SPECTRAL ANALYSIS OF TIDAL FLUCTUATIONS IN GROUND WATER LEVEL¹

Abstract

Water level data at 16 ground water wells and two sea water gauging stations, coupled with barometric measurements in an alluvial plain in the central‐west region of Taiwan, are analyzed using spectral analysis in the time and frequency domains. The semi‐diurnal component from water level station is observed to be the most noticeable signal while the diurnal component is the less distinct signal recorded at the water level stations. Both semidiurnal and diurnal components are coupled with atmospheric pressure measurements. From the atmospheric pressure data, spectral analysis indicates that both the raw and the pressure adjusted water levels are almost in phase and retain the same amplitude in this area. It implies that the effect of pressure variations is not significant for the sea water and ground water level nearby; the astronomical tidal components, as expected, are the main factor causing fluctuation of ocean water and ground water levels in the Choshuihsi alluvial plain.

Spectral analysis of water level fluctuations in aquifers

“…The spectral analysis indicates that both the raw, and the atmospheric pressure adjusted water levels are almost in phase and retain the same amplitude in this area. It implies that the effect of pressure variations is not significant for sea water and groundwater level nearby; the astronomical tidal components, as expected, are the main factor causing fluctuation of seawater and groundwater levels in Choshuihsi alluvial plain (Shih et al, 2000).…”

“…From that study, the tidal effects of diurnal, semidiurnal, and quarter-diurnal components are significantly different. The water level data at sixteen groundwater wells and two sea water gauging stations, coupled with atmospheric pressure measurements in an alluvial plain in the central-west region of Taiwan, are analyzed by using spectral analysis in the time and frequency domains (Shih et al, 2000). The semidiurnal component in water level is observed to be the most noticeable signal while the diurnal component is the less distinct signal recorded at the water level stations.…”

Application of spectral analysis to determine hydraulic diffusivity of a sandy aquifer (Pingtung County, Taiwan)

“…The 95% confidence interval for the autospectral density function and the non-zero coherence level for cross-spectral density function are also evaluated to pick up significant components in the frequency domain. The basic development of spectral analysis and its expansion to the application in tidal hydrological aspects can be demonstrated in relevant literature (Bendat and Piersol, 1991;Shih et al, 1999Shih et al, , 2000Shih, 2002;Shih and Lin, 2002) …”

“…Conventional tests and methods for finding aquifer parameters can be found in the literatures (Bear, 1979;Freeze, 1979;Driscoll, 1986;Batu, 1998). For aquifers adjacent to an ocean, river or lake the groundwater table fluctuates with the change of water level in the nearby surface water (Godin, 1972, p. 9;Shih et al, 1999Shih et al, , 2000Shih, 1999bShih, , 2002Shih and Lin, 2002). Such a disturbed groundwater table can be expressed mathematically providing relevant boundary conditions, which can be analysed by the spectral relationships through time-frequency domain of tidal effects.…”

Identification of phase propagation of water level in tidal river by spectral analysis

“…The theory of statistical development of spectral analysis is presented in this section for review (Bendat and Piersol, 1991;Shih et al, 1999Shih et al, , 2000Shih, 1999aShih, , b, 2000Shih and Lin, 2002).…”