| Publication date | December 12, 2018 |
|---|---|
| Sector | Water Environment and Water Resources ／ Agriculture, Forestry, Fisheries |
| Region name | Kyushu（Okinawa Prefecture） |
In Okinawa, where water shortages have always been an issue, securing water resources for farming is a significant problem. Moreover, for remote island regions such as Okinawa, the vulnerability associated with climate change is extremely high, and it is important to sustainably use and develop groundwater as a stable water resource.
The national government in conjunction with Okinawan prefectural, and municipal authorities complete the world's first large-scale subsurface dam. This is a waterproof barrier that blocks the passage of water underground. Rainwater soaking into the ground is met with a semi-impervious layer of clay; the water is sandwiched between the clay layer and waterproof barrier accumulating in areas of highly porous Ryukyu limestone (fig.).
The subsurface dam has two main functions; firstly, to increase stores of groundwater. Secondly, in coastal areas, it also prevents seawater from mixing with groundwater and prevents it from becoming saline. The construction of the subsurface dam has secured a stable supply of agricultural water, enabling the cultivation of profitable cash crops. New agricultural produce, such as vegetables, mangoes, and tobacco, are now being cultivated in a region primarily known for sugar cane.
