[A-HW25] 同位体水文学 2018

[AHW25-08] 甲府盆地の笛吹川氾濫域における河川伏流水の分布

*中村 高志¹、石平 博¹、馬籠 純¹、西田 継¹、大澤 俊太²、土田 元気³、坂本 守³ (1.山梨大学大学院・国際流域環境研究センター、2.山梨大学・土木環境工学科、3.国土交通省・関東地方整備局・甲府河川国道事務所)

キーワード：甲府盆地、氾濫域、河川水の涵養、安定同位体

The river water recharge is a very important source of groundwater in the Kofu basin (Nakamura et al. 2017). This study was thus focused on identifying the distribution of river water recharge on the floodplain area at the middle stream of the Fuefuki River in Kofu Basin. The stable isotope of oxygen and hydrogen with chloride ion was used to identify the groundwater recharge sources and contribution of river water recharge. The differences and correlations of isotopes in various water bodies were examined to evaluate the groundwater recharge sources. The contribution of recharge sources was calculated on the basis of the result from mass balance analysis of the isotope composition and chloride concentration obtained from the water samples in the floodplain area. The contribution of the river water accounted approximately 30% area within the 500m from Fuefuki River and 50-80% around 1.4-1.8km from Fuefuki River.

Previously, the Fuefuki River was located around 1.3 km north from the current river line whose course was then changed by the large floodplain event at 1907. The current position of Fuefuki River, located in the area of the clay deposit. These geological settings might be the reason affecting the low contributions of river water recharge around the current Fuefuki River side.

Reference:
Nakamura T., Nishida K., Kazama F. (2016) Influence of a dual monsoon system and two sources of groundwater recharge on Kofu basin alluvial fans, Japan. Hydrology Research, 48(4), 1071-1087.

Acknowledgement:
This study is supported by the “River and sabo technology development for regional problems (Project Manager:Hiroshi Ishidaira)” of Ministry of Land, Infrastructure, Transport and Tourism(MLIT, Japan).