规则波作用下珊瑚砂岛地形演变实验研究

Experimental Study of the Morphological Evolution of a Reef Island under Regular Waves

基于概化的水平一维珊瑚砂岛模型,开展物理模型实验,通过对规则波作用下砂岛剖面高程随时间变化的测量,重点分析砂岛形态因素(初始高度和宽度)和砂岛初始位置变化对砂岛地形演变的影响。结果表明:波浪作用下珊瑚砂岛发生高程的下降和砂岛向潟湖侧的延长及迁移,砂岛达到平衡冲淤地形所需要的时间随着砂岛初始高度、初始宽度和距离礁缘初始位置的增大而减小;砂岛高程的冲刷下降量随着砂岛初始高度的增加而增大,随着砂岛初始宽度的增大而减小,随着岛前坡脚距礁缘初始距离的增大而减小;3种影响因素中,砂岛初始高度对高程的变化影响最大;砂岛向潟湖侧的相对迁移量随着砂岛初始高度的增加而减小,随着砂岛初始宽度的增大而增大,随着岛前坡脚距礁缘初始距离的增大而减小;3种影响因素中,砂岛初始位置对迁移的变化影响最大。通过回归分析得出预测砂岛高程变化和水平迁移的经验关系式。

Reef islands are composed of unconsolidated carbonate sediment from the reef that has been organized and deposited on an atoll and platform reef by ocean hydrodynamics.They are frequently found in remote mid-ocean locations within tropical and subtropical waters and are the sole source for habitable land of some island nations.It is anticipated that sea level rise and more frequent and intense storms resulting from global climate change will destabilize these low-lying reef islands,thus there is increasing concern about the persistence and habitability of these islands during future extreme wave events.The reef island morphodynamic response to the action of regular waves has not been reported in the literature.Therefore,this study performed laboratory experiments based on a horizontally one-dimensional reef island physical model in a wave flume.The temporal variation of the island profile under regular waves was measured to analyze the effects of island morphological factors(initial island height and width)and initial island location on its topographic evolution.The results showed that the reef island lost crest elevation and migrated and extended toward its lagoon side under the action of regular waves.Accretion also occurred on the lagoon side beach and random ripples appeared.The time required for the island to reach its equilibrium profile decreased with increasing of initial island height,initial island width,and initial island distance from reef edge.The island crest lowering due to scouring increased with increase of initial island height,but it decreased with increasing of initial island width and initial island distance from the reef edge.Among the three factors,initial island height had the greatest impact on the crest lowering.The island lagoonward migration decreased with increasing of both initial island height and initial island distance from reef edge,but it increased with the increase of initial island width.Among the three factors,initial island location was the most influential factor to lagoonward migration,but no island lagoonward migration was detected when the initial island distance D≥2 m.Regression analysis was used to obtain empirical formulae to predict the island crest lowering and island lagoonward migration,respectively.The outcomes of this study provide a habitability assessment for such low-lying island nations in the context of global climate change.