Comparison between Topographic and Bathymetric LiDAR Terrain Models in Flood Inundation Estimations

Round 1

Reviewer 1 Report

The manuscript presents an original study on comparison of DEMs obtained using two different LiDAR technologies, topographic and bathymetric, in order to assess their suitability for the estimation of flood inundation. The content is a significant contribution and may be helpful for flood hazard assessment and prevention. The manuscript is clear and relevant for the field. The figures and tables properly show the data and are easy to interpret and understand. The research is design appropriate. The statements and conclusions are drawn coherent. For these reasons I recommend the manuscript entitled “Comparison between topographic and bathymetric LiDAR terrain models in flood inundation estimations” for publication in Remote Sensing. However, some corrections and improvements should be considered.

General comments:

1. Data on study sites are very scarce. There are 11 sites, located in different counties in Norway, chosen for analyses based on the availability of LiDAR data. The reader only learns what the catchment area, discharges and reach length are. What about environmental conditions? Are the sites similar to each other or are there any differences between them that could affect the results? A few more facts about hydrological conditions, river regime or land cover of chosen sites would be helpful to understand the differences in the obtained inundation errors and interpreting them.
2. Two reaches, Guala and Lower Lærdal, were chosen to test the corrections of flood inundation. Why were these reaches chosen? In the Results section the authors write that they are “the most flood protected reaches”, in the Discussion section the reader finds out that they “appear as the most prominent sites” and one may think they are somehow extraordinary. If so, can they be good and representative reaches for these analyzes?
3. The Discussion section needs to be re-arranged. There are statistical analyses (ANOVA, correlation test) described which should be rather in the Methodology section. Also the description of the results of statistical analyses should be rather placed in the Results section. The authors mostly present the interpretation of their results but the discussion against the results of other studies is rather poor. Please refer your results to other studies or other areas (see specific comments).

Specific comments:

Line 53: Reference numbers should be placed in one square bracket.

Line 68: Additional space before Bhuyian.

Line 69: (2018) is not necessary.

Line 100: Instead of “… of the rivers?” it should be “… of the river channels?”.

Lines 100-101: The sentences “Can this be used …” is difficult to understand. There are twice “this” occurring – what does it mean? The relationship? Do both “this” mean the same?

Line 108: Delete the dot after topographic.

Line 109: “Three” should start with a lowercase letter because it is not the beginning of a sentence.

Line 221: Should there be space between reference numbers? In other brackets there are no spaces.

Lines 234-235: Please explain why these two reaches were selected for corrections testing.

Line 312: Reference numbers should be placed in one square bracket.

Line 314: Instead of (2019) should be [21].

Lines 317-319: The ANOVA is one of the methods used to analyze data and should be described in the Methodology section.

Lines 319-323: This is the description of the ANOVA results and should be rather in the Results section and in the Discussion section should be only the interpretation of the results left. “… for the sites that have flood protection coverage of 24% or more they follow the peaking error trend …” – here it should be explained why it is so. Does the higher or lower flood protection coverage result from higher or lower flood risk? Perhaps this can also be explained by the shape of the catchment area or hydrological conditions or land cover etc. if we know more details about the study sites. Perhaps discussing this issue a little more with other studies would help establish that the bathymetric data is particularly good for some types of catchment, and that topographic data can also be used for others.

Lines 333-348: Do the differences in the level of inundation error result only from channel parameters? Does the type of flood affect the level of the inundation error? Please see the previous comment and discuss it a little more.

Lines 334-336: The correlation test is one of the methods used to analyze data and should be described in the Methodology section.

Lines 336-338: This is the description of the correlation test results and should be rather in the Results section.

Lines 361-364: This finding was to be expected because as the flood magnitude increase, the importance of the local river channel structure decreases. This fact has already been published and it would be worth referring to it here; e.g. Hassan and Reid, 1990 or Płaczkowska and Krzemień, 2018 or any other.

Lines 388-402: Please explicitly refer to the research questions stated in the introduction.

Table 1: The authors used once m3/sec and once m3/s. Are they the same units? If so, it should be unified.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

In this paper, the RL terrain model and the GL terrain model are compared when generating flood areas at multiple Norwegian sites. In particular, analysis using GL LiDAR data is valuable, and comparison with various flood scenarios is considered appropriate. However, I recommend that you consider making corrections to the following items.

 

1. Is the LiDAR used in the research an aircraft LiDAR? Information such as the accuracy of the original LiDAR device and the acquisition method is insufficient. The summary should be mentioned not only in the website information but also in the text.
2. Figure 2 shows the characteristics of GL well, but can we agree with the depth of the river? Also, is the water quality of the river affected by the accuracy of GL? Furthermore, the name on the vertical axis should be added to the figure on the left.
3. In relation to Figure 5, I would like you to explain in a little more detail the reason why the inundation error is large in the cross section where the angle of the average embankment slope is small. It may be obvious to me, but it will not be understood by readers who are not familiar with flood analysis.

 

That’s all

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

I attach a word file.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 4 Report

The manuscript entitled “Comparison between topographic and bathymetric LiDAR terrain models in flood inundation estimations” is of a very interesting topic. A comparison was conducted between the RL and GL terrain models in producing flood inundation extent for eleven sites in Norway. The topic of the manuscript is absolutely within the scopes of “Remote Sensing” journal.  

The methodology is described in detail and the conclusions are based on the results.

I am not a native speaker but in my opinion the manuscript reads quite well!

Here are my suggestions that could improve the final version of the manuscript:

• In my opinion the description of the study sites could be a separate section entitled “Study Area” and it should not be part of the section “Data”.
• I think that a flow diagram showing the main steps of the methodology followed should be appreciated by the readers of the final version of the paper.
• I am not sure if the longitudinal profiles in Figure 4 have been constructed correctly. I mean did the authors follow the deepest points of the channel? The profiles are not “smooth” and have many peaks that are not usual for a longitudinal profile.

Author Response

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Author Response File: Author Response.pdf