Bed Sediment Research Articles

River suspended-sand flux computation with uncertainty estimation using water samples and high-resolution ADCP measurements

Abstract. Measuring suspended-sand fluxes in rivers remains a scientific challenge due to their high spatial and temporal variability. To capture the vertical and lateral gradients of concentration in the cross-section, measurements with point samples are performed. However, the uncertainty related to these measurements is rarely evaluated, as few studies of the major sources of error exist. Therefore, the aim of this study is to develop a method to determine the cross-sectional sand flux and estimate its uncertainty. This SDC (for sand discharge computing) method combines suspended-sand concentrations from point samples with ADCP (acoustic Doppler current profiler) high-resolution depth and velocity measurements. The MAP (for multitransect averaged profile) method allows obtaining an average of several ADCP transects on a regular grid, including the unmeasured areas. The suspended-sand concentrations are integrated vertically by fitting a theoretical exponential suspended-sand profile to the data using Bayesian modeling. The lateral integration is based on the water depth as a proxy for the local bed shear stress to evaluate the bed concentration and sediment diffusion along the river cross-section. The estimation of uncertainty combines ISO standards and semi-empirical methods with a Bayesian approach to estimate the uncertainty due to the vertical integration. The new method is applied to data collected in four rivers under various hydro-sedimentary conditions: the Colorado, Rhône, Isère, and Amazon rivers, with computed flux uncertainties ranging between 18 % and 32 %. The relative difference between the suspended-sand flux in 21 cases calculated with the proposed SDC method compared to the International Organization for Standardization (ISO) 4363 standard method ranges between −40 % and +23 %. This method that comes with a flexible, open-source code is the first to propose an applicable uncertainty estimation that could be adapted to other flux computation methods.

Coherent turbulent flow structure under plunging breaker on movable grain bed simulated by 3D DEM-MPS method

ABSTRACT Breaking waves transport momentum, gas, and sediment vertically. Recent particle image velocimetry (PIV) measurements have elucidated the coherent vortex and turbulence structures under breaking waves. However, clarifying three-dimensional fluid motion under breaking waves with PIV remains challenging. Although particle methods have performed wave-breaking simulations, they have never been validated through velocity distributions for breaking waves above movable sediment beds. This study simulated the sediment transport process under plunging waves using a 3D Lagrangian fluid-particle mixture model. The investigation focuses on the first wave plunging for a fundamental investigation. Our simulation shows the instantaneous velocity distributions at different wave phases, which agree with the PIV measurement. A physically-based turbulence extraction method is introduced: a numerical filter based on the coherence between the water elevation and horizontal velocity. Visualized three-dimensional vortex and turbulence structures are consistent with previous studies. The transport equation of the kinetic turbulence energy investigates the turbulence budget near the bed surface and emphasizes the negative contribution of the fluid-particle interaction. Our findings show that a contribution of the pressure gradient to offshore sediment transport. The pressure gradient is difficult to correlate to the water surface gradient and is derived from the large vortex induced by the plunging wave.

The contribution of seasonal variations and Zostera marina presence to the bacterial community assembly of seagrass bed sediments

BackgroundMicroorganisms play pivotal roles in seagrass ecosystems by facilitating material and elemental cycling as well as energy flux. However, our understanding of how seasonal factors and seagrass presence influence the assembly of bacterial communities in seagrass bed sediments is limited. Employing high-throughput sequencing techniques, this study investigates and characterizes bacterial communities in the rhizosphere of eelgrass (Zostera marina) and the bulk sediments across different seasons. The research elucidates information on the significance of seasonal variations and seagrass presence in impacting the microbial communities associated with Zostera marina.ResultsThe results indicate that seasonal variations have a more significant impact on the bacterial community in seagrass bed sediments than the presence of seagrass. We observed that the assembly of bacterial communities in bulk sediments primarily occurs through stochastic processes. However, the presence of seagrass leading to a transition from stochastic to deterministic processes in bacterial community assembly. This shift further impacts the complexity and stability of the bacterial co-occurrence network. Through LEfSe analysis, different candidate biomarkers were identified in the bacterial communities of rhizosphere sediments in different seasons, indicating that seagrass may possess adaptive capabilities to the environment during different stages of growth and development.ConclusionsSeasonal variations play a significant role in shaping these communities, while seagrass presence influences the assembly processes and stability of the bacterial community. These insights will provide valuable information for the ecological conservation of seagrass beds.

