Suspended Sediment Deposition Research Articles

How do plants reduce erosion? An Eco Evidence assessment

AbstractSoil erosion adversely impacts natural and human environments globally. Vegetation is often used as a sustainable approach to mitigate erosion. Although using vegetation to reduce erosion is a widely accepted concept, how different plant traits mitigate different mechanisms of erosion, and the generality of these mechanisms has not been well demonstrated. We developed ten hypotheses on how different plant traits (roots, leaves, and stems) act to reduce erosion through different mechanisms (binding soil particles, promoting suspended sediment deposition and reducing the energy of waves, runoff, and wind). We then conducted a rapid evidence assessment of the scientific literature using the Eco Evidence method. We found strong evidence to support our overarching hypothesis—an increase in plant abundance reduces erosion. We also found support for the specific hypotheses that plant roots bind soil particles and that greater plant stem density and leaf area reduce surface run-off and promote sediment deposition. There was insufficient evidence to support the hypotheses that an increase in stem density or leaf area reduces wave or wind energy. None of our hypotheses were rejected. Species with higher root and stem densities and greater leaf area will be the most effective in mitigating erosion. Our review highlights that there is insufficient evidence regarding some potentially important mechanisms between vegetation and erosion, making these prospective areas for further research. Our results have the potential to aid environmental engineers when designing schemes to reduce erosion and ecologists and managers who are concerned about the conservation and restoration of erosion-prone environments.

Hydrodynamic effects and water environment improvement of topographic reconstruction in shallow lakes

This paper focuses on a typical shallow lake, Lake Changdanghu, which is subject to frequent hydrodynamic disturbances and suspended sediment deposition, resulting in reduced water clarity and the degradation of the grass-type ecosystem. Using a combination of long-term systematic observations and numerical simulations, the impact of terrain modification on the hydrodynamic characteristics of Lake Changdanghu and its resulting environmental improvements are systematically analyzed. The results indicate that there is a significant correlation between the wind wave intensity, suspended solids concentration of the water, and water clarity. The artificial shoal project effectively reduces the local wind wave intensity, increases the water area of the weak waves, and alters the flow structure and transport path of the lake. The wave reduction effect of the artificial shoal significantly improves the transparency of the local water, especially under high wind wave conditions, with a 60% increase in the sheltered area, significantly improving the physical habitat environment. Additionally, the flow resistance and guidance roles of the artificial shoal concentrate the impact of the poor water quality of the inflow in a local area, reducing its adverse effects on the main body of the lake. Our research demonstrates that for shallow lakes, the water transparency can be improved, the physical habitat conditions for aquatic vegetation can be enhanced, and grass-type ecosystems can be gradually restored through artificial intervention and vegetation recovery projects by reducing the wave energy, flow resistance, and guidance through the construction of artificial shoals. This approach achieves long-term maintenance of eutrophication control and water quality improvement in shallow lakes.

Field monitoring of alluvium accumulation in the riverine floodplain of the Oka River, European Russia

Sedimentation traps were used to assess the annual surface renewal dynamics of the low floodplain of the Oka River (a major tributary of the Volga River in central European Russia). Trap-mats and platforms made of crushed bricks were installed in positions near the meandering and relatively straight riverbed, in different sedimentation environments. Stationary research in 2014–2020 covered a section of the bottom of the Oka River valley with a length of more than 400 km along the main channel. The graphical-analytical processing of field data using Ferret's Triangles and sedimentation diagrams showed that transport and deposition of suspended sediment dominated in the accumulation of 87% of alluvium samples. The formation of ripples was not recorded, which was lithologically reflected in the horizontal layering of the new sediment. The determination of the granulometric composition of the removed sediment and their thickness on the traps showed the absence of statistically significant differences according to the Kruskal–Wallis test between the data samples from the trap-mats and trap-platforms. The reference to the daily calendar of synoptic mechanisms according to the classification of Dzerdzeevsky contributed to the identification of meteorological prerequisites for the variation of the hydrograph curve of the Oka River in its middle reaches. Prolonged floods caused by the premature arrival of spring lead to massive deposition of silt and clay particles even on sandbanks. On the other hand, short (15–35 d) March floods and abnormal high water in June, caused by Atlantic cyclone intrusions, can stabilize sand accumulation on the riverine floodplain. The thickest sediment layers on the traps were obtained in 2018 after a very cold March and a powerful April flood, and the overall distribution of alluvium thickness and its particle size distribution also depends on the morphology of the riverine relief. The siltation is caused by the accumulation of silts; the most finely dispersed sediment was deposited in those facies environments for which siltation was also characteristic in historical times.

