the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 22 Mar 2023
Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments. Part 2: suspended sediment dynamics
Abstract. A proper understanding of sediment transport dynamics, critically including resuspension and deposition processes of suspended sediments, is key to the morphodynamics of shallow tidal environments. Aiming to account for deposition mechanics in a synthetic theoretical framework introduced to model erosion dynamics, here we investigated suspended sediment dynamics. A complete spatial and temporal coverage of suspended sediment concentration (SSC) required to effectively characterize resuspension events is hardly available through observation alone, even combining point measurements and satellite images, but it can be retrieved by properly calibrated and tested numerical models. We analyzed one-year-long time series of SSC computed by a bi-dimensional, finite-element model in six historical configurations of the Venice Lagoon in the last four centuries. Following the peak-over-threshold theory, we statistically characterized suspended sediment dynamics by analyzing interarrival times, intensities and durations of over-threshold SSC events. Our results confirm that, as for erosion events, SSC can be modeled as a marked Poisson process in the intertidal flats for all the considered historical configurations of the Venice Lagoon because exponentially distributed random variables well describe interarrival times, intensity and duration of over-threshold events. Moreover, interarrival times, intensity and duration describing local erosion and over-threshold SSC events are highly related, although not identical because of the non-local dynamics of suspended sediment transport related to advection and dispersion processes. Owing to this statistical characterization of SSC events, it is possible to generate synthetic, yet realistic, time series of SSC for the long-term modeling of shallow tidal environments.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-320', Anonymous Referee #1, 23 Apr 2023
This is an interesting paper combining a modeling approach and a statistical analysis of suspended sediment dynamics in the Venice Lagoon. The paper is well written, but the findings bring very little new insight, in comparison with its companion paper Part I on erosion dynamics.
Although this is probably more of an editorial issue, I am questioning the relevance of making two papers out of this study. Indeed, both papers have basically the same structure, with very similar introduction and method sections. In addition, the results of both studies are highly correlated (see lines 300-305), which is not surprising as SSC dynamics (Part II) is itself highly correlated with erosion dynamics (Part I). To further support this, the authors keep referring to the companion paper on erosion dynamics to discuss their results on suspended sediment dynamics (section 3).
In the companion paper, the choice of a peak over threshold analysis is very natural, as erosion processes are physically triggered when the bed shear stress exceeds a threshold value. Here, the choice of such an analysis is less obvious, and determining an SSC threshold is highly arbitrary. Although the authors justify quite elegantly their choice of threshold value (line 212), they should at least discuss the sensitivity of their results and conclusions to this threshold value.
Something that intrigue me is hidden in lines 310-311. I am wondering if the results of this paper can be combined with the results of the companion paper to better constrained the erosion coefficient “e” (equation 3, companion paper). The value of this parameter is highly uncertain, given the values encountered in the literature range over more than one order of magnitude. If that is possible, that would be a very interesting result of this study.
In conclusion, I don’t deny the interest of this study, but I suggest to merge both companion papers into one.
Other minor remarks:
- Lines 97-98: This somewhat contradicts results from the companion paper about erosion work, which increased then decreased over time, due to increase inter arrival time.
- Lines 124-127: Provide the Strickler equation.
- Lines 128-136: Provide the equation of the BSS induced by wind waves and the equation of the maximum (total?) BSS.
- Line 153: Missing prime for the total BSS?
Citation: https://doi.org/10.5194/egusphere-2023-320-RC1 - AC1: 'Reply on RC1', Davide Tognin, 14 Jun 2023
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RC2: 'Comment on egusphere-2023-320', Anonymous Referee #2, 08 May 2023
This work is part 2 of the study that introduces the idea of using random processes to model the wave-tidal-induced events along the coastal area. The Venice Lagoon, Italy is chosen as the study site due to the availability of multiple bathymetry surveys over the past centuries. The WWTM model coupled with STABEM sediment transport model is used to simulate morphodynamics. Statistics are extracted from simulation results. The author found that over-the-threshold suspended sediment concentration (SSC) events follows can be modeled as marked Poisson process. As Part 1 paper, this work paved a new way to upscale short-term simulations in a wave-tidal environment to long-term, while following the statistical characteristics. This paper has a very similar structure to the Part 1 paper, as well as employed identical analysis using morphodynamics results. However, different from hydrodynamics simulations, simulating the dynamics of SSC is much more complicated which means more uncertainties. Hence, I recommend the author show more validation of the modeling results. Maybe some changes also need to be adapted in the analysis to address the differences. Secondly, although I understand the idea behind the "threshold of SSC", in my opinion, the author did not show the physical meaning or mathematical definition of it, which makes it not well-defined, I recommend the author add more work to its definition. Thirdly, I believe when dealing with a time scale over 4 centuries, the climate can play an important role, and the analysis should take into consideration of it. As the revision in Part 1 paper, I recommend the author add more model details, and the choice of constants. There are more things that need to be addressed, which are listed below. Overall, I think this work has good potential, but still needs more work.
