Round 1

Reviewer 1 Report

General comment

The paper deals with an interesting topic which is within the aim of the Journal. The background provided in the introduction is limited to the behaviour of the loess soils and to studies carried out in regions of China. The authors should provide a more general framework for the relationship between micro-topography and erosion processes.  Moreover, several parts require a careful revision, as detailed in the comments hereafter. English language should also be improved.

 

Detailed comments and suggestions

Line 24: check the sentence. I think  that “…the microtopographic factors of the slopes…”, should be “…the microtopographic factors of the sand slopes…”,

Line 80. The term “powder” should be replaced by “silt” (check all the text)

Line 90. this sentence doesn’t seem completely correct: from figure 3 it is evident that the rainfall duration is not 30 minutes in the first rainfall experiment. Looking at the figures, it seems that the rainfall duration was always 30 minutes after runoff beginning (therefore the actual duration is higher because it includes the time to runoff). This should be better explained in the methods section. Also the reason for this choice should be provided because, according to this methodological scheme, the rainfall amount received by the sand and loess slopes in the first rainfall experiment, are not the same.

Lines 88-93. The authors indicate only few characteristics of the simulated rainfall (intensity and uniformity). However, a proper characterization of simulated rainfalls should also include indications about the rainfall kinetic energy and the drop size distribution. Both characteristics are important to provide a complete description of the simulated rainfall. In fact, usually, nozzle-type rainfall simulators has much lower energy than natural rainfalls of similar intensity.

Line 110. Check if the sentence is correct: the density is usually measured in kg·m^-3 and area in m². Therefore the unit of measure of erosion obtained by multiplying density and area is kg /m, while in the paper it is expressed (correctly) in Kg. Moreover, the authors should explain how they measure the density. The authors indicate that the dry bulk density is 1.3 g/cm³ , but then the soil is subject to wetting and rainfalls which can change the bulk density. In particular, I suppose that the density of the eroded material is difficult to estimate:  in fact the material in the slope has a bulk density that is different from that of the eroded material (which is more a particle density). Moreover, the material eroded is formed in part by loess and in part by sand, but it is difficult to determine the two proportions because this depends on the rill depth and this varies during erosion events.

Lines 110-112. In my opinion the sentence is not clear. I understand that the DEM-estimated erosion amounts were compared with the corresponding measured values to validate the DEM estimation, but I cannot understand the meaning of “….the error range of both was between 0.35% and 14.5%.” “both” means that you were able to estimate the error also for the measured erosion…how did you evaluate this?

Figure 2. The title of the y-axis is not clear. According to the text, it should be called “Sediment yield estimated from DEM differences” or something similar.

Figure 3. The interval time between subsequent rainfalls should be indicated.

Figure 4. Cowering should be covering.

Figure 4. The spatial distribution of erosion shown in these maps  should be analysed in more detail. In particular there are some areas showing negative values (mainly in the upper part of the slope, for example for the 0-cm sand covering). According to the text, soil erosion was computed as the difference between the DEM-before and the DEM-after rainfall. Therefore, negative values should indicate depositional areas. However, the reason for the presence of depositional areas in the upper part of the slope is not clear for me and should be carefully discussed.

Figure 5. This figure doesn’t seem completely consistent with figure 4 because, for example, I would expect negative erosion amounts in Figure 5A for the positions around 11 and 13 m.

Figure 5. Maybe the authors should use the same scale of the y-axis for all the graphs.

Line 180 I suggest to change this sentence because the 0-cm sand cover cannot be characterized in terms of sand-producing areas (maybe soil-producing or erosion-producing)

Lines 182 and following. The erosion amounts indicated in this section are given as the ratio of the amounts of the different sand-covers and the loess slope (being equal the rainfall treatment, i.e. 1, 2, 3). First of all, some numbers are not clear: for example the value 0.96 should indicate that the erosion amount in the first rainfall of the 0.5 sand cover is more or less the same of the loess slope. But the comparison of Fig. 5 A and 5B tells us a very different thing (as already indicated in previous figures).  Moreover, what is the difference between the ratios indicated in these lines and those presented in lines 141-144? Please clarify.

Line 275. How did you measure the flow velocity in each section?

 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Good work here, relevant and timely. Just a few minor revisions suggested for clarity.

Noting that there are few studies on the spatial variation of local micro. factors and soil erosion on a loess slope is not the best way to justify why they are doing the study. This is good work and they identify interesting issues in the literature review, but can they rewrite lines 66 to 75 to summarize in one sentence the main gap they are targeting with the study, another sentence stating the objectives of the study, and then go into "Here we use 3D laser..."

The authors seem to indicate in lines 72 -74 that they are comparing two different groups loess and sand, but it's unclear if that's actually the case because of the way the methodology is written and even the results.  The material just needs clarity in what they did. They don't have to be so succinct in section 2. More is better in the methods section. If they paved sand on the bottom at .5 cm interval, and tested for each paved layer, then put the loess on as the last layer and last test, it would be helpful if they explicitly say this in lines 78-87. They state that 40cm sifted loes sand was paved and rammed at 10cm intervals - so this is in addition to each sand layer thickness of 0.5, 1.0 and 1.5 cm? Just a bit more clarity and text would help as to what each "test" and "sample" is.

In the results section, the text seems to suggest some kind of comparison is taking place between loess and sand (lines 146, 152,165, etc), et there is no visual comparison made in the figures. There is very little explanation in what the figures are in fact in terms of which data pertain to which test/sample. 

In figure 4, what is sand "cowering"?

I might suggest comparing apples with apples and place figure 6a with 5a to make a direct comparison or perhaps a hybrid measure of the two curves on a single graph would make a good visual comparison.

Please round your coefficient of determinations to two decimal places.