Delft3D model-based estuarine suspended sediment budget with morphodynamic changes of the channel-shoal complex in a mega fluvial-tidal delta

ABSTRACT Reduced riverine sediment supply and sea-level rise (SLR) threaten land building and ecosystem in deltas. However, the sediment-morphodynamic processes in a channel-shoal complex are not well understood. Here, based on bathymetry and the Delft3D model, geomorphic changes and suspended sediment budgets in the South Passage, Nanhui and Jiuduansha Shoal in the mega-Changjiang Delta were examined. Results reveal that with riverine suspended sediment concentration (SSC) decreased by 75%, the net sediment deposition rate was reduced from 4.20 cm/yr in 1979–1990 to 3.21 cm/yr in 1990–2003, and further declined to 2.21 cm/yr in 2003–2013 and 0.40 cm/yr in 2013–2020. Severe erosion occurred along the upper South Passage and extended toward the mouth bar. Strong accretions accumulated in the Nanhui and Jiuduansha Shoal. After river SSC declined from 0.53 kg/m3 to 0.35 kg/m3, 0.16 kg/m3, and 0.12 kg/m3, net suspended sediment deposition was lowered by 3.13%, 7.35% and 8.67%, respectively. Moreover, SLR of 5 cm, 15 cm, 25 cm, and 50 cm resulted in a further 1.11%, 4.18%, 4.16%, and 14.79% reduction in sediment trapping efficiency. Our findings highlight the strong likelihood that reduced river sediment input, SLRs and intensified anthropogenic effects will exacerbate sediment deficit and erosion in mega fluvial-tidal deltas.

Study on the Impact of Offshore Wind Farms on Surrounding Water Environment in the Yangtze Estuary Based on Remote Sensing

Offshore wind farms (OWFs), built extensively in recent years, induce changes in the surrounding water environment. The changes in the suspended sediment concentration (SSC) and chlorophyll-a concentration (Chl-aC) induced by an OWF in the Yangtze River Estuary were analyzed based on Chinese Gaofen (GF) satellite data. The results show the following: (1) The flow near the wind turbines makes the bottom water surge, driving the sediment to “re-suspend” and be lost, deepening the scour pit around the bottom of the wind turbines, which is known as “self-digging”. The interaction between the pillar of a wind turbine and tidal currents makes hydrodynamic factors more complicated. Blocking by wind turbines promoting the scour of the bottom seabed of the OWF results in speeding up the circulation rate of sediment loss and “re-suspension”, which contributes to the change in the SSC and Chl-aC. This kind of change in sediment transport in estuarine areas due to human construction affects the balance of the ecological environment. Long-term sediment loss around wind turbines also influences the safety of wind turbines. (2) The SSC and Chl-aC are mainly in the range of 200–600 mg/L and 3–7 μg/L, respectively, in the OWF area, higher than the values obtained in surrounding waters. The SSC and Chl-aC downstream of the OWF are higher than those upstream, with differences of 100–300 mg/L and 0.5–2 μg/L. High SSC and Chl-aC “tails” appear downstream of wind turbines, consistent with the direction of local tidal currents, with lengths in the range of 2–4 km. In addition, the water environment in the vicinity of a wind turbine array, with a roughly 2–5 km scope (within 4 km during flooding and around 2.5 km during ebbing approximately) downstream of the wind turbine array, is impacted by the OWF. (3) In order to solve the problem of “self-digging” induced by OWFs, it is suggested that the distance between two wind turbines should be controlled within 2–3.5 km in the main flow direction, promising that the second row of wind turbines will be placed on the suspended sediment deposition belt induced by the first row. In this way, the problems of ecosystem imbalance and tidal current structure change caused by sediment loss because of local scouring can be reduced. Furthermore, mutual compensation between wind turbines can solve the “self-digging” problem to a certain extent and ensure the safety of OWFs.

