[A-HW22] 流域圏生態系における物質輸送と循環：源流から沿岸海域まで

[AHW22-11] Estimation of groundwater flow in an urbanizing catchment for healthy groundwater and material cycle managements

*小野寺 真一¹、Kimbi Sharon¹、齋藤 光代¹、浅野 敏久³、友澤 裕介¹、浅井 和由² (1.広島大学大学院先進理工系科学研究科、2.（株）地球科学研究所、3.広島大学大学院人間社会科学研究科)

キーワード：地下水、地表水、水収支、トレーサー

As urbanizing catchments have issues of water stress and waste treatment, it is significant to manage water and material cycle with confirming natural and artificial cycles. In this research, estimations of groundwater flow were conducted in an urbanizing catchment for healthy groundwater and material cycle managements. The research area is Saijo area in Higashi-Hiroshima city of Hiroshima Prefecture, western Japan, where is a medium size with 200,000 of population but one of urbanizing city. The long-term water budget using SWAT model and observed data indicated that the catchment is more sensitive to land use change than to climate change. Surface runoff increased with decrease in baseflow due to land use change from paddy field to residential area, in addition evapotranspiration increased due to air temperature rising. Consequently, groundwater recharge declined from 184.5 mm in the 1980s to 120.2 mm in the 2000s. Water quality and isotopic information from the upstream to the downstream indicated that main source area of groundwater is mountainous headwater and midstream agricultural area. Unfortunately, a part of main groundwater recharge area had been lost due to the change from paddy fields to residential area for last 4 decades. Therefore, healthy groundwater and material cycle managements will be needed, such as the artificial groundwater recharge in the agricultural lands, forest management in headwaters and mountains, rainwater infiltration system in the residential area, carbon and nutrient recycle of forestry, agriculture and industry wastes and residues etc. We have opened the symposium, workshop and ground work for forest managements in 2023 to 2024.