Inferring Sediment Transport Capacity from Soil Microtopography Changes on a Laboratory Hillslope

Round 1

Reviewer 1 Report

Dear Authors

I spent considerable time reviewing your manuscript. The experiments are interesting and publishing the results will be worthwhile. The readers of the journal are scientists just like you. They can make their own conclusion based on the data. You deny the reader this opportunity to view the observed data. Instead, you present the interpreted results in a nonstandard way that is difficult to understand with probabilities and with unconventional parameters that do not have units.  The only graph I could check seems to be in error. 

I am not sure why the material and methods and theory are all about probabilities.  You have measured data for each replicated treatment.  Presenting the observed data would be straightforward   Summaries of the spatial data averaged over the width of the plot for each replicate would be very interesting.  No probabilities are needed here.  One could make also similar plots about the FAC (and explain the units and how they are obtained). Once you have presented this in the results section you can discuss the results with probabilities if you believe that is useful

In the current form, the paper cannot be published. My detailed comments are below and I truly hope that you decide to resubmit the paper with the comments of the reviewers in mind

Regards  and best wishes for a healthy 2021

Comments for author File: Comments.pdf

Author Response

We appreciate the reviewer's comments. Responses have been provided in the attached documents.

Best wishes,

Author Response File: Author Response.docx

Reviewer 2 Report

The authors of the paper will take up an interesting task with the aim of  propose a methodology to quantify Tc from surface change information collected during rainfall simulation experiment and apply this new methodology. Through these experiences they have achieved their goal by describing their research properly.

Author Response

We appreciate the reviewer's favorable reception of our manuscript.

Best wishes.

Reviewer 3 Report

This study present a new methodology to evaluate the effect of shallow subsurface hydrology on Tc. The manuscript is well-organized, the objective is clear and concise. The description of the research method are informative and easy to follow and replicate. However, some Figures in the manuscript should be further improved.

(1)Figure 3: It should show the spatial distance. I suggest that the distance from the top of upslope along the flow direction be supplemented on the abscissa.

(2)Figure 5: There should be a scatter plot here, not a line plot. The trend between the adjacent points are not real.

(3)All references were published before 2015. I suggest the author should look up some latest references and quote them.

Author Response

We appreciate the reviewer's favorable evaluation of our work. Below are responses to the specific comments made.

(1)Figure 3: It should show the spatial distance. I suggest that the distance from the top of upslope along the flow direction be supplemented on the abscissa.

Response: Figure 2 (Figure 3 in the original manuscript) has been amended to show the plot dimension along the flow direction

(2)Figure 5: There should be a scatter plot here, not a line plot. The trend between the adjacent points are not real.

Response: Figure 4 (old Figure 5) shows the result of probability calculations that pixels experiences a given level of hydraulic stress underwent erosion or deposition. While it is true that the line interpolation between points is not measured. These lines were used to illustrate the location of the PE = 0.5 crossing point.

(3)All references were published before 2015. I suggest the author should look up some latest references and quote them.

Response:  The manuscript has been amended to include references published since 2015.

Round 2

Reviewer 1 Report

Dear Authors

The responses and the changes in the text helped much to appreciate the experiments carried out and the significance of the results. 

I asked about the water table in my previous comments, and I was assured that the drainage system would keep the water table down.  Despite this assurance, it might be useful in the next set of experiments to test if the water table is really at the bottom of the topsoil by using some piezometers (that can be read outside the box) or with some electronic pressure transducers.  It could be very well that the increase in saturation is at elevated stream powers is related to saturation.  In Ethiopia, the local farmers told us that gullies started from springs after the forest was cut and the watershed discharge increased.  At saturation, the soil loses its strength and is easily eroded. Note also that the stream power function used in this paper has many similarities to the topographic index used in hillslope hydrology to indicate where the soil is saturated.

Some minor comments

• Line 125 “where z is the elevation at point i and t is time and PE + PD” Should be a capital Z
• Figures should stand alone. So the abbreviations should be explained in the figures. It was missing for Figure

It was a pleasure to review the paper and I appreciate that my comments were taken seriously and led to an improvement in the presentation of the manuscript

Best regards

Tammo Steenhuis

Author Response

Reviewer's comment: The responses and the changes in the text helped much to appreciate the experiments carried out and the significance of the results. 

Response: We highly appreciate the reviewer's acknowledgment of the significance of the results of this study.

Reviewer: I asked about the water table in my previous comments, and I was assured that the drainage system would keep the water table down.  Despite this assurance, it might be useful in the next set of experiments to test if the water table is really at the bottom of the topsoil by using some piezometers (that can be read outside the box) or with some electronic pressure transducers.  It could be very well that the increase in saturation is at elevated stream powers is related to saturation.  In Ethiopia, the local farmers told us that gullies started from springs after the forest was cut and the watershed discharge increased.  At saturation, the soil loses its strength and is easily eroded. Note also that the stream power function used in this paper has many similarities to the topographic index used in hillslope hydrology to indicate where the soil is saturated.

Response: We thank the reviewer for this suggestion for future work. This is certainly a simple great idea that would provide an accurate measure of the actual pore pressures experienced by the soil during the erosive event. We take note for future research.

Reviewer: Some minor comments

• Line 125 “where z is the elevation at point i and t is time and PE + PD” Should be a capital Z

Response: The correction has been made in the attached revised version

Reviewer:

• Figures should stand alone. So the abbreviations should be explained in the figures. It was missing for Figure

Response: All abbreviations used on figures in the main paper and in supplemental figures have been explained in the captions (see revised manuscript and supplemental document).

Reviewer: It was a pleasure to review the paper and I appreciate that my comments were taken seriously and led to an improvement in the presentation of the manuscript

Response: Again we appreciate the reviewer's thorough feedback that helped improve this manuscript.

Best wishes,

The corresponding author.