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- Title
Evaluation of mountain block recharge using sulfur hexafluoride in Ono basin, Fukui prefecture, Japan.
- Authors
Numa, Yurina; Tsujimura, Maki
- Abstract
In the mountain-plain transitional areas, the possible sources of the groundwater recharge arethe rainfall on the plain and the surface water/ the groundwater at the headwaters. Previously,the mountain block recharge has been supposed to be not dominant, because the faults /geological borders generally exist at the boundary between the mountain and theplain. In Ono basin, Fukui Prefecture, north-west Japan, previous papers showedthat the surface water from the mountain is a dominant source of the groundwaterin the plain. However, the observed groundwater contour map suggests that themountain block recharge also would contribute. Thus, we evaluated the role of themountain block recharge for the basin groundwater using sulfur hexafluoride (SF6)as atracer. Ono Basin itself has an area of approximately 75 km2, and whole watershed of Ono Basinhas an area of 942.5 km2 with an altitude ranging from 154.8 m to 1972.1 m. We sampledthe groundwater at 20 monitoring wells and the surface water at 2 locations ofRiver Mana at Ono in July and August 2018. We also observed the depth of thegroundwater table at the wells to construct the groundwater contour map in thebasin. The SF6 concentration, inorganic constituent concentrations, stable isotopiccompositions of the deuterium and the oxygen-18 were determined on all watersamples. The SF6 concentration in the groundwater ranged from 3.1 fmol to 6.3 fmol, whereas thatof the river water ranged from 2.6 fmol to 3.2 fmol. Also, the SF6 concentration of thegroundwater was lower in the southwestern area of the basin as compared with that ofnorthern area and area nearby the river, suggesting the contribution of mountain blockrecharge is dominant in the southwestern area of the basin. We applied an End MemberMixing Analysis (EMMA) using SF6 as a tracer and evaluated the contribution ratio of themountain block recharge to the total recharge in the basin. The contribution of themountain block recharge was estimated to be ranging from 19% to 99%, whereasthat of the river water was estimated to be ranging from 1% to 81%. Especially,the mountain block recharge ratio showed more than 95% at the mountain-plaintransitional area in the southwestern area of the basin. Our results indicate that themountain block recharge is an important recharge source of groundwater in the basin.
- Subjects
JAPAN; SULFUR hexafluoride; WATER; GROUNDWATER recharge; WELL water; AQUIFERS; GROUNDWATER monitoring; MOUNTAIN watersheds
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article