Abstract
Atoll islands are subject to a variety of processes that influence their geomorphological development. Analysis of historical shoreline changes using remotely sensed images has become an efficient approach to both quantify past changes and estimate future island response. However, the detection of long-term changes in beach width is challenging mainly for two reasons: first, data availability is limited for many remote Pacific islands. Second, beach environments are highly dynamic and strongly influenced by seasonal or episodic shoreline oscillations. Consequently, remote-sensing studies on beach morphodynamics of atoll islands deal with dynamic features covered by a low sampling frequency. Here we present a study of beach dynamics for nine islands on Takú Atoll, Papua New Guinea, over a seven-decade period. A considerable chronological gap between aerial photographs and satellite images was addressed by applying a new method that reweighted positions of the beach limit by identifying “outlier” shoreline positions. On top of natural beach variability observed along the reweighted beach sections, we found that one third of the analyzed islands show a statistically significant decrease in reweighted beach width since 1943. The total loss of beach area for all islands corresponds to 44% of the initial beach area. Variable shoreline trajectories suggest that changes in beach width on Takú Atoll are dependent on local control (that is, human activity and longshore sediment transport). Our results show that remote imagery with a low sampling frequency may be sufficient to characterize prominent morphological changes in planform beach configuration of reef islands.
Highlights
Trends of prevalent erosion along sandy shorelines have been recognized as a global phenomenon [1]and are commonly attributed to the interplay between natural and anthropogenic activities [2,3].shoreline behavior along linear siliciclastic coasts depends on fluvial sediment supply and longshore drift, which is greatly influenced by the construction of dams in the hinterland and groynes at the coast [1]
Atoll islands are inherently dynamic and shoreline movement is controlled by a number of additional natural and anthropogenic influences that can result in erosion and/or accretion over different temporal and spatial scales ([13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28], Table 1)
The studied islands are variable in terms of size and shape
Summary
Trends of prevalent erosion along sandy shorelines have been recognized as a global phenomenon [1]and are commonly attributed to the interplay between natural and anthropogenic activities [2,3].shoreline behavior along linear siliciclastic coasts depends on fluvial sediment supply and longshore drift, which is greatly influenced by the construction of dams in the hinterland and groynes at the coast [1]. A relative increase in water depth across the reef resulting from sea-level rise or a deterioration of the coral reef ecosystems (e.g., by seawater warming or ocean acidification) increases the wave energy on the reef flat [8,9,10]. Atoll islands are inherently dynamic and shoreline movement is controlled by a number of additional natural and anthropogenic influences that can result in erosion and/or accretion over different temporal and spatial scales ([13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28], Table 1)
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