Contribution of precipitation to groundwater flow systems in three major alluvial fans in Toyama Prefecture, Japan: stable-isotope characterization and application to the use of groundwater for urban heat exchangers

Okakita, Nagisa; Iwatake, Kaname; Hirata, Hiromichi; Ueda, Akira

Contribution of precipitation to groundwater flow systems in three major alluvial fans in Toyama Prefecture, Japan: stable-isotope characterization and application to the use of groundwater for urban heat exchangers | Contribution des précipitations aux systèmes hydrogéologiques d’écoulement dans trois principaux deltas alluviaux de la Préfecture de Toyama, Japon: caractérisation à l’aide des isotopes stables et application à l’exploitation des eaux souterraines pour des échangeurs urbains de chaleur Contribución de la precipitación a los sistemas de flujo de agua subterránea en tres abanicos aluviales principales en Toyama Prefecture, Japón: caracterización de isótopos estables y aplicación al uso de aguas subterráneas para intercambiadores de calor urbano 日本Toyama县三个主要冲积扇中降水对地下水水流系统的贡献:稳定同位素特征描述及其在城市热交换器地下水中的应用富山県 (日本)内の3扇状地の地下水系への天水の寄与:安定同位体組成の特徴と都市型熱交換への地下水利用 Contribuição da precipitação aos sistemas de fluxo de águas subterrâneas em três leques aluviais na Prefeitura de Toyama, Japão: caracterização de isótopos estáveis e aplicação para o uso das águas subterrâneas para trocadores de calor urbanos

2019

Okakita, Nagisa | Iwatake, Kaname | Hirata, Hiromichi | Ueda, Akira

The isotopic compositions (D and ¹⁸O) of 177 precipitation samples collected at seven observation stations in Toyama Prefecture and one station in Gifu Prefecture in the northern part of central Japan were determined. The source and characteristics of the isotopes were clarified and their contribution to the groundwater flow systems of three major alluvial fans in the same area were investigated. The δD and δ¹⁸O values ranged from −113.3 to −26.7‰ and − 16.4 to −4.2‰, respectively. Precipitation samples collected from May to September (summer) and November to March (winter) plotted along two meteoric water lines, with d-excess = 10 and 30, respectively. Conversely, precipitation samples collected in April and October, and some samples in November to March, plotted between the two meteoric water lines. The contribution of precipitation to the groundwater systems was modelled based on the assumption that groundwater is a mixture of major river water and precipitation. According to the observed δ¹⁸O values for the precipitation, river water, and groundwater samples, the contribution of local precipitation to groundwater reservoirs ranged from 5 to 100%. Groundwater flows near the rivers did not always originate from 100% river runoff; however, the contribution of river runoff to groundwater decreased with increasing distance from the rivers, and groundwater flows far from the river were generated mainly by precipitation. The possibility of using groundwater for a ground-source heat pump system, for air conditioning in houses and to melt the snow on roads, is also discussed.

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