Field investigations for sustainable groundwater utilization in the Konan Basin

The Konan groundwater basin of Kochi Prefecture, Japan, is experiencing freshwater shortages for the past few years, particularly during the winter season. The present study aimed at analyzing the problem and exploring increased groundwater withdrawals to meet burgeoning freshwater demands in various sectors. The trend analysis of water consumption indicates that the groundwater demand would increase by 43 and52% by the years 2010 and 2025, respectively, compared to 32100 m³ d^-1 at present. The streamflow of the Monobe River reduces to a minimum in winter and it shows a decreasing trend in recent years. The geologic investigation results indicate that unconfined (phreatic) aquifers comprising alluvial sand and gravel and/or diluvial silty sand and gravel are dominant, and that the northwesternand western portions of the basin have greater potential for groundwater. Groundwater flows essentially from north to south into the ocean. Groundwater level fluctuations over the basin vary appreciably in space and time, indicating a wide variation of natural recharge. Field observations confirm the hypothesis that stream-aquifer interactionalso significantly contributes to groundwater recharge, besides the rainfall infiltration. Further, the pumping tests results demonstratethat though the aquifers are low-yielding, enhanced groundwater withdrawals could be possible. The aquifer hydraulic conductivity is characterized as high and ranges from 65 to 804 m d^-1 (mean = 229 m d^-1), thereby suggesting great aquifer heterogeneity. Finally, it is concluded that the long-term sustainability of the scarce groundwater resource of the Konan basin is doubtful, and that acomprehensive analysis of the groundwater system is essential prior to formulating plans for the future groundwater development and management. [ABSTRACT FROM AUTHOR]