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The rapid expansion of laver (Porphyra yezoensis) cultivation on lower tidal flats has become integral to the local economy, yet it also raises concerns regarding its potential impact on the morphological evolution due to increasing human activities. This study utilizes integrated near-bed field measurements to assess morphological dynamics and quantify sediment erosion processes, highlighting the significant impact of laver harvest on tidal flat stability. Our results show that erosion and bed coarsening in the cultivated areas experienced a notable intensification immediately after harvest, with net erosion in cultivated areas reaching approximately −38.2 mm during the first tide post-harvest, markedly higher—more than an order of magnitude—compared to adjacent uncultivated areas. The erosion rate notably spiked with the average bed level change rate increasing to −13.8 × 10−4 mm/s, compared to a rate of +0.3 × 10−4 mm/s during the unharvest period. Subsequently, the cultivated areas entered a recovery phase with a deposition amount of +12.5 mm, while the net cumulative erosion thickness throughout the entire observation period was −25.2 mm. The cultivation method, characterized by consistent harvests every 10 days, means that even minor erosion from continuous harvests can escalate into significant degradation. This study suggests that long-term cultivation cycle practices may result in irreversible changes to the depositional environment, potentially jeopardizing the habitat viability and ecological function. Sustainable agricultural strategies, including site selection, infrastructure planning, monitoring environmental changes, ecological assessments and sustainable practices, are recommended to mitigate the negative impacts of cultivation on regional stability and preserve the coastal ecological balance. [Display omitted] • Post-harvest erosion rates illustrate dramatic sediment loss in cultivated areas. • Regular harvesting practices lead to cyclic environmental degradation. • Strategies for sustainable cultivation enhance tidal flat ecosystem resilience. [ABSTRACT FROM AUTHOR]

— The sediment transport plays a major role in every aquatic ecosystem. However, the lack of instruments to monitor this process has been an obstacle to understanding its effects. We present the design of a single sensor built to measure water velocity, suspended sediment concentration and depth in situ , and how to associate the three variables to estimate and analyse sediment transport. During the laboratory calibrations, the developed instrument presented a resolution from 0.001 g/L to 0.1 g/L in the 0–12 g/L range for the measurement of suspended sediment concentration and 0.05 m/s resolution for 0–0.5 m/s range and 0.001 m/s resolution for 0.5–1 m/s range for the measurement of water velocity. The device was deployed for 6 days in an estuarine area with high sediment dynamics to evaluate its performance. During the field experiment, the sensor successfully measured the tidal cycles and consequent change of flow directions, and the suspended sediment concentration in the area. These measurements allowed to estimate water discharge and sediment transport rates during the different phases of tides, and the daily total volume of water and total amount of sediment passing through the estuary. • Development of an instrument for in-situ continuous monitoring of sediment transport. • Methodology to calibrate the sensor for flow velocity and sediment concentration. • Field experiment in an estuarine environment to measure hydraulic dynamics. • Measurement of the stream flow inversion during high and low tides. • Estimation of water discharge and sediment transport rate. [ABSTRACT FROM AUTHOR]