The Investigation of Local Scour around Bridge Piers with the Protection of a Quasi-Stumps Group

In this study, a quasi-stumps group structure was proposed and placed upstream of the bridge piers to mitigate the scour of the waterflow on the riverbed. Both experiment and numerical simulations using FLOW 3D were employed to study the protective effect of this structure. The numerical results were in good agreement with the experimental findings. It was found that the quasi-stumps group can effectively reduce the flow velocities around the bridge piers, thereby promoting the deposition of suspended sediment. As a result, there was no erosion around the piers, and instead, siltation was formed, which contributed to the stability of the piers. The deposition height around the piers increased as the L (the horizontal distance between the quasi-stumps group and the piers) decreased and both the P (the height of the quasi-stumps group) and S (the ratio of the area of a single leaf on the quasi-stumps group to the cross-sectional area of a single pier) increased. As the L, P, and S increased, the quantity of suspended sediment deposition over the entire riverbed increased. The optimal combination of the quasi-stumps group’s protective effect was determined to be L = D (pier diameter), P = H (water depth), and S = 0.148.

Suspended sediment deposition and sediment yields at Lake Peters, northeast Brooks Range, Alaska: Fluvial‐ and lake‐based approaches

AbstractLake‐based studies can provide seasonal‐ to millennial‐scale records of sediment yield to improve our understanding of catchment‐scale sediment transfer and complement shorter fluvial‐based sediment transport studies. In this study, sediment accumulation rates at 40 coring locations in Lake Peters, Brooks Range, Alaska, over ca. 42 years, calculated using fallout radionuclides and sediment density patterns, were spatially modelled based on distance from the primary inflow and lake water depth. We estimated mean interdecadal specific sediment yield (Mg km−2 year−1) using the spatially modelled sediment accumulation rates and compared that result to fluvial‐based sediment delivery for 2015–2016 open‐channel seasons, as well as to yields reported for other Arctic catchments. Using the lake‐based method, mean yield to Lake Peters between ca. 1973 and 2015 was 52 ± 12 Mg km−2 year−1, which is comparable with fluvial‐based modelling results of 33 (20–60) Mg km−2 year−1 in 2015 and 79 (50–140) Mg km−2 year−1 in 2016 (95% confidence intervals), respectively. Although 2016 was a year of above average sedimentation, the last extreme depositional event probably occurred between ca. 1970 and 1976 when a basal layer of fine sand was deposited in a broadly distributed, relatively thick and coarse bed, which we used for lake‐wide correlation. The dual lacustrine–fluvial method approach permits study of within‐lake and catchment‐scale processes. Within Lake Peters, sedimentation patterns show decreasing fluxes down‐lake, sediment bypassing near the primary inflow, the influence of secondary inflows and littoral redistribution, and a focusing effect in the deep proximal basin. At the watershed scale, sediment yield is largely driven by intense summer rainfall and strong seasonal hydroclimatic variability. This research informs paleo‐environmental reconstruction and environmental system modelling in Arctic lake catchments.

Design and Numerical Simulation of the Headworks in the Shizuishan Section of the Yellow River

Irrigation water for agriculture in Ningxia during the summer is primarily sourced from the Yellow River self-flow irrigation region. However, the water conveyance system in this region is significantly influenced by hydrodynamic factors, morphological factors, human factors, and the infrastructure used for social purposes, all of which directly impact the irrigation water utilization coefficient. In order to improve the irrigation water utilization coefficient, reduce suspended sediment deposition in the water conveyance channels, and mitigate negative effects on the water supply system, this study implemented a sediment diversion system at the channel head. This is expected to increase water usage efficiency to a certain degree. Using actual data on hydrodynamic factors from the Shizuishan section of the Yellow River in Ningxia, a two-dimensional numerical simulation was performed, and a two-dimensional hydrodynamic model and sediment model of the Shizuishan section of the Yellow River in Ningxia were developed using MIKE 21. The water conveyance method at the channel head was simulated under two different operating conditions. Results indicated that compared to operating condition 1, operating condition 2 had a beneficial effect on diverting and reducing sediment at the fish mouth of the channel head: the sediment accumulation thickness of one day in operating condition 1 was 0.16 m, 0.003 m, 0.15 m, and 0.21 m under actual flow, scenario 1, scenario 2, and scenario 3, respectively; whereas in operating condition 2, the sediment accumulation thickness of one day was 0.11 m, 0.001 m, 0.09 m, and 0.12 m under the same conditions, respectively. Additionally, as the computation period lengthened, the sediment accumulation thickness of operating condition 2 was significantly smaller than that of operating condition 1. In conclusion, operating condition 2 is superior for the design of the channel head in the Yellow River self-flow irrigation region.