Terrestrial support of wetland food webs via a dissolved inorganic carbon pathway

AbstractStudies of terrestrial support of aquatic food webs have focused primarily on terrestrial organic matter (t‐OM) directly used by animal and microbial consumers. However, dissolved inorganic carbon (DIC) released from t‐OM might also support aquatic primary producers, a key resource for zooplankton and upper trophic levels. Using 2‐yr 13C measurements of algae, zooplankton, terrestrial detritus, sediments, dissolved and particulate organic matter from six seasonal wetlands, we found that in January when algal concentration was low, zooplankton used t‐OM directly or heterotrophic microbes that decompose t‐OM, but in March and May zooplankton was mainly supported by algae as their basal resources, and the algae used DIC derived from the mineralization and methanogenesis of t‐OM, suggesting the DIC pathway of terrestrial support of aquatic food webs. The decomposition of abundant t‐OM from both bed sediments and water column caused high concentrations of DIC. Despite uptake by algae, about half of DIC produced in January and March ended up as emissions to the atmosphere in the form of CO2. This finding revealed the dual roles of t‐OM in maintaining the productivity and stability of aquatic food webs and in contributing to global carbon emissions. This duality poses challenges for simultaneously mitigating carbon emissions and conserving biological communities in seasonal wetlands. Finally, wide seasonal differences in δ13C in DIC (−12.4‰ to 6.7‰) were observed, mainly driven by air–water CO2 exchange and photosynthesis, suggesting that 13C may be a powerful tool to investigate carbon cycling in shallow, temporary freshwater ecosystems that are widespread but understudied.

Response of a patchy intertidal mudflat‐marsh transition zone to a typhoon

AbstractWhile tidal marshes are valued for their ability to reduce the impact of storm waves on shores, there is still more limited understanding of how storm waves impact the integrity of tidal marshes, particularly in mudflat‐marsh transition zones with patchy vegetation cover. This study aims to investigate changes in hydrodynamics, sediment bed elevation, and patchy vegetation cover along the sea‐to‐land elevation gradient in response to super typhoon IN‐FA, making landfall in 2021 in a mudflat‐marsh transition zone of the Yangtze Estuary (China). Utilizing in‐situ measurements and drone surveys, our results show: (1) A landward decrease in storm‐induced wave energy, flow velocities, turbulence, and erosion across a 200‐m mudflat‐marsh transition zone; (2) Elevation‐dependent spatial reconfiguration of marsh vegetation patches in response to the storm; (3) Different marsh response below and above an elevation threshold where a shift between marsh gain and marsh loss occurred. The observed landward decrease in storm‐induced marsh loss is attributed to a trade‐off between reduced disturbances due to landward increasing friction from the sediment bed and vegetation, and the landward increasing capacity of the vegetation to cope with disturbances. Our findings provide new insights relevant to the response of marsh systems to storms, and highlight the importance of the gradual and adequately wide sea‐to‐land gradient in delivering marsh resistance to extreme events.

