Why in the News
According to a research paper published in Nature on 21 October 2026, the capacity of a salt marsh to stop very high waves was tested in a large laboratory experiment. The researchers brought blocks of real marsh from the Wadden Sea coast of the Netherlands, placed them in the Delta Flume (Deltares, Delft) and ran waves of up to 2 metres over them. This finding is based on the conditions of this experiment.
Key Figures
| Set-up of the experiment | About 306 square metres of marsh; a Delta Flume 300 metres long, 5 metres wide and 9.5 metres deep; the marsh blocks were taken from the Peazemerlannen nature reserve on the mainland coast of the Wadden Sea. |
| Range of waves | Significant wave height away from the coast from 0.75 metre to 2 metres; in all about 29 hours of exposure, of which 21 hours with above-ground vegetation and the last 8 hours without it. |
| Marsh surface | After 21 hours the surface lowered by only 7 mm on average; according to the researchers erosion was negligible. |
| Contribution of vegetation | Wave attenuation of 6% to 22% on waves of 0.75 metre and 0% to 6% on waves of 2 metres. |
| Global analysis | The model's estimate for storm surges occurring once in 100 and 1,000 years: on low-energy coasts with waves up to 1 metre, attenuation by vegetation generally more than 10% (maximum 50%); on high-energy coasts with waves higher than 1 metre, not more than 10%. |
What Does This Mean?
The base of the marsh held: According to the paper, despite the high waves the high surface (platform) of the marsh stayed nearly stable. This surface also reduces the energy of waves.
The vegetation broke down gradually: Under continuous waves the above-ground vegetation was progressively damaged and its contribution decreased.
Limited benefit in high waves: According to the authors, the larger attenuation by vegetation is found mainly on low-energy coasts (waves up to 1 metre).
Green-grey protection: The paper begins with the background that thinking is growing on the strategy of combining artificial structures such as dams and sea walls with ecosystems (green-grey).
Exam Perspective
In Prelims, salt marsh, wave attenuation and nature-based solutions are useful concepts. In Mains, an analysis may be asked on the role of natural systems in reducing coastal disaster risk and on its limits.
Limits
This is a controlled experiment. It had mainly one European marsh plant (Elymus athericus) and two soil types. The global figures are estimates of a model built from the experiment, not measured coastal outcomes. The authors have considered this vegetation a conservative estimator. No direct conclusion for India's coasts comes from this paper.
Prelims Practice Questions
1. Consider the following statements regarding the Delta Flume experiment on salt marshes of 21 October 2026:
- In the experiment the significant wave height reached 2 metres.
- The marsh surface showed negligible erosion even after the high waves.
- On coasts with waves higher than 1 metre too, the attenuation by vegetation was more than 10%.
Which of the statements given above is/are correct?
(a) Only 1
(b) Only 1 and 2
(c) Only 2 and 3
(d) 1, 2 and 3
See answer and explanation
Answer: (b). Statements 1 and 2 are in line with the paper. Statement 3 is wrong, because according to the paper, on high-energy coasts (waves higher than 1 metre) the attenuation does not exceed 10%.
2. On which coasts was the wave attenuation by vegetation generally found to be more than 10% (maximum 50%) in the global model analysis of salt marshes?
(a) Coasts where waves were higher than 1 metre
(b) Coasts where waves were up to 1 metre
(c) Only those coasts where the marsh had no above-ground vegetation
(d) All coasts without any wave limit
See answer and explanation
Answer: (b). According to the paper, on low-energy coasts with waves up to 1 metre the attenuation was generally more than 10% (maximum 50%). On coasts with waves higher than 1 metre it was not more than 10%.
Mains Practice Question
How useful are nature-based solutions such as salt marshes in protecting against coastal floods and storm waves? Discuss their limits in the context of the findings of a recent controlled experiment. (250 words, 15 marks)
Answer Outline
Introduction:
The surface and vegetation of a salt marsh reduce the energy of waves; the experiment in Nature (21 October 2026) tested this on waves up to 2 metres.
Main Body:
Stability of the surface: on average 7 mm lowering in 21 hours, that is, negligible erosion.
Vegetation: gradually damaged; contribution 6-22% on waves of 0.75 metre and 0-6% on 2 metres.
Model estimates: more than 10% on low-energy coasts (up to 1 metre), not more than 10% on high-energy coasts.
Limits: one controlled experiment; mainly one plant and two soil types; global figures based on a model; local studies necessary.
Policy: treat the marsh as a complement, not a substitute, to structures such as dams.
Conclusion:
Conservation of marshes on low-energy coasts is useful, but it cannot be considered sufficient alone for high waves.
Sources
- Willemsen, P.W.J.M. et al., "The contribution of salt marshes to wave attenuation during extreme storms", Nature, 21 October 2026
- Deltares, "Salt marshes are proving to be powerful allies in building a climate-resilient coastline", 21 October 2026 - summary of the experiment; figures checked against the Nature paper.
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