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"Tidal currents"
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Seasonal and Interannual Variations in M2 Tidal Current in Offshore Guangdong
Understanding tidal changes and their potential forcing mechanisms enables a better assessment of non-stationary tidal effects for projecting extreme sea levels and nuisance flooding. In this study, we investigate the seasonal and interannual changes in the M2 tidal current off the Guangdong coast using currents observed via two different types of high-frequency radar from 2019 to 2022. The results indicate significant seasonal changes in the M2 tidal current in the coastal areas of the Pearl River Estuary and Cape Maqijiao, with the largest relative deviations occurring in summer, reaching 10–20%. Observations of thermohaline profiles from 2006 to 2007 and 1978 to 1988 show that runoff in summer can reach these two areas and change the stratification of seawater, in turn affecting tidal currents. A comparative analysis of the two areas suggests that the greater the runoff, the wider the area where the M2 tidal current experiences significant seasonal variation. No significant interannual changes in the M2 tidal current were detected offshore of Guangdong during the observation period. However, an abrupt change occurred in the coastal area of Shantou in 2021, primarily caused by the distortion of the antenna patterns.
Journal Article
Study on the Characteristics of Tidal Current Velocity in Estuarine and Bay Areas
In estuarine and bay regions, reciprocating tidal currents frequently constitute the predominant hydrodynamic forces. Nonetheless, there exists a paucity of research concerning the hydrodynamic characteristics under intricate tidal conditions. This study employs tidal current data collected from nine sites within the Yellow River Estuary and Hangzhou Bay to examine the periodic characteristics of tidal currents, the vertical velocity distribution, and the attributes of ebb and flood peak velocities. The study revealed that the Yellow River Estuary and Hangzhou Bay predominantly exhibit nearly symmetrical reciprocating tidal currents. Nevertheless, certain regions within Hangzhou Bay also demonstrate asymmetrical tidal currents. The vertical velocity distribution throughout various phases of a single tidal cycle generally adheres to the characteristics described by the SOULSBY distribution. The peak velocities of ebb and flood tides are correlated with the rate of change in water depth (hm/tm), and an equation for calculating these peak velocities has been derived through fitting data.
Journal Article
Hydrodynamic Modelling of Tides and Tidal Currents in Cochin Estuary
The present study utilized two-dimensional numerical modelling to understand the tides and tidal currents in the Cochin estuary. The model shows a relatively good comparison with observation. In the estuary, the dominant constituent is M2 followed by K1, S2, and O1. The Form Numbers indicated that the tide is mixed, the mainly semi-diurnal tide having values ranging from 0.80 - 0.85, with the lowest Form number at the mouth of the estuary. The study reveals a significant relationship between dredge depth and tidal current speed in the narrow region of the mouth of the Cochin estuary. It is found that when the depth is decreased to 5 m and is increased to 20 m at mouth the current speed increases about 0.06 m/s and decreases about 0.24 m/s respectively. Tidal velocity is about 0.3 m/s near the inlet and a decreasing towards upstream. Tidal current analysis for M2 shows, U amplitude of 0.3 m/s at the mouth of the estuary, decreasing to 0.03 m/s in the northern and southern arms, while V amplitude ranges from 0.03 – 0.21 m/s towards the northern arm. For K1, the U amplitude reduces from 0.15 m/s at the mouth of the estuary to 0.03 m/s in both the arms with V amplitude higher in the northern arm than the southern arm. This research will enhance our understanding of tidal hydrodynamics in the estuary, contributing to sustainable estuarine management.
