An Intensive Analysis of Shallow Water Tides

Abstract

The intensive application of the conventional harmonic method of analysis to the distorted tidal regime of the Thames estuary leads to the identification of some 54 ‘new’ tidal lines of significant amplitude, and hence to an extended harmonic method (E.H.M.) of analysing and predicting shallow water tides. The improvement in predictions is evaluated and compared with the Doodson harmonic shallow water process. The frequency dependence and coherence of residual energies in the data sets are examined. They are a maximum in the 2 c.p.d. band, and are shown to be consistent with short bursts of phase modulation of the tidal line by meteorological disturbances. The typical ‘hump’ in the spectrum associated with this phenomenon is compared with the tidal ‘cusp’ suggested by Munk et al., leading to the possibility that tides are not strictly a time-stationary phenomenon.