Suspended Sediment Transport Processes Research Articles

Water-sediment synergistic relationship in the flood season in the coarse sand source regions of the loess plateau, China

A number of studies have been conducted to determine the relationships between runoff and sediment under different conditions. However, the water-sediment synergistic relationship, which refers to the degree of intervention between the runoff and suspended sediment transport processes in the flood season, must be further analyzed. This study proposed the concept of the synergy degree between water and sediment based on the discipline of synergetics created by Haken (Haken, 1983). The flood and suspended sediment transport processes in the flood season and the measured water-sediment coordination levels were adopted in this study to obtain their synergy degree by taking as an example the largest and most continuous region from the Huangfu River to the Jialu River in the coarse sand source regions of the Loess Plateau. The results of this investigation are as follows. The degree of synergy between runoff and suspended sediment transport was below 0.722 from 1958 to 2016. Approximately 70% of the flood events in the five river basins had poor degrees of synergy between the flow and sediment processes in the flood season. Moreover, the synergy degrees of the water-sediment relationship were relatively low in the runoff and suspended sediment transport processes in the flood season due to the low order degrees of these two process subsystems. The low synergistic relationship between these two subsystems shows that the coordination and buffering abilities between the flood and suspended sediment transport processes were weak. These findings demonstrate the successful adoption of synergetics to ascertain the water-sediment synergistic relationship and also provided critical information for designing water conveyance systems with high sediment concentrations for irrigation in the coarse sand source regions of the Loess Plateau, China.

Mechanism of Formation and Estuarine Turbidity Maxima in the Hau River Mouth

Observation of the Hau River distributary of the Mekong River delta in Vietnam, conducted in dry and flood season (2009, 2014, and 2015), is utilized to investigate the mechanism of formation, distribution of estuarine turbidity maxima (ETM), and links with sediment transport in the system. Additionally, 3D (three-dimensional) numerical models are applied to simulate the seasonal tidal variation (flood and dry seasons) of the water and suspended sediment transport processes of the Mekong River Delta. The 3D model, with a combination of hydrodynamic-wave and suspended sediment transport, was set up and validated with measured data in the study area. The mechanism that measures ETM is the process of suspended sediment from the river when it interacts with seawater and speeds up the flocculation, combined with the asymmetry of the tidal current, which will create the region with ETM by moving in/out with the tidal current’s ups and downs. As there is surface flow velocity towards the sea, the bottom baroclinic flow has a decisive role in deposition and erosion, and it causes the suspended sediment concentration (SSC) to be maximized. During the flood season, the salt wedge near the river’s mouth, at the peak of the tide, pushes towards the sea’s direction when there are ebbing tides, with a scope of about 20 km. In the dry season, there is estuary disturbance as well; the salt wedge forms, but is relatively weak or does not exist, depending on the time of the tide. The maximum turbidity zone in the flood season moves the subaqueous delta with a scope of about 20 km and SSC of about 0.1 to 0.6 g L−1, whereas in the dry season, the seawater has high salinity, and seaward SSC penetrates the estuaries to cause a disturbance and flocculation. The penetration scope is up to 50 km and creates a water mass that has high SSC, from 0.2 to 0.7 g L−1, to run in/off by the tidal current’s ups and downs for several kilometers in the tidal phase.

Numerical Approaching of Beach Profile Change by Suspended Sediment Transport Process

Laksmi, A.A.; Kim, T.K., and Lee, J.L., 2019. Numerical approaching of beach profile by using suspended sediment transport process. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 86-90. Coconut Creek (Florida), ISSN 0749-0208.The coastal process in a surf zone is very complicated, especially when the wave breaks and it associates turbulence. In a coastal area with wave angle influence the cross-shore process, the energy dissipated per unit water volume by breaking waves generate seabed sediment suspension then drive the materials to offshore along with the undertow in the swash zone. This situation could lead beach profile evolution due to the sediment erosion and deposition across an area in the surf zone. As a result, a sand bar located around the breaking line and berm at the landward region caused by overwash are formed. Furthermore, the beach profile is presumed to be in an equilibrium condition when the total positive and negative littoral transport approaches zero. The equilibrium stage which commonly used is expressed with a power of 2/3 which provide the best representative to the natural beach profile shapes. Under this concept, an analysis on the correlation between the beach profile response due to the incident wave energy and suspended sediment transport in a cross-shore view is carried out. Furthermore, this study develops a simple equilibrium beach profile prediction by analyzing the sediment characteristics and is supported by numerical modeling. Lastly, this study is expected to be practically used for coastal infrastructure design works, especially in the process of mean shoreline position prediction as the basis of the design judgements.

