10:45 〜 12:15
[SGL23-P06] 秋吉台石灰岩地域における地表水・地下水の水循環と地質過程 ―岩石物性測定と水理モデリングからのアプローチ
キーワード：秋吉台、石灰岩、地下水
Dissolutions in carbonate aquifers are known to form conduits and high-permeability channel networks that facilitate the transport of ground water, resulting in distinct landscapes of karst terrains and cave systems in carbonate platforms (e.g. White, 2001). Understanding the hydrogeology of aquifer systems and its mechanisms of material transport are important for sustainable water resource use and its safety. However, a complete characterization of aquifer systems is often difficult due to its complex nature and heterogeneous architecture.
The Akiyoshidai Plateau limestone area, located in Mine city, Yamaguchi prefecture, is Japan’s largest carbonate platform with an area of ~130 km2. The Akiyoshidai limestones originate from coral reef complex deposited during the Early Carboniferous to Middle Permian, which has later been incorporated into the accretionary prism of the Japanese Islands. Here, karst landforms and limestone caves at Akiyoshidai contain abundant ground water in underground cavities and cracks, playing an important role in regional water resources. Akiyoshidai has nine major springs unevenly distributed from the west to the southwest margin, and it has been thought that most of the ground water in the platform is discharged from these springs (Yoshimura and Ikura, 1992). The water temperature of the spring water is constant at ~14°C throughout the year, and the amount of water discharged is 50,000 m3 per day. It is utilized for water use for local residents, and for agriculture and municipal trout farming (Shimano and Nagai, 1995; Kaihatsu et al. 1999; Akiyoshidai Science Museum HP). The drainage basins in the Akiyoshidai Plateau can be identified by several surrounding topographic divides.
Ground water modeling is a tool used to simulate and analyze the behavior of ground water in an aquifer, involving the use of mathematical equations to represent physical processes that govern the movement of ground water in the subsurface, allowing to predict how changes in the aquifer system (such as pumping or recharge) will affect water levels, flow rates, and water quality (e.g. Stevanovic´, 2015). While previous studies have documented the average discharge and run-off, temperature, and chemical composition of ground water along major springs in the Akiyoshidai region, the knowledge of aquifer properties, specifically rock physical properties such as porosity and hydraulic conductivity have been limited. The movement of water among intergranular matrix porosity, fracture porosity, and conduits are likely to play important roles in water circulation in carbonate aquifers.
In this study, we examine the physical properties of limestone porosity and hydraulic conductivity at representative groundwater upwelling points (rise) and groundwater sinking points (sink) distributed in Akiyoshidai region. By collecting and integrating information on aquifer properties (hydraulic conductivity and porosity), the surface and subsurface topography, and the hydrologic boundary conditions (including precipitation and evapotranspiration), we develop a conceptual and numerical model to verify the interaction between surface water and ground water.
At Akiyoshidai, with the registration of the Ramsar Convention and the designation as a specific natural monument, eco-tourism (autonomous and highly adaptable tourism by continuous sharing and utilization of knowledge about the environment) is also an important component that can be achieved by constantly updating information through research related to the environment, balancing tourism with natural environment conservation.
The Akiyoshidai Plateau limestone area, located in Mine city, Yamaguchi prefecture, is Japan’s largest carbonate platform with an area of ~130 km2. The Akiyoshidai limestones originate from coral reef complex deposited during the Early Carboniferous to Middle Permian, which has later been incorporated into the accretionary prism of the Japanese Islands. Here, karst landforms and limestone caves at Akiyoshidai contain abundant ground water in underground cavities and cracks, playing an important role in regional water resources. Akiyoshidai has nine major springs unevenly distributed from the west to the southwest margin, and it has been thought that most of the ground water in the platform is discharged from these springs (Yoshimura and Ikura, 1992). The water temperature of the spring water is constant at ~14°C throughout the year, and the amount of water discharged is 50,000 m3 per day. It is utilized for water use for local residents, and for agriculture and municipal trout farming (Shimano and Nagai, 1995; Kaihatsu et al. 1999; Akiyoshidai Science Museum HP). The drainage basins in the Akiyoshidai Plateau can be identified by several surrounding topographic divides.
Ground water modeling is a tool used to simulate and analyze the behavior of ground water in an aquifer, involving the use of mathematical equations to represent physical processes that govern the movement of ground water in the subsurface, allowing to predict how changes in the aquifer system (such as pumping or recharge) will affect water levels, flow rates, and water quality (e.g. Stevanovic´, 2015). While previous studies have documented the average discharge and run-off, temperature, and chemical composition of ground water along major springs in the Akiyoshidai region, the knowledge of aquifer properties, specifically rock physical properties such as porosity and hydraulic conductivity have been limited. The movement of water among intergranular matrix porosity, fracture porosity, and conduits are likely to play important roles in water circulation in carbonate aquifers.
In this study, we examine the physical properties of limestone porosity and hydraulic conductivity at representative groundwater upwelling points (rise) and groundwater sinking points (sink) distributed in Akiyoshidai region. By collecting and integrating information on aquifer properties (hydraulic conductivity and porosity), the surface and subsurface topography, and the hydrologic boundary conditions (including precipitation and evapotranspiration), we develop a conceptual and numerical model to verify the interaction between surface water and ground water.
At Akiyoshidai, with the registration of the Ramsar Convention and the designation as a specific natural monument, eco-tourism (autonomous and highly adaptable tourism by continuous sharing and utilization of knowledge about the environment) is also an important component that can be achieved by constantly updating information through research related to the environment, balancing tourism with natural environment conservation.