Fukuzato Underground Dam
Fukuzato Dam is an underground dam constructed in Miyakojima, Okinawa Prefecture. An underground dam is a wall constructed to save underground water from pouring into the sea so that it can be put to human use.
Generals
Fukuzato Dam adjoins Sunakawa Underground Dam and experimental underground Minafuku Dam. An underground wall, 27 meters in height and 1790 meters in width stops incoming seawater and outgoing water within the island. The saved water is pumped up through 85 wells for use such as irrigation into the sugarcane fields. One of the good points of underground dams is that the areas above the dams are used as fields, sugarcane fields in Miyakojima and there is no sight of dam lakes.Geology
Miyakojima is covered with the limestone and beneath the layer is a water-resistant Shimajiri layer. There are 8 underground valleys along which underground water flows into the sea of the southern areas of the island. These valleys are indications for underground dams. The Minafuku Dam stops the underground water of the 3rd valley and the Fukuzato Dam stops water of the 4th valley.Construction
Originally a main dam and three side dams were planned but later only two side dams were evaluated as necessary and constructed. The dam proper is situated more than 20 meters underground, and cannot be seen. For construction, a pile driver equipped with an auger drill first opens a hole, 60 cm in diameter at a distance of 90 cm, and between the holes, the auger drill forms a plate-formed cavity and concrete is poured into the cavity.Together with the Sunakawa Dam, an area of 8400 hectares of agricultural fields is well irrigated with these facilities.