Estuarine and sediment dynamics in a microtidal tropical estuary of high fluvial discharge: Magdalena River (Colombia, South America)

Relation among estuarine processes, mixing mechanisms and turbidity maximum zone (TMZ) formation was evaluated in a microtidal tropical estuary of high fluvial discharge (Magdalena River, northwestern South America). Particularly, assessing the effects of vertical stratification over mixing, estuarine circulation and suspended sediment transport processes. Measurements of salinity, temperature, density, currents and suspended sediment concentration (SSC) were performed at the Magdalena river mouth during high and low streamflows to distinguish among two contrasting seasonal conditions (flow conditions, wind patterns, wave energy). Salinity, temperature, density and location of the freshwater-saltwater interface (FSI) exhibited a sharp seasonal variability. The river mouth and delta front were stratified regardless of the hydrologic season, whereas the riverine section was stratified during the low streamflow season, reflecting the balance between fluvial advection and vertical stratification. Reduction of the vertical mixing led to a more clearly defined and extended stratification. Bottom friction is the main mixing mechanism, but as stratification is strengthened along the river mouth, the vertical mixing weakens, promoting the developing of TMZ (SSC >4500 mg l−1). Our results indicate that TMZ developing is caused by the convergence of stratified layers near the nodal point and the weakening of bottom turbulence by stratification. Although the TMZ exhibited a strong seasonal variation in its magnitude and extent, it usually formed in the convergence front demarcated by saltwater intrusion. Streamflow is the major influence on the TMZ formation since it allows the development of stratified conditions, which weaken turbulent mixing, and thus promotes particulate matter settling. The Magdalena River estuary can be classified as turbid (4000 mg l−1 < SSCmax < 10,000 mg l−1) and extremely turbid during low streamflow seasons (SSCmax > 10,000 mg l−1). These values are of the same order as the SSC reported for the Yangtze and Yellow estuaries, classified as having the largest SSC values of the world.

Scaling and Self-Similarity of One-Dimensional Unsteady Suspended Sediment Transport with Emphasis on Unscaled Sediment Material Properties

AbstractCurrent methods utilized in scaling sediment transport in unsteady open-channel flow result in a number of model and scale effects, decreasing the accuracy and applicability of scale models. Identifying the conditions under which the governing equations of sediment transport are self-similar, and require no sediment diameter or density scaling, can reduce scale effects and increase model applicability. Conditions for self-similarity of one-dimensional unsteady suspended sediment transport are identified by applying the one-parameter Lie group of point scaling transformations, both for the general case and with unscaled sediment diameters. Under the scaling ratio relations found when holding sediment diameter to be unscaled, sediment diameter, density, critical and total shear, porosity, kinematic viscosity, and particle Reynolds number are all unscaled. It is shown that under Lie group scaling, the unsteady one-dimensional suspended sediment transport process as an initial-boundary value problem i...

Intratidal and neap-spring variations of suspended sediment concentrations and sediment transport processes in the North Branch of the Changjiang Estuary

Profiles of tidal current and suspended sediment concentration (SSC) were measured in the North Branch of the Changjiang Estuary from neap tide to spring tide in April 2010. The measurement data were analyzed to determine the characteristics of intratidal and neap-spring variations of SSC and suspended sediment transport. Modulated by tidal range and current speed, the tidal mean SSC increased from 0.5 kg/m3 in neap tide to 3.5 kg/m3 in spring tide. The intratidal variation of the depth-mean SSC can be summarized into three types: V-shape variation in neap tide, M-shape and mixed M-V shape variation in medium and spring tides. The occurrence of these variation types is controlled by the relative intensity and interaction of resuspension, settling and impact of water exchange from the rise and fall of tide. In neap tide the V-shape variation is mainly due to the dominant effect of the water exchange from the rise and fall of tide. During medium and spring tides, resuspension and settling processes become dominant. The interactions of these processes, together with the sustained high ebb current and shorter duration of low-tide slack, are responsible for the M-shape and M-V shape SSC variation. Weakly consolidated mud and high current speed cause significant resuspension and remarkable flood and ebb SSC peaks. Settling occurs at the slack water periods to cause SSC troughs and formation of a thin fluff layer on the bed. Fluxes of water and suspended sediment averaged over the neap-spring cycle are all seawards, but the magnitude and direction of tidal net sediment flux is highly variable.