An uncertainty‐based evaluation of sulphuric compounds transport in reservoirs considering sensitivity analysis

AbstractDeepwater bodies such as dam reservoirs are among the most prominent water resources that supply societies' water demand. Hence, water quality in these resources requires continuous and meticulous monitoring. This study evaluated the water quality of Changuleh Dam, a dam under construction in western Iran, using the CE‐QUAL‐W2 model to predict fluctuations in sulphate (SO42−) and hydrogen sulphide (H2S) concentrations. A sensitivity analysis was conducted to assess the dependence of model outputs on input variables. Additionally, an uncertainty analysis was performed using MATLAB to address the inherent uncertainties of the input variables through an ARIMA (2, 2, 1) time series model and Monte Carlo simulations. The results indicated a high sulphate concentration averaging 955.6 mg/l, considerably exceeding the drinking water standard of 400 mg/l, identifying the reservoir as a sulphate‐rich water resource. Seasonal fluctuations of H2S concentrations were also observed in the reservoir's anaerobic bed sediments, peaking at 87 mg/l. The sensitivity analysis showed that nitrate and total dissolved solids (TDS) varied more noticeably than dissolved oxygen (DO) at different depths, with the greatest variation at 50 m. This study highlights the critical need for continuous and meticulous monitoring of water quality in dam reservoirs to meet water supply standards.

Bedform generation beneath shoaling nonlinear internal waves on a mild slope

Subaqueous sand waves have been observed where nonlinear internal waves (NLIWs) shoal on continental margins. To investigate their generation mechanisms, we propagated periodic NLIWs of depression to shoal upon a sloping bed in a laboratory flume. Following fission of the incident waves, ripple-type bedforms were observed between the point of incipient suspension and interaction point (where the quiescent pycnocline intersects the sediment bed). The largest ripples were centered on the bolus birth point, where the NLIWs of elevation, generated by fission, transform into boluses and maximum near-bed velocities occurred. The ripple height and wavelength were consistent with fluvial scaling. In two experiments, where bedload transport was not predicted, the observations showed resuspension to influence ripple generation. Net upslope sediment movement was observed beyond the turning point.

Inundation Processes with Active Sediment Transportation in the Floodplain of West Rapti River, Nepal

The present study discusses flood hazard characteristics in the lower reaches of the West Rapti River based on the results obtained from field surveys and numerical computations using depth averaged 2-D numerical models for flood flow and associated sediment transportation. To evaluate the inundation process with sediment erosion and deposition in the floodplain, a new erosion term was introduced into the mass conservation equations for suspended sediment and bed sediment. The results obtained from numerical computations indicated that field data on the spatial distributions of depths for inundation, and sediment erosion and deposition can be evaluated by the numerical model. Thus, numerical predictions were performed for the inundated areas, and the accumulated volumes of sediment erosion/deposition for floods with return periods of 50, 100, and 200 years, as a step towards damage assessment and risk assessment due to floods with active sediment transportation in the floodplains.

Effects of Leafy Flexible Vegetation on Bed‐Load Transport and Dune Geometry

AbstractThe development of sustainable river management strategies requires knowledge of the effect of vegetation on hydrodynamics and sediment transport. To date, the complex physical processes involving the combined effects of leafy flexible vegetation and mobile bedforms are not completely understood. Most sediment transport models have been developed for bare bed conditions so that their performance in the presence of leafy flexible vegetation remains unclear. On the other hand, recently developed models consider vegetated conditions but they typically account only for the presence of rigid cylinders and in some cases scour at their base. For this purpose, laboratory experiments were conducted with mobile dune bed conditions and artificial flexible plants with varying Leaf Area Index to investigate the effect of flexible vegetation on bed morphology and sediment transport. Sediment transport rates and bedform characteristics such as height, wavelength and celerity, were measured in specifically designed experimental runs. The collected data show that the presence of leafy vegetation alters bed morphology, tending to reduce the average dune wavelength and leading to the formation of complex 3D geometries. Bed‐shear‐stress‐based models for predicting sediment transport were verified to be valid under conditions of low vegetation roughness density. On the contrary, the collected data emphasize that the measured bed‐load transport rate increased in the presence of leafy flexible vegetation with higher frontal area. Recent bed‐load models for vegetated channels provide a better interpretation for dense leafy vegetation but are less effective when predominant effects related to dunes are present.

