Morphological evolution of paired sand spits at the Fudu river mouth: Wave effects and anthropogenic factors

Sand spits are fragile landforms that have rich values in economic, ecology, landscape and many other respects. They are quite diverse in morphology and their evolution mechanisms are influenced by various hydrodynamic and morphologic factors. Although morphological evolution of sand spits has been well documented, emanative paired sand spits stretching in opposite directions are relatively unexplored. In this study, a pair of emanative sand spits, which have experienced a dramatic evolution in the past decades, at the Fudu river mouth, on the eastern coast of the Bohai Sea, China, are investigated. The shoreline data detected from satellite images between 1984 and 2020 obtained through a free cloud-based platform Google Earth Engine were used to quantify the morphological evolution of the paired sand spits. The offshore wave data derived from a high temporal and spatial resolutions wave hindcast database along the Chinese coast were combined to explore their evolution mechanisms. Results show that the morphological evolution of the paired sand spits is dominated by the different breaking wave characteristics at flanks of the river mouth, which is formed by the geomorphic modulation of the bimodal offshore wave climate. The sand spit at south flank is typically formed by longshore sediment transport like many other cases, while the spit at north flank is fed by intertidal bars through onshore sediment transport and presents good resilience to storm waves and human disturbances. Although several degradation charac-teristics were caused by storm waves, it is indicated that sediment supply reduction and interception of sediment transport caused by intense human activities are the primary reasons for the degradation of the paired sand spits. The present investigation enriches the maintaining and degradation mechanisms of paired sand spits and sug-gests that sufficient attention should be paid to the resilience of geomorphic systems in coastal exploitation.