ADCP 표층유속 자료처리방법 개선을 통한 영산강 하구 표층 방류수 이류속도 산정

It has been customary to exclude top 10-20% of velocity profiles in the Acoustic Doppler Current Profiler (ADCP) measurement due to side lobe effects at the boundary. To better understand the mixing in the Yeongsan estuary, the freshwater advection speed (FAS) was recovered from highly contaminated ADCP data near the surface. The velocity profiles were measured by using ADCP at two stations in the Yeongsan estuary during August 2011: one was located in front of the Yeongsan estuarine dam and the other was deployed near Goha Island. The FAS was recovered from the ADCP data set by applying rigorous post-processing methods and compared with the sediment advection speed (SAS). The SAS was determined by the peak time difference of suspended sediment concentration between two stations in the channel, divided by the distance of two stations. The FAS and the SAS showed very similar value when the freshwater discharge was greater than ton and the SAS was a bit greater when the freshwater discharge was smaller. Since the FAS was on average about 0.8 m/s greater than the velocity at 0.8 of water depth from the bottom, the net discharge, estimated with recovered FAS and integrated over water depth and tidal cycle, was directed seaward during the high discharge contrary to the onshore direction of the net discharge estimated with 0.8 of water depth from the bottom. Moreover, the velocity shear and Richardson number changed when the FAS was used. Thus, the importance of the true FAS is appreciated in the investigation of the surface layer stability. If currents, temperature and salinity were observed for longer time in the future, it could be possible to more accurately understand the formation and decay of stratification as well as the suspended sediment transport processes.

Improved Understanding of Suspended Sediment Transport Process Using Multi-Temporal Landsat Data: A Case Study From the Old Woman Creek Estuary (Ohio)

We used historical water quality data, continuous in situ water quality monitoring data, and multi-temporal Landsat-7 ETM+ imagery for the period of September 1999-April 2003 to study the distribution of total suspended sediments (TSS) in Old Woman Creek (OWC), a freshwater coastal wetland adjacent to Lake Erie. A multiple linear regression model was developed to describe the relationship between turbidity and atmospherically corrected reflectance from Landsat-7 ETM+ bands 2 and 4 (R2 = 0.65). Turbidity was then converted to total suspended sediments (TSS), based on in situ historical data. Mapped spatial patterns of TSS provided useful information on key physical drivers affecting the transport process of suspended sediment. This study demonstrates the potential and limitations of using medium- spatial scale multispectral data, such as Landsat, to understand important factors that control suspended sediment transport processes within an estuary.

An overview on the use of backscattered sound for measuring suspended particle size and concentration profiles in non-cohesive inorganic sediment transport studies

For over two decades, coastal marine scientists studying boundary layer sediment transport processes have been using, and developing, the application of sound for high temporal–spatial resolution measurements of suspended particle size and concentration profiles. To extract the suspended sediment parameters from the acoustic data requires an understanding of the interaction of sound with a suspension of sediments and an inversion methodology. This understanding is distributed around journals in a number of scientific fields and there is no single article that succinctly draws together the different components. In the present work the aim is to provide an overview on the acoustic approach to measuring suspended sediment parameters and assess its application in the study of non-cohesive inorganic suspended sediment transport processes.

Continuous simulation of suspended sediment through a stream section

This paper presents the development of a one-dimensional stream water quality model for the continuous simulation of suspended sediment transport and deposition processes along a particular stream section. The model integrates stream hydraulics and suspended sediment transport and deposition processes. The stream hydraulic model was developed using the Muskingum-Cunge method of channel routing. The well-known suspended sediment processes have been modified and integrated with the developed hydraulic model. The developed model was applied and simulated for the Saltwater Creek, Gold Coast, Australia. Sensitivity analysis of the model showed that all the particles’ characteristics within the incoming stream flows are important for the better prediction of suspended sediment loads.