Sandspits at river mouths are important socio-ecological but fragile coastal ecosystems. Due to their significant role, particularly in shielding areas behind them from wave impact, sandspits are crucial, albeit they also pose challenges such as increased fluvial flooding, which often necessitates substantial engineering interventions such as artificial breaching. Here, four wave-dominated sandspits are compared to determine their common behavior. The study sites at river mouths have in common a high control of waves on longshore sediment transport leading to sandspit development; the Langue de Barbarie at the Senegal River delta, the Bouche du Roi at the mouth of the Mono River in Benin, the Mataquito River mouth in Chile, and the Pomene River mouth in Mozambique, each characterized by unique hydrodynamic conditions and geomorphologic features that influence their evolution and susceptibility to natural and anthropogenic impacts. Their cycles of opening and development, typically spanning decades, are studied by collecting 37 years of shoreline and wave reanalysis data from the Landsat and Sentinel-2 missions. It is shown that part of the morphodynamics is truly intrinsic and that climatic wave evolution drives only a small part of their evolution. A simplified model is introduced to predict the cyclic behavior of spits. The proposed model for sandspit development is based on a cyclic behavior, where newly formed spits mature and eventually break, resetting the cycle. This cyclic perception is represented as a function of time, where the elongation of the spit relative to its maximum length is modeled as a function of time and a constant wave-driven longshore sediment transport component. The model is tested at several sites with similar environmental conditions and blindly at one site with reasonable results. The present work also highlights the importance of spit evolution and the associated variability they impose on coastal downdrift and updrift, especially when considering anticipating the implementation of engineering solutions. • Cyclic behavior of sand spit lengthening. • Predicting sand spit length with a conceptual model. • Updrift and downdrift coastal impact of a sand spit lengthening. [ABSTRACT FROM AUTHOR]

The distribution of Holocene sediments in the Mekong River shelf area was investigated using shallow seismic and core data. The results show that the shelf depositional stratigraphy since the last glacial period can be classified into four depositional units (U1, U2, U3 and U4). The average thickness of the Holocene deposit in the nearshore area of the Mekong River estuary is approximately 20 m and decreases seaward. In addition to a thickened deposit in the palaeo-river channel, two sedimentary centres have developed, namely, the Mekong River estuary and the Cape Ca Mau area. In contrast to nearshore deposition, the Holocene sedimentation rate rapidly decreased offshore, even in the transgressive systems tract. To understand the driving mechanisms for the variation in Holocene deposition, a three-dimensional numerical model and Geographic Information System(GIS)-based model were applied to reconstruct the oceanographic and sediment transport patterns on the South Vietnam shelf. The simulation results reveal that the Mekong River shelf has undergone significant transformations since the Last Glacial Maximum (LGM). During the LGM, the coastline was situated near the shelf break, and as the sea level rose rapidly, the shoreline retreated. When the sea level reached its peak, the modern Mekong Delta emerged. Furthermore, the distribution of Holocene deposits is controlled by monsoon-influenced seasonal variations in currents, resulting in a triangular delta and narrow strip-like subaqueous clinoform. Our simulation results also show obvious erosional capacity in the offshore area, leading to an evident erosional through to the east of Cape Ca Mau and erosion of Pleistocene sediments in the shelf break area. By combining stratigraphic interpretation and oceanographic simulations, our study provides new insights into sediment transport and erosion processes mediated by ocean currents driven by East Asian monsoons. [Display omitted] • We investigated Holocene depositional features reworked using East Asian monsoon dynamics. • We explored the palaeo-geographic evolution of the southwestern South China Sea. • Simulation results confirm that offshore seafloor erosion is controlled by monsoon-driven currents. [ABSTRACT FROM AUTHOR]

Fluvial discharge and freshwater runoff are recognized as the main sediment sources in many estuaries worldwide. Precipitation is, however, limited in arid and semi-arid areas, allowing for high aeolian dust activity, and inducing limited river runoff. As such, aeolian dust could contribute to the estuarine sediment sources in such areas. Uniquely, the Northern Arabian/Persian Gulf (NG) is continuously loaded with vast amounts of aeolian desert dust annually. This study focuses on the role of desert dust in the distribution of suspended sediment in the Northern Arabian/Persian Gulf (NG), employing in-situ measurements of physical parameters (collected in 2015–2016), satellite imagery, and a flexible mesh hydrodynamic model (Delft3D-FM) coupled with a sediment transport model (Delft-WAQ). The model showed reasonable performance in representing the complex system of NG. The study revealed that more than 90% of the sediment along the NG is aeolian dust, with the remaining being fluvial. Owing to salinity-induced density gradients, estuarine circulation keeps the fluvial sediment confined to the estuarine zone of the Shatt Al-Arab even during the events of increased freshwater discharges. In the NG most of the suspended sediments have an aeolian origin. They were found in shallow zones within the 5 m isobath, including the estuary of Shatt Al-Arab where they are mixed with the fluvial sediment fractions. Tides were found to play a key role in sediment mixing and horizontal dispersion in the shallow area of the NG most of the time, while the Shamal increased the transport of fine sediment to offshore areas (seaward). Based on current knowledge, this study represents a rare instance where estuarine sediment dynamics are primarily governed by aeolian deposits from a nearby desert. [Display omitted] • Aeolian desert dust dominates suspended sediment in the NAG. • Fluvial sediment is mainly found in the estuarine region of Shatt Al Arab, the rest is aeolian. • Tides play a key role in horizontal sediment transport. • Increasing climate temperatures may result in greater desertification, potentially leading to higher turbidity in the NAG. [ABSTRACT FROM AUTHOR]

