海滩养护影响下的海岸风沙堆积——以福建平潭岛龙凤头海滩养护工程为例

Effect of Beach Nourishment on the Coastal Aeolian Sand Accumulation:a case study in Pingtan,Fujian,China

海滩养护工程实施后,在保护海岸抵御侵蚀的同时往往还产生其他的环境问题。尤其在强风区海岸,海滩养护造成了滩面环境的改变,使滩面风沙搬运和沉积特征都发生了显著变化。对福建平潭岛龙凤头海滩养护工程实施前后的风沙沉积对比研究表明,养护后海滩的干滩宽度、滩面沉积物粒径、表层湿度、海滩高程等环境要素变化对滩面风沙搬运与沉积过程都产生了重要的影响。主要结论为:(1)养护海滩干滩滩肩高程的提高增加了滩面风速,增大了滩面风沙输沙率;(2)养护海滩干滩宽度的增加既扩大了风区长度也为风沙搬运提供了充足的物源,且不受潮汐过程影响,提供了持续的风沙物源供给,增加了风沙作用时间;(3)养护海滩剖面形态的变化使得海滩滩面沉积物含水率减小,降低风沙起动风速,增强了滩面风沙搬运。

After the implementation of the beach nourishment project,some environmental issues come up accompanying with the function of mitigating beach erosion and protecting the coast.Especially in the coast with strong wind,nourishment alters the environmental factors of beachface,which significantly impact the characteristics of aeolian sand transport and wind-blown sand flux.To study the aeolian sand transport and sediment accumulation after beach nourishment,Longfengtou beach in Pingtan Island,Fujian province,has beach taken as a typical study area.It is indicated that the beach characters such as dry beach width,surface sediment grain size,surface moisture and beach elevation,have significant impacts on beach aeolian sand transport and deposition process.The main conclusions of this study are showed as：（1）the increase of dry beach elevation enhance the wind speed of beach surface,which improves beach surface aeolian sand transport rate and wind-blown sand flux;（2）the elongation of dry beach width of nourished beach increases the fetch and provides sufficient sediment resource for aeolian sediment transport,and also elongates the duration of sediment transport;（3）after nourishment,the lower sediment moisture of beach surface decreases beach sediment transport threshold velocity and reinforces beach surface aeolian transport.