In order to investigate the instability mechanism of caisson-type composite breakwater under tsunami condition, a scale of 1/100 model experiment was performed in laboratory. Loading tests were also carried out to investigate the reduction of bearing capacity under the existence of seepage flow. From the results of laboratory experiment and finite element analysis, it was confirmed that the bearing capacity of rubble-mound can considerably decrease due to the tsunami-induced seepage flow. It is concluded that the effect of seepage flow in the rubble-mound should be taken into account when making a design of the caisson-type composite breakwater against tsunami. The following conclusions are drawn from this study; (1) The occurrence of seepage failure of the harbor-side rubble-mound under tsunami condition is experimentally confirmed. The rubble filled gabion on the harbor-side rubble-mound is useful for preventing from the seepage failure. (2) In this study, the reduction of bearing capacity due to seepage flow attains no less than 40% of the bearing capacity without the seepage flow. The rubble filled gabion on the harbor-side rubble-mound is not effective improving the bearing capacity of breakwater since the effective weight of rubble filled gabion is not large enough to increase the strength of harbor-side rubble-mound. (3) In the design of caisson type composite breakwaters against tsunami, the influence of seepage flow and seepage force on the stability should be taken into account. (4) The failure plane and plastic zone in the rubble-mound under tsunami condition become shallow by the effect of seepage flow and force.

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Although many artificial tidal flats had been constructed in Japan, there was not enough monitoring data that can prove the restoration of the natural environment after the construction of the tidal flats. Hiroshima Port and Airport Office at Chugoku Regional Development Bureau constructed three tidal flat as environment restoration projects in Onomichi-Itozaki Port area, Hiroshima, Japan. Total area of three tidal flats is c. a. 60 ha. After the completion of the tidal flats, geo-morphological change, sediment quality, benthos abundance, and sea-grass(Zostera marina)habitats have been monitored since 1984 to 2002. Especially, during FY 2000 to 2002, high biological diversity as natural tidal flats, abundance of many endangered spices, and 8 ha of sea-grass(Zostera marina)habitat restoration had been observed.

In case of ocean space utilization, the factors which have to be taken into consideration in order to form an international basic container route are geographical factors which are the position on a global scale, the economic scale of port hinterland, the ocean climatic condition for setting the route etc. as well as factors from the viewpoint of transport such as the volume of container cargo and both size of container ships and container terminals. It is important to consider these geographical factors not only in order to study the port placement from the global point of view but also to devise the port policy. Although there are many studies on factors from the viewpoint of transport, there is almost no study on these geographical factors. Then, the authors made a new simulation model and analyzed these geographical factors of the international container ports in all parts of the world. As a result of analysis, the authors got the conclusion that there were three port placement patterns. The first type is ‘the Continent Base Port Type’, which it is located in the continent and has the large economic hinterland. Typical ports of this type are Antwerp, LA, LB and Shanghai. The second type is ‘the Ocean Base Port Type’, which is located in the ocean space where geographical predominance is high. This type forms route hubs. Typical ports of this type are Singapore, Malta and Kaohsiung. The third type is ‘the Tight Hinterland Port Type’, which is located in an island and has the tight economic hinterland where the economic activities density is very high. This type has characteristics that the distance between the ports is short and there are a lot of numbers of ports, which is unique and special in the world. Japan’s ports are classified in the third type. Furthermore, Japan has a characteristic that there are many large-scale earthquakes and has to consider earthquake measures to reduce disaster risks. The authors will suggest the most suitable port placement theory in consideration of these characteristics in case of ocean space utilization.