Water erosion poses a significant environmental threat in the Mediterranean region, with pronounced impacts observed throughout Morocco. It impairs soil quality and disrupts both sediment transport and water availability. Contributing factors range from natural (climate, topography, and geology) to anthropogenic (land use, vegetation cover, and management). This study introduces an improved Priority Actions Program/Regional Activity Centre (PAP/RAC) model, enriched with GIS and the Caesium-137 (137Cs) technique, to investigate erosion within Morocco's Raouz basin. Enhanced with additional variables including soil types, slope length, rainfall erosion potential, slope orientation, soil moisture, and land surface temperature, the model transcends the classical approach, promoting granularity and precision in predictions. In addition to the comprehensive model, the 137Cs method, which discerns long-term soil erosion and redistribution, provides a dual-faceted validation, bolstering the robustness of this project's erosion risk evaluation. This study's outcomes underscore the gravity of the erosion hazard with significant soil depletion rates ranging from 8.1 to 20 t ha−1 yr−1, demonstrating the model's alignment with empirical data, affirming its utility. The modified PAP/RAC model concurs with the 137Cs data, demonstrating its usefulness for water erosion assessment and management in similar areas. • The modified PAP/RAC model enhances erosion prediction. •Model validated with extensive 137Cs data. •GIS integration identifies erosion hotspots. •A comparative study with global erosion data. • The model adapts to diverse Mediterranean climates. [ABSTRACT FROM AUTHOR]

Dam-break-driven experimental tests are conducted to explore the intricate dynamics of water and sediment movement during a swash process. Utilizing a combined approach of a high-speed camera and an acoustic doppler velocity profiler, detailed records of flow velocity and sediment movements are captured. This study offers novel insights regarding flow shear stress, layer thickness and velocity of sediment transport in the backwash process, as well as behaviors of individual sand particles. Linear relationships serve to depict alterations in bed shear stress over time. The changing rate of bed shear stress can be influenced by the factors such as the beach slope, sediment grain size, and location on the beach. Increasing layer thickness of sediment transport corresponds with increasing outer layer velocity, exhibiting a linear-exponential relationship. A tentative interpretation of the inflection point (of linear and exponential relationship) designates it as a division between sheet load and a conjunction of sheet load and suspended load. With the onset of a bore and under the influence of turbulence and bubbles, sediment predominantly moves upwards, leading to sediment pickup. However, during both the late uprush phase and the backwash phase, the primary direction of sediment movement reverses downwards, favoring sediment settling. Empirical equations are formulated to estimate the parameters on the bed shear stress and the sediment transport layer. This study enhances understanding of water and sediment movement in swash processes, supplying validation data for numerical models. • The dynamics of water and sediment movement during a swash process are investigated through a series of flume tests driven by dam-break. • An analysis is performed on the factors that affect the changing rate of bed shear stress throughout the swash process. • The thickness of the sediment transport layer increases proportionately with outer layer velocity, demonstrating a linear-exponential relationship. • A thorough analysis is conducted on the behaviors of individual sediment particles, focusing on aspects such as moving direction and moving velocity. • Empirical equations are given to estimate parameters on the bed shear stress and the sediment transport layer. [ABSTRACT FROM AUTHOR]

