Review of Subsurface Dam Technology Based on Japan’s Experience in the Ryukyu Arc

Based on the success of an irrigation project that utilized two subsurface dams as water sources on Miyako Island, ten additional subsurface dams have now been completed. The technologies that have made the giant subterranean dam possible are the integrated storage model for creating water utilization plans and the Soil Mixed Wall method for constructing cut-off walls. Although it might be tempting to assume that all subsurface dams in the Ryukyu limestone region were built under identical topographical and geological conditions, the reality is quite different. Each dam faced unique geological and construction challenges that engineers skillfully overcame during the building process. The purpose of this paper is to introduce information on the planning and construction technology of agricultural subsurface dams in the Ryukyu Arc, which has not been reported in English so far, and to clarify the characteristics of agricultural subsurface dams in the Ryukyu Arc. There is a strong correlation between the gross reservoir capacity and the active capacity of large-scale subsurface dams. Eleven percent of the construction cost was the cost of design and investigation. The water price is the same as or slightly higher than that of surface dams.