Short-term sedimentation dynamics in mesotidal marshes

One of the key questions about wetlands resilience to sea-level rise is whether sediment supply will be enough to keep them coping with growing inundation levels. To address this question, researchers have put a lot of effort into field data collection and ecogeomorphic modelling, in an attempt to identify the tipping points of marsh survival. This study uses fieldwork data to characterize the sediment fluxes between the tidal flats and salt marshes, in the Ria Formosa lagoon (Portugal). Sediment fluxes were measured from the tidal channel towards the mid-upper marsh, during neap and spring tide conditions. The flow magnitude was measured, and induced transport was determined based on shear velocities. Deposition rates, instantaneous suspended sediment and near-bed velocities were linked through theoretical formulas and used to characterize time-averaged conditions for sediment delivery and deposition to the site. The results showed that suspended sediment concentrations and sediment deposition varied across the transect with no specific relation to elevation. Maximum water depths were recorded in the vegetated tidal flat, and the maximum currents were flood dominated, in the order of 0.20 m/s, in the low marsh due to flow-plant interactions and an increase of turbulence. Deposition rates ranged between 20 to 45 g/m2/hr, after a complete tidal cycle, and were higher in the mid-upper marsh. Hydroperiod was not the main contributor to sediment deposition in the study area. Sediment transport was tidally driven, strongly two-dimension during the cycle, and highly influenced by the vegetation. Measurements of marsh sediment flux obtained in our work are diverse from the ones found in the literature and evidence the importance of considering spatio-temporal variability of vegetated platforms in assessing overall marsh bed level changes.

Promotive Effects of Siltfence on Deposition of Suspended Particles: Evaluations of Diffusion Suppression of Radionuclides in Rectangular Open Channel via Numerical Simulations

A siltfence is installed to prevent the spread of suspended sediments generated by engineering construction works in rivers and on the coast. Thus, the siltfence is regarded to be a tool to prevent radioactive materials adsorbed on suspended sediments from diffusing into the sea in ports of nuclear power plants during nuclear accidents. However, the prevention effects of the siltfence as sediment control structures have not yet been fully evaluated. Therefore, in this paper, we simulate the behaviors of suspended sediment particles using a coupled simulation scheme composed of water flow and deformation of the siltfence in a rectangular open channel under uniform steady flow, and evaluate the promotive effects of the installed siltfence on suspended sediment deposition. The results demonstrate that the installation of the siltfence significantly promotes deposition, especially of particles with low settling velocities. However, it should be noted that the opposite case is also possible, i.e., the siltfence promotes the diffusion of suspended sediments under particular conditions. These results suggest that a careful installation strategy is necessary. The present simulation scheme is useful in assessing the prevention effects of siltfences prior to their installation.

Estimate of uncertain cohesive suspended sediment deposition rate from uncertain floc size in Meghna estuary, Bangladesh

Suspended sediment in the Meghna estuary, Bangladesh, typically consists of fine to medium silt near the water surface, silty sand at increasing depth, and sandy silt close to the bed. The behavior of fine, cohesive sediment in a complex environment with multiple drivers, such as river and tidal flows, is comparatively little understood because the deposition and erosion processes depend on many chemical, biological, and physical factors. This article examines the propagation of uncertainty from input floc size to output sedimentation rate in the Meghna estuary, Bangladesh, using a fine-sediment hydro-morphodynamic model that utilizes the cohesive sediment transport module in Delft3D. We assume that sediment particles and flocs are both single-sized throughout the solution domain. The effect of uncertainty in floc size on output sediment transport statistics is examined at three sites of interest located in the Meghna estuary using a novel numerical derived distribution approach. After deriving the probability distribution of suspended cohesive sediment, we find the coefficient of variation to range from 20% to 38% across the three locations. Planners therefore need to consider substantial uncertainty in cohesive sediment transport estimates for the coastal zone of Bangladesh, especially given the increased risk of flooding in deposition-prone areas as they become shallower. The methodology may be readily extended to the estimation of uncertainty in land reclamation and erosion control planning studies.

