Search

Tidal flat variations (curvature) in macro‐tidal turbid bays highly correlate with sediment dynamics. Interactions between tidal flats and sediment dynamics in macro‐tidal turbid estuaries, like Hangzhou Bay, China, have been studied through a fully validated 3D sediment model by considering high‐turbidity, flocculation, and water‐sediment density coupling. Numerical results show that the circulation and sediment flux in the curvature of Andong tidal flat have similar magnitudes in the along‐estuarine and lateral directions, demonstrating the important impact of the geometry on hydrodynamics and sediment transport processes. Sediment moves toward the southern/northern bank near the bottom/surface level in curvature. Tidally averaged net sediment flux is southward in the curvature. Tidal flat reclamation changes the curvature of the tidal channel, and modulates the circulation and sediment transport, and then feeds back to the tidal flat evolution subsequently. Bottom friction, nonlinear advection, and centrifugal force are dominant forces for inducing the lateral circulation, followed by the Coriolis force and sediment‐induced baroclinic process. Lateral circulation combined with the suspended sediment concentration (SSC) profile controls the distribution of instantaneous and tidally averaged net sediment fluxes in the curvature. The sediment flux positively correlates with the curvature of channel bends. The increased curvature of channel bends enhances the southward sediment fluxes mainly by increasing the effects of the centrifugal force, nonlinear advection, and Coriolis force on the lateral circulation and SSC. This study revealed a two‐way feedback system between tidal flat and sediment dynamics, which contributes to the impact of anthropogenic activities on geomorphological evolution of similar estuaries worldwide. Plain Language Summary: In macro‐tidal turbid estuaries like Hangzhou Bay, tidal flat reclamation changes the curvatures of tidal channels, and modulates the currents and sediment transport, and feeds back to the tidal flat evolution subsequently. The sediment flux positively correlates with the curvature of tidal channel bends, as shown by numerical sensitivity tests. Bottom friction, nonlinear advection, and centrifugal force dominate the lateral circulation. The lateral circulation combined with the suspended sediment concentration (SSC) profile control the distribution of instantaneous and tidally averaged sediment fluxes in the curvature. The increased curvature of channel bends due to reclamation activities changes the lateral circulation mainly by modulating the effect of the centrifugal force and nonlinear advection. The lateral sediment fluxes are then modulated by lateral circulation and SSC. This study addresses a positive feedback process between the tidal flat variation and sediment dynamics in macro‐tidal turbid estuaries. Key Points: Tidal channel curvature and its impact on lateral sediment flux in macro‐tidal Hangzhou BayPositive feedback between tidal flat reclamation and sediment deposition at the channel bendCentrifugal force and nonlinear advection are dominant forcings driving lateral circulation and sediment flux at the bend [ABSTRACT FROM AUTHOR]

Acquiring accurate and timely datasets on tidal flat topography is fundamental for studies, management, and policy‐making in coastal zones. In this study, we report a fusion method of freely accessed and global‐scale Sentinel‐2 (imagery) and Ice,Cloud, and Land Elevation Satellite‐2 (ICESat‐2) (laser altimetry) datasets for deriving tidal flat topography. The basic idea is to construct a model on characterizing the specific relationship between the elevations of the tidal flat (from ICESat‐2 data) and corresponding inundation frequencies (from Sentinel‐2 time‐series). The proposed method was validated for the largest tidal flat on the Chinese continental shelf with a root mean square error of 0.23 m. We highlight that this method solely relies on satellite data and does not require any in‐situ data because ICESat‐2 provides dense and accurate along‐track points as valuable prior elevation information, which enhance the ability to obtain tidal flat topography in many coastal regions even in the absence of local in‐situ data. Plain Language Summary: Global tidal flat topography is still unavailable at present, although it is the foundation of many global‐scale coastal‐related issues, such as coastal vulnerability estimation to sea level rise and flooding, coastal wetland monitoring, habitat conservation, site selection of offshore wind farms and ports, and land use planning. To generate tidal flat topography, accurate vertical and horizontal information is simultaneously acquired. The Ice, Cloud, and Land Elevation Satellite‐2 (ICESat‐2) satellite provides dense three‐dimensional points with high vertical accuracy, which can replace field surveying (e.g., by handheld/airborne/shipborne devices) for obtaining these three‐dimensional points. The time‐series imagery of the Sentinel‐2 satellite can map accurate inundation frequencies of tidal flats (i.e., the frequency of a location heaves out or is covered by water due to ocean tides) with high horizontal resolution. Integrating the advantages of ICESat‐2 and Sentinel‐2 makes it possible to obtain global topography for tidal flats with only satellite remotely sensed data. With freely accessed and global‐scale ICESat‐2 and Sentinel‐2 data, it can be expanded to obtain tidal flat topography in many specific coastal regions or even globally. Key Points: A method to generate tidal flat topography in coastal zones was proposed using satellite remotely sensed dataIce,Cloud, and Land Elevation Satellite‐2 provides accurate along‐track profiles as prior elevation information; therefore, in‐situ data are no longer neededGoogle Earth Engine was used to speed up implementation and can expand this method for large scale applications [ABSTRACT FROM AUTHOR]