Hydro-morphological threats impact the natural physical characteristics of river ecosystems, such as flow regimes, sediment transport, and channel morphology. These negative effects can occur at multiple scales, ranging from local microhabitats to geographic regions. Understanding these interactions can be useful for an integrated conservation approach and is needed for effective freshwater management. The aim of the study was to elucidate the combined effects of hydro-morphological threats on macroinvertebrates at three spatial scales: macroscale, including whole catchments, mesoscale (hydro-morphological changes in individual river sections) and the microscale, describing the microhabitat conditions of European rivers. The diversity and trophic structure of 1120 local macroinvertebrate communities in 28 catchments of various hydro-morphological disturbance levels, ranging from 0 to 2400 m asl, were analyzed. The response of macroinvertebrates to the main disturbance gradient differed between mountain and lowland communities. Random forest analysis indicated that the most important predictor of the ecological, diversity, and trophic indices was described by flow rate reduction. Generalized additive mixed models showed that decreased flow combined with river incision explained most of the variation in macroinvertebrate indices. Our results emphasize that based on multi-spatial scale analysis, hydro-morphological threats are very important factors in invertebrates biodiversity loss. Thus, to implement effective river management, we should pay more attention to the combined effects of geomorphological threats. • Hydro-morphological disturbances lead to the loss of invertebrate biodiversity. • The effects of hydro-morphological pressure were studied at various spatial scales. • Incision and flow reduction described most of the river macroinvertebrates variation. • The most favourable microhabitats for macrofauna are shallow and redeposited sites. • Efficient river management should focus on the combined effects of multiscale threats. [ABSTRACT FROM AUTHOR]

A puzzling fact for the Partheniades-Krone formula is the adoption of very contrasting values for the empirical parameters (e.g., the erosion coefficient and the critical shear stresses) but satisfactory reproduction of the suspended sediment concentration (SSC). Here, a theoretical equation for the tidally-averaged equilibrium (TAE) condition is derived by setting the integrated erosion flux throughout a tidal period equivalent to the integrated deposition flux throughout the same tidal period, leading to a new constraint condition on these parameters if values of the TAE-SSC are available. A preliminary check using the measured data of the Yangtze Estuary shows that a larger critical shear stress for erosion would require a smaller critical shear stress for deposition, both of which must be enhanced if the erosion coefficient further increases. Contrasting sets of parameter values derived by this constraint are fed into a coupled hydro-sediment-morphodynamic model to simulate cohesive sediment transport in the Yangtze Estuary. The results confirm that very contrasting parameter values can indeed lead to satisfactory reproduction of the temporal variations of the SSC (e.g., those in July 2016, including both spring tide and neap tide). This is further demonstrated by the numerical modelling of cohesive sediment transport in an idealized symmetrical estuary. These results indicate that the TAE condition can be used as a constraint for determining the erosion coefficient and the critical shear stresses for erosion and deposition. In addition, two simplified equations of the bed sediment mass conservation (no erosion version and the no deposition version) are derived as complements for obtaining a unique set of the three parameter values, provided that the simultaneous measured time series of SSC, bed shear stress and bed level can be collected at the same gauging station. • Very contrasting erosion coefficient and critical shear stresses can lead to satisfactory reproduction of the SSC. • Tidally averaged equilibrium condition can constrain the estimation of the erosion coefficient and the critical shear stresses. • A larger critical erosion shear stress requires a smaller critical deposition shear stress for a given erosion coefficient. • An increase in the erosion coefficient requires enhancement of the critical shear stresses for both erosion and deposition. [ABSTRACT FROM AUTHOR]

