Spectral analysis of water level fluctuations in aquifers

.   The water level of a seawater gauging station and 18 groundwater wells coupled with atmospheric pressure in southwestern Taiwan are analyzed by using spectral analysis in time and frequency domain. The semidiurnal component is found to be the most significant signal from the measurement of water level and atmospheric pressure, and the diurnal component is less distinctive in part of water level and atmospheric pressure record. Although auto-spectral and cross-spectral density functions are significant in atmospheric pressure and water level, the pressure variations do not significantly affect the seawater and the majority of groundwater level in the study area with amplitude of time series observations. The astronomical tidal components are likely the main factor causing seawater and groundwater level to fluctuate in Pingtung, Taiwan. Time lags are estimated from 20 min to a few hours in aquifers. It concludes that the disturbance on groundwater levels from the effect of oceanic astronomical tide is different from the varying hydrogeological characteristics of aquifer. In this study, the spectral analysis of water level in time and frequency domains gives strong indications of sensitive variations to water level fluctuation.