台湾海峡西岸两个典型复合型海滩砂泥转换带对比研究

Comparative study of sand-mud transition on two sandy-muddy transitional beaches along west coast of the Taiwan Straits

根据福建沿海砂泥复合型海滩的分布特征,选取闽江口左坑和九龙江口南太武两个典型砂泥复合型海滩作为研究对象,开展SMT土力学和空间分布特征初步研究。基于两个海滩SMT位置及两侧共6个柱状沉积物样品的土力学性质分析,完善了砂泥转换带(sand-mud transition,简称SMT)野外判定方法;结合SMT空间分布特征及洪、枯两季差异分析,初步探讨了影响SMT分布的主要因素及控制过程。研究结果认为,对于表层砂泥分界明显的海滩,可根据SMT的定义结合沉积物粒度变化快速判定;而对于无法直接判定SMT位置的复合型海滩,可将海滩表层沉积物抗剪强度作为快速准确判定SMT位置的辅助指标,本次研究取15 kPa作为SMT判定阈值。闽江口左坑和九龙江口南太武海滩SMT高程及其空间分布特征有明显差异,这种差异在洪、枯水季又发生一定改变,主要与泥沙物源和水动力条件变化有关,SMT具体变化情况由砂质和泥质的输运或水动力强度决定。

According to the distribution characteristics of the sandy-muddy transitional beaches of Fujian coast, two typical sandy-muddy transitional beaches in the estuary area (Zuokeng beach, CL-ZK in the Minjiang River Estuary and Nantaiwu Beach, ZZ-NTW in Zhangzhou near the Jiulongjiang River Estuary) were investigated. The soil mechanics experiments were carried out on 6 sediment cores retrieved from these two beaches, and the spatial distribution characteristics of SMT(Sand-Mud Transition) were collected. Based on the analysis of soil mechanics properties, the method of distinguishing SMT was improved;and based on the spatial distribution characteristics of SMT and the diffusion analysis of flood seasons and dry seasons, the main control factors and controlling processes were discussed preliminarily. The results show that the beach with obvious sand-mud demarcation can be determined quickly according to the definition of SMT, also considering the change of sediment’ grain size. But for the beach without obvious demarcation, it is hard to identify the precise location of SMT, so the shear strength (15 kPa is the threshold) is recommended to help quickly identify the SMT location during the investigation. There are obvious differences in SMT elevation and spatial distribution characteristics between the Zuokeng beach and the Nantaiwu beach, which are changed in flood seasons and dry seasons. The migrations of SMT location and changes of SMT elevation are mostly ascribed to both the supply variations of sand and mud and the wave hydrodynamic conditions, and the specific changes of SMT are determined by the transport of sand and mud or the hydrodynamic strength.