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• Storm intensity and sediment availability control tidal flat evolution during a storm. • Storms enhance sediment supply for the studied flats undergoing long-term erosion. • A moderate storm offsets rather than accelerates tidal flat erosion. Accretion rates of estuarine tidal flats have strongly decreased globally due to the combined impacts of sea-level rise, reduction in sediment supply, and human interventions. Storms and associated high-energy activities influence sedimentary processes on tidal flats. A better understanding of the role of storm events on the evolution of tidal flats can facilitate better coastal management. This study assesses the impacts of storms on intertidal sedimentary processes. We monitored tidal water levels, tidal currents, waves, suspended sediments, and morphological changes of the eroding Diaokouhe lobe in the Yellow River Delta during and after a storm event. The estimated bed shear stress during the storm event (average 1.60 N/m2) was much higher than that during fair-weather conditions (average 0.71 N/m2). However, surface erosion of tidal flats was negligible during the storm, which was ascribed to the high critical bed shear stress owing to the compacted bed surface. The tidal flats were inundated for a longer time with a higher water depth and higher suspended sediment concentrations (average 1.13 g/L) during the storm, indicating sediment supply from the subtidal zone and adjacent sea. These conditions, namely moderate storm strength, high sediment compaction, and high sediment availability, led to deposition rather than erosion on the intertidal flats. Overall, the results imply that storm-induced erosion is less likely to occur on tidal flats with rich sediment supply and high erosion resistance. [ABSTRACT FROM AUTHOR]

De-reclamation is a common strategy used for the restoration of tidal flats. In this study, we investigate the morphodynamic response of tidal channel networks and tidal flats after de-reclamation initiatives using the Delft3D numerical model. We find that tidal channel networks that have undergone reclamation and retreat projects have a lower drainage density (8.95 km−1) than that of channel networks that formed naturally (11.33 km−1), and the drainage efficiency of natural formed channel networks is almost three times greater than restored channel networks. These findings indicate that de-reclamation alone cannot fully erase the imprinting of the previous reclamation. We also find that the ultimate effectiveness of de-reclamation is affected by the geographical layout and unchanneled path length of the inchoate main creek system. In addition, following the implementation of de-reclamation, the immediate opening of previously enclosed areas amplifies the tidal prism, thereby intensifying tidal scouring and resulting in significant erosion, with erosion rate reaching hundreds of millimeters per day. Such losses can be remediated under sufficient sediment supply and prevented through the construction of artificial channels. However, this severe erosion may escalate under an insufficient sediment supply or a heightened tidal prism, potentially leading to permanent loss. These findings constitute an important reference for future engineering practices that support the safety and sustainability of coastal resources. • De-reclamation cannot fully eliminate the impact of previous reclamation projects. • Tidal flats experience severe erosion shortly after de-reclamation. • This severe erosion can gradually be mitigated under adequate sediment supply. [ABSTRACT FROM AUTHOR]

Examination of large scale, alluvial estuarine morphology and associated time evolution is of particular importance regarding management of channel navigability, ecosystem, etc. In this work, we analyze morphological evolution and changes of the channel-shoal system in the Changjiang Estuary, a river- and tide-controlled coastal plain estuary, based on bathymetric data between 1958 and 2016. We see that its channel-shoal pattern is featured by meandering and bifurcated channels persisting over decades. In the vertical direction, hypsometry curves show that the sand bars and shoals are continuously accreted while the deep channels are eroded, leading to narrower and deeper estuarine channels. Intensive human activities in terms of reclamation, embankment, and dredging play a profound role in controlling the decadal morphological evolution by stabilizing coastlines and narrowing channels. Even though, the present Changjiang Estuary is still a pretty wide and shallow system with channel width-to-depth ratios >1000, much larger than usual fluvial rivers and small estuaries. In-depth analysis suggests that the Changjiang Estuary as a whole exhibited an overall deposition trend over 59 years, i.e., a net deposition volume of 8.3 × 10 8  m 3 . Spatially, the pan-South Branch was net eroded by 9.7 × 10 8  m 3 whereas the mouth bar zone was net deposited by 18 × 10 8  m 3 , suggesting that the mouth bar zone is a major sediment sink. Over time there is no directional deposition or erosion trend in the interval though riverine sediment supply has decreased by 2/3 since the mid-1980s. We infer that the pan-South Branch is more fluvial-controlled therefore its morphology responds to riverine sediment load reduction fast while the mouth bar zone is more controlled by both river and tides that its morphological response lags to riverine sediment supply changes at a time scale >10 years, which is an issue largely ignored in previous studies. We argue that the time lag effect needs particular consideration in projecting future estuarine morphological changes under a low sediment supply regime and sea-level rise. Overall, the findings in this work can have implications on management of estuarine ecosystem, navigation channel and coastal flooding in general. [ABSTRACT FROM AUTHOR]