10:50 AM - 11:10 AM
[AHW21-01] Integrated Watershed Modelling for Groundwater Use at Emergency in the Kanto Plain, Japan: Long-Term Calibration from World War II to Present
★Invited Papers
Keywords:Emergency use of groundwater, Watershed surface/subsurface coupled modelling, Hydrogeologic parameter identification, Groundwater potential
Serious water outage/shortage could occur after natural disasters, such as great earthquakes centered directly under big cities, extensive flooding induced by extreme rainfalls, and long-term droughts. In the aftermath of disasters, significant water demand would rapidly rise for the service at evacuation shelters and hospitals. In disaster preparedness plans of many local governments in Japan, groundwater is regarded as a good alternative water supply source under emergency situations. However, the groundwater potential depends on the local hydrogeology which is usually uncertain, and hence, scientific information of aquifer distribution and unconsolidated muddy layers for subsidence might be quite useful for safe utilization of groundwater. This study aims to provide local governments with site specific guidance of safe groundwater usage under emergency situations by integrating information of both from geosphere and human activity into up-to-date numerical models.
We focused on the groundwater modeling in the Kanto Plain, Japan. The Kanto Plain covers a land area of around 40,000 km2, where multiple metropolitan areas and watersheds are surrounded by mountainous areas. Relevant information on climate, geology, land use, groundwater and river runoff observations were collected. For pumping, which has a significant impact on groundwater levels, we used statistical data and organized them by municipality, but for periods when statistical data were not available, we used GDP as an index of social activity to estimate the amount of pumping. The hydrogeological model was constructed by interpolating data from 195 deep boreholes and modeled to represent the spatial distribution of the Shimousa and Kazusa formations, which are the major aquifers in the Kanto Plain but are very complex.
To evaluate surface/groundwater resources, we developed a 3D numerical model by using the simulator GETFLOWS that solves fully coupled surface/subsurface hydrological flows. The model was discretized into 46 million grid blocks, including 250 m regular grid system based on 5 m DEM in the horizontal direction and 60 layers based on the geological structure/facies distributions in the vertical direction. Information on vegetation and other land uses was assigned to the model surface.
The calibration processes were done by changing hydraulic parameters for the period of drought around 1994, and for the period from 1945 to present including the time when a large amount of groundwater was used for lives/industries from 1945 to 1970s. External conditions like meteorology and ground water use were imposed monthly.
The tendency of recovering groundwater levels with the lapse of time from the considerably low level was roughly reproduced in the Kanto Plain. And groundwater flow toward the center of the Kanto Plain and the subsurface flow crossing below river channels were visualized in the model.
In the presentation, we will introduce the method of modeling, calibrated performances and tentatively identified hydrogeological structure, together with discussion of spacial reliability.
We focused on the groundwater modeling in the Kanto Plain, Japan. The Kanto Plain covers a land area of around 40,000 km2, where multiple metropolitan areas and watersheds are surrounded by mountainous areas. Relevant information on climate, geology, land use, groundwater and river runoff observations were collected. For pumping, which has a significant impact on groundwater levels, we used statistical data and organized them by municipality, but for periods when statistical data were not available, we used GDP as an index of social activity to estimate the amount of pumping. The hydrogeological model was constructed by interpolating data from 195 deep boreholes and modeled to represent the spatial distribution of the Shimousa and Kazusa formations, which are the major aquifers in the Kanto Plain but are very complex.
To evaluate surface/groundwater resources, we developed a 3D numerical model by using the simulator GETFLOWS that solves fully coupled surface/subsurface hydrological flows. The model was discretized into 46 million grid blocks, including 250 m regular grid system based on 5 m DEM in the horizontal direction and 60 layers based on the geological structure/facies distributions in the vertical direction. Information on vegetation and other land uses was assigned to the model surface.
The calibration processes were done by changing hydraulic parameters for the period of drought around 1994, and for the period from 1945 to present including the time when a large amount of groundwater was used for lives/industries from 1945 to 1970s. External conditions like meteorology and ground water use were imposed monthly.
The tendency of recovering groundwater levels with the lapse of time from the considerably low level was roughly reproduced in the Kanto Plain. And groundwater flow toward the center of the Kanto Plain and the subsurface flow crossing below river channels were visualized in the model.
In the presentation, we will introduce the method of modeling, calibrated performances and tentatively identified hydrogeological structure, together with discussion of spacial reliability.