Morphological properties of two-dimensional and three-dimensional bedforms in open channel flow: A flume experiments study

Bedforms are formed by sediment particles under the action of flow, which in turn affect flow and sediment movement. However, the fundamental mechanisms behind the formation and development of bedforms under varying flow conditions, the interconnection between sediment particle movement and bed morphology development, as well as the influence of bedforms on flow and sediment transport, are still not well understood. In the current study, the moveable bed load transport flume experiments under different flow conditions were done, and the development processes of two-dimensional and three-dimensional dunes formed under different flow intensities were simulated. The detailed structure of the bedforms was measured by laser scanning technology, the characteristics of the bedforms were analyzed in detail, and the relations between the formation of the bedforms and the movement of sediment particles are discussed. The results found that the correlation coefficients of the longitudinal profile curve can serve as a quick reference for distinguishing two-dimensional and three-dimensional dunes. When the crestline ratio is used as the criterion for two-dimensional and three-dimensional dunes, the relative amplitude of the dune crestline and the included angle with the flow direction should also be comprehensively considered. The lee side angles of dunes calculated using the triangle generalization method and local section tangent method are compared and show that the values obtained by the former method are only about half of that of the latter. It is also found that the lee side angles of dunes are related to the dune height. The superimposed dunes generally exist in the downstream area of the stoss side of the dunes. The local bed slopes on the stoss side of the dunes show reverse slopes. The superimposed dunes improve the local bed height and further increase the reverse slope degree of the stoss side. A streamwise ridge is an important form located in the upstream area of the dunes stoss side, and they are symmetrically distributed on both sides. Multiple streamwise ridges divide the stoss side of the dunes into relatively independent movement areas, restricting the movement of sediment particles to specific regions. According to the distribution characteristics of bed morphologies, the effects of dunes on sediment particle movement and flow energy consumption are analyzed.

The Foraminifera Fossil Record of the Sedimentary Rock at Kotadjawa, Lampung, Indonesia: The Significance of Marine Paleontological Insight

Kotadjawa, located on the west coast of Lampung, directly faces the Indian Ocean. Lithified calcareous sedimentary beds are prevalently outcropped along this coastline. These beds likely belong to the Simpangaur Formation, which may be associated with the paleocoastal depositional environment and tectonic uplift of the Indian Ocean. Therefore, we investigated the paleontological record, focusing on foraminifera as potential indicators of the paleoenvironment. This study aimed to identify, record, and calculate the relative abundance of benthic foraminifera in the sedimentary beds of Kotadjawa, Lampung. The samples were prepared via chemical treatment of 10% H2O2 for 48 hours. Our results revealed a diversity of benthic foraminiferal fossils within the sedimentary rock. Notably, 11 benthic foraminifera genera were fossilized in the observed outcrop: Textularia (18.4%), Sigmoilopsis (16.5%), Rectobolivina (15.4%), Uvigerina (15.5%), Nodosaria (14.5%), Elphidium (11.5%), Lenticulina (7.7%), Hormosina (6.8%), Bolivina (6.8%), and Globobulimina (5.8%). These results suggested that the sedimentary beds exposed in our study area ranging from the foreshore to the deep ocean floor ecosystem. This suggests that a sediment mixing event, possibly triggered by a paleocatastrophic event, influenced the deposition of these beds. This study provides new insights into marine paleoenvironmental conditions and paleocatastrophic events along the west coast of Lampung, Sumatra.

