On analysis and prediction of tides on the west coast of Great Britain

Abstract

Long-period tidal records from eight ports on the west coast of Great Britain are analysed, using both the harmonic method and the response function. Time series up to 9.5 yr were used so that fine structure of certain regions of high energy in the tidal residual spectrum may be examined. This also assisted in accurate separation of tides from surges. According to the currently accepted formulation of MI, its composition is not compatible with its actual composition in the real tide and, as such, has no useful purpose to serve in computation of predictions. Constituents Sa, Ssa, MA, and MB, are adversly affected by weather and long records are essential for their accurate separation. It has been observed that annual perturbations of Sz, similar to those confirmed in recent years for M2, also exist but these are not readily recognisable because their speeds are the same as those of constituents T, and R,. These perturbations, being highly sensitive to meteorological forces, are mainly responsible for cusps or humps in the vicinity of major tidal constituents in tidal residual spectra. The relationship of radiational and gravitational tides is found to be in very good agreement with theoretical results. In summer months non-predictable variance reduces to about half of the annual variance, reflecting the regional weather conditions of summer and winter.

Differences between mean tide level and mean sea level

“…Many years of experience with Liverpool data (e.g. an unpublished study in the NOC archives of 8 years of Liverpool hourly values by A.T. Doodson in the 1930s) showed that MTL-MSL is about 0.19 feet (6 cm), which is consistent with the 6.5 cm one would calculate using the 110 constituents of Amin (1982). However, if only the shorter set of constituents in Appendix 1 is used, one obtains a smaller value of 4.4 cm.…”

“…A first topic is a demonstration of the contribution of M6, using constants for M2, M4 and M6 from Amin (1982). These three constituents have amplitudes of 312.8, 23.4 and 5.3 cm respectively.…”

Changes in extreme high waters at Liverpool since 1768

“…First, there is evidence that the amplitude of the ocean tide at Liverpool is slightly larger now than it was in Hutchinson's time (Woodworth, 1999b). Consequently, the subtraction of predictions based on Amin (1982a) will result in surge values biased low. Second, the Amin (1982a) constituents comprise a detailed, but necessarily incomplete, description of the tide, especially with regard to shallow water and seasonal terms.…”

“…(See Graff (1981) for a discussion of the apparent time dependence of extreme level estimates at several UK ports based on short subsets of data). Figure 5 shows four extreme level curves for AMxHW obtained by the GEV method derived from sets 1-3 of real data and from tidal predictions for Liverpool based on the harmonic constituents of Amin (1982a). Some 40 years (i.e.…”

Tide–surge interactions and their effects on total sea levels in Irish coastal waters

“…As surge heights are related to water depth, they are larger in shallow water than in deeper water (McInnes et al 2011). Shallow water interactions between tides and surges are likely to be responsible for the surge amplitude modification as a result of more energy being lost from tides and surges travelling together, than would be lost if they were travelling separately (Amin, 1982). Horburgh and Wilson (2007) showed that modulation of surge production is due to changes of depth during the tidal cycle.…”