The complexity of micro-tidal inlets arises from the combined action of littoral drift and tidal range on their stability. Consequently, understanding and evaluating their stability poses a significant challenge. This study aims to shed some insight on the assessment of inlet stability by employing Delft 3D model. The stability of the inlet between the ocean and estuary relies on the balance between the longshore transport rate and the spring tidal prism. Disrupting this equilibrium results in the closure of the inlets. The movement of sediments in the surf zone is primarily driven by longshore velocity, which acts as the driving force for littoral drift, which is estimated using Delft 3D wave model. The longshore transport rate is estimated by employing empirical relationships and numerical codes based on the obtained driving force. Subsequently, the stability of the inlet is assessed based on these estimations. The spring tidal prism refers to the discharge of water flowing into the ocean from inlets and estuaries. Flow velocity is determined using Delft 3D flow model. The input data for nearshore circulation resulting from waves and currents is primarily collected through field measurements and data collected from I ndian N ational C entre for O cean I nformation S ervices (INCOIS). For the current study, Muttukadu (12°47′13″N, 80°15′01″E) inlet, Kovalam along the East Coast of the Indian Peninsula is investigated by assessing its seasonal variations. This study contributes to the management of marine biological ecology, the expansion of small-scale artisanal fishing, the promotion of water sports-related tourism, the advancement of fishing harbor development, and the execution of coastal engineering projects. • This study tackled a complex challenge in coastal and hydraulic engineering. • The study aimed to understanding nearshore wave and current dynamics and its influence on sediment accretion in tidal inlet. • The Delft 3D model was used to estimate longshore velocity, currents, and sediment transport rates. • The stability assessment of the Muttukadu estuarine inlet was performed. [ABSTRACT FROM AUTHOR]

The depositional history of alluvial fans on Mars provides insight into the climatic conditions during the time of fan formation in the late Hesperian to early Amazonian. However, traditional stratigraphic analysis of the alluvial fan deposits is not possible across most of Mars. This study assesses the use of thermal inertia data as a tool for sedimentologic interpretation of 437 Mars alluvial fans. Based on previous work demonstrating the relationship between depositional style, grain size, and thermophysical properties, this study uses analysis of the thermal inertia of alluvial fan surfaces across the global population of fans on Mars to make an assessment of depositional styles that built the alluvial fans. The thermal inertia values across the global population of fans are indicative of sand- to pebble-sized sediment. The variability of grain sizes across the global population is more homogenous than expected based on comparisons to terrestrial alluvial fans. Nearly all Mars alluvial fans have an average thermal inertia that corresponds to pebble and smaller grain size, and < 1% of Mars alluvial fans have an average thermal inertia that corresponds to cobble-sized grains. Spatial patterns of thermal inertia variability on alluvial fan surfaces show a small number of fans with evidence for either downslope fining or channelization, but the majority of fans show no recognizable geologic patterns in surface thermal inertia. The interpretation of the thermal inertia-derived grain size suggests that either there is widespread mantling of unconsolidated sand across the surface, or that Mars alluvial fans were built by primarily sand-sized sediment, which may be indicative of lower energy sediment transport events. • Thermal inertia of alluvial fan surfaces indicates primarily sand-sized sediment. • Thermal inertia of Mars alluvial fan surfaces is surprisingly homogeneous globally. • Alluvial fans built by sand-sized sediment suggest low energy fluvial processes. • Fluvial depositional processes may correlate to lack of clay in catchments. [ABSTRACT FROM AUTHOR]

