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The erosion on a part of the 4.3km long sandy beach on the right side of Cai river mouth in Nha Trang Bay, Vietnam, which is widely considered as among the world's most beautiful bays, has been observed. This study investigates the mechanism of the shoreline variation based on the analysis of the aerial photographs which cover a long time period. The effect of the hotel which playing the function similar to a jetty in the coastal area has been discussed. The analysis also points out that the variation of the shoreline clearly related to the seasonal variation of wave. The erosion occurs from autumn to winter in every years with the dominant of the northeast monsoon. While, in the remaining periods shoreline is advance. Images from real-time monitoring cameras clearly show the variation process of shoreline from season to season.

The Great East Japan Tsunami in March, 2011 caused the significant changes of morphology on Sendai Coast. The flushing of sand spit in front of Nanakita River mouth and the breaching at Akaiko area can be observed. This study investigates the erosion of shoreline on the right side of Nanakita River mouth and the recovery of the breaching after the tsunami. Estimation of diffusion coefficient, which is an important parameter in numerical simulation of shoreline change, has been carried out for both study areas from measured data of erosional area propagation. These values of diffusion coefficient have been used to reproduce the erosion and the recovery of shoreline positions at study areas. The results show good agreement between the analytical result and measurement.

Recovery of sandy beach from severe erosion by the 2011 tsunami can be observed on Sendai Coast even 3 years after the tsunami. The long-term effect of such a severe morphology change on sediment transport system is investigated through analysis of aerial photographs. Empirical Orthogonal Function (EOF) analysis is applied to shoreline positions extracted from the aerial photographs. The first and third modes express the recovery process of shoreline from the severe erosion with respective time-scale, and the superposition of their contribution rate is more than 70%. Comparison of shoreline change rate before and after the tsunami clearly shows that the recovery process of severely eroded area caused completely different trend of sediment transport processes.

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