Observation of gravity changes associated with variations of ground water table

Gravity changes due to variations of groundwater level were measured at a ground water monitoring well, which is located at Kum-san, Korea, from November 2008 to September 2009 using Portable Earth Tide (PET) gravimeter. Groundwater level was monitored simultaneously with gravity observations. To extract gravity information from groundwater, we reduced gravity effect from atmospheric surface pressure, earth tides and its loading effect, polar motion and meter drift. During our measurement period, there was an abnormally strong monsoon season in East Asia. As a result, groundwater level was significantly fluctuated and associated gravity changes were observed. In addition, In June 4, 2009, there was a pumping test at the observation well, and groundwater level and gravity variations were observed together successfully. In this paper, we present about one year time series of gravity and ground water level variations. With an analysis of gravity and water table observations, we show that water mass variations and estimate porosity of an aquifer. Observation of gravity along with groundwater level is potentially useful for monitoring of aquifer water mass balance and water resources.