Dear Authors,

The paper discusses methods of expressing and evaluating resistance to flow in an unsteady flow. Both reviewers raised important issues concerning the objectives, the dataset, the methodology, the results and conclusions. In their responses, the authors propose to restructure the paper (following a classical structure: introduction (motivation, objectives), experimental data, methods, results, conclusions) and give responses to some of the critics raised by the reviewers, but some important issues raised by reviewers still need complementary responses, for example there is a need: i) to clarify the objective(s) (especially in the title which remains unclear); ii) to highlight the novelty of the work in comparison to the literature; iii) to demonstrate the utility of the approach for practical applications in comparison to classical methods; iv) to discuss the strengths and weaknesses of the new approach, the domains and limits of application of the approach. The paper will be reconsidered after “Major revisions” for a complete review process. In the revised version, authors are invited to respond point by point to each comment of each reviewer, conducting additional analysis, and giving convincing proofs to all problems raised by reviewers. Please highlight clearly what you changed in the revised manuscript, so the reviewers are able to assess your changes.

Kind regards,

Roger Moussa

Dear Authors,

Thank you for submitting a revised version of your paper which takes into account the main comments of the reviewers. The paper was sent for a re-review. The paper was improved but reviewer #1 raised important issues which still need revision. In the revised version, authors are invited to respond point by point to each comment of reviewer #1. Please highlight clearly what you changed in the revised manuscript, so the reviewers are able to assess your changes.

Kind regards,

Roger Moussa

Dear Authors,

I can now inform you that the reviewers and editor have evaluated the revised version of your manuscript which is drastically improved over the earlier versions. As you will see from the comments below, minor revision has been requested.

Please consider the reviews to see if revision would be feasible. Should you disagree with any part of the reviews, please explain why. I hope that you will find the comments to be of use to you and am looking forward with interest to receiving your revision.

Thank you for submitting your work to Hydrology and Earth System Sciences.

Kind regards,

Roger MOUSSA

Dear Authors,

All reviewers’ comments were addressed in a satisfactory manner. I can now inform you that the manuscript "A methodological approach of estimating of resistance to flow under unsteady flow condition" is accepted for publication.

Thank you for submitting your best work to Hydrology and Earth System Sciences.

Kind regards,

Roger MOUSSA