『Abstract
Four times of observation of the ocean tide and groundwater levels
in the coastal aquifers near Beihai, China show that fluctuation
in the tide-induced groundwater levels follows the tide, with
the highest and lowest water levels corresponding to the high
water level syzygy tide and the low water level neap tide. The
tidal coefficient is less than 0.5, decreasing approximately exponentially
with the distance from the coast. The tide can affect the groundwater
levels at observation wells as far as about 4,200 and 3,300 m
in the southern and northern coasts in Beihai. Observations and
spectrum analyses of the time series of the tide and water levels
suggest that the tide and water levels have similar changes with
complex fluctuations of a long period of 14.37 days and two short
periods of 24.7 and 12,5 h. Time lags of water levels to the tide
at observation wells last several hours and increases roughly
linearly with the distance from the coast. Mathematic models consisting
of a periodic term plus a linear term are established to describe
the changes in the tide and the groundwater levels. The periodic
terms for the tide and water levels are constructed using finite
Fourier's series consisting of 7 to 11 terms other than a single
term of a sine function in earlier work. Computed water levels
with the models can fit the observed water levels with reasonable
accuracy and satisfactory prediction of the changes in the water
levels is also obtained.
Keywords: Coastal aquifers; Tidal effect; Period and lag; Fitting
and prediction』
Introduction
Hydrogeology
Observation data
Tidal range, amplitude of water levels and tidal coefficient
Tidal period and time lag
Models describing the tide and water levels
Summary
Acknowledgments
References