Change of groundwater-level caused by enhancing embankment of an agricultural reservoir

Enhancement for embankments of agricultural reservoirs has been steadily conducted in order to prevent the farm fields from the flood and to cope with the drought in accordance with climate change in Korea. This study was conducted to identify/forecast change of groundwater-level caused by the enhancement near one representative reservoir in Korea, which is planned to be enhanced and not completed. From results of slug tests, hydraulic conductivities of a shallow aquifer near the reservoir ranged of 2.85-9.92 x 10-4 cm sec-1. Piper diagram using major cations and anions showed reservoir water quality were slightly affected by its tributary streams, showing (Ca, Na+K)-(HCO3, Cl) type while groundwater showed Ca-HCO3 type. Hourly monitoring data for reservoir water- and groundwater-level have been collected from automatic observing equipment. Magnitude for groundwater-level variation was weaker compared with it of reservoir, exhibiting below 46% of reservoir water-level variation. Results of auto-correlation analysis to the time-series data on groundwater-level showed decreasing trends, indicating groundwater-level was rarely affected by artificial factors. Cross-correlations between groundwater-level and rainfall were relatively greater than those between reservoir- and groundwater-level. From simulation results using MODFLOW, groundwater-level would be risen maximum-level of 1.1 m at the zone (1.17 km2 in size) around the reservoir after completion of the enhancement while reservoir water-level would rise 2.9 m. The rise of groundwater-level near the reservoir caused by the enhancement would remain below the enhanced height of the embankment. The increment of groundwater-level would significantly decrease in inverse proportion to the distance from the reservoir.