| Abstract: | Exploitation of the Beppu hydrothermal system started mainly in the lowland areas as early as the 1880s, and by the 1920s the number of wells had increased to about 1000. This caused the piezometric head of the thermal groundwater to draw down, and seawater to intrude into the thermal groundwater aquifer near the coast. A second flurry of exploitation occurred during the 1960s–70s, by which time there were over 2300 wells, and the mass and heat flows had increased due mainly to the discharge of high-temperature chloride waters in the highland areas. This caused a decline in piezometric head of the deep chloride water, a decline in the subsurface flow of chloride water towards the lowlands, and intrusion of steam-heated shallow water into the chloride water layer. |