A study of sediment transport in the Madeira River, Brazil, using MODIS remote-sensing images

The Madeira River may contribute nearly half of the Amazon River sediment discharge to the Atlantic Ocean, showing the highest erosion rates in the Amazon Basin. However, few studies have assessed the Madeira River sediment budget and the transport processes occurring in the main stem of the river. In this study, MODIS space-borne sensors were used to analyze the suspended sediment transport processes along the main stem of the Madeira River. Field measurements of suspended sediment concentration, spectral radiometry and granulometry were performed during 10 cruises from 2007 to 2011. The relationship between the spectral reflectance and the surface suspended sediment concentration (SSSC) was analyzed using both field radiometric measurements and satellite data. Ten-day SSSC samples acquired by the HYBAM monitoring network were used to match satellite observations with field measurements performed from 2000 to 2011. Over 900 MODIS images of 6 different locations were processed to monitor the SSSC dynamics in space and time. Satellite reflectance was found to be significantly correlated with the SSSC. However, a seasonal dependency was demonstrated, most likely caused by a variable granulometric distribution along the annual cycle. The ratio between the red and near-infrared bands was found to be free of the seasonal dependency (r = 0.79, N = 282), and a SSSC retrieval model was built from the satellite data using a bootstrap resampling technique. The satellite-retrieved SSSC time series showed excellent accuracy over the 11-year period and at two different stations located 800 km from each other. The satellite data were averaged to analyze the SSSC pattern temporally and spatially along the entire Madeira River, which provided evidence of significant sedimentation and resuspension. The backwater effect caused by the two-to-three-month lag between peak water in the Madeira and Amazon Rivers was used to predict local sedimentation near the Madeira River mouth. Our results facilitated a precise assessment of such sedimentation, which demonstrated an SSSC decrease 400 km upstream from the Madeira–Amazon confluence.

Transport capacity models for unsteady and non-equilibrium sediment transport in alluvial channels

This study investigates transport capacity models based on different dominant variables-shear stress, stream power, unit stream power, flow discharge, flow velocity, and energy slope – in a model of unsteady and non-equilibrium sediment transport in alluvial channels. The model simulates fully coupled system of water flow, suspended sediment, and bed load sediment transport processes in two-layer system of water flow phase and movable bed. The model employs conservation of mass equation for the water in both the layers; suspended sediment in the water flow phase; sediment in the movable bed layer; and the momentum equation for the water flow in the flow phase. The system is closed by relating the sediment flux in the movable bed layer to the sediment concentration in the same layer by employing the kinematic wave theory. Using the sediment transport capacity expression with different dominant variables, a series of numerical experiments are carried out for unsteady and non-equilibrium sediment transport. The results seem theoretically reasonable for hypothetical cases. The model is calibrated and validated using different experimental data sets. The calibrated value for the transport capacity model’s exponent (ki) is found to be 1.50, 1.65, 0.24, 0.56, 4.80, and 0.22 for shear stress, stream power, unit stream power, discharge, velocity, and slope approaches, respectively. The numerical investigation results show that transport capacity model based on any dominant variable can be employed for modelling unsteady and non-equilibrium sediment transport.

Sediment transport over an accretional intertidal flat with influences of reclamation, Jiangsu coast, China

