Study on the evolution of nourished beaches under the influence of artificial islands:taking Haikou Bay as an example
Beach nourishment,as a widely-adopted soft solution to coastal erosion,can effectively alleviate the beach erosion induced by the construction of artificial islands.This paper takes the nourished beaches on both sides of the wave shadow zone of an artificial island in Haikou Bay as an example.Based on the bimonthly surveys of beach profiles and shorelines since nourishment,the characteristics of beach erosion and accretion and the associ-ated driving factors were analyzed by using empirical orthogonal function(EOF)and digital shoreline analysis sys-tem methods.The EOF results showed that the first two eigenvalues accounted for more than 90%of the total vari-ance,which could reflect the main spatio-temporal changes of the beaches.The area with conspicuous changes,cor-responding to the first spatial mode,was located between the outer edge of the beach berm to the mean sea level,in which there were significant differences between the nourished beaches on both sides of the wave shadow zone and the natural beach in the wave shadow zone.The temporal mode showed that the most significant changes of the nourished beaches occurred in the initial four months after nourishment,followed by mild profile changes.The second spatial mode demonstrated the impact of typhoons on the beaches,resulting in the accumulation and level-ing of some low-lying sites on the beach berms in the wave shadow zone.This study found that the evolution of nourished beaches under the influence of an artificial island in Haikou Bay could be divided into two stages.The first stage was the adaptation period,during which the artificially designed beach profile adjusted to the equilibri-um state for adapting to the local hydrodynamics.The equilibrium time of nourished profiles was approximately 4 months,during which beach changes were dominated by cross-shore sediment transport.The second stage was dom-inated by the longshore sediment transport induced by the artificial island,resulting in sediment transport from the eastern and western sides of the artificial island to the wave shadow zone.At that time,the nourished beach shoreline in Haikou Bay had not reached the equilibrium state.The beaches on both sides of the wave shadow zone would continue to retreat in the future,while the shoreline in the wave shadow zone would advance into the sea for about 690 m until it reaches the equilibrium.This study would be helpful for the analysis of the beach evolution and beach restoration of similar cases.
beach nourishmentempirical orthogonal functionbeach profilesediment transport
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