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The survival of salt marshes, especially facing future sea‐level rise, requires sediment supply. Sediment can be supplied to salt marshes via two routes: through marsh creeks and over marsh edges. However, the conditions of tides and waves that facilitate sediment import through these two routes remain unclear. To understand when and how sediment is imported into salt marshes, 2‐month measurements were conducted to monitor tides, waves, and suspended sediment concentration (SSC) in Paulina Saltmarsh, a meso‐macrotidal system. The results show that the marsh creek tends to import sediment during neap tides with waves. A tidal cycle with a small tidal range result in weaker flow in the marsh creek during ebb tides, reducing the export of sediment. Waves enhance sediment supply to the marsh creek by eroding mudflats. However, strong waves can directly resuspend sediment in marsh creeks during spring tides when the water level is above the marsh canopy, enhancing sediment export through creeks. Net sediment import over marsh edges requires the opposite tidal and wave conditions: spring tides with weak waves. Spring tides provide stronger hydrodynamics, facilitating sediment import over the marsh edge. Increased SSC during the ebb phase can occur with strong waves over the marsh edge, resulting in net sediment export. Therefore, the net import or export of sediment, through the creek and over the marsh edge, depends on the combination of tidal and wave conditions. These conditions can vary between estuaries and even individual marshes. Understanding these conditions is crucial for better management of salt marshes. Plain Language Summary: The future of salt marshes greatly depends on receiving enough sediment, especially in the face of rising sea‐level. This sediment can reach salt marshes via two routes: through marsh channels or over the seaside boundary of the marsh. It is not fully understood under what tidal and wave conditions sediment can be supplied to salt marshes, either through marsh channels or over the marsh boundary. Therefore, 2‐month data sets on hydrodynamics and sediment dynamics were collected in Paulina Saltmarsh to investigate the optimal conditions of tides and waves for importing sediment into salt marshes. We found that sediment supply along marsh channels and over the marsh boundary requires contrasting tidal and wave conditions. Strong waves and small tidal ranges are favorable conditions for marsh channels to bring sediment into salt marshes. Conversely, sediment tends to be brought into salt marshes during tidal cycles with large tidal ranges and weak waves. This work highlights when and how sediment can be transported into the marsh, contributing to better salt marsh management. Key Points: Tidal ranges determine the direction of residual sediment flux in the marsh creek, while wave intensity determines the magnitudeWave intensity determines the direction of residual sediment flux over the marsh edge, whereas tidal ranges determine the magnitudeUnlike mudflats, waves cause erosion in marsh creeks only during tides with large tidal ranges [ABSTRACT FROM AUTHOR]

Aiming at the foot trajectory outputs by Theo Jansen's linkages, the dimensional parameters of a novel planar closed-loop legged mechanism were optimized. The kinematic models of the mechanism were derived using the Assur groups methods. According to the structural characteristics, he number of design variables was reduced to one by using the position limitation of a crank-rocker mechanism. A single-objective optimization problem was established by minimizing the minimal deviation of the foot trajectories of two mechanisms subjected to the geometric constraints of the dimensional parameters. This problem was solved by the one-dimensional search method, leading to the design and fabrication of an eight-leg mobile robot. The feasibility of the design was verified by experimental results. [ABSTRACT FROM AUTHOR]

Net sediment transport is predominantly seaward in fluvial‐dominated estuaries worldwide. However, a distributary branch in the Changjiang Estuary, the North Branch, undergoes net landward sediment transport, which leads to severe channel aggradation. Its controlling mechanism and the role of human activities remain insufficiently understood, although such knowledge is necessary for better management and restoration opportunities. In this study we revisit the centennial hydro‐morphodynamic evolution of the North Branch based on historical maps, field data, and satellite images and provide a synthesis of the regime change from ebb to flood dominance. The North Branch was once a major river and ebb‐dominant distributary channel. Within which alternative meandering channels and sand bars developed. Deposition of river‐borne sediment leads to infilling of the branch, while tidal flat embankment reduces the bankfull width and modifies the channel configuration, resulting in a profound decline in the sub‐tidal flow partition rate. The North Branch then becomes tide‐dominant with an occurrence of tidal bores and elongated sand ridges. Once tidal dominance is established, extensive tidal flat reclamation enhances the funnel‐shaped planform, amplifying the incoming tides and initiating a positive feedback process that links tidal flat loss, sediment import, and channel aggradation. Overall, the shift in branch dominance is a combined result of a natural southeastward realignment of the deltaic distributary channels and extensive reclamation. One management option to mitigate channel aggradation is to stop the aggressive reclamation and allow tidal flats to build up, which might reduce the sediment import and eventually lead to a morphodynamic equilibrium in the longer term. Understanding the impact of tidal flat reclamation is informative for the management of similar tidal systems under strong human interference. [ABSTRACT FROM AUTHOR]