Effects of small-scale patterns of vegetation structure on suspended sediment concentration and sediment deposition in a salt marsh

Salt marshes contribute to coastal protection by attenuating waves and reducing flow velocities. Nevertheless, coastal salt marshes are threatened by rising sea levels. In order to keep pace with rising sea levels, salt marshes need to grow vertically by sediment input. Although major processes contributing to sediment deposition in salt marshes are known, there is still a lack of understanding of the influence of canopy height and biomass on suspended sediment concentration and sediment deposition and on the spatial scale beyond which an influence of vegetation on sediment deposition comes into effect. Furthermore, vegetation can be heterogenous and little is known on the role of small-scale patterns of vegetation structure on suspended sediment concentration and sediment deposition. We investigated the effects of small-scale patterns of vegetation on suspended sediment concentration and sediment deposition in a field experiment with two vegetation types (i.e. Spartina anglica in the low marsh and Elymus athericus in the high marsh). Partial mowing of the vegetation resulted in a pattern of mown subplots and control subplots with a size of 4 m2 in various combinations adjacent to a creek. Based on the results, it can be concluded that on the spatial scale of 4 m2, there is no effect of the vegetation on water flow as the sediment deposition between mown and control subplots did not differ in both the high and the low marsh. Furthermore, a mown or a control subplot next to the creek had no influence on the sediment deposition on a mown or control subplot behind. In summary, based on the results of our study, it can be concluded that the presence of salt marsh vegetation not automatically leads to higher sediment deposition on vegetated patches compared to mown patches in both the low and high marsh.

Sustainable Development of Coastal Areas: Port Expansion with Small Impacts on Estuarine Hydrodynamics and Sediment Transport Pattern

With the expansion of global trade and the growing traffic of increasingly larger ships to meet this demand, the need to expand port infrastructure appears as the main alternative. In this way, dredging operations for the maintenance and deepening of navigation channels, as well as the expansion of evolution basins and berthing wharf areas become fundamental, generating large amounts of material removed from the bottom. Aiming at port expansion based on a sustainable development and minimization of the environmental impacts generated by these operations, it is necessary to seek alternatives for the destination of large volumes of dredged material. A sustainable alternative is to dispose these volumes on land in order to expand coastal areas (such as fattening beaches) and mooring pier areas. The present work presents a numerical modeling case study using the TELEMAC-3D model coupled to the suspended sediment module SEDI-3D. As an alternative, an existing island (Ilha do Terrapleno) will receive material dredged from the access channel to the Port of Rio Grande (southern Brazil) and will have its mooring area expanded. The study evaluated the impact that this change in the island’s configuration would generate on the hydrodynamics and on the deposition patterns of fine suspended sediments in its surroundings and in the adjacent navigation channel. Results indicated that in the navigation channel adjacent to Ilha do Terrapleno, the new configuration promoted changes in the hydrodynamics with a decrease in the mean current velocity around the island and throughout the water column, mainly in the north and central portions of the channel. This difference decreased towards the southern portion of the channel. This change in local hydrodynamics promoted small changes in the suspended sediment deposition patterns and in the bottom evolution. Thus, the sustainable expansion of the Port of Rio Grande operational capacity considering the creation of 3600 m of berthing wharf areas and minimum environmental impact proved viable when considering the Ilha do Terrapleno proposed configuration. Furthermore, this idea offers the possibility to dispose in land 722,910 m3 of dredged material, a sustainable alternative to the Port of Rio Grande development, and an inspiration for the sustainable development of other ports worldwide.

