At first glance, the Netherlands seems to be more densely populated than Japan. However, Japan has many steep mountains, volcanoes and more or less uninhabitable islands. The total surface area of these landscapes is approximately 75% of the land area. If this is included, the number of inhabitants per square kilometre is 1340. Japan is therefore in fact much more densely populated than the Netherlands.
This has also led to the construction of many polders in Japan, with a total surface area of approximately 980 square kilometres. This is considerably less than the surface area of polders in the Netherlands of approximately 20,000 square kilometres. The construction of large polders such as polder Flevoland is actually not possible in Japan. However, Japan does have many small polders.
The construction of a number of these polders has been very expensive. This was because the circumstances were often more difficult than in the Netherlands. For example, the tide in a number of places where polders have been constructed is considerably larger, and extreme precipitation and river discharge are more extreme than corresponding situations in our country. As a result, various land reclamations involve a sea dike, inner dikes, an irrigation and a drainage system. The last two systems may have been combined in part. Although the land reclamations have sometimes been expensive, they certainly pay for themselves, if only in view of the very high land prices in Japan.
The largest polder by far, with over 172 square kilometres, is the Hachirōgata Polder. This polder was created with the Dutch involvement of Prof. Pieter Philippus Jansen, former head of the Delta Service, and Prof. Adriaan Volker. I wrote about this in an earlier contribution to Flevolands Geheugen. Many other Dutch hydraulic engineers had preceded Jansen and Volker, usually not so much for specific land reclamation projects, but for river improvements and harbour construction, which also involved land reclamation. From 1872 onwards, the following can be mentioned: Cornelis van Doorn, Isaac Lindo, George Escher, Johannis de Rijke, Anthonie Rouwenhorst Mulder, Dick Arnst and Johannes Westerwiel.
In recent decades, coastal reclamations have also been quite controversial in various Asian countries, such as Japan and Korea. Opposition to proposed reclamations mainly comes from fishermen and environmental groups. The fishermen are mainly against it because of the loss of their fishing area. The environmental groups mainly object in connection with the loss of coastal environment, which can have a long-term effect, for example in connection with bird migration routes. In Japan, for example, discussions about the proposed construction of the enclosing dam of the Isahaya Polder have taken several decades.
In the photo collection of Prof. Adriaan Volker at Batavialand there are a number of photos of a visit by him and Prof. Jansen to the area in 1954 in connection with the proposed reclamation. In the bay of Isahaya there is a tidal difference of 6 metres, which made the construction and closing of the sea dike rather complicated.
In 2016 I attended a short course in Tainan, Taiwan. One of the speakers was Prof. Shinsuke Ota from Japan. He gave an interesting presentation on the planning of the Isahaya reclamation. He showed three stages in the plans from 1953, 1980 and 1986 respectively. In the latter plans the polder was considerably smaller than in the former plans. The last plan was eventually realised, with the sea dike being closed in 1997. The surface area of the polder is approximately 18 square kilometres. The future will have to show whether this was the last reclamation in Japan.