Complex Principal Component Analysis of Medium-term Nearshore Geomorphology at North Sendai Coast, Japan

Complex principal component analysis (CPCA) is applied to examine medium-term geomorphological behavior of an exposed sandy beach adjacent to a gigantic breakwater of the Port of Sendai located near a river mouth in the Sendai Coast, Japan, using a 12-year series of bathymetry survey data. The results of CPCA and conventional real-PCA demonstrate that erosion and subsequent accretion of the submerged terrace formed in front of the river mouth appear in the first mode of CPCA and have the most significant influence on the medium-term geomorphology of the study area. The first mode is mostly caused by northward alongshore sediment transport driven by wave energy flux, explained from the observed wave data. The second mode of CPCA demonstrates that the sediments previously discharged from the river return again into the nearshore region, and furthermore, the topography changes due to cross-shore sediment transport emerge in the third mode of CPCA.