Salt marshes are ecologically and physically essential habitats in coastal intertidal flats. In addition to providing nursery grounds for various wildlife, vegetation in marshes acts as a buffer zone that slows flooding waters. Extensive marsh platforms can also attenuate wave energy to protect coastal communities. Complex geometries make it challenging for models to capture the spatiotemporal variabilities in the transport of lateral water and sediment over tidal creek‐marsh complexes. To study water exchange processes between tidal creeks and marshes, field observations were conducted within tidal creeks in the Chongming Dongtan Shoal of the Changjiang Estuary, an area dominated by Phragmites australis, Scirpus mariqueter, and Spartina alterniflora. A coupled wave‐current‐sediment‐vegetation model that parameterized the three vegetation species was developed and applied to the tidal creek complex of Chongming Dongtan. Validated with the observational data, the modeling results were used to examine the influence of vegetation on flooding/draining processes within tidal creeks and mudflats. The model showed that vegetation not only modified the flow pattern at high tide in the high‐elevation marsh but also significantly intensified the tidal flows in tidal creeks in the low‐elevation regions. Both the observations and model detected significant transport of water and sediment from the marsh to tidal creeks, seaward sediment export over tidal cycles. The simulated salinity exhibited a considerable spatial gradient, matching well with the salt tolerances of the major vegetation types. This model can be potentially used to determine how future scenarios of hydrodynamics could affect vegetation zonation. Key Points: A vegetation model was developed to simulate the impacts of multiple vegetation species on flow, turbulence, waves and sedimentThree vegetation species were parameterized in the module, which was successfully applied to the tidal creek complex of Chongming DongtanModel demonstrated seaward sediment export from creeks, and consistency between the predicted salinity and the vegetation zonation [ABSTRACT FROM AUTHOR]

The morphology of the Yangtze Estuary has changed substantially at decadal time scales in response to natural processes, local human interference and reduced sediment supply. Due to its high sediment load, the morphodynamic response time of the estuary is short, providing a valuable semi‐natural system to evaluate large‐scale estuarine morphodynamic responses to interference. Previous studies primarily addressed local morphologic changes within the estuary, but since an overall sediment balance is missing, it remains unclear whether the estuary as a whole has shifted from sedimentation to erosion in response to reduced riverine sediment supply (e.g. resulting from construction of the Three Gorges Dam). In this paper we examine the morphological changes of two large shoals in the mouth zone (i.e. the Hengsha flat and the Jiuduan shoal) using bathymetric data collected between 1953 and 2016 and a series of satellite images. We observe that the two shoals accreted at different rates before 2010 but reverted to erosion thereafter. Human activities such as dredging and dumping contribute to erosion, masking the impacts of sediment source reduction. The effects of local human intervention (such as the construction of a navigation channel) are instantaneous and are likely to have already resulted in new dynamic equilibrium conditions. The morphodynamic response time of the mouth zone to riverine sediment decrease is further suggested to be >30 years (starting from the mid‐1980s). Accounting for the different adaptation time scales of various human activities is essential when interpreting morphodynamic changes in large‐scale estuaries and deltas. © 2019 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Separation zone and shear face generate most turbulence in confluence junctions. Flume experiment studies show the variation of a separation zone from the water surface to the bottom and impacts of the two circulation cells (secondary flow) on the sediment transportation in a confluence zone. The turbulence generated by the shear face is anisotropic, so it needs to be cautious to choose appropriate turbulence models in the simulation of confluence flow. This article utilizes the standard k − ϵ, RNG k − ϵ, and RSM turbulence models to simulate the secondary flow and separation zone in the confluence junction, and a quantificational comparison with the experiment data is provided. [ABSTRACT FROM AUTHOR]

The effects of roughness on the flow structure in a gravel-bed channel were investigated by using particle image velocimetry. The bed was composed of gravel particles, of which the median diameter, d50, (i.e., the diameter at which 50% are smaller) ranged from 2.5 to 35.0 mm. The flow covered a wide range of Reynolds numbers (R=3,048-69,982). The experimental results showed that the logarithmic-law region of the velocity profile changed with the size of the roughness elements. Under the large-scale roughness condition, that is, h/d50=1.78 (the ratio of flow depth to median diameter), the mean velocity distribution deviated from the logarithmic law in the near-wall region. In addition, a new formula was established to calculate the Darcy-Weisbach friction factor for the gravel bed, expressed for the Reynolds number and the surface geometric parameters. On the basis of the boundary layer theory, the displacement thickness was introduced to estimate the limit of the roughness effect, and it was found to be greatly affected in the range of 35,000

• 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]

Wave nonlinearity significantly influences wave attenuation and can cause sediment transport imbalances in vegetated zones, impacting shoreline stability and ecosystem-based coastal defences. Despite its importance, the parameterisation and mechanisms of wave nonlinearity evolution over flexible vegetation remain unclear. This study examines the mechanisms behind non-breaking wave nonlinearity evolution over flexible vegetation and provides parameterisation of wave nonlinearity, based on experimental data collected by Anderson and Smith (2014). The study derives a new set of empirical formulae for predicting wave nonlinearity in Spartina alterniflora, which considers Ursell number, relative vegetation width, vegetation submergence, and vegetation density. The predictions made using these formulae are in good agreement with the measurements. The results indicate a decrease in wave skewness across the span of vegetation, whereas wave asymmetry increases until it reaches a maximum before decreasing. The findings suggest a preferential dissipation of high harmonics compared to low harmonics in the vegetation zone. Additionally, bispectrum analysis reveals that vegetation enhances the difference interaction while suppressing the sum interaction between wave components. The findings enable improvements in our understanding of wave nonlinearity in vegetation, providing better predictive capabilities for wave attenuation and sediment transport, which are crucial for the design and optimization of coastal defence systems. • Non-breaking wave skewness keeps decreasing over the vegetation, while wave asymmetry initially rises to a maximum and then decreases. • Vegetation enhances the difference interaction while suppressing the sum interaction between wave components. • A new empirical formula for predicting non-breaking wave nonlinearity takes into account both vegetation properties and wave characteristics. [ABSTRACT FROM AUTHOR]