Temporal Variation of Shallow-Water Tides in Basin-Inlet Systems
Temporal variations occur in the flood or ebb duration differences of asymmetrical tides in basin-inlet systems. These variations are due largely to the conjunction of a few tidal constituents at adjacent semi-diurnal and quarter-diurnal frequencies rather than time-dependent variation in the tidal harmonic constants themselves. Where shallow-water tidal distortions are present, they thus can be modelled by the combination of a semi-diurnal oscillation at the M2 frequency with a quarter-diurnal oscillation at the M4 frequency, given amplitudes and phase angles that reflect time-varying behavior. Indices of tidal asymmetry such as the M4/M2 amplitude ratio vary as a function of time according to this model as revealed by complex demodulation of tidal time series at the M2 and M4 frequencies. The demodulation shows that the amplitude of the quarter-diurnal tide varies approximately as the square of the amplitude of the semi-diurnal tide.
KeywordsAmplitude Ratio Tidal Constituent Diurnal Tide Tidal Inlet Tidal Asymmetry
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