River Sedimentation Due to Tin Mining Activities in Bangka Island

Sedimentation in rivers is a major issue of environmental damage in the Kepulauan Bangka Belitung Province. In the last two decades, since tin mining was carried out by the community, massive sedimentation has occurred in the river. The purpose of the study is to investigate the characteristics of sediment materials and the effects of illegal tin mining on river sedimentation on Bangka Island. Sediment characteristics can be seen from the distribution of grain size and specific gravity of the bed sediment material and the concentration of suspended sediments seen from their position along the river. Sediment grain size is classified according to the American Geophysical Union. A total of 45 sediment samples spread across 12 rivers in the district capital area on Bangka Island were collected at the end of the rainy season in 2023, and 4 more samples were added in the dry season of 2023 in the Muntok River. The MPM formula was applied to estimate bedload transport and statistical methods were used to estimate suspended sediment rates. Additionally, the sedimentation rates are estimated based on dependable continuous flow with a probability exceeding 50% (Q50%). The study’s findings indicate that Illegal tin mining in Bangka Island has a major impact on river sedimentation. The particle size distribution of bed material sediments does not align with what is typically found in nature, which often exhibits coarser particles upstream and finer downstream. Similarly, in areas downstream of tin mining operations, the concentration of suspended particles increases significantly, up to 12 times higher than natural conditions.

Experimental investigation on the mechanism of local scour around a cylindrical coastal pile foundation considering sloping bed conditions

Sea-crossing bridges are often subjected to local scour, significantly impacting the bearing capacity of the foundation system and potentially leading to bridge failures. This study presents experimental investigations of local scour around a cylindrical pile under different sediment slope conditions in unidirectional currents. Unlike previous studies that focused on horizontal sediment beds, this research explores the influence of inclined sediment beds, which reflect coastal and offshore topographies, which have some angles of inclination. Utilizing flume tests, the research investigates the evolution of scour depth, scour range, and the morphology of the sediment bed across various angles of inclination. The study also evaluates the effectiveness of a scour countermeasure involving rip-rap material around the pile on sloping beds. Specifically, a steeper inclination angle induces a faster flow velocity, resulting in increased scour depth at the upstream side of the pile and a reduced scour range at the downstream side due to backfilling. The countermeasure scenario reveals a significant reduction in both scour depth and range. This research provides analysis of the effects of inclined sediment beds, which reflect coastal topographies than horizontal ones, thereby providing insights for the design and protection of bridge foundations in diverse coastal conditions.

Revealing the role of land-use features on macrolitter distribution in Swiss freshwaters

Macrolitter, especially macroplastics, (> 0.5 cm) negatively impact freshwater ecosystems, where they can be retained along lake shores, riverbanks, floodplains or bed sediments. Long-term and large-scale assessments of macrolitter on riverbanks and lake shores provide an understanding of litter abundance, composition, and origin in freshwater systems. Combining macrolitter quantification with hydrometeorological variables allows further study of leakage, transport, and accumulation characteristics. Several studies have explored the role of hydrometeorological factors in influencing macrolitter distribution and found that river discharge, runoff, and wind only partially explains its distribution. Other factors, such as land-use features, have not yet been thoroughly investigated. In this study, we provide a country-scale assessment of land-use influence on macrolitter abundance in freshwater systems. We analyzed the composition of the most commonly found macrolitter items (referred to as ‘top items’, n = 42,565) sampled across lake shores and riverbanks in Switzerland between April 2020 and May 2021. We explored the relationship between eleven land-use features and macrolitter abundance at survey locations (n = 143). The land-use features included buildings, city centers, public infrastructure, recreational areas, forests, marshlands, vineyards, orchards, other land, and rivers and canals. The majority of top items are significantly and positively correlated with land-use features related to urban coverage, notably roads and buildings. Over 60% of top items were found to be correlated with either roads or buildings. Notably, tobacco, food and beverage-related products, as well as packaging and sanitary products, showed strong associations with these urban land-use features. Other types of items, however, did not exhibit a relationship with land-use features, such as industry and construction-related items. Ultimately, this highlights the need to combine measures at the local and regional/national scales for effective litter reduction.