This paper focuses on the hydrodynamic and suspended sediment transport processes in response to sequential reclamations over the intertidal flat, Jiangsu coast, which used to be one of the widest intertidal flats in China. Investigations into the sediment transport patterns reveal that net suspended sediment fluxes increased from 102kgm−1 on the upper intertidal flat to 103–4kgm−1 on the lower intertidal flat, per tidal cycle. This variation was caused mainly by the phases of the current velocity, suspended sediment concentration (SSC), local bed geomorphology, inundation patterns, and extreme weather conditions. The longshore component of tidal currents intensifies seaward over the intertidal flat. Extreme weather conditions (e.g. storms) and strong winds were important factors affecting the current velocity structures, the intensity of residual currents, and the SSCs. The SSCs were characterized by several peaks throughout the tidal cycle. These peaks were associated with strong currents, combined wave-current interactions and intense turbulences due to the initial flood surge. Furthermore, the suspended sediment was finer and contained more clay materials during the flood phase of the tidal cycle, than during the ebb. Fine particles were transported within the upper water column by landward residual currents, but coarse particles were transported within the lower water column by seaward residual currents. Overall, residual currents were apt to transport fine-grained sediment landward and coarse-grained sediment seaward. This pattern indicates that the suspended sediment fluxes are highly variable in the water column, even for very shallow tidal environments. The cross-shore component accounted only for a small percentage of the total sediment flux. However, this part of sediment supply dominated accretion over the intertidal flat.The intertidal flat has become narrower and steeper, following sequential reclamations. A negative feedback process existed to maintain the convex profile shape, although the human activities (i.e. reclamation) could have modified the natural process. The surficial sediment tended to become finer on the mid-upper intertidal flat but coarser on the lower intertidal flat following reclamations, in response to a reduction in the tidal currents over the intertidal zone and enhancement of wave action over the lower intertidal flat. Accretion, with high rates, was maintained by landward transport of sediment. In such an accretional system with influences of reclamation, the width or slope of the intertidal flat is adjusted continuously. Before the cease of reclamation, the intertidal flat is unable to achieve an equilibrium shape.

Dual Behavior of Suspended Sediment Concentration in a Regulated River

Better understanding of suspended sediment transport processes allows for better management of both rivers and coasts. Based on field data and sediment transport energy theory, this study presents an analysis on the suspended sediment hysteresis in the Lower Tenryu River of Japan in connection to the channel carrying capacity of suspended sediment and morphological characteristics. The transport of suspended sediment in the river exhibited dual behaviors according to the magnitude of flood. It was transport-limited in a 10-year flood while supply-limited in a 30-year flood. In the supply-limited case, the temporal variation of suspended sediment concentrations followed the hydrograph well. In the transport-limited case, however, there was a time lag between peak discharge and maximum suspended sediment concentration. The mechanism of time lag was further clarified to be different for the 10-year flood and a small flood. The objective of this paper is to shed some new light on the relationship of suspended sediment to flow and channel conditions.

Cross-shore suspended sediment flux in the salt marsh pioneer zone of Chongming eastern beach in the Changjiang Estuary in China

Between April 2002 and April 2003, in situ measurements of water depth, current velocity and suspended sediment content were carried out in edge region of East Chongming salt marsh and neighboring bald flat in the Changjiang (Yangtze) Estuary under different weather conditions. Cross-shore suspended sediment flux was calculated and analyzed. The results show that under calm weather conditions, the current velocity process in bald field and salt marsh area varied differently during semidiurnal tidal cycles. Owing to current velocity asymmetry, mean SSC during flood tide phase was 1.8 times higher than that of ebb tide phase. As a result, net onshore sediment flux controlled cross-shore suspended sediment transport process and salt marsh pioneer zone was generally accreting. There was significant positive correlation between total sediment flux and quartic power of maximum water depth. It indicates that tidal ranges dominate suspended sediment transport and sedimentation process in the salt marsh pioneer zone under the calm weather condition. The sedimentation rate on the adjacent mudflat was higher than the salt marsh, which induced stable accreting of salt marsh towards the sea. The wind events enhanced SSC and current velocity during the semidiurnal tides. And the remarkable onshore net sediment flux could occur on the high marsh and mudflat close to the marsh fringe during the short period under the rough weather condition.

Geomorphological dynamics of subhumid mountain badland areas — weathering, hydrological and suspended sediment transport processes: A case study in the Araguás catchment (Central Pyrenees) and implications for altered hydroclimatic regimes

This study investigates the geomorphological dynamics of badland areas in the Araguás catchment (0.45 km2) in the Central Pyrenees. The genesis and development of badlands in the Central Pyrenees is favoured by the presence of Eocene marls and a markedly seasonal climate. The Araguás catchment has been monitored since 2004. Analysis of weathering processes and regolith dynamics showed that alternating freeze-thaw and wetting-drying cycles are the main causes of regolith development and weathering, and effectiveness and intensity of these processes is maximum in winter and summer. Evolution of the badland surfaces is related to regolith moisture level and temperature, closely associated with the season and slope exposure, which cause cyclical variations in regolith physical conditions. The most important effect associated with regolith dynamics is the temporal delay between maximum rainfall erosivity and variation in maximum surface runoff generation, reflected in seasonal differences in sediment transport. The dynamics of weathering and erosion processes affecting badland areas are the principal factors controlling geomorphological development, and the extreme hydrological and sedimentological responses of badlands are the main effects of such morphologies. From a hydrological point of view, badlands increase water production, and flood frequency relative to neighbouring areas; from a sedimentological point of view, suspended sediment transport from badland areas can reach amounts two or three orders of magnitude higher than other nearby environments. Given these results, possible responses of badland dynamics to altered hydroclimatic regime are briefly discussed.

