Bedload Sediment Transport Estimation in Sand-Bed Rivers Comparing Traditional Methods and Surrogate Technologies

Round 1

Reviewer 1 Report

The paper presented a bedload measurement method using ADCP, and comparisons with empirical formulas. Some contents are better to be furtherly highlighted.

1.     ADCP is feasible to sample the bottom topography and the velocity distribution through the water depth, however, how to measure the bedload transport velocity? In the context, the ADCP was used to measure the bottom topography, which means the quantification of the dune envelope propagation velocity. The sand wave velocity doesn’t consist with the material transport velocity. 

2.     The bedload is transported in a layer in which the material transport velocity varies through the layer. For formula (1), is the adopted velocity the sand wave surface velocity or the depth-averaged velocity ?

 3. How to evaluate the usability of the calculation of the bedload layer thickness?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Major comments

·        Bedload measurements is an area in great need for improvements, thus research efforts like the one described in the manuscript are more then welcome. From this perspective, the manuscript is an excellent effort that has to be commended. While this study involved an impressive amount of work (from data collection to processing), there are some outstanding issues to be clarified before to evaluate the significance of the reported results. This reviewer assessment is that the manuscript can be published after changes in measurements’ description and addressing formatting issues described below.

·        A first general comment: the paper is too long. A max of 15 pages is desirable, as more text interrupts the fluency of the story telling. I think that descriptions such as in lines 120-123; 144-153; 307-318, etc. can be removed. You can direct the reader to the citations without providing the details in the text. Avoid redundancy and consolidate text, e.g., same or similar ideas are described in lines 247 – 255 and 634-642 and again in lines 743-750!

·        We fully understand the difficulty to acquire and present this large amount of measurements  However, the spatial-temporal aspects of the of the reported measurements are of critical importance for this paper and should be further enhanced. Table 1 is useful in this regard but not sufficient to provide all the needed details to easily grasp where and when these measurements were taken. There is mentioning of transects and fixed-point measurements with different instruments and for various purposes but the description is poor on the visualization side. Similarly, there is a need for visualization of the timing of the measurements in parallel with the streamflow variation.  

Suggestions:

o   In view of the importance of both temporal and spatial resolutions of the measurements Section 3.1 needs to be re-organized to be better understood. Do not mix settings of the instruments, execution of measurements, and data processing in the same place. Describe them separately.

o   There is a need to add a time diagram of the measurements with each approach (what was measured when) on the overall variation of the hydrograph for the flow during the 3 days of measurements. Please provide in a plot the time duration of the measurements for each method along with the discharge hydrograph to be able to assess the impact of the aforementioned aspects on the mean values reported as results. Make comment of the relevance of reporting results obtained over 3 days of non-stationary flow conditions.

o   There is also a need for a representation of the spatial resolution aspect of the measurements. Increase considerably the size of Figure 2a and indicate the location of all measurements (including the fix point ADCP) and their timing. Add the ISSDOT assessment area by moving Figure 5 to Figure 2a.

o   In Figure 3, show the interpolated bathy from ADCP surveys for both days.

·        Regarding the ISSDOT implementation: The author state: “Each bathymetric survey lasted 3 hours and the time interval between them was 24 hours.”,  How should we know that the 24h interval between the ADCP surveys for capturing the bedform dynamics are measuring on the same bedforms (even if the ISSDOT 20% variation of the profile is fulfilled)? The proof provided by the authors in lines 701-710 is not satisfactory given that the measurements were taken during a flood wave propagation with discharges varying from 261 to 373 m³/s. It is quite debatable if the 3 hours for each ADCP survey are not affected by the flow non-stationarity in such a rapid changing flows.  Furthermore, the authors state: “The result of the mISSDOTv2 method (776 ton/day), however, represents the mean bedload transport between the last two days (01/Feb/2018 and 02/Feb/2018), since it uses longitudinal profiles from two DEMs generated with bathymetric data measured on two distinct hydraulic conditions.” I am not sure that ISSDOT method was developed to measure over such large variations in bedload transport. 

·        The conclusions of this paper are depending on when and where the measurements with each type of instruments were acquired and what type of sediment transport was involved over the three days. The present reviewer is confident that the data processing was done according to the best available knowledge, but the inferences from unknown data acquisition details preclude to validate the comparison conclusions.

o   Suggestions: split Figure 15a in three components, one for each day.

Minor comments

·        The style of citations used in the paper is not conventional; i.e., (Latosinski et al. [1]). Should be either [1] or (Latosinski et al., 2017]). Due to the paper length, I suggest the former citation version.

·        Given that the paper title and introduction hint to a review of existing methods, it is appropriate to mention the Acoustic Mapping Velocimetry Method that was initially used with laboratory measurements (Muste et al., 2016). The method is based on dune tracking but distinct from ISSDOT as it calculates bedform velocity instead of geometric changes in time in the Exner equation. Recently, the same method was successfully implemented in situ (You et al., 2021a, 2021b).

References

Muste, M., Baranya, S., Tsubaki, R., Kim, D., Ho, H-C., Tsai, H-W. and Law, D. (2016). “Acoustic Mapping Velocimetry,” Water Resources Research, 52, doi:10.1002/2015WR018354.

You, H., Muste, M., Kim, D. and Baranya, S. (2021). Considerations on Acoustic Mapping Velocimetry (AMV) application for in-situ measurement of bedform dynamics, Frontiers in Water, Special Issue on “Advances in Image Velocimetry for Sensing River Flows”, (3) 715308, doi: 10.3389/frwa.2021.715308

Author Response

Please see the attachment.

Author Response File: Author Response.pdf