Journal Article
Tides and the ocean : water's movement around the world, from waves to whirlpools
\"Tide is the vertical motion of water, something so subtle it is impossible to see with the naked eye. Inspired by his travels around the world's coastline in a camper van with his young family, William Thomson captures the cycles of the sea's movement, and intersperses his adventures surfing the waves and charting the tides. Throughout Tides and the Ocean are his graphic renderings of unusual tidal maps, as well as other forms of water movement, including rip, rapids, swell, stream, tide, wave, whirlpool, and tsunami. Tides and the Ocean explains how the tides surge when the moon and sun align with the earth; how ocean streams alternate direction every six hours (which is invaluable information for kayakers, paddle boarders, and fishermen); why skyscraper-sized tsunamis occur frequently in an Alaskan Bay; and the most deadly beach orientation for rip currents. Also emphasized throughout is the importance of keeping the world's oceans healthy and full of life.\"--Amazon.com
Book
Tidal Current Energy Assessment and Exploitation Recommendations for Semi-Enclosed Bay Straits: A Case Study on the Bohai Strait, China
Against the backdrop of increasingly depleted global non-renewable resources, research on renewable energy has become urgently critical. As a significant marine clean energy source, tidal current energy has attracted growing scholarly interest, effectively addressing global energy shortages and fossil fuel pollution. Semi-enclosed bay straits, with their geographically advantageous topography, offer substantial potential for tidal energy exploitation. China’s Bohai Strait exemplifies such a geomorphological feature. This study focuses on the Bohai Strait, employing the Delft3D model to establish a three-dimensional numerical simulation of tidal currents in the region. Combined with the Flux tidal energy assessment method, the tidal energy resources are evaluated, and exploitation recommendations are proposed. The results demonstrate that the Laotieshan Channel, particularly its northern section, contains the most abundant tidal energy reserves in the Bohai Strait. The Laotieshan Channel has an average power flux density of 50.83 W/m2, with a tidal energy potential of approximately 81,266.5 kW, of which about 12,189.97 kW is technically exploitable. Particularly in its northern section, favorable flow conditions exist—peak current speeds can reach 2 m/s, and the area offers substantial effective power generation hours. Annual durations with flow velocities exceeding 0.5 m/s total around 4500 h, making this zone highly suitable for deploying tidal turbines. To maximize the utilization of tidal energy resources, installation within the upper 20 m of the water layer is recommended. This study not only advances tidal energy research in semi-enclosed bay straits but also provides a critical reference for future studies, while establishing a foundational framework for practical tidal energy development in the Bohai Strait region.
Journal Article
Dynamics of a Tidal Current System in a Marginal Sea: A Case Study of the Yellow Sea, China
Tidal currents belong to the main driving forces shaping the bathymetry of marginal seas. A globally unique radial sand ridge field exists in the South Yellow Sea off the central Jiangsu coast, China. Its formation is related to the distinctive “radial tidal current” pattern at that location. A generally accepted hypothesis is that the “radial tidal current” is a consequence of the interference between the northern amphidromic tidal wave system and the southern incoming tidal wave. In this study, a schematized numerical tidal model was designed to investigate the tidal current system and the factors of influence in the South Yellow Sea. Concepts of the tidal current amphidromic point (CAP) and the tidal current inclination angle are utilized to analyze the inherent structure of the tidal current system. By conducting a series of numerical experiments, it is found that the Poincaré modes are necessary for the existence of “radial tidal current,” and the e-folding decay length should be smaller than the basin length. In the Yellow Sea, cross-basin phase differences due to lateral depth differences as well as open boundary conditions favor the emergence of the “radial tidal current.” Further analyses indicate that the CAP system (i.e., the co-inclination lines, the CAPs, and the tidal ellipticity) deepens the understanding on the dynamic structure of a tidal current system, and therefore, it deserves more attention in future studies.
Journal Article
Characteristic Analysis of Vertical Tidal Profile Parameters at Tidal Current Energy Site
Many mathematical models have been proposed to estimate vertical tidal current profiles. However, as previous studies have shown that tidal current energy sites have different characteristics in their vertical tidal current profiles, it is necessary to estimate the profiles from field-measured data for practical purposes. In this study, we measured layered tidal currents over two months using an acoustic Doppler current profiler (ADCP) to analyze the characteristics of vertical tidal current profiles at the Jangjuk Strait, a candidate site for tidal current energy. As a result, the power law parameter α and bed roughness β were estimated as 4.51–12.41 and 0.38–0.42, respectively. Additionally, the maximum roughness length representing seabed roughness in the logarithmic profile was estimated as 0.221 m, and the estimated friction velocity was 0.038–0.194 m/s. Furthermore, a high correlation was observed between the depth-averaged tidal current velocity and friction velocities at all sites during flood and ebb tide conditions. A high correlation was also found between the bed roughness, roughness length, and power law exponent at relatively deeper sites. Tidal current energy sites display distinct characteristics compared to other sea areas. Therefore, it is essential to account for field conditions when conducting numerical modeling and design.
Journal Article