- AC2: 'Reply on RC2', Davide Tognin, 14 Jun 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-320', Anonymous Referee #1, 23 Apr 2023
This is an interesting paper combining a modeling approach and a statistical analysis of suspended sediment dynamics in the Venice Lagoon. The paper is well written, but the findings bring very little new insight, in comparison with its companion paper Part I on erosion dynamics.
Although this is probably more of an editorial issue, I am questioning the relevance of making two papers out of this study. Indeed, both papers have basically the same structure, with very similar introduction and method sections. In addition, the results of both studies are highly correlated (see lines 300-305), which is not surprising as SSC dynamics (Part II) is itself highly correlated with erosion dynamics (Part I). To further support this, the authors keep referring to the companion paper on erosion dynamics to discuss their results on suspended sediment dynamics (section 3).
In the companion paper, the choice of a peak over threshold analysis is very natural, as erosion processes are physically triggered when the bed shear stress exceeds a threshold value. Here, the choice of such an analysis is less obvious, and determining an SSC threshold is highly arbitrary. Although the authors justify quite elegantly their choice of threshold value (line 212), they should at least discuss the sensitivity of their results and conclusions to this threshold value.
Something that intrigue me is hidden in lines 310-311. I am wondering if the results of this paper can be combined with the results of the companion paper to better constrained the erosion coefficient “e” (equation 3, companion paper). The value of this parameter is highly uncertain, given the values encountered in the literature range over more than one order of magnitude. If that is possible, that would be a very interesting result of this study.
In conclusion, I don’t deny the interest of this study, but I suggest to merge both companion papers into one.
Other minor remarks:
- Lines 97-98: This somewhat contradicts results from the companion paper about erosion work, which increased then decreased over time, due to increase inter arrival time.
- Lines 124-127: Provide the Strickler equation.
- Lines 128-136: Provide the equation of the BSS induced by wind waves and the equation of the maximum (total?) BSS.
- Line 153: Missing prime for the total BSS?
Citation: https://doi.org/10.5194/egusphere-2023-320-RC1 - AC1: 'Reply on RC1', Davide Tognin, 14 Jun 2023
-
RC2: 'Comment on egusphere-2023-320', Anonymous Referee #2, 08 May 2023
This work is part 2 of the study that introduces the idea of using random processes to model the wave-tidal-induced events along the coastal area. The Venice Lagoon, Italy is chosen as the study site due to the availability of multiple bathymetry surveys over the past centuries. The WWTM model coupled with STABEM sediment transport model is used to simulate morphodynamics. Statistics are extracted from simulation results. The author found that over-the-threshold suspended sediment concentration (SSC) events follows can be modeled as marked Poisson process. As Part 1 paper, this work paved a new way to upscale short-term simulations in a wave-tidal environment to long-term, while following the statistical characteristics. This paper has a very similar structure to the Part 1 paper, as well as employed identical analysis using morphodynamics results. However, different from hydrodynamics simulations, simulating the dynamics of SSC is much more complicated which means more uncertainties. Hence, I recommend the author show more validation of the modeling results. Maybe some changes also need to be adapted in the analysis to address the differences. Secondly, although I understand the idea behind the "threshold of SSC", in my opinion, the author did not show the physical meaning or mathematical definition of it, which makes it not well-defined, I recommend the author add more work to its definition. Thirdly, I believe when dealing with a time scale over 4 centuries, the climate can play an important role, and the analysis should take into consideration of it. As the revision in Part 1 paper, I recommend the author add more model details, and the choice of constants. There are more things that need to be addressed, which are listed below. Overall, I think this work has good potential, but still needs more work.
- AC2: 'Reply on RC2', Davide Tognin, 14 Jun 2023
Peer review completion
Journal article(s) based on this preprint
Data sets
Statistical characterization of suspended sediment dynamics in shallow tidal environments D. Tognin, A. D'Alpaos, and L. Carniello https://doi.org/10.25430/researchdata.cab.unipd.it.00000729
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Andrea D'Alpaos
Luigi D'Alpaos
Andrea Rinaldo
Luca Carniello
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.