Investigating Flow around Submerged I, L and T Head Groynes in Gravel Bed

Riverbank erosion poses a significant threat to the stability and integrity of river training structures. River training structures such as groynes are important components of sustainable development as they play a crucial role in mitigating flood risks, controlling erosion, and supporting the habitat for aquatic organisms. The habitats vary largely according to the groyne type. A comprehensive comparative analysis of the flow field around the I, L, and T head groynes in the gravel bed is drawn. This study will be of immense use for riverbank protection in hilly terrain where streams are mostly dominated by the gravel bed. Laboratory experiments were conducted in a channel with a sediment bed as gravel of size 9.36 mm. Consistent flow conditions were maintained, with a flow depth (D) of 0.136 m and Froude no (Fr) of 0.61. The performance of these groynes, quantified using Lp (length of bank protection), was investigated. LHG and THG, notably, instigate more profound scour depths, recording values of 0.295 D and 0.29 D, respectively, while IHG trails with the value of 0.21 D. The complex flow field involving velocity peaks, decelerated, and negative flow is discussed and is attributed to flow separation at the groyne tip and the horseshoe vortex. The Lp for each groyne was estimated, with the IHG providing the maximum bank protection of 1.2 L1, L1 being the transverse length of the groyne. The cost–benefit analysis revealed IHG as the most cost-effective structure. These findings contribute to optimization of riverbank stabilization efforts, enhancing the resilience of hydraulic infrastructure and ensuring the safety and wellbeing of affected communities and ecosystems. The results also provide valuable insight into bank protection by various groynes and highlight their contribution to enhancing the resilience of river systems.

Preservation of groove mark striae formed by armoured mud clasts: The role of armour sediment size and bed yield stress

AbstractStriated grooves in tool marks are common at the base of sandstones, especially in deep‐marine successions, but their use in physical‐process and environmental reconstruction is underdeveloped. To fill this gap in knowledge, striations in the central groove of chevron marks and in chevron‐less groove marks were formed in the laboratory by dragging tools armoured with silt, sand or gravel across muddy substrates. These experiments simulated the formation of striated grooves by armoured mud clasts carried at the base of quasi‐laminar and fully laminar debris flows, aiming to: (1) delineate the bed shear strengths for the formation of striated grooves at different armour sediment sizes; (2) examine how the preservation potential of striated grooves depends on clay bed rheology and size of armour sediment and (3) discuss how the pre‐lithification clay bed consolidation state and size of armour sediment can be reconstructed from striated grooves in the geological record. The experimental results revealed that tools with small‐diameter silt and sand armours dragged along soft beds lack striations or, at best, leave poorly defined striations, whereas firm beds and gravel armours exhibit well‐defined striations. The spacing of striations formed by gravel clasts corresponds well with the clast diameter, implying that striation spacing is a good proxy for the diameter of armoured gravel under natural conditions. In contrast, the spacing of striae formed by sand armours is greater than the grain diameter, suggesting that the spacing of fine striations can only be used to predict a maximum armour sand size. A comparison of different processes of formation of armoured mud clasts demonstrated that the armouring of mud clasts most probably happens after incorporation of the clasts by erosion into the head of the debris flow and subsequent movement across a loose sandy or gravelly bed surface.

A Godunov-type scheme for the Saint-Venant-Exner equations with a moving steady states

The Saint-Venant-Exner system is widely used in industrial codes to model the transport of bed sediments. In practice, most of the methods used for its numerical resolution suffer from significant stability problems due to the fact that they are mainly guaranteed by separation techniques which allow weak coupling between hydraulic and morphodynamic software. The search for an adequate alternative method to this problem is a focus towards which several approaches converge. Recently, many authors have proposed acceptable methods but they are not so trivial to implement in an industrial context and some do not take into account all aspects such as mobile steady states. In this work, we derive a well-balanced scheme that takes into account all stable states, to approach weak solutions of the sediment transport model in shallow waters. We demonstrate that it captures exactly all regular steady solutions with non-evanescent velocities, retains water level positivity and is able to degenerate to a classical shallow water model when the sedimentary transport flow is null. A number of numerical test cases are also presented to illustrate these properties.

