5:15 PM - 7:15 PM
[AHW30-P05] Identification of the process of water quality formation in surface water in the Minami-Alps region
Keywords:Minami-Alps, Process of water quality formation , Gypsum , Groundwater of Midai alluvial fan
Groundwater in the Midai alluvial fan in the Kofu Basin, located in central Japan, is highly used as a source of drinking water and industrial water. In order to use groundwater resources sustainably, it is extremely important to understand groundwater recharge and flow processes. Groundwater in the Midai alluvial fan is largely supplied from the Minami-Alps area due to its location, but the process of water quality formation in the mountain area has not yet been clarified. Although there have been many studies on groundwater in alluvial fan area throughout Japan, the detailed water quality and formation process of water sources in mountainous areas have not been considered, and it is not known where the water is recharged from within the mountainous areas. In this context, this study aimed to clarify the distribution characteristics of water quality in the mountainous area by understanding the process of water quality formation in the Minami-Alps, which is adjacent to the Midai alluvial fan, and to consider water recharge from the mountainous area by calculating the contribution ratio to groundwater in the Midai alluvia fan based on these characteristics.
The Minami-Alps in this study area can be roughly classified into three geological Formation: the Fujikawa Formation, the Nishiyatsushiro Formation, and the granitic area. Surface water sampling in the Minami Alps area and groundwater sampling in the Midai alluvial fan were conducted.
The analysis revealed that gypsum (CaSO4) is the dominant leaching source in the Fujikawa Formation, and carbonate rock (CaCO3) is the dominant leaching source in the Nishiyatsushiro Formation /granite area. Using the difference in dominant leaching sources, we conducted End-Member Mixing Analysis and calculated the contribution ratio of the Fujikawa Formation and the Nishiyatsushiro Formation in the river water of the Midai River. The contribution from the Fujikawa Formation was 58% at the lowest point of the Midai River in this study, indicating that it has a greater influence on the formation of the water quality of the Midai River. In addition, the contribution of the Fujikawa and Nishi-Yatsushiro formations from the Minami-Alps and the Kamanashi River water were calculated in the groundwater of the Midai alluvial fan. As a result, it was found that a large amount of water (89.8%) is supplied from the Minami-Alps area, and most of it is recharged from the Nishiyatsushiro Formation.
These results indicate that in order to sustainably use the groundwater resources in the Midai alluvia fan, it is effective to conserve the recharge sources in the Minami-Alps area.
The Minami-Alps in this study area can be roughly classified into three geological Formation: the Fujikawa Formation, the Nishiyatsushiro Formation, and the granitic area. Surface water sampling in the Minami Alps area and groundwater sampling in the Midai alluvial fan were conducted.
The analysis revealed that gypsum (CaSO4) is the dominant leaching source in the Fujikawa Formation, and carbonate rock (CaCO3) is the dominant leaching source in the Nishiyatsushiro Formation /granite area. Using the difference in dominant leaching sources, we conducted End-Member Mixing Analysis and calculated the contribution ratio of the Fujikawa Formation and the Nishiyatsushiro Formation in the river water of the Midai River. The contribution from the Fujikawa Formation was 58% at the lowest point of the Midai River in this study, indicating that it has a greater influence on the formation of the water quality of the Midai River. In addition, the contribution of the Fujikawa and Nishi-Yatsushiro formations from the Minami-Alps and the Kamanashi River water were calculated in the groundwater of the Midai alluvial fan. As a result, it was found that a large amount of water (89.8%) is supplied from the Minami-Alps area, and most of it is recharged from the Nishiyatsushiro Formation.
These results indicate that in order to sustainably use the groundwater resources in the Midai alluvia fan, it is effective to conserve the recharge sources in the Minami-Alps area.