北部ヴェトナム紅河平原における輪中型堤防形成に関する試論

Abstract

The present Red River plain in northern Vietnam is a dense distribution area of the enclosed-type dyke system, in which several settlements are surrounded by dykes within a limited area. This type of dyke is similar to Japan's Waju (輪中) dyke but often on a larger scale. Vietnamese historical documents record the construction of unenclosed horse hoof-shaped dykes after the tenth century in this area, and enclosed-type dykes were already present in the nineteenth century. This study considers the early formation of enclosed-type dykes. Archeological research in Bach Coc, Nam Dinh, and several other locations in Hanoi, Bac Ninh, and Hai Duong has confirmed several common features of settlement formation around the seventeenth century. First, settlements inside the dykes were expanded in space and heightened in altitude through the heaping of soil, which was frequently observed in the lower area inside the dyke. Second, settlements outside the dykes were also heightened by heaping soil or flooding deposits, and some settlements on the dyke lines or outside the dyke were abandoned. I argue that these changes resulted from the construction of enclosed-type dykes with sluice gates and that this formed the present landscape of densely habitated villages within limited areas in this region.