Field Observation on Suspended Sediment Transport Process off Tidal Flat in Upper Ariake Bay

A field measurement was carried out to elucidate fine sediment transport processes off the north-western shore of the Ariake Bay, Japan. Time series data analysis of hydrodynamic forcing and suspended sediment properties shows that the increments of suspended sediment concentration during a tidal cycle under spring tide condition are due to multi processes including both local resuspension by strong tidal current and advection effect of turbid water from near shore region. The field data also shows the variability in the suspended sediment properties such as settling velocity and particle size over a tidal cycle indicating relatively higher settling velocity during ebbing tide and finer median grain size during low tide.

Modeling Sediment Suspensions in an Idealized Tidal Embayment: Importance of Tidal Asymmetry and Settling Lag

Suspended sediment transport processes in a short tidal embayment with a simple geometry are investigated using analytic and numerical models. On the basis of numerical results, the horizontal gradient of depth-averaged suspended sediment concentration can be parameterized with a combination of the first harmonic and mean. Using the parameterization, the solution of the analytic model is obtained. Evaluation of the major terms from the solution of the analytic model shows that a quarter-diurnal frequency is significant near the mouth while a semidiurnal component dominates the interior area. The settling lag consists of local and nonlocal components. The local phase lag is a function of the ratio between tidal period and settling time. The nonlocal phase lag is determined by the phase difference between tidal velocity and the horizontal gradient of sediment concentration and by the strength of erosion and horizontal advection.

Imaging of Large‐Scale Sediment Transport Dynamics with Multibeam Sonar

Multibeam Echo‐Sounder (MBES) systems have developed rapidly over recent decades and are routinely deployed to provide high‐resolution bathymetric imaging. Modern data handling and storage technologies have facilitated the logging of the back‐scatter information previously discarded by these systems. This paper develops a novel methodology to exploit this logging capability to quantify the concentration and dynamics of suspended sediment within the water column. This development provides a multi‐purpose tool for the holistic surveying of sediment transport by imaging suspended sediment concentration, associated flow structures and providing concurrent high‐resolution bathymetry. This paper presents the results obtained from the deployment a RESON 7125 MBES in the field, with the aim of examining the dynamics of suspended sediment transport over dune bedforms and in the region of flow mixing between large rivers of significantly different suspended sediment concentration. Results from controlled tank tests are also presented, obtained using different types and mixes of sediment. The results demonstrate the capability of MBES systems to successfully resolve the contrast in suspended sediment concentrations. The large sets of data recorded in the two‐dimensional MBES swath enables the real‐time monitoring of suspended sediment transport and related flow processes on a scale previously unrealisable with single‐beam acoustic systems.

Calibrating multi-frequency acoustic backscatter systems for studying near-bed suspended sediment transport processes

The utilisation of sound backscattered from sediments in suspension, to measure profiles of near-bed particle size and concentration, has been gaining increasing acceptance and usage by sedimentologists and coastal engineers over the past two decades. To obtain the sediment parameters from the backscattered signal requires an inversion to be conducted on the signal and this necessitates a system calibration. The calibration can be carried out by detailed acoustic and electronic measurements, or alternatively by measuring the backscattering from suspensions with known scattering characteristics. Here, we explore the latter approach and describe in some detail the calibration of a triple frequency acoustic backscatter system. The aim is to provide coastal scientists involved in using acoustics as a tool for sediment transport research, with a clear exposition of the calibration process. Suspensions of glass spheres of varying particle size were used as the calibration scatterers. To interpret the signal backscatter from the suspension of glass spheres a simple model for sphere scattering is presented. The results show that consistent calibration results can be obtained in a relatively simple and robust manner.