Copyright of Canadian Journal of Remote Sensing is the property of Taylor & Francis Ltd and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Surface suspended sediment concentration (SSC) retrieved from the satellite data was used to study the multidecadal (1984–2015) dynamics of the surface turbidity maximum zone (TMZ) in Hangzhou Bay (HZB), China. A correlation algorithm was calibrated to estimate the surface SSC using the remote sensing data. The averaged deviation of the retrieved SSC from the field data was 15.6%. The impacts of tidal amplitude and phase on remote sensing data were specifically considered and accurately removed. Five periods were organized to analyze the multidecadal variability of surface SSC: (a) 1984–1988, (b) 1990–1994, (c) 1997–2001, (d) 2002–2006, and (e) 2013–2015. Results showed that the areas of low turbidity zone (<200 mg L–1) increased from period a to e, indicated by the trend ratio (Ts) of 2.58%. The area of TMZ (>700 mg L–1) decreased significantly from 2205 km2 in the period a to 647 km2 in period e, with Ts = −4.57%. The distribution pattern of the SSC was more skewed in period e (Sk = 2.03) than that in the period a (Sk = 0.63). Tidal flat reclamation around HZB contributed to the multidecadal reduction of the surface SSC from 1984 to 2015, through changing the hydrodynamics and reducing sediment source. The decreased sediment load from the Changjiang River contributed to the decline in the surface SSC in HZB, by reducing the sediment source. Flooding of the Qiantang River during wet seasons played an important role in increasing the surface SSC at the bay head, as the deposited sediment during wet seasons reduced the water depth and increased the resuspension. This study helps the estuarine morphology and environment management worldwide. [ABSTRACT FROM AUTHOR]

A three-dimensional, high-resolution tidal model coupled with the UNSW sediment model (UNSW-Sed) based on Finite Volume Coastal Ocean Model (FVCOM) was set up to study the suspended-sediment dynamics and its change in Jiaozhou Bay (JZB) due to land reclamation over the period 1935 to 2008. During the past decades, a large amount of tidal flats were lost due to land reclamation. Other than modulating the tides, the tidal flats are a primary source for sediment resuspensions, leading to turbidity maxima nearshore. The tidal dynamics are dominant in controlling the suspended-sediment dynamics in JZB and have experienced significant changes with the loss of tidal flats due to the land reclamation. The sediment model coupled with the tide model was used to investigate the changes in suspended-sediment dynamics due to the land reclamation from 1935 to 2008, including suspended-sediment concentrations (SSC) and the horizontal suspended-sediment fluxes. This model can predict the general patterns of the spatial and temporal variation of SSC. The model was applied to investigate how the net transport of suspended sediments between JZB and its adjacent sea areas changed with land reclamation: in 1935 the net movement of suspended sediments was from JZB to the adjacent sea (erosion for JZB), primarily caused by horizontal advection associated with a horizontal gradient in the SSC; This seaward transport (erosion for JZB) had gradually declined from 1935 to 2008. If land reclamation on a large scale is continued in future, the net transport between JZB and the adjacent sea would turn landward and JZB would switch from erosion to siltation due to the impact of land reclamation on the horizontal advection of suspended sediments. We also evaluate the primary physical mechanisms including advection of suspended sediments, settling lag and tidal asymmetry, which control the suspended-sediment dynamics with the process of land reclamation. [ABSTRACT FROM AUTHOR]

Abstract: In recent decades, the reclamation of tidal flat carried out by the authorities around the Bohai Sea, Yellow Sea, and East China Sea (BYECS) has reached new heights as a consequence of significant economic expansion in the coastal areas. We are concerned that the tidal flat reclamation may have not only local but also far-field effects on tidal dynamics in the entire BYECS. Numerical study shows different tidal patterns due to tidal energy redistribution when tidal flats around the BYECS are removed, in which the tidal range and phase are changed, and the amphidromic points are displaced. Tidal flats provide storage and dissipation for tidal energy; the former is much more significant than the latter. Loss of these functions caused by tidal flat reclamation will induce a redistribution of the extra tidal energy. Furthermore, we show that far-field effects on tidal dynamics would be observed on the west coast of Korea following significant reclamation on the Chinese Jiangsu coast. In turn, reclamation on the west coast of Korea may generate the far-field effects on the Chinese coast. Reclamation in the BYECS can result in rise of tidal amplitude and onshore sediment transport. The former may enhance the coastal hazards such as storm surge, and the latter may result in severe siltation. Therefore, careful consideration must always be given to any proposed artificial changes to tidal flat, given the effects of these on both the local environment and further afield. [Copyright &y& Elsevier]

Xiangshan Bay consists of a deep tidal channel and three shallow inlets. A large-scale tidal flat has been utilized through coastal construction. To ascertain the accumulate influences of these engineering projects upon the tidal dynamics of the channel-inlets system, this study uses FVCOM to investigate the tides and flow asymmetries of the bay, and numerically simulate the long-term variations of tidal dynamics caused by the loss of tidal flats. It was found that the reduction of tidal flat areas from 1963 to 2010 slightly dampened M 2 tidal amplitudes (0.1 m, ∼6%) and advanced its phases by reducing shoaling effects, while amplified M 4 tidal amplitudes (0.09 m, ∼27%) and advanced its phases by reducing bottom friction, in the inner bay. Consequently, the ebb dominance was dampened indicated by reduced absolute value of elevation skewness (∼20%) in the bay. The tides and tidal asymmetry were impacted by the locations, areas and slopes of the tidal flats through changing tidal prism, shoaling effect and bottom friction, and consequently impacted tidal duration asymmetry in the bay. Tides and tidal asymmetry were more sensitive to the tidal flat at the head of the bay than the side bank. Reduced/increased tidal flat slopes around the Tie inlet dampened the ebb dominance. Tidal flat had a role in dissipating the M 4 tide rather than generating it, while the advection only play a secondary role in generating the M 4 tide. The full-length tidal flats reclamation would trigger the reverse of ebb to flood dominance in the bay. This study would be applicable for similar narrow bays worldwide. [ABSTRACT FROM AUTHOR]