抄録
In Japan, there are many coasts where heavy coastal erosion has been accelerated within the past century and investigations on coastal erosion have been carried out by many reseachers. In relation to this, the author focussed upon changes of sandy shorelines of Japanese major islands by comparing early topographic maps with the recent ones (scale, 1: 50, 000).
The results are shown in Figs. 1, 2 and Tabe 1. During the period of 1890 1965 about 70 years), seaward advance appeared extensively on sandy shorelines of Japan. The ratio of the total length of advanced beaches to that of retreated beaches (ASR ratio) is 1.24 during the last 70 years. However, ASR ratio is only 1.05 during the last 20 years (Table 2).
This difference of A/R ratios suggests that the sandy shorelines of Japan have been retreating gradually due to the poor supply of sands during the recent years. For one of the responsible factors to this fact, we must consider the effects caused by human economic activities such as construction of reservoirs, excessive exploitation of sands and gravels from river beds and so on.
