Abe Hiroaki, Tang Changyuan, Takeuchi Nozomu, Kondoh Akihiko
Department of Environmental Science and Landscape Architecture, Chiba University, 648 Matsudo, Matsudo-shi, 271-8510, Chiba, Japan.
Department of Earth Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba-shi, 263-8522, Chiba, Japan.
Ground Water. 2018 May;56(3):470-481. doi: 10.1111/gwat.12600. Epub 2017 Oct 17.
Intensive groundwater development in the urban area of the Nagaoka Plain, Japan, has induced changes in the pH and saturation index of calcite in groundwater. To account for these chemical changes, it is important to determine seasonal variations of recharge and the groundwater flow system in the aquifer. This study identified the sources and flow system of groundwater in this urban area by a comprehensive method using stable isotope data and a numerical groundwater model of the Nagaoka Plain. Stable isotope evidence shows that the groundwater is recharged by meteoric water originating from low-elevation areas rather than the mountains surrounding the plain. The water table in the study area is drawn down during the winter and recovers in the other seasons. Numerical modeling shows that discharge occurs primarily along the Shinano River during the recovery period, whereas discharge is centered in urbanized areas during the drawdown period, when a conical depression of the water table stimulates recharge from the immediate area. These results are indications of a local groundwater flow system, with its recharge area between the Shinano River and the urban areas, which is governed by intensive seasonal groundwater extraction.
日本长冈平原市区对地下水的过度开发，已导致地下水中方解石的pH值和饱和指数发生变化。为解释这些化学变化，确定含水层补给的季节性变化以及地下水流系统非常重要。本研究通过综合运用稳定同位素数据和长冈平原地下水数值模型的方法，确定了该市区地下水的来源和流系统。稳定同位素证据表明，地下水由源自低海拔地区而非平原周边山区的大气降水补给。研究区域的地下水位在冬季下降，在其他季节回升。数值模拟显示，在水位回升期，排泄主要沿信浓川发生，而在水位下降期，排泄集中在城市化区域，此时地下水位的锥形凹陷促使附近区域进行补给。这些结果表明存在一个局部地下水流系统，其补给区位于信浓川和市区之间，该系统受季节性地下水过度开采的控制。
