| 14 Nov 2025
Tsunami-Sediment Interactions Amplify Coastal Hazard and Reshape Inundation Dynamics in Tumaco Bay, Colombia
Abstract. Tumaco, situated on the Colombian Pacific coast, is particularly vulnerable due to its location within the Pacific Ring of Fire. Although studies on tsunami risk in the region have been conducted, the interaction between these events and sediment transport has been little explored, despite its impact on flooding dynamics. This study addresses this gap by comparing two scenarios – those with and without sediment transport – and evaluating the morphodynamic effects of tsunami events on proposed mitigation measures for Tumaco. The results show that including sediment transport in the simulations increases wave heights, flooding depth and extent, as well as coastal impacts. In particular, maximum flood depths increase by 24.4 % on Morro Island, 11.57 % on Tumaco Island, and 30.91 % on the mainland. Likewise, flooded areas increase by 4.12 %, 5.15 %, and 13.43 %, respectively, due to increases in flow density and momentum. The mitigation measures reduce the extent of flooding, although they cause local increases in wave heights due to reflection effects. It is noteworthy that in the simulations with mitigation measures, sediment transport does not cause erosion that compromises these coastal defenses. These findings underscore the importance of incorporating sediment transport into tsunami modeling to enhance hazard assessments and refine mitigation strategies, ultimately contributing to the development of more effective coastal resilience plans.
In the reviewed article, Sanchez-Escobar and collaborators present a numerical exercise aimed to assess the possible effect on tsunami intensity metrics, as a result of a)including sediment transport on the modeling, b) by assessing the impact of proposed mitigation strategies. I note these can be treated as independent goals, yet there are somewhat mixed in the article.
The results are a bit counterintuitive, especially for the sediment transport results, where noticeable changes are reported in the text. I note that following the text is extremely difficult, because in general the quality of the figures is very, very poor (more on this regard below), hence the reader can not follow the argumentation. For example, a change of the maximum wave height from 5.0 m to 6.6 is reported (a 30% increase!) but the reader does not know whether this is colocated. In contrast, Fig. 7 shows minimal changes, of less than 5%. How are these two reconciled?
The main problem with the article, is that the justification for this results is very superficial. The authors resort to arguments by Apotsos et al., 2011, and Yamashita et al., 2016. However, I still find these results counterintuitive because even though the argument of the flow carrying more mass and momentum due to the sediment (in suspension??) might be true, but one can think of this process as the flow doing work to transport the sediment. Hence, less mechanical energy is available for the flow itself. The initial energy of the flow remains the same, as the source is unchanged, hence I find the argumentation somewhat unsubstantiated. Is it possible that that movable sediment causes bathymetric changes (eg, fig 12) which in turn change propagation characteristics (something that Yamashita et al. suggest when they analyze the effects of sediment transport on a wave by wave fashion) ? I think the presentation is too light to learn more from this.
Similarly for the goal of assessing the effect of the mitigation projects. One has to take to face value the argumentation that the flow is reoriented in such a way that reflection and constructive interference are the main drivers of the change. The figures do not provide compelling evidence on this regard.
As it stands, I do not think that this is going beyond a case study, but it has certainly picked my curiosity.
Some questions I think would need to be answered in the text:
- is sediment conserved (e.g. Fig 12 adds up to zero) ? Does not look like it but then the colorscale is hard to read.
-is the sediment thickness uniform over the domain? if not, how is it distributed? If yes, what kind of evidence does support this claim?
-using high tide indeed may change exposure, but from the sediment standpoint, shallower flows can have much larger velocities hence more sediment transport capacity. Comments?
-the authors mention “sensitivity analyses” (section 3.3) but only a single simulation is shownper case. How is this sensitivity carried on?
-the Manning friction coefficient is rather low. Why? Usual practice has it at 0.025, which is also a low value.
Figures:
All figures are very poor and very hard to read.
Axes are usually intelligible.
Colorscales change across figures. For example Fig 1 outer figure and inset, with Fig 2.
Many figures are overlain the terrain, with makes them very hard to read. I suggest removing it completely as it adds no value.
Colorscales for difference are non symmetrical and eventhough are divergent, the zero is set to a yellowish color that makes it confusing. Use Python's “seismic” or similar colorscale for differences.
Locations mentioned in the text are not clearly described in the Figures. Places such as Bajito, Morro or others are not included in the Figures, except in the last one! (and here is hard to know where they are, exactly.)
The only Figure with some naming in it early in the text, is Fig 2, which has no axis. Trying to place the Evaluation points of Table 2 is not possible.
Figures are usually presented on a 3 column by 1 row format, with a lot of space to the sides. This makes it very hard to read (Figs 6,8,9, 11, etc). In contrast, Figures with time series are gigantic in comparison.
Points of interest of Table 4 have no correlation with figures.
Fig 1, Does not show clearly the coastline awhile also having a large portion of land that is absolutely irrelevant. The inset is very small.
Fig 1 and 2 can be merged.
Fig 3 and 4 can be merged. By the way, where was the LIST measurement taken? Is it representative?
Figure 3 and 7. I have no idea where are these gages located in the map. It says “near” Morro and Tumaco Islands...that can be anywhere!
Other technical comments:
+”Validation” against TUNAMI.:
--Not really a validation, but a comparison. However, more important than flow depths are velocities, especially for sediment transport. How do they compare?
--How is the Pearson coefficient computed?
--Lesser and Van Rijn references are more pertinent to gravity waves as source of transport. How do the model equations compare with those of , say, Yamashita et al. (op.cit.)
+ I would suggest to use flow depth, coastal amplitudes (peak) and more standardized terms for the Tsunami Intensity Metrics. As a community we have been very lax in terminology and we should be more cautious.
In summary, an interesting numerical experiment with flavor of just a case study, that needs stronger support for some of its claims. At the minimum, improving figures and text, but I would also recommend more physics!