Before reviewing the paper, I had a look to the online discussion. I agree with referee 1 that the paper suffers from a series of drawbacks and can largely be improved. However I will not be as severe as he was, and I consider that it is a nice experiment which results deserve to be presented to the community, after major revision of the paper. Major comments My main comments concern the experimental set-up. When reading the paper the first time, I wondered if I missed something when I discovered the experimental set-up: why do you need a gravel sand transition for studying the armor breakup and reformation? This is an enigma. You could have done the same experiment without the sandy part of the flume? Or maybe this was motivated by a particular reason, but it is not explained in the paper. Actually your experiment is far to be out of interest, but what you studied seems more to be a gravel sand transition. This is a situation present in many rivers, which physics is also poorly understood. With your experiment you could describe precisely how the coexistence of armor and sand patches behave during flood: starvation and erosion of the sandy place, replacement by the gravel wave, impact of reduced slope in the propagation of the gravel wave and armor reformation. . .. Such experiment allows very well documented measurements, and we would expect a very fine analysis of the hydraulics. What were the hydraulics conditions: flow depth, velocity, energy slope, Fr, Shear stress, Shields stress. . .? Was there any side wall effects, and if yes can you propose a correction? The results you present in the paper are essentially descriptive. With the hydraulics, you could propose a much convincing quantitative analysis of your results, with a focus on what happens in the sand gravel transition zone. It would be very interesting. To conclude on this comment: either you justify the need of a sandy section for studying the armor breakup and reformation, of you reconsider the paper objective (which also means to reconsider the literature review). I also found a bit frustrating the description of the grain size measurement technique1.
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