| Project/Area Number |
18K14543
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| Research Category |
Grant-in-Aid for Early-Career Scientists
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| Allocation Type | Multi-year Fund |
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| Review Section |
Basic Section 41030:Rural environmental engineering and planning-related
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| Research Institution | University of the Ryukyus (2019-2020)
Hirosaki University (2018) |
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Principal Investigator |
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| Project Period (FY) |
2018-04-01 – 2021-03-31
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| Project Status |
Completed (Fiscal Year 2020)
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| Budget Amount *help |
¥4,160,000 (Direct Cost: ¥3,200,000、Indirect Cost: ¥960,000)
Fiscal Year 2020: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2019: ¥1,170,000 (Direct Cost: ¥900,000、Indirect Cost: ¥270,000)
Fiscal Year 2018: ¥1,820,000 (Direct Cost: ¥1,400,000、Indirect Cost: ¥420,000)
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| Keywords | 琉球石灰岩 / 地下水 / 水中ラドン濃度 / 滞留時間 / ラドン散逸係数 / 地下水挙動 / 水中ラドン / 地下水浸透 / 石灰岩 / ラドン |
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| Outline of Final Research Achievements |
In order to clarify the specific groundwater behavior in the limestone area, a ground water radon concentration estimation model was devised considering the generation of radon in soil and rocks and the supply to groundwater. Then, the practicality was examined by comparing the estimated value and the measured value. A emanation coefficient measurement system was constructed to quantify the supply form soil to the pores. The radon emanation coefficients of the soil which was distributed in the limestone area were about 0.30. The estimated values of underground radon concentration were calculated from a model that estimates the time variation of soil radon concentration. During the research period, the radon concentration in the dripping water in limestone cave and the spring water in the surrounding area were measured. The permeation rate of Ryukyu limestone was estimated to be about 3 m/day from the comparison between the estimated radon concentration and those measured values.
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| Academic Significance and Societal Importance of the Research Achievements |
石灰岩体中では, 不均一な透水性のため, 既存の数値モデルによって地下水システムを予測することが困難な場合も多い。沖縄島の南部地域には, 琉球石灰岩が広く分布しており, 複数の地下ダムが整備されており, 地下水が農業用水等の貴重な水資源として利用されている。今後の持続的な地下水利用のためには, 地下水の挙動を定量的に評価することが不可欠であった。本研究では水中に溶存するラドンに着目して当該地域における特異的な地下水挙動を数値解析と濃度測定の両面から明らかとした。その結果，降水が地下に浸透し地表に湧出するまでの各層における滞留時間を推定することが可能となった。
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