The Potential of Gully Erosion on the Yamal Peninsula, West Siberia

Round 1

Reviewer 1 Report

REVIEW OF THE PAPER “The potential of gully erosion on the Yamal Peninsula, West Siberia” by Aleksey Sidorchuk. This paper presents an interesting approach to describe the potential of gully erosion in the Peninsula of Yamal. The author tries to set the theoretical background for the gully erosion process based on the geomorphological threshold theory which is interesting but shows also some drawbacks, the most important, in my opinion is that once gully erosion has initiated, the process may continue although the trigger factors-threshold are not activated anymore.

On the other hand, the threshold theory based on local slope and contributing area performs properly for gullies produced by overland flow but processes in the Yamal peninsula seem to be much more complex than that with soil properties varying a lot during the hydrological year.

Other main concern for me is that every data and parameter used come from a model, which is something that I may understand due to the location of the study area but no validation about the results (the potential distribution of gullies or “erosion potential” for different values of critical velocity) is presented, just using aerial images (a DEM or satellite images) the author may delineate the actual extent-location of gullies and compare this with the potential distribution of erosion estimated by the proposed methodology. Due to this circumstance it is very difficult to link results with conclusions presented.

Finally, I think the paper is so methodological that sometimes seems disorganized with methodological points showed in the results.

TITLE: change “on” by “in”

ENGLISH: I am not a native English speaker but the paper needs a professional English editing.

Figures should improve notably, let’s take Fig. 1, is there any situation map or has the reader to know exactly where is the Yamal Peninsula, do you have a scale bar? Why the reader cannot read every label in this map? What is the source of this map? It is yours?

L44: “is an area” instead “is the”

L47: a reference for this figure data is needed here (i.e. density of gullies)

L60-61: as I told before, gullying, once initiated, may continue even if triggering conditions are not active anymore.

L159: “some of them” be specific, this is a scientific paper.

L166-167: explain how did you estimate these values.

Fig. 3: data source to estimate these relationships?

L198 and ahead: these are not results, these are methodological points.

L228: why do you refer to rivers if they are not showed-represented in Fig. 5 and 6?

Fig. 5: what are black lines? Contours? What interval? What elevation?

L244: for a few more catchments, be specific, this is a scientific paper.

Table 1: “Erosion” instead “erosion” in the fourth row.

L259: “some constants” be specific.

L280: delete “is”

Author Response

Thank you very much for your comments

The answers are in bold

REVIEW 1 OF THE PAPER “The potential of gully erosion on the Yamal Peninsula, West Siberia” by Aleksey Sidorchuk. This paper presents an interesting approach to describe the potential of gully erosion in the Peninsula of Yamal. The author tries to set the theoretical background for the gully erosion process based on the geomorphological threshold theory which is interesting but shows also some drawbacks,

 the most important, in my opinion is that once gully erosion has initiated, the process may continue although the trigger factors-threshold are not activated anymore.

We are talking about gully erosion potential, which is calculated for the points and lines on the catchment, were erosion by water can be initiated because flow velocity is more than critical. Outside these points and lines erosion by water can not be initiated at a given morphological, hydrological, lithological and vegetation cover conditions. All the processes of gully formation, related to water flow, can occur only within the area with initially critical trigger factors, despite these factors (flow velocity and slope) can change through time. This area is the territory of the risk of erosion by concentrated flow, i.e of linear erosion. This statement was included into the text (lines 163-168)

On the other hand, the threshold theory based on local slope and contributing area performs properly for gullies produced by overland flow but processes in the Yamal peninsula seem to be much more complex than that with soil properties varying a lot during the hydrological year.

Yes, the processes of gully erosion on the Yamal peninsula are more complicated than simple erosion by water. The main additional processes are 1) thermoerosion – melting of frozen soil by water and washing away of the melted layer (see lines in the new text 169-172), and 2) slumping of melted soil from gully walls. As is was pointed at lines 169-172, thermoerosion is always less intensive, than mechanical erosion. The slumping from walls reduces the rate of gully incision. Therefore, the erosion potential calculated only for one process – erosion by water, is close to maximum of possible. Some increase of gully erosion potential above calculated by proposed method is due to gravitation processes. This statement was included into the text (lines 173-186)

Other main concern for me is that every data and parameter used come from a model, which is something that I may understand due to the location of the study area but no validation about the results (the potential distribution of gullies or “erosion potential” for different values of critical velocity) is presented, just using aerial images (a DEM or satellite images) the author may delineate the actual extent-location of gullies and compare this with the potential distribution of erosion estimated by the proposed methodology. Due to this circumstance it is very difficult to link results with conclusions presented.

It is not easy to validate the results of erosion potential calculations, as this potential is almost never reached in nature, maybe only at the badlands. Usually erosion potential is calculated to prevent the dangerous results of erosion by some soil conservation measures, and gully erosion is stopped at some degree of development. The second difficulty in validation procedures is the inaccuracy of existing DEMs, which are used for erosion potential calculations. Linear erosion can follow along such lines on the catchment (vehicle tracks, linear damages of vegetation, the local sources of water, etc.) which can not be implemented into DEM of any resolution. I included the section with a validation procedure including all these remarks (lines 257-282).

Finally, I think the paper is so methodological that sometimes seems disorganized with methodological points showed in the results.

The methodological points were removed to the methodological section

TITLE: change “on” by “in”- cannot agree

ENGLISH: I am not a native English speaker but the paper needs a professional English editing. – the text was edited by experienced person

Figures should improve notably, let’s take Fig. 1, is there any situation map or has the reader to know exactly where is the Yamal Peninsula, do you have a scale bar? Why the reader cannot read every label in this map? What is the source of this map? It is yours? – the map was improved

L44: “is an area” instead “is the” – was changed

L47: a reference for this figure data is needed here (i.e. density of gullies) – the map of erosion net density was added (fig 2)

L60-61: as I told before, gullying, once initiated, may continue even if triggering conditions are not active anymore. – see my explanations above

L159: “some of them” be specific, this is a scientific paper. – the parameters and variables were specified (L 189-191)

L166-167: explain how did you estimate these values. – see the reference [23] and fig.3. Additional explanations are at L190-201

Fig. 3: data source to estimate these relationships? – added to the fig.3 caption

L198 and ahead: these are not results, these are methodological points. – these points were moved to methodology section (now L 233 and ahead)

L228: why do you refer to rivers if they are not showed-represented in Fig. 5 and 6? – I refer to the basins of small river, which can be found on the detailed digital maps of Russia. – the map with this small river was added to the fig. 6

Fig. 5: what are black lines? Contours? What interval? What elevation?

Fig was improved

L244: for a few more catchments, be specific, this is a scientific paper.

Was done

Table 1: “Erosion” instead “erosion” in the fourth row.

Was done

L259: “some constants” be specific.

“with some constants” is deleted

L280: delete “is” - yes

Reviewer 2 Report

Erosion is a global problem, so I consider the topic to be highly topical.

Questions:

How long (time period) was the modeled area monitored for erosion phenomena? Have the research results been verified e.g. by geodetic surveying in field in the area?

Author Response

Thank you very much for your comments

answers are in bold

Rev 2

Questions:

How long (time period) was the modeled area monitored for erosion phenomena?

Field measurements were performed in 1990-1997, 2007, images used are of 1986-1995, 2007, 2016 – added to the text 

Have the research results been verified e.g. by geodetic surveying in field in the area?

The validation section was added to the text (L 257-282)

Round 2

Reviewer 1 Report

Authors addressed all comments.