[A-HW22] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

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

*Shin-ichi Onodera¹, Sharon Bih Kimbi¹, Mitsuyo Saito¹, Toshihisa Asano³, Yusuke Tomozawa¹, Kazuyoshi Asai² (1.Graduate School of Advanced Science and Engineering, , Hiroshima University, 2.Chikyu-kagaku Institute Co., 3.Hiroshima University)

Keywords:groundwater, surface water, water badget, tracer

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.