波控中等潮差海滩剖面时空变化过程研究

Spatial and temporal variability of the wave-dominated,meso-tidal beach profile

通过对一波控中等潮差海湾切线段16个月海滩剖面数据,采用EOF分析提取了占数据总方差91.32%的前3个空间特征函数研究海滩剖面空间变化。结果发现第一空间特征函数指示了滩肩顶至碎波带海滩剖面变动逐渐增强的特征,是海滩剖面变化的主要模式;第二空间特征函数指示了滩肩形成与消亡;第三空间特征函数指示了大潮高潮位的巨型滩角的存在。通过对EOF分析得到的时间特征函数作连续功率谱分析,反映该海滩剖面波能在大小潮汐约半月潮周期、近塑望月潮频率周期和大小潮汐约2个月潮周期内对这些空间过程的控制,体现了这一波控中等潮差海岸近岸区,叠加在周期性潮汐之上的波浪是海滩演变的主要动力因素,这在以前的研究中所忽略。

The 16-month beach profile data set from the tangent segment of a wave-dominated, meso-tidal bay is selected. An EOF analysis is used to extract the first three eigenfunctions which account for 91.32%of the total profile variability and to indentify the spatial characteristics of the beach profile. The first spatial eigenfunction is the primary mode and indicates the gradually enhanced change feature from the berm crest to the surf zone. The second spatial eigenfunction describes the formation and elimination process of the berm. The three spatial modes identify the existence of the giant cusps at the high water level of spring tides. By using the successive power spectrum method to first three temporal eigenfunctions associated with first three spatial eigenfunctions, results show that these three processes are dominated by the three tidal frequencies that are respectively about the half spring-tide cycle, a lunar tide cycle and 2-month spring-tide cycle. This conclusion illustrates that the wave superimposed on the periodic tide is the main dynamic factor of this wave-dominated, meso-tidal beach evolution, which was ignored in previous studies.