Reclamation projects generally change the hydrodynamics and thus affect the topography of the seabed, which is the main threat to the safety of marine engineering. The Caofeidian Reclamation Project, the largest reclamation project in China to date, involved the reclamation of coastal regions of the Hebei Province. However, the project also created several issues and flaws due to the size of the reclaimed area. Through the comparative analysis in the Caofeidian sea area of multi-phase bathymetric topography, shallow stratigraphic changes, and numerical simulation of sediment dynamics, the characteristics of surface sediments and spatial distribution of erodibility were summarized. New marine geological hazards were discovered, such as submarine landslides and erosion depressions. It was concluded that after the reclamation of the Caofeidian, the south of the deep trough was still in an erosion state, and the erosion rate increased slightly. The shear stress formed by strong tidal currents in the deep trough was greater than the critical erosion shear stress of surface sediments, which caused the erosion transport of sediments. It was the primary dynamic mechanism leading to the long-term erosion state of the deep trough. • The characteristics of surface sediments and spatial distribution of erodibility were summarized. • New marine geological hazards were discovered near the Caofeidian Reclamation Project. • The south of the deep trough was still in an erosion state, and the erosion rate increased slightly. [ABSTRACT FROM AUTHOR]

Sediment associated carbon and nitrogen loss under rainfall, an important cause of soil quality degradation and water eutrophication, strongly depends on the intrinsic properties of original soil types. Relative to total loss, the transport behaviors of organic carbon and nitrogen among sediment size classes and response to soil types remain poorly understood. The concentrations of organic carbon (OC) and total nitrogen (TN) in different sediment size classes (>1, 0.25–1, 0.10–0.25, and <0.10 mm) and their contributions to total sediment load during rainfall erosion were determined under field plot rainfall simulation (at 90 mm h−1) on three contrasting soil types (Luvisol, Alisol and Ferralsol) with increased aggregate stability. During rainfall erosion, the concentrations of OC and TN in total and different sized sediments decreased first and then reached a steady state. The variability of OC and TN concentrations (coefficient of variations in 4.2–53.1% and 6.6–41.9%) among sediment size classes decreased from Luvisol to Ferralsol. Compared to original soils, sediments exhibited larger C/N ratios for Luvisol, and smaller values for Alisol, indicating the more selective transport of labile organic matter for weaker aggregated soils. Among sediment size classes, fine particles (<0.10 mm) accounted 69–88% of total OC and TN losses for Luvisol, and decreased to 30–39% for Ferralsol; and the main transport mechanisms of sediment associated OC and TN shifting from suspension-saltation (<0.10 mm) to rolling (>0.25 mm) with increased aggregate stability. Among original soil properties, inorganic cementing agents (including amorphous iron oxides and clay minerals) showed closer relationships with sediment OC and TN losses (|r| = 0.61–0.89, p < 0.001) than organic matter properties (|r| = 0.55–0.87, p < 0.001), further implying the important role of soil aggregate stability across soil types. This study provides an in-depth understanding on soil carbon and nitrogen losses and their divergent characteristics among soil types deserves consideration in the development of erosion model and land management in agricultural systems. • Variability of OC and TN concentrations among sediment sizes decreased from Luvisol to Ferralsol. • Suspension-saltation (<0.10 mm) dominated OC and TN losses for weak aggregated soils. • Contribution of coarse particles by rolling to OC and TN losses increased with aggregate stability. • Runoff rate, iron oxides and sediment size controlled the loss characteristics of OC and TN. [ABSTRACT FROM AUTHOR]

The aim of this work is to construct efficient finite volume schemes for the numerical study of sediment transport in shallow water, in the framework of the Exner model [7,10]. In most cases, the velocity related to the sediment is much lower that the fluid velocity, which, in turn, may be much lower that the free-surface wave speed. Explicit methods that resolve all waves require small time steps due to the CFL stability restriction because of fast surface waves. Furthermore, if Rusanov flux is adopted, slow sediment waves may be affected by the large numerical diffusion. The objective of the present work is to drastically improve the efficiency in the computation of the evolution of the sediment by treating water waves implicitly, thus allowing much larger time steps than the one required by fully explicit schemes. The goal is reached by suitably semi-implicit schemes obtained by the use of implicit-explicit Runge-Kutta methods. [ABSTRACT FROM AUTHOR]