10:45 AM - 12:15 PM
[AHW19-P03] Discharge processes of spring water inferred from water quality and isotope ratio in the alpine foothills, Kamikochi, Japan
Keywords:mountainous region, mountain-block groundwater, rainfall-runoff process, stable isotopes
In a region with a large hydraulic gradient due to steep topography and a large amount of precipitation, understanding rainfall-runoff processes are vital for disaster prevention and water resource management. Recent studies have discussed the hydrological role of mountain blocks associated with their water storage function. However, groundwater discharge and recharge processes through mountain blocks have not been well understood. Therefore, the objective of this study is to clarify the role of mountain-block on the water discharge in the alpine foothills, Kamikochi. For this, we conducted hydrological observations (water temperature, water discharge) and chemical and stable isotopic analysis for water samples collected at two types of springs.
The water temperature of the floodplain spring seasonally varied, which might correspond to the variation of daily mean air temperature. On the other hand, the water temperature of the mountain-block spring was almost stable throughout the year except during high-intensity precipitation events. The water discharge of both springs increased during high-intensity precipitation events; but, it did not change clearly during low-intensity precipitation events in the mountain-block spring. Comparing the δ-diagrams of both springs and the main river, the plotted areas of the floodplain spring and river roughly overlapped, whereas the mountain-block spring data was plotted in a different area. The δ values of the mountain-block spring tended to be higher than the floodplain spring in summer (June-August) when there was a large amount of rainfall. The difference in δ values was larger when precipitation and antecedent precipitation index (API) over 30 days were high.
Observed constant water temperature in the mountain-block spring indicates that the mountain block contains abundant groundwater with a longer residence time. The mountain-block spring discharged a large amount of isotopically different water from the floodplain spring and main river, especially during high-intensity precipitation events. This suggests that mountain-block groundwater may be discharged as if pushed out by high-intensity precipitation. In alpine foothill regions, the baseflow can be maintained by the stable discharge of mountain-block groundwater into the valley. In other words, mountain-block groundwater has the role of controlling the mountain hydrological cycle as a beginning water supply source.
The water temperature of the floodplain spring seasonally varied, which might correspond to the variation of daily mean air temperature. On the other hand, the water temperature of the mountain-block spring was almost stable throughout the year except during high-intensity precipitation events. The water discharge of both springs increased during high-intensity precipitation events; but, it did not change clearly during low-intensity precipitation events in the mountain-block spring. Comparing the δ-diagrams of both springs and the main river, the plotted areas of the floodplain spring and river roughly overlapped, whereas the mountain-block spring data was plotted in a different area. The δ values of the mountain-block spring tended to be higher than the floodplain spring in summer (June-August) when there was a large amount of rainfall. The difference in δ values was larger when precipitation and antecedent precipitation index (API) over 30 days were high.
Observed constant water temperature in the mountain-block spring indicates that the mountain block contains abundant groundwater with a longer residence time. The mountain-block spring discharged a large amount of isotopically different water from the floodplain spring and main river, especially during high-intensity precipitation events. This suggests that mountain-block groundwater may be discharged as if pushed out by high-intensity precipitation. In alpine foothill regions, the baseflow can be maintained by the stable discharge of mountain-block groundwater into the valley. In other words, mountain-block groundwater has the role of controlling the mountain hydrological cycle as a beginning water supply source.