Use of hydrologic time series data for identification of recharge mechanism in a fractured bedrock aquifer system

Correlations between hydrologic time series data were analyzed to characterize the hydrogeologic processes of a fractured bedrock aquifer system in Wonju, Korea. The natural groundwater-level fluctuations and site rainfall data were used for the analyses. Wells of different depths at the same site show distinct transformation behaviors for the same input stress (rainfall). A shallow well in the soil zone responds quickly to rainfall at the site while a deep well in the fractured zone shows slower response but longer duration. These differences are mainly related to the different recharge mechanisms of direct infiltration through the upper soil zone and the somewhat regional recharge from a distance through a network of fractures. The seasonal difference in the system responses can be explained by the fall or rise of the water level that changes the transmission properties of the pressure pulse generated by rainfall. Time delay, specific storage and porosity computed from the time series data are highly consistent with the analysis results of aquifer and tracer tests at this site.