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The massive earthquake with a magnitude of 9.0 occurred at 14:46 on March 11, 2011, with an epicenter 130 km offshore from the Oshika Peninsula in Japan’s northeastern Miyagi Prefecture. After the earthquake, large tsunamis were generated owing to abrupt crustal subsidence and uplift, which inundated Japan’s eastern Pacific Ocean coastline. We carried out field observations to investigate the deformation of a previous river-mouth bar by comparing oblique photographs, and investigated the damage to seawalls and the tsunami inundation depth on the Iwama-Sanuka coast, located north of the Same River in southern Fukushima Prefecture. Here, the results of the field observations on the deformation of the sandy beach and the inundation of the Iwama-Sanuka coast are reported.

Sand movement in the field experiment of beach nourishment offshore of south Kujukuri Beach was numerically simulated using the BG model, given the wave field predicted by an angular spreading method of irregular waves on the basis of wave data measured at Choshi. The effectiveness of the model was confirmed, and then numerical simulation of the recovering effect of sandy beach in full-scale beach nourishment was carried out under the conditions that the artificial headlands have the present shapes, they are half and fully extended. It is found that although the best one is the shape fully extended, significant effect can be expected in artificial headland with a half length.

The bathymetric changes and changes in longshore sand transport passing through the tip of the headland were investigated using the contour-line-change model, while changing the shape and scale of the artificial headland. The maximum shoreline recession and eroded area downcoast of the headland, and rate of decrease in longshore sand transport were compared each other. It is concluded that the groin part of the headland must be extended first to reduce longshore sand transport off the artificial headland.

Beach erosion and accretion of the south Kujukuri coast was investigated based on the aerial photographs and field observation. The sand supply by northward longshore sand transport has been decreasing on this coast, causing erosion of the south part of the coast close to the sand source (sea cliff). In contrast, on the north end of the coastline, a long breakwater of the Katakai fishing port was extended and a large amount of sand has been deposited in the wave shelter zone. Furthermore, the ground subsidence up to 60cm occurred along the coastline due to the pumping-up of the ground water to obtain the water-soluble gas. The coastal situation of the south Kujukuri coast has devastated year by year due to all these impacts. To save the coast, full scale sand nourishment is required.

The effect of the offshore nourishment using sand with several grain sizes was investigated on south Kujukuri Beach. Beach profiles were first measured along four survey lines of the coast as well as the sampling of sea bottom materials. Based on these field data, beach changes were predicted using the contour-line-change model which considers the sorting effect owing to different grain size. It is concluded that the most appropriate method to recover the foreshore and to prevent further beach erosion is to carry out the beach nourishment using sand with mixed grain sizes at a rate of 2×104m3/yr.

Since the artificial reef has a submerged shape near the sea surface, strong shoreward currents are generated over the crown in general. These shoreward currents return offshore as rip currents from the openings of the reef, causing significant local scouring. A new type of artificial reef was developed in this study, preventing the development of shoreward strong currents, rip currents and resulted local scouring on the basis of the hydraulic model tests. The new type of artificial reef has the crown close to the mean sea level, and the offshore slope is protected by concrete armor units to enhance the stability.

The Hamaju coast, located on the west part of a sandy beach with 11 km length extending west from the mouth of the Kuzuryu River in Fukui Prefecture, has been eroded by various anthropogenic factors in recent years. As a measure against beach erosion, 15 detached breakwaters had been constructed between 1973 and 1994. The shoreline advanced behind the detached breakwaters, showing the conservation effect, but in the offshore zone, water depth has been increasing. This caused damages of subsiding concrete armor units. In this study, beach changes of this coast were investigated, and numerical simulation was carried out, using the contour-line-change model. Measured beach changes were well reproduced by the model.

Disappearance of sandy beach caused by the excess development of coastal forest was investigated along the Kujyukuri coast facing the Pacific Ocean. Since World War II, coastal forest has been created to prevent damages due to wind blown sand. However, coastal forest zone was excessively widened in the natural sand dune areasas well as the construction of protection facilities of themselves such as an earth dike, increasing potential against beach erosion. Furthermore beach erosion took place due to the decrease in longshore sand supply. Thus sandy beach of Kujyukuri coast has narrowed by these causes.

Factors of rapid change from natural sandy beach to artificial coastline covered by concrete armor units were investigated at the Setohama Beach in Sotobo area in Chiba Prefecture. The Setohama Beach was famous for oceanic recreation in the past, and along the coastline a national road runs. With the shoreline recession, wave overtopping became severe, and land reclamation over the sandy beach was carried out as well as the construction of gently sloping revetment in front as the measure at the sacrifice of natural sandy beach. A part of local people welcomed land reclamation because of widening of parking lot and the others claimed loss of nature. This process of change was investigated by field observation and comparison of past aerial photographs.