Regime Shift to Hyperturbid Conditions in the Loire Estuary: Overview of Observations and Model Analysis of Physical Mechanisms

AbstractThe Loire estuary (France) was extensively deepened during the 20th century. Coincidentally, suspended sediment concentrations increased drastically from ∼0.1 g/l to ∼1–5 g/l at the surface and the estuarine turbidity maximum (ETM) moved upstream. In this study we, for the first time, brought together a century of observations of estuary bed level, tidal amplitude, and sediment concentration to demonstrate these large changes. Next, we analyzed a minimal set of physical mechanisms that explain the dramatic increase in sediment concentration. To this end, we used the iFlow model representing dynamic equilibrium conditions in the Loire. Novel in the model is that it dynamically resolves salt stratification and corresponding damping of turbulence. For conditions representing the year 2000, high sediment concentrations were found with satisfactory correspondence to observations. Low sediment concentrations were found when using the year 1900 bed level but keeping all other model parameters the same. Varying the bed level gradually between these two extremes, the equilibrium solution suddenly increases for intermediate bed level, constituting an abrupt regime shift. Robustness of this result was established in an extensive sensitivity study featuring 13,200 model experiments. The regime shift is enabled by a feedback between increasing sediment concentration, reducing turbulence due to sediment and salt stratification, and increasing sediment importing capacity of the estuary. The essential sediment importing mechanisms in this feedback are related to the tidal asymmetry and gravitational circulation. This is the first time gravitational circulation and salt stratification are shown to be important factors in a transition to hyperturbidity.

Shear induced remobilization of buried synthetic microfibers

Microplastics are known to accumulate in sediment beds of aquatic environments where they can be buried. Once buried they can remobilize due to high energetic events, entering the water column again. Here, turbulence induced by an oscillating grid device was used to investigate the remobilization of microfibers (MF) buried into the sediment bed. Four different types of plastic fibers commonly used for several industrial applications (PET, PP, PA and LDPE) and two types of soils (cohesive and non-cohesive) were investigated. Particles were in depth characterized via 3D reconstruction to estimate important parameters like the Corey shape factor and the settling velocity. Experimental runs explored a wide range of shear stresses. Measurements were taken at different time steps (between 15 min and 240 min from the start of each run). The results have shown that the remobilization of MFs is directly proportional to the value of the shear rate and the duration of the disturbance. Also, buoyant MFs were found more prone to remobilize respect to the denser ones. Drawing from experimental observations of the key parameters affecting MF remobilization, a non-dimensional predictive model was developed. A comparison with previous studies was performed to validate the model in order to predict MF remobilization in aquatic environments.

Nature‐based shoreline protection in newly formed tidal marshes is controlled by tidal inundation and sedimentation rate

AbstractMany tidal marshes have been lost by past land use changes, but are nowadays increasingly restored and created to provide valuable ecosystem services such as nature‐based flood and erosion protection along estuarine shorelines. To be functional for flood and shoreline erosion protection, restored and created tidal marshes should develop erosion resistant sediment beds. Here, we investigated which factors drive the spatial variations in sediment strength and erosion resistance in a developing tidal marsh restoration site. Our results show that decreasing tidal inundation frequency, decreasing sedimentation rate, and better drainage led to stronger consolidation in deeper sediment layers. This consolidation resulted in greater sediment strength, quantified here by shear strength and penetration resistance. Generally, sediment strength was greater when sediment had higher bulk density, while a higher water and fine fraction (= clay and silt) content decreased sediment strength. Overall, all measurement locations were relatively erosion resistant, likely caused by the dense root network and cohesive sediment. To restore or create resilient tidal marshes for nature‐based flood and shoreline erosion protection, we should thus aim for sites with relatively low tidal inundation frequency, moderate sedimentation rates, and cohesive sediment mixtures of clay, silt, and sand, which are well drained and have potential for vegetation establishment. These conditions have a high likelihood of resulting in restored or created tidal marshes that contribute to nature‐based flood and shoreline erosion protection.