| 19 Mar 2025
Integrating smartrock and seismic monitoring to investigate bedload transport dynamics during rapid increase of stages in ephemeral streams
Abstract. Bedload transport dynamics during rapid increases of stage remain poorly constrained, particularly in ephemeral streams where such conditions are common. We combined two cutting-edge monitoring techniques – smartrocks and seismic measurements – to investigate bedload transport patterns during rapid increase of stage in two ephemeral channels with different morphologies. The later technique was used to characterize bedload activity through the Power Spectral Density (PSD) of recorded seismic signals. Our observations reveal three distinct stages of bedload response: (1) At shallow relative depth (h /d84 ≤ 0.9), rapid increase of stage enhanced bed material activity compared to steady flow, with PSD ratios (PSDrapid stage rise /PSDsteady flow) above unity and a higher prevalence of vibrational movement under rapid stage rise conditions relative to steady flow; (2) At intermediate relative depths (0.9 ≤ h /d84 ≤ 2.5), the rapid increase of stage effect on bedload activity diminished; (3) At greater relative depths (h /d84 ≥ 2.5), bedload activity is once again enhanced during rapid increase of rise, with both seismic energy and particle motion exceeding values observed under steady flow conditions. The transitions between these stages occurred at similar relative depths in both channels despite their different morphologies, suggesting that channel roughness strongly influences how rapid stage rises affect bedload transport.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Earth Surface Dynamics.
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Dear authors, dear editor
This is a very interesting article on sediment dynamics in ephemeral streams. It is based on two different measurement techniques that are currently very popular in our field of research and which are combined here.
This parallel use of smartrock and seismic measurements is new and extremely exciting in bedload transport research. Quantifying seismic energy in the range where (artificial) bedload particles transition from vibration to actual displacement will certainly also be helpful for future studies using seismometers along torrents and mountain rivers outside semi-arid areas. The authors' focus on the moment in the discharge hydrograph when the water level/discharge rises sharply is clearly emphasised. Such rises occur, for example, during flash floods. Experts in the field are well aware that studying sediment transport dynamics during such rapid rises in discharge is of fundamental importance. This is because, compared to steady flow conditions, sediment transport rates are higher during the arrival of flash floods, when there is an intense and rapid increase in water levels. The fact that high sediment transport rates also greatly increase the risk of damage along watercourses could be explicitly mentioned (in the Introduction or Discussion sections) in order to also convince non-experts of the importance of this research.
I strongly support the publication of this article in Earth Surface Dynamics. It represents a step forward and will be important for the research community dealing with bedload transport. I can't think of any significant reasons why this manuscript shouldn't be published quickly. And below, I would like to list only two points of a more general nature.
However, as is well known, the devil is in the detail. This is evident in the considerable number of specific questions and comments attached as a supplement. However, I am confident that the authors will be able to respond to these comments and provide clarifications relatively easily, thereby strengthening their manuscript further.
[1] In the Introduction section (L44-46), the authors state that "Rapid increases of stage are often unpredictable, infrequent, and short-lived, posing challenges for traditional bedload monitoring methods." Further down the page (L59-61), several of these traditional measurements are listed in the text (samplers, impact sensors and hydrophones). In an innovative approach, the authors decided to use smartrock technology alongside seismic measurements. This combination is very well suited for improving the description of bedload transport dynamics during rapid increases in discharge in ephemeral streams.
However, in addition to a detailed description of the dynamics, it would also be interesting to be able to make quantitative statements about bedload transport rates or transported volumes during a bore. It might therefore be interesting for readers to learn briefly about the challenges or limitations of traditional methods of measuring sediment transport in semi-arid and arid regions especially in very unsteady flows. A reference to the relevant literature would be helpful. Perhaps to the work carried out in the nearby Nahal Eshtemoa (e.g. Halfi et al. 2018; https://doi.org/10.1051/e3sconf/20184002036)? Could the seismic-smartrock combination also be used along Nahal Eshtemoa, where both direct and indirect sampling methods were employed? Provided, of course, that the slot samplers and pipe/plate microphones are still operational. I realise that there is not much space for this in the Introduction section of the article. I would therefore ask the authors to consider whether this point could be covered in a new, brief sub-section of the discussion.
[2] The authors introduce water level stages (1–3) for both monitoring techniques applied in this study. Stages 1-3 based on gyro velocity ratios are shown in Figure 5 (and introduced in the text in lines 213-214). Stages 1-3 based on PSD ratios are shown in Figure 9 (and introduced in the text in line 272). The only place in the Results section where the authors point out that there are two differently defined sets of stages (1–3) is in the caption of Figure 9, lines 289–290.
To avoid confusion among readers, I strongly recommend that these two differently defined sets of water level stages (1 to 3) also be named/labelled differently. This is all the more important given that yet another set of stages is introduced in Figure 10 (and in the text on line 280). These are also defined based on the PSD ratio. However, they refer to the relative water depth and apply to both study sites.
Figure 11 concludes the presentation of the results by showing how the PSD varies with smartrock gyro velocity. Here, the authors once again introduce stages (this time two, Stage 1 and Stage 2). These have no direct connection to the set of “stages” mentioned above. They should definitely be designated differently.
I do realise that the authors clarify this right at the start of the Discussion in section 4.1 and distinguish between the three stages determined using the PSD ratio and gyro velocity ratio. Nevertheless, I would like to insist on my comment regarding the need for greater clarity in the Results section. I think the manuscript would benefit from this.
In summary, I would be glad if this article could be published in ESURF. I suggest the manuscript be re-evaluated following moderate revisions. Attached is a document containing specific comments on the text, figures and tables, as well as technical corrections. I would ask the authors to consider these.