Spectral responses of water level in tidal river and groundwater

Abstract

The water level of ®ve river stages and seven groundwater wells in the Taipei Basin were analysed by spectral analysis in the frequency domain. The diurnal, semi-diurnal and quarter-diurnal tidal components of the Tanshui River appear to relate closely to astronomical tides as K 1 , M 2 and M 4 , respectively. It is also found that the diurnal component reveals a reversed phase angle in the middle section of the Tanshui River; the phase of the quarter-diurnal component is also found to be reversed at stations upstream in the Tanshui River and Hsintien Stream. It is believed that these phenomena could be caused by local variation in the river channel topography. The autospectrum and cross-spectrum between groundwater elevation and nearby river stage were observed to correlate highly with the frequency of the astronomical tides K 1 , M 2 and M 4 . From the study of the phase shift and time lag of water level¯uctuations at river stages and groundwater wells, it was found that the tidal eects of diurnal, semi-diurnal, and quarter-diurnal components were signi®cantly dierent. The relationships between phase and the¯uctuated range of atmospheric pressure and water level imply that change in atmospheric pressure does not aect water level¯uctuation in the river stage and groundwater well.

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

“…Many hydrologic phenomena change periodically with time: such as the disturbance of wind wave generated by seasonally wind and ocean tides affected by the interaction between astronomical planets; the change of groundwater level caused by infiltration from surface water; the groundwater level variation due to the tidal effect by nearby rivers or coasts; the change of water level in river stage affected by astronomical tidal components by nearby seawater (Shih et al, 1999). In Holland, Maas and De Lange (1987) investigated the propagation characteristics of earth tides between the Hollandshe River and the underlying aquifer, they found that the tidal phase shift resulted in a constant of p/4, which is equivalent to 1.5 h of time lag.…”

“…The results of spectral analysis in the study area are systematically described and significance of fluctuations in water level is also discovered. This research promote the study of Shih et al (1999) using higher frequency resolution up to 10 )4 cph. The standard deviation of phase angle is analyzed and identification of phase propagation in space is accurately demonstrated.…”

“…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).…”

“…By using spectral analysis in time-frequency domain, the phenomenon of a continental shelf wave with periods of 4 and 6 days propagating along both Taiwan's east and west coasts was studied (Shih, 1986). Spectral analyses for tidal groundwater level and river stages have been studied in the local area of Taiwan (Shih et al, 1999Shih and Lin, 2002). Spectral analysis for determining hydraulic diffusivity in aquifers has been studied by using natural tidal disturbances (Shih, 1999a(Shih, , b, 2000.…”

Spectral analysis of water level fluctuations in aquifers

“…The water level data of five river stages and seven groundwater wells in Taipei Basin were analyzed by spectral analysis in time and frequency domains (Shih et al, 1999). In that study, the diurnal, semi-diurnal, and quarter-diurnal tidal components of Tanshui River appear to be closely related to astronomical tides as K 1 , M 2 , and M 4 , respectively.…”