A snapshot of sediment dynamics on an inshore coral reef

Sediments are ubiquitous on coral reefs. However, studies of reef sediments have largely focused on isolated reservoirs, or processes, and rarely consider hydrodynamic drivers. We therefore provide a quantitative snapshot of sediment dynamics on a coral reef. Across a depth profile, we simultaneously examined: suspended sediments, sediment deposition and accumulation, and hydrodynamic and biological movement processes. We reveal the marked potential for the water column to deliver sediments. Currents carried 12.6 t of sediment over the 2,314 m2 study area in 6 days. Sediment traps suggested that a surprisingly high percentage of this sediment was potentially deposited (5.2%). Furthermore, wave-driven resuspension and reworking by parrotfishes separated a highly dynamic sediment regime on the shallow reef flat (3 m), from a more stagnant reef slope (4.5 m–12 m). This study provides a comprehensive model of how hydrodynamic forces and on-reef processes may shape sediment dynamics on a coral reef.

Evaluating the concrete grade-control structures built by modified fish-nest bricks in the river restoration: A lab-based case study

Concrete grade-control structures (CGCSs) have broad application prospects in the restoration of large rivers. But there is a lack of indicators to evaluate CGCSs at laboratory study. In this study, we proposed two evaluation indicators from the perspective of the impact of CGCSs on geomorphology change and fish habitat, namely the spatial-averaged occurrence probability of sweep events near the bed and flow diversity. To verify the reasonableness of these indicators, flume experiments were conducted with CGCSs built by modified fish-nest bricks in different Reynolds number and layout condition. Data of the flow field around structures in streamwise, transverse and vertical direction was obtained and analyzed. Results of mean flow field show that large recirculation zones are found in the cavity and behind the element. The mechanism of suspended sediment deposition around CGCSs in the flow can be further clarified by combining sweep and ejection according to quadrant analysis. In the vertical direction, the ratio of sweep to total events near bed after spatial-averaged processing is found to be higher for the staggered array. According to the Shannon's entropy, water flow diversity was calculated to quantify the fish habitat. The water flow diversity index around the CGCSs is higher for the staggered. It can be concluded that the elements of CGCSs in staggered manners have a better protection for riverbed and can provide a more stable fish habitat suitability. The results anticipated by the spatial-averaged occurrence probability of sweep events near bed and flow diversity in the experiment are consistent with the result of previous research on landform change and fish habitat. The research could provide a theoretical basis for the application of CGCSs for river restoration.

Reach-scale experiments on deposition process in vegetated channel: Suspended sediment capturing ability and backwater effect of instream plants

Instream plants, which act as biological processors, have emerged as potentially advantageous eco-morphologic tools to be used in river management and restoration. Most of the study on the geomorphic role of vegetation as it interacts with flow and sediment has focused on local patch-scale dynamics. In this study, we present flume experiments aimed at improving our understanding of how vegetation patches link together to impact reach-scale hydraulics and suspended sediment transport and disposition. On the hydraulics side, we investigate a) the relationship between the imposed instream vegetation configuration and water surface slopes, b) the secondary flow patterns which arise because of the imposed vegetative obstructions, and c) the role of vegetative resistance on residence time within reach. We also examine how different vegetation arrangements determine the patterns, quantity, and caliber of suspended sediment deposited in the flume. A key result of vegetation within the channel is the overall non-uniformity in flow conditions it imposes upstream, within, and downstream of the vegetated reach. At steady-state, vegetated patches locally increase the resistance, leading to a backwater condition upstream of the patch and high water-surface slopes within the patch. In general, this leads to enhanced deposition of suspended sediment upstream of the patch and reduced deposition within the patch relative to a case with no vegetation at all.

Spatial self-organization of marine agglutinated microbial carbonate build-ups: Insights from stratigraphic forward modelling using Stromatobyte3D

