Elucidaion of mantle structure of groundwater flow in freshwater lens by dense water-temperature observations

2016 Fiscal Year Final Research Report

• Project/Area Number: 26660194
• Research Category: Grant-in-Aid for Challenging Exploratory Research
• Allocation Type: Multi-year Fund
• Research Field: Rural environmental engineering/Planning
• Research Institution: National Agriculture and Food Research Organization
• Principal Investigator: Shirahata Katsushi 国立研究開発法人農業・食品産業技術総合研究機構, 農村工学研究部門地域資源工学研究領域, 主任研究員 (10648281)
• Co-Investigator(Renkei-kenkyūsha): ISHIDA Satoshi 国立研究開発法人農業・食品産業技術総合研究機構, 農村工学研究部門 地域資源工学研究領域, ユニット長 (30414444)
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: 地下水 / 淡水レンズ / 温度観測 / 降雨応答 / 潮汐応答

Outline of Final Research Achievements

This study clarified by field observations that a freshwater lens is composed of two part, a core where the groundwater is stable and old, and a mantle where the flow is fast and the groundwater is young. On an island where a typical freshwater lens exists, three observations were made: dense temperature observations near the groundwater surface, multi-depth EC observations near the lower surface adjacent to blackish water, and observations using current meter in groundwater cropping out in a cave at the horizontal margin of the freshwater lens. They revealed that (1) large rainfall events occasionally produce a layer of groundwater just added to the freshwater lens with lower or higher temperature than the original groundwater part, (2) the lower surface of the freshwater lens fluctuates not only affected by the addition of rainwater, but also significantly by tides and others, and (3) at the horizontal margin the water flows periodically seaward and landward affected by tide.

Free Research Field

地下水資源学