 

Minor corrections:

DEMs are simply representations of a parameter like elevation or slope but they are not computational models, thus statements like (line 188) "calculated by DEM" is mis-stated. I believe it should be "with the DEM" or "from the DEM".

Subscript mean on Hmean line 129

It's microtopography not microtopographic in line 132

 

Author Response

Responses to Reviewers

Dear editor and reviewers:

We would like to thank the editor very much for giving us a chance to revise the paper, and also thank the reviewers so much for the constructive suggestions which help us significantly to improve the quality of the paper. According to the comments and suggestions, we have made a thorough revision and resubmit the new version of the manuscript entitled “Response Relationship between Microtopographic Variation and Slope Erosion under Sand-Cover” (ID: Water-635207). In the revised manuscript, we highlighted all the changes in red. Should you have any query for the revision, the authors are pleased to make further revisions.

  With best regards

  Guoce Xu, corresponding author

Reviewer #2:

Point 1: Noting that there are few studies on the spatial variation of local micro. factors and soil erosion on a loess slope is not the best way to justify why they are doing the study. This is good work and they identify interesting issues in the literature review, but can they rewrite lines 66 to 75 to summarize in one sentence the main gap they are targeting with the study, another sentence stating the objectives of the study, and then go into "Here we use 3D laser..."

Response: Thank you for comment. We have written this paragraph “Few researches focused on the quantitative evaluation of soil erosion amount spatial and the response of sediment to the microtopography factor on sand-cover loessal slope. To sum up, the objectives of this study are (1) to elevate the response of the soil erosion to thickness of sand on the loessal-sand; (2) to quantify the spatial distribution of soil erosion amount (3) to analyze the relationship between the microtopography factor and sediment.” Regarding the 3D laser should be the measuring means, we put the useful of 3D laser into Section 1.1 in Line 102-106.

Point 2: The authors seem to indicate in lines 72 -74 that they are comparing two different groups loess and sand, but it's unclear if that's actually the case because of the way the methodology is written and even the results. The material just needs clarity in what they did. They don't have to be so succinct in section 2. More is better in the methods section. If they paved sand on the bottom at .5 cm interval, and tested for each paved layer, then put the loess on as the last layer and last test, it would be helpful if they explicitly say this in lines 78-87. They state that 40cm sifted loessal sand was paved and rammed at 10cm intervals - so this is in addition to each sand layer thickness of 0.5, 1.0 and 1.5 cm? Just a bit more clarity and text would help as to what each "test" and "sample" is.

Response: Thank you for comment. We have rewritten this sentence “Firstly, 20 cm natural sand was laid on the bottom of the flume to keep the water permeability. of the experimental soil was close to natural state and soil moisture infiltrated uniformly. Then, the 40 cm depth sieved loess was put into the flume depending on the layered filling method at 10 cm intervals. Layered filling soil can keep the same bulk density on soil-filled flume. Finally, three thickness of sand: 0.5 cm, 1.0 cm, and 1.5 cm were covered on the soil surface, respectively.” in the test.

Point 3: In the results section, the text seems to suggest some kind of comparison is taking place between loess and sand (lines 146, 152,165, etc), et there is no visual comparison made in the figures. There is very little explanation in what the figures are in fact in terms of which data pertain to which test/sample

Response: Thank you for pointing it out. We have modified the legend in figures and change 0cm to loessal slope.

Point 4: In figure 4, what is sand "cowering"?

Response: Thank you for pointing it out. We have changed “cowering” to “covering” in Fig.4.

Point 5: I might suggest comparing apples with apples and place figure 6a with 5a to make a direct comparison or perhaps a hybrid measure of the two curves on a single graph would make a good visual comparison.

Response: Thank you for suggestion. We have merged two figures 5 and figures 6.

Point 6: Please round your coefficient of determinations to two decimal places.

Response: Thank you for suggestion. Done as you suggested.

Point 7: DEMs are simply representations of a parameter like elevation or slope but they are not computational models, thus statements like (line 188) "calculated by DEM" is mis-stated. I believe it should be "with the DEM" or "from the DEM".

Response: Thank you for pointing it out. Done as you suggested. We have written the statement in line 122.

Point 8: Subscript mean on Hmean line 129.

Response: Thank you for pointing it out. Done as you suggested.

Point 9: It's microtopography not microtopographic in line 137.

Response: Thank you for pointing it out. Done as you suggested.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors provided replies to all my previous comments. Regarding the method they used to measure the flow velocity, they provided a reply in the comments, but I think that it should be also included in the manuscript (methods section).

Finally, I'm not an expert, but I think that the English, especially in the revised parts, should be carefully reviewed before the final acceptance of article.

 

Author Response

Responses to Reviewers Dear editor and reviewers: We would like to thank the editor very much for giving us a chance to revise the paper, and also thank the reviewers so much for the constructive suggestions which help us significantly to improve the quality of the paper. According to the comments and suggestions, we have made a thorough revision and resubmit the new version of the manuscript entitled “Response Relationship between Microtopographic Variation and Slope Erosion under Sand-Cover” (ID: Water-635207). In the revised manuscript, we highlighted all the changes in red. Should you have any query for the revision, the authors are pleased to make further revisions. With best regards Guoce Xu, corresponding author Reviewer #1: 1. Point 1: Regarding the method they used to measure the flow velocity, they provided a reply in the comments, but I think that it should be also included in the manuscript (methods section). Response: Thank you for pointing it out. We have added this sentence as your suggestion in Line 100-101. 2. Finally, I'm not an expert, but I think that the English, especially in the revised parts, should be carefully reviewed before the final acceptance of article. Response: Thank you for comment. We have checked the English expression.

Author Response File: Author Response.docx