the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Mar 2023
Statistical characterization of erosion and sediment transport mechanics in shallow tidal environments. Part 1: erosion dynamics
Abstract. Wave-induced bottom shear stress is one of the leading processes that control sediment erosion dynamics in shallow tidal environments, because it is responsible for sediment resuspension and, jointly with tidal currents, for sediment reworking on tidal flats. Reliable descriptions of erosion events are foundational to effective frameworks relevant to the fate of tidal landscape evolution. However, the absence of long-term, measured time series of bottom shear stress (BSS) prevents a direct analysis of erosion dynamics. Here we adopted a fully-coupled, bi-dimensional numerical model to compute BSS generated by both tidal currents and wind waves in six historical configurations of the Venice Lagoon in the last four centuries. The one-year-long time series of the total BSS were analyzed based on the peak-over-threshold theory to statistically characterize events that exceed a given erosion threshold and investigate the effects of morphological modifications on spatial and temporal erosion patterns. Our analysis suggests that erosion events can be modeled as a marked Poisson process in the intertidal flats for all the considered configurations of the Venice Lagoon, because interarrival times, durations and intensities of the over-threshold exceedances are well described by exponentially distributed random variables. Moreover, while the intensity and duration of over-threshold events are temporally correlated, almost no correlation exists between them and interarrival times. The resulting statistical characterization allows for a straightforward computation of morphological indicators, such as erosion work, and paves the way to a novel synthetic, yet reliable, approach for long-term morphodynamic modeling of 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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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-2023-319', Anonymous Referee #1, 13 Apr 2023
This work introduced the idea of using random processes to model the wave-tidal-induced erosion 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 numerical model Wind Wave Tidal Model (WWTM) is used to simulate hydrodynamics conditions, and statistics are extracted from simulation results. The author found that the interarrival time of the erosion events follows an exponential distribution, hence the events can be modeled as marked Poisson process. 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 statistical model-based upscale technique is the major scientific contribution of this work. My main comments on this work are on the boundary conditions, that are used in the upscale analysis (erosion work). I believe when dealing with a time scale over 4 centuries, the climate can play an important role, the analysis and boundary conditions should take into consideration of it. There are some details such as knowledge gaps that need to be improved, which are listed below. I also recommend the authors show more details on how the model is set up and validated; show the reasoning behind the choice of several important constants such as critical shear stress and erosion coefficient. Overall, I think this work is of high quality, and it should be rated as a minor revision or on the editor's decision.
- AC1: 'Reply on RC1', Davide Tognin, 02 Jun 2023
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RC2: 'Comment on egusphere-2023-319', Anonymous Referee #2, 23 Apr 2023
This is a very interesting paper combining a modeling approach and a statistical analysis of erosion dynamics in the Venice Lagoon. The paper is well written and the findings of potential interest for assessing long-term erosion processes in a computationally-efficient way.
I only have minor remarks.
- I miss a discussion about the potential applicability of the marked Poisson model for intertidal flats in other environments (e.g., with a different wind regime and/or different tidal regime).
- I also miss a discussion on the sensibility of the study results and conclusions to some key parameters (e.g., critical bottom shear for erosion, here fixed at 0.4 Pa, but greatly varying in the literature).
Other minor remarks:
- Line 67: Not clear if this tidal range or amplitude.
- Line 105: Provide the Strickler equation.
- Line 112: Provide the BSS induced by wind waves.
- Lines 144-145: I am wondering if the largest exceedance of the threshold is really the most appropriate here. I feel that the integral of the exceedance makes more sense, as it will determine the total amount of sediments that will be eroded during that event. Can you comment on that?
- Lines 150-162: This paragraph seems central to the entire paper. However, it is very short and does not cite any reference where the supporting theory is fully developed. I expect more details to support the theory, either as supplementary material or as cited literature.
- Lines 167-171: This should be in the methods section.
- Lines 184-186: Results in Figures 4-6 correspond to areas in red or yellow in Figure 3. Why not to areas in red only? Can you elaborate on that choice? Is it not relevant whether intensity and/or duration are exponentially distributed random variables?
- Lines 233-236: Please elaborate on the morphological features that remain the same through the last four centuries.
Citation: https://doi.org/10.5194/egusphere-2023-319-RC2 - AC2: 'Reply on RC2', Davide Tognin, 02 Jun 2023
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2023-319', Anonymous Referee #1, 13 Apr 2023
This work introduced the idea of using random processes to model the wave-tidal-induced erosion 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 numerical model Wind Wave Tidal Model (WWTM) is used to simulate hydrodynamics conditions, and statistics are extracted from simulation results. The author found that the interarrival time of the erosion events follows an exponential distribution, hence the events can be modeled as marked Poisson process. 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 statistical model-based upscale technique is the major scientific contribution of this work. My main comments on this work are on the boundary conditions, that are used in the upscale analysis (erosion work). I believe when dealing with a time scale over 4 centuries, the climate can play an important role, the analysis and boundary conditions should take into consideration of it. There are some details such as knowledge gaps that need to be improved, which are listed below. I also recommend the authors show more details on how the model is set up and validated; show the reasoning behind the choice of several important constants such as critical shear stress and erosion coefficient. Overall, I think this work is of high quality, and it should be rated as a minor revision or on the editor's decision.
- AC1: 'Reply on RC1', Davide Tognin, 02 Jun 2023
-
RC2: 'Comment on egusphere-2023-319', Anonymous Referee #2, 23 Apr 2023
This is a very interesting paper combining a modeling approach and a statistical analysis of erosion dynamics in the Venice Lagoon. The paper is well written and the findings of potential interest for assessing long-term erosion processes in a computationally-efficient way.
I only have minor remarks.
- I miss a discussion about the potential applicability of the marked Poisson model for intertidal flats in other environments (e.g., with a different wind regime and/or different tidal regime).
- I also miss a discussion on the sensibility of the study results and conclusions to some key parameters (e.g., critical bottom shear for erosion, here fixed at 0.4 Pa, but greatly varying in the literature).
Other minor remarks:
- Line 67: Not clear if this tidal range or amplitude.
- Line 105: Provide the Strickler equation.
- Line 112: Provide the BSS induced by wind waves.
- Lines 144-145: I am wondering if the largest exceedance of the threshold is really the most appropriate here. I feel that the integral of the exceedance makes more sense, as it will determine the total amount of sediments that will be eroded during that event. Can you comment on that?
- Lines 150-162: This paragraph seems central to the entire paper. However, it is very short and does not cite any reference where the supporting theory is fully developed. I expect more details to support the theory, either as supplementary material or as cited literature.
- Lines 167-171: This should be in the methods section.
- Lines 184-186: Results in Figures 4-6 correspond to areas in red or yellow in Figure 3. Why not to areas in red only? Can you elaborate on that choice? Is it not relevant whether intensity and/or duration are exponentially distributed random variables?
- Lines 233-236: Please elaborate on the morphological features that remain the same through the last four centuries.
Citation: https://doi.org/10.5194/egusphere-2023-319-RC2 - AC2: 'Reply on RC2', Davide Tognin, 02 Jun 2023
Peer review completion
Journal article(s) based on this preprint
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Statistical characterization of erosion mechanics in shallow tidal environments Davide Tognin, Andrea D'Alpaos, and Luca Carniello https://doi.org/10.25430/researchdata.cab.unipd.it.00000728
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Cited
Andrea D'Alpaos
Laura Tommasini
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.