Microbialites span a substantial fraction of Earth history, and have important meanings for understanding long-term history of life and environment. Key controls on microbialite morphology and distribution include substrate topography, hydrodynamic conditions, water depth, salinity, light intensity, and sedimentation rates. This leads to potentially complex combinations of control by internal spatial feedbacks and also external factors. This complexity is explored here using Stromatobyte3D, a new numerical stratigraphic forward model that calculates microbialite accumulation due to in-situ precipitation, sediment trapping and binding, and sedimentation from suspension, controlled by evolving topography and water flow due to waves, tides or other currents. Results show that with increasingly strong spatial interactions of microbialite growth with water and suspended sediment, particularly the influence of hydrodynamics on in-situ microbialite growth and suspended sediment deposition patterns, three distinct microbialite morphologies are produced, from isolated columns, through elongated mounds, to ridges elongated in the dominant flow direction. Quantitative analysis demonstrates a dominant antecedent substrate topographic control on microbialite nucleation and growth in the absence of water flow, declining as hydrodynamic processes and strong spatial interactions are introduced causing mounds to accrete and coalesce laterally in the flow direction. Formation of coherent morphological patterns, produced by spatial interactions between topography, hydrodynamics, microbialite growth, and sedimentation from suspension, and independent of initial condition, is evidence of spatial self-organization. Modelled morphologies are strikingly similar to observations from modern marine agglutinated microbialite strata, suggesting modelled processes and their behaviours are realistic, and can therefore be useful to assist field interpretations of observed microbialite morphologies where similar processes were operating together.

Bedform segregation and locking increase storage of natural and synthetic particles in rivers

While the ecological significance of hyporheic exchange and fine particle transport in rivers is well established, these processes are generally considered irrelevant to riverbed morphodynamics. We show that coupling between hyporheic exchange, suspended sediment deposition, and sand bedform motion strongly modulates morphodynamics and sorts bed sediments. Hyporheic exchange focuses fine-particle deposition within and below mobile bedforms, which suppresses bed mobility. However, deposited fines are also remobilized by bedform motion, providing a mechanism for segregating coarse and fine particles in the bed. Surprisingly, two distinct end states emerge from the competing interplay of bed stabilization and remobilization: a locked state in which fine particle deposition completely stabilizes the bed, and a dynamic equilibrium in which frequent remobilization sorts the bed and restores mobility. These findings demonstrate the significance of hyporheic exchange to riverbed morphodynamics and clarify how dynamic interactions between coarse and fine particles produce sedimentary patterns commonly found in rivers.

Stochastic Simulation of the Suspended Sediment Deposition in the Channel With Vegetation and Its Relevance to Turbulent Kinetic Energy

AbstractThe aquatic vegetation patch plays a significant role on sediment net deposition in the vegetated channels. Particularly, the flow is decelerated at the leading edge of a patch that tends to induce vertical updraft, that is, a diverging flow region, in which vegetation greatly affects the pattern of sediment net deposition. This study focuses on the simulation of the sediment net deposition in the whole vegetation patch region through an innovative random displacement model, a Lagrange method, with probability‐based boundary conditions, instead of the reflection or sorption boundary at the channel bottom. The probability model of deposition and resuspension is proposed according to the flow field characteristics in the different regions of the vegetation patch. The variation of the sediment deposition and resuspension with the turbulent kinetic energy is analyzed to illustrate the effect of the turbulence induced by vegetation, represented by the dimensionless turbulent kinetic energy (ψ), on the sediment deposition and resuspension. The sediment deposition predicted by the proposed model agrees well with the experimental measurements. Results show that the effect of vegetation on the sediment deposition and resuspension motions begins to prevail when the vegetation‐induced ψ is larger than its threshold, ψ * . The threshold of ψ is predicted to be within 6.8–10 according to the simulation results in this study. As the turbulent kinetic energy increases, the deposition probability decreases continuously when ψ > ψ * .

ОСАДКИ ПРИРОДНЫХ ВОД НАХЧЕВАНСКОЙ АР КАК ДОПОЛНИТЕЛЬНЫЙ РЕЗЕРВ ХИМИЧЕСКИХ ЭЛЕМЕНТОВ

The introduction of riverwater accumulated over the years in reservoirs and canale for agricultural crops can contribute to the emergence of new representatives of mikrofloraandmikrofauna, wich, in turn, contribute to improving soil fertility, improving soil amelioration and reducing the dosage of mineral fertilizers, thus improving the ecological condition of the soil composition, in the Nakhchivan Autonomous Republic, water supply to agricultural areas is provided by reservoirs and canals including the Vaikhyr reservoir, the Syrabian reservoir, the Neckram canal and the Turian canal. Over the years, as the Nakhchivanriver waters flow in to them suspended sediment deposition has bettaking pleace. Key words:gross composition, chemistry, sediments, river load, minerals, fertility