LONG-TERM MONITORING OF BEACH CHANGES AROUND THE PORT OF HIRONO BUILT OFF SEA CLIFF

Long-term monitoring of beach changes around the port of Hirono Thermal Power Plant in Fukushima Prefecture facing the Pacific Ocean was carried out. Topographic surveys have been conducted around this port since 1972, and beach changes were analyzed by using these data sets. Longshore sand transport rate (Q) wasestimated to be around 8.5×104m3/yr from the change in accumulated sand volume inside the port. This value has the same order of magnitude with 14×104m3/yr predicted by the relation |Q|=780hc5/2 given by the author, where (hc) is the critical depth for beach changes. Measured value is 39% smaller than calculated one. This defference is considered to be due to that a large part of this coast is covered by exposed rock and, therefore, the amount of littoral sediment is small compared with the sandy beach.