentioning ‘increase in vegetation’ or ‘significant sand accumulation’.
- Line 19: I would remove the line about the GCD toolset.
Introduction:
- Lines 29-30: Check the order of some references in the text, I’m not sure they are placed correctly.
- Line 34: Not sure these are the best references.
- Line 36: For consistency, it is better to use only one term. Before the authors were using ‘UAV’ and now ‘UAS’
- Lines 45-49: it is a bit repetitive
- Line 49: There are already some studies in the Emilia-Romagna region, please check the paper of Duo et al (2021): https://doi.org/10.3390/rs13091823
- Figure 1: The legends are hard to read
- Lines 92-95: there is no mention about the characteristics of the blowouts in the area, which are mentioned in the abstract but not here.
- Figure 2: Legends and numbers are really small. Also, what are the red dots (A, B, and C) indicating?
- Line 101: how frequent were the drone surveys?
- Line 102: qualitative data analysis?
Materials and methods:
- Lines 114-116: which UAV software? what was the flight elevation? 70% of front and side overlap? How were the targets distributed in the area and how many did you use? In figure 3 targets are referred to as GCPs, use the same term for consistency.
- Lines 120-121: not important, I would remove these lines
- Line 125: how many points did you use? Check points are also used to assess the horizontal and vertical accuracy of the 3D models, how did you assess those? These lines are a bit hard to understand, please re-phrase. Also, how did you remove the vegetation from the DEM?
- Lines 125-134: I think there is too much info that is not needed here
- Line 137: ArcGIS 10.x?
- Lines 125-163: I suggest to simplify and re-phrase these lines, they are a bit confusing and hard to follow as they are right now.
- Line 166: why 1 x 1 m of grid resolution? Also, how was the accuracy of the unsupervised classification assessed? This is important but it is not mentioned
Results:
- Line 175: Maybe explain where those values are located, in which profiles? help the reader a bit to understand what happened in your area of study, and especially what happened with the dune (do not forget it is the goal of your work)
- Figure 5: profile 10 is not included.
- Line 184: if no vertical accuracy of the 2016 DEM could be obtained, which error associated to this DEM did you propagate to obtain the DoD? only the error of the 2021 DEM?
- Line 185-193: These lines are a bit repetitive and confusing. It could help if you describe in which areas of the study site you found the erosion or the deposition of sand, using the map of Figure 6. Was erosion identified at the dune or the beach? Or both? Again, these results should be focused on describing the changes on the dune especially, as it is the ‘goal’ of your work
- Line 186: use erosion and deposition instead of lowering and raising, also in the figures
- Figure 6: the numbers and letters are very small. Also, use metres instead of km for the distance bar at the map (also in the rest of the figures).
- Figure 7: please, check carefully the units of each variable, in all the figures and the text. And also the scale of the Y axis, why the vertical scale is not consistent along the negative and positive values in the elevation graph?
- I am missing some measurements here about the dune progradation that were mentioned in the abstract?
- Line 201: what happens with profile 10? It is not included in the previous analysis but it is included in Figures 8 and 9, but no results associated to it are explained. It looks like vegetation cover did not increase that much compared to the debris or logs. At this point, I wonder whether the unsupervised classification method differentiates well both classes (logs or debris from vegetation)? Did you assess the classification accuracy?How did you do it? In the methods is not explained and neither is here, and it is quite important
- Figure 8: the 2021 dune crest and shoreline are shown over the 2016 orthomosaic, please be careful. Why are not the rectangles perpendicular to the shoreline? The transition between blue and green is not easy to see, maybe change the colours
Discussion:
- Line 208: significant compared to what? are any other similar areas experiencing less deposition for the given time span of 5 years? You could compare accretion values and progradation rates measured in other similar areas, in order to know if is significant or not. Maybe it would be good to explain what’s the sediment budget in the area, is there enough sediment arriving or the sediment is scarce there?
- Line 210: no dune slope analyses were included in the methodology nor the results so this information here is new, and makes everything confusing.
- Line 214: the driftwood and debris reached the dune because the waves transported them and reached that area? Or were they blown by the wind? If it was the waves (in the 2021 orthomosaic it looks like the water mark is really close to the dune), maybe is worth stating that those fences are likely to be washed away and/or destroyed over time, maybe with the impact of storms, jeopardizing the restoration of the dunes. Please check
- Line 217: I am not sure what you mean, did Puijenbroek et al (2016) study the same dune?
- Line 224: How were these fences installed? What was the geometry, orientation, etc? It would be good to know which fence configuration worked and which one didn’t.
- Line 241: you should mention which fence configuration worked
- Line 249: errors could also be the result of the GCPs configuration and number used, but this was not explained in the methods.
Conclusions:
- Line 271: which decrease of blowout features? The is no description of the blowouts before, how many blowouts were in the area? The reader cannot reach to a conclusion related to something that has not been correctly introduced before. Please check. Also, do you mean that the blowouts were naturally sealed by vegetation growth promoted by the fence installation? How long did it take for the blowouts to be sealed? This could be interesting to know.
Citation: https://doi.org/10.5194/egusphere-2023-474-RC1
Regine Anne Faelga et al.
Regine Anne Faelga et al.
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