人工前丘槽形风蚀坑形态变化及其动力学机制——以福建平潭岛为例

Morphological changes and its dynamic mechanism of trough blowout in artificial foredune:A case study in Pingtan Island

风蚀坑是风沙地貌学的重要研究对象,风蚀坑形态−动力过程是风蚀坑研究的核心问题。近期人为干扰促使海岸人工前丘产生后,伴随着大量风蚀坑的出现亟待开展相应研究,但目前缺少关于人工前丘上发育的风蚀坑的相关研究。选择人工前丘上风蚀坑发育典型的平潭岛为研究区域,运用高精度RTK GPS对人工前丘上的槽形风蚀坑进行重复地形测量和使用二维超声波风速仪进行气流观测,研究了槽形风蚀坑形态变化与气流的反馈机制。结果表明:①人工前丘槽形风蚀坑受人工黏土结构控制,形成了一个输沙通道→完全发育风蚀坑→消亡阶段风蚀坑→新的输沙通道4个阶段的特殊演化模式;②槽形风蚀坑的形态控制了气流在侵蚀盆内的循环,这种正反馈促进了侵蚀盆的增长;③风蚀坑形态−动力过程之间存在一个过程塑造形态、形态影响过程运行方式的双向反馈,尤其是随着风向与槽形风蚀坑长轴向夹角(48°~99°)的不断增大,风蚀坑内气流偏转越明显,且存在大型螺旋流。

Blowouts are the main subject of aeolian geomorphology study,and the morphological-dynamics process is the important issue of studying blowouts.Recently,after the artificial foredunes on the coast was generated due to artificial interference,it is urgent to carry out corresponding research along with the emergence of a large number of blowouts,but there is a lack of relevant research on the blowouts developed on the artificial foredunes so far.Pingtan Island,which has a typical development of wind blowouts on the artificial foredune,was selected as the study area,Here we study the feedback mechanism between aerodynamics and morphodynamics processes on artificial blowouts through surveying topography by high-resolution RTK-GPS,and monitoring aerodynamics process by 2 dimensional ultra-sound anemometers.The preliminary results show that:1)The trough blowout was developed in artificial foredunes controlled by artificial filled clay structures.It displayed a different development path(a cycle)from previous observation,which started with the sediment-transport channel,to a fully developed blowout until died out,lastly went back a new sediment-transport channel.2)The morphology of trough blowout controlled how wind flow moved within blowout,which promoted deflation basin of blowout increasing due to positive feedback.3)The two-way feedback between blowout topography changes and aeolian process,which aerodynamic process lead to the morphology changes and morphology affect the operation mode of the process.As the angle between wind direction and long axis of trough blowout increases(48°~99°),flow deflection in the blowout was clearly visible and the helicoidal flow usually appeared.