EFFICIENCY OF GROUNDWATER DAM USING LONG-TERM GROUNDWATER LEVEL MONITORING DATA

Groundwater dam, a well-known groundwater reservoir for securing additional groundwater resources by placing an impermeable cut off wall in alluvium aquifer, has suggested as an alternative one against drought. In South Korea, five agricultural groundwater dams have been constructed and operated for irrigation to the farm-fields by Korean Government aid during 1980 s. A total of 654 ha farm-field has been benefited from these five groundwater dams in which up to 120,210 ㎥ day^-1 groundwater was irrigated. This study was conducted to identify efficiency of groundwater dam based on long-term groundwater level data. Standardized Groundwater level Index (SGI), a drought index to evaluate groundwater condition of the aquifer, was applied to estimate quantitative drought condition on upstream and downstream zone from groundwater dam. The Ian groundwater dam, one representative groundwater dam in South Korea, was chosen to be a test-facility for identifying an application of the index. The Ian groundwater dam has been operated from April to September every year and irrigation area from the dam was accounted for 120 ha. From 2016 to 2019, average yields from the dam were determined to be 1,052 × 10³ m³ yr^-1 meanwhile average water demands were assumed to be 1,268 × 10³ m³ yr^-1. Average groundwater levels were 79.81 m and 78.32 m (above sea level) in upstream and downstream area of the dam, respectively during the monitoring period from June 2016 to December 2019. Maximum difference between upstream and downstream was 2.14 m. Daily change of groundwater levels was similar in those of stream water levels. During the dry seasons, groundwater levels declined less than 3.38 m and SGI showed higher than -1.0, which meant little effect of drought on the groundwater. During the rice growing periods, maximum groundwater drawdown in the upstream was monitored to be 1.89 m due to pumping from several radial collector wells, meanwhile it was to be 0.56 m in downstream where has no the radial collector wells. In this period, average SGI value was 0.87 and 0.92 in upstream and downstream area, respectively. Results of this study demonstrated the monitored groundwater levels and calculated SGI values were useful tools to estimate possible amounts of groundwater and evaluate drought in the groundwater system.

Acknowledgement: This study was supported by Korea Environment Industry & Technology Institute (KEITE) through Water Supply Service Program corresponding to Groundwater Requirement, funded by Korea Ministry of Environment (MOE).