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Basic Characteristics of Tides and Tidal Propagation
Published in S.N. Ghosh, Tidal Hydraulic Engineering, 2017
As ocean tides approach a coast or an estuary they produce a coastal or estuarine tide.The behaviour of the tide is conditioned by the depth and shape of the ocean basin as well as the fact that motion takes place on a rotating spheroid. If the natural period of oscillation of water in a basin is close to one of the components of the tide-producing forces, oscillation of that period will build up. In many parts of the world the semi-diurnal tide becomes predominant. In others the diurnal components are amplified so much that the diurnal tide becomes dominant, even though the diurnal components of tidal forces are considerably less than the semi-diurnal components. Further, the effect of the earth’s rotation on tidal propagation is fundamental. The tidal wave, instead of advancing in a direction determined simply by the east-west movement of the tide-generating force, rotates around a series of points of zero amplitude known as amphidromic points (Fig. 1.5). Thus the amplitude of tidal waves near a coast or estuary is substantially altered due to local effects.
Coastal water level variations
Published in Dominic Reeve, Andrew Chadwick, Christopher Fleming, Coastal Engineering, 2018
Dominic Reeve, Andrew Chadwick, Christopher Fleming
The geometry of the land can have a significant effect on the propagation of the tide wave. Amplification of the tide wave can occur in much the same way it may occur for other long-period waves; see Section 4.8.3. At the scale of a sea (such as the North Sea or Gulf of Mexico) the rotation of the Earth has an additional affect. The crest of the tide moves anti-clockwise (counter-clockwise) around the sea. The usual way of drawing tidal variations is in terms of the amplitude, A, and phase, φ, so that the tidal elevation is written as η=Asin(ωt−φ). Contours of A are called co-range lines, while contours of φ are termed cotidal lines and the phase is usually given in degrees. Due to the Earth's rotation and the geometrical effects, tides in coastal regions can exhibit interference patterns. Points at which the tidal amplitude becomes close to zero are called amphidromic points. They appear as ‘bullseyes’ on tidal charts, at the centre of concentric co-range lines. The cotidal lines will appear to meet at the amphidromic point, indicating that the tide wave propagates around the amphidromic point over a tidal cycle. Tidal charts are usually compiled on the basis of harmonic analyses of measurements or model output, and charts are drawn for each major tidal constituent. Further details may be found in Gill (1982) and DoE (1990). Figure 4.20 shows the cotidal chart for K1 in the Gulf of Thailand derived from the results of a numerical model (Fang et al. 1999).
Hydrodynamical and morphological patterns of a sandy coast with a beach nourishment suffering from a storm surge
Published in Coastal Engineering Journal, 2022
Xuejian Han, Cuiping Kuang, Lei Zhu, Lixin Gong, Xin Cong
The tidal type in Qinhuangdao waters is determined as regular diurnal tide with the tidal ratio of 4.73, and the tidal current type is classified as regular semidiurnal tidal current (Kuang et al. 2011). The discrepancy between tide and tidal current is due to the M2 amphidromic point near Qinhuangdao coast, which further results in the weak tidal environment there with a maximum tidal range of 1.5 m and the mean tidal range of 0.74 m which is smaller than that of most other coastal areas of China (Kuang et al. 2019). The monthly mean tidal level presents a periodical change with the annual cycle, and the maximum value of 0.27 m occurs in August and the minimum value of −0.25 m occurs in January. Based on the wave measurements in 2017 from the wave station near Jinshan Cape (a natural headland located in the middle of Qinhuangdao coastline), the dominant wave direction is SSE, SE, and ESE, which accounts for 54% and the wave height between 0.1 and 0.5 m accounts for nearly 80%.
Development of a global high-resolution marine dynamic environmental forecasting system
Published in Atmospheric and Oceanic Science Letters, 2018
Li-Ying WAN, Yang LIU, Tie-Jun LING
Using theoretical analysis and numerical hindcasts, a parameterization of the theoretical sea–ice–wave model based on WaveWatch III has been provided. From the governing equations of motion, the global hydrodynamic tidal equations for integrated tide-generating forces have been derived. A study on the WENO algorithm and adaptive grid is currently in progress. A global tide model, considering both the solid tide and load tide, has been established based on Finite-Volume Coastal Ocean Model (FVCOM), with the simulation showing reliable results, especially in terms of agreement between the simulated results and observations at the amphidromic point for the M2 partial tide.