The assertion made in article 00934, titled “Sandy coastlines under threat of erosion,” that global sea-level rise (SLR) will lead to the near extinction of sandy beaches by 2100 has sparked considerable debate within the coastal science community. This original study, identified here as 00934, utilizes global datasets and a simplified model based on the Bruun rule to project shoreline retreat, concluding that beaches retreating more than 100m are essentially doomed. However, we argue that this conclusion, central to article 00934, is fundamentally flawed and presents a potentially misleading outlook on the future of these dynamic coastal environments.
The Misapplication of the Bruun Rule in Study 00934
A core issue with the methodology employed in 00934 lies in its reliance on the Bruun rule as the primary predictive model. This rule posits that SLR causes offshore sediment transport, leading to shoreline retreat. While acknowledging the potential for offshore sediment movement in specific scenarios, particularly those involving steep coastal topography, we contend that this model oversimplifies the complex reality of beach response to SLR. The study 00934‘s assumption that SLR-induced retreat is solely dependent on “the transfer of sediment from the subaerial to the submerged part of the active beach profile” overlooks crucial onshore sediment dynamics.
Beach Migration: The Overlooked Resilience Factor in 00934
Contrary to the pessimistic predictions of article 00934, the inherent capacity of beaches to migrate landward as sea levels rise is a critical factor often underestimated in simplistic models. Historical evidence and geomorphological understanding demonstrate that beaches are not static features; they are dynamic systems capable of adapting to changing sea levels. Many of today’s beaches were formed thousands of years ago, successfully migrating inland during the postglacial SLR period. This natural process of landward migration, a testament to beach resilience, is not adequately considered in the extinction projections presented in 00934.
Real-World Beach Behavior Contradicts 00934’s Predictions
Global observations further challenge the dire predictions of beach extinction put forth in study 00934. Numerous beaches worldwide have experienced significant shoreline retreat for over a century, yet they persist and have not vanished. A compelling example is found in southwest France, where shorelines have receded by more than 100 meters. Despite this substantial retreat, these coastlines still boast wide and healthy beaches, directly contradicting the extinction threshold defined in 00934. Such real-world examples underscore the limitations of models like the Bruun rule when applied broadly, especially without considering site-specific geomorphology and sediment budgets.
Onshore Sediment Transport: A Dominant Process Ignored by 00934
The fundamental flaw in the Bruun rule, and consequently in the methodology of 00934, is its neglect of onshore sediment transport during SLR in many coastal settings. While offshore transport might occur in limited circumstances, prevailing scientific consensus and extensive research indicate that onshore sediment transport is a more common and significant process during sea-level rise. This onshore movement of sediment is crucial for beach maintenance and landward migration, effectively countering the erosion-centric view presented in article 00934.
Image alt text: Coastal geomorphology featuring sandy beach backed by vegetated dunes, illustrating natural landward accommodation space crucial for beach survival during sea-level rise, a factor often overlooked in simplistic models like those used in study 00934.
Conclusion: Reframing the Narrative on Beach Survival Beyond 00934
In conclusion, while acknowledging the threats posed by SLR, we argue that the alarmist perspective presented in article 00934 regarding the imminent extinction of sandy beaches is not supported by comprehensive coastal science. The over-reliance on the Bruun rule and the underestimation of beach migration and onshore sediment transport mechanisms lead to an inaccurate and overly pessimistic prediction. A more nuanced understanding of coastal processes, incorporating site-specific conditions and the inherent resilience of natural beach systems, is necessary for effective coastal management strategies. Instead of declaring near-extinction based on simplified models as in 00934, future research should focus on adaptive management approaches that work with natural beach dynamics to ensure their long-term survival in the face of rising sea levels.
References
[1] Vousdoukas, M. I. et al. Sandy coastlines under threat of erosion. Nat. Clim. Change 10, 260–263 (2020).
[2] Carter, R. W. G. & Woodroffe, C. D. Coastal Evolution (Cambridge Univ. Press, 1994).
[3] Bird, E. C. F. Coastline Changes: A Global Review (Wiley, 1985).
[4] Castelle, B. et al. Spatial and temporal patterns of shoreline change of a 280-km high-energy disrupted sandy coast from 1950 to 2014: SW France. Estuar. Coast. Shelf Sci. 200, 212–223 (2018).
[5] Woodroffe, C. D. Coasts: Form, Process and Evolution (Cambridge Univ. Press, 2002).
