Suspended Load Concentration Research Articles

Numerical modelling of local scour around a spur dike with porous media method

ABSTRACT A 3D numerical model is developed to investigate the flow motion and sediment transport around a spur dike. In this model, fluid motion is described by the Navier–Stokes equations, adopting large eddy simulation to capture turbulent transport and dissipation. The spur dike and sand bed are treated by the porous media method. The suspended load concentration and the bed load transport rate is calculated separately, and then the bed variation is updated using the mass-balance equation. A series of flume experiments are employed to validate the model’s performance before being applied for the case of partially emergent spur dikes and submerged spur dikes, respectively. Detailed analyses on the spatial-temporal variation of flow intensity, sediment concentration and shapes of scour holes are made, based on which some innovative findings are discussed such as the scouring process patterns, as well as the influence of flow conditions on the maximum scour depth and location, and then useful engineering suggestions are provided to improve structural safety.

A MATLAB GUI program for reservoir management to simultaneously optimise sediment release and power generation

Sedimentation affects the normal function of reservoirs and is a decisive factor in the reservoir's service life. Flushing sediment during reservoir operation is an effective non-engineering measure to alleviate reservoir sedimentation; however, lowering water level to discharge more flow conflicts with hydropower generation. In this study, reservoir management software is developed to simultaneously optimise sediment discharge and hydropower generation with the reservoir discharge as the decision variables. The sediment transport rate is calculated by an integral of the vertical distribution of suspended load concentration and flow velocity instead of empirical formulas. The model is solved by the most widely used multi-objective optimisation algorithm NSGA-II, resulting in the optimal schedule corresponding to the maximal sediment discharge and hydropower generation, which can be displayed graphically in the software. The software was developed in MATLAB with a Graphical User Interface (GUI) and applied to a large reservoir and can be generalised to other reservoirs. The results show that within the recommended discharge variation of 5%, the sediment release can be increased by 2.07 × 106 t as a reduction of per 1010 kW h in annual power generation. Compared with the original scheme, sediment release can be increased most by 3.31% at the cost of 0.03% loss of power generation. Moreover, the dual objective in the flood season was optimised by 7.30% and 3.92%, respectively.

Analysis of the evolution pattern and causes of downstream gigantic hydraulic projects

Abstract The Jingjiang reach, located in the middle Yangtze River, downstream of the Three Gorges Reservoir (TGR), is a typical curved reach. After TGR impoundment, the evolution behaviors of the Jingjiang reach changed, mainly because one or more original factors, including geological conditions, existing projects, bending radius, upper reaches' regimes, and incoming water and sediment changed. In this paper, these influencing factors were investigated by using the measured data and the mathematical models that were proposed by the authors in a previous paper, and consequently, the evolution laws of the curved reach were analyzed. The results showed that the existing river nodes reduced the influence of the upstream river regime on the evolution of curve reaches and also slowed the speed of convex bank scouring and concave bank depositing. Constructed projects could reduce sediment transport intensity from the concave bank to the convex bank. The decrease in incoming sediment after TGR impoundment was beneficial to convex bank scouring. The increase in median water period duration was favorable for convex bank scouring and concave bank depositing. Both convex bank and concave bank were scoured when the incoming sediment concentration decreased sharply. The sediment concentration of suspended load would stabilize near the saturation point, and the riverbed would be scoured when there is sediment concentration under the saturation point, while the riverbed would be deposited when the sediment concentration reaches the saturation point.

Pre-development denudation rates for the Great Barrier Reef catchments derived using 10Be

Understanding of the pre-development, baseline denudation rates that deliver sediment to the Great Barrier Reef (GBR) has been elusive. Cosmogenic 10Be in sediment is a useful integrator of denudation rates and sediment yields averaged over large spatial and temporal scales. This study presents 10Be data from 71 sites across 11 catchments draining to the GBR: representing 80% of the GBR catchment area and provide background sediment yields for the region. Modern, short-term, sediment yields derived from suspended load concentrations are compared to the 10Be data to calculate an Accelerated Erosion Factor (AEF) that highlights denudation “hot-spots” where sediment yields have increased over the long-term background values.The AEF results show that 58% basins have higher modern sediment yields than long-term yields. The AEF is considered a useful approach to help prioritise on-ground investments in remediation and the additional measured empirical data in this paper will help support future predictive models.

Sediment and morphological changes along Yangtze River\u2019s 500\xa0km between Datong and Xuliujing before and after Three Gorges Dam commissioning

The impoundment of the Three Gorges Dam on the Yangtze River begins in 2003 and a full pool level is first attained in 2010. This process leads to reciprocal adjustments in flow discharge, sediment transport and morphology downstream of the dam. Based on 26-year recorded hydrologic data 1990–2015 and surveyed bathymetries 1998, 2010 and 2015, this study elucidates, before and after the commissioning of the dam, the alterations along the 500-km reach of the river. Two-dimensional numerical simulations are performed to predict future morphological changes by 2025. The analyses demonstrate that the impoundment modulates the seasonal flow discharges and traps an appreciable amount of sediment, resulting in enhanced erosion potential and coarsening of sediment. On a multi-year basis, the maximum discharge varies by a factor of 1.3 and the corresponding suspended load concentration and transport rate differ by a factor of 3.0 and 3.8, respectively. Combinations of surveyed and simulated bathymetries reveal its morphological responses to the changes. A general pattern of erosion is observed along the reach. In its upper 120 km, the process slows down towards 2025. In the middle 200 km, the erosion shifts, following the gradual impounding, to slight deposition, which then shifts back to erosion around September 2018. In the final 180 km, erosion continues without any sign of de-escalation, which is presumedly ascribed to tidal actions. The reach has not yet achieved a hydro-morphological equilibrium; the riverbed down-cutting is supposed to continue for a while. The combination of the field and numerical investigations provides, with the elapse of time, insight into the morpho-dynamics in the 500 km river reach.

Investigation of the sediment transport capacity in vegetated open channel flow

The suspended sediment transport capacity is important for estimating the suspended load concentration and the ecological environment of the river. So far, few studies have been conducted to investigate the suspended sediment transport capacity in the vegetated sediment-laden flow. In this study, a new formula is derived to predict the sediment transport capacity in a vegetated flow by considering the absolute value of the energy loss between the sediment-laden flow and the clear water flow. Finally, the formula is expressed in a practical form by using the logarithmic matching method.

Contributions of suspended load from Missouri River tributaries, southeast South Dakota, and northeast Nebraska: Building a sediment budget

AbstractSuspended sediment plays a critical role in riverine ecosystem health and river processes and is respondent to human alterations such as dams and increased land use. Gavins Point Dam, located on the Missouri River near Yankton, South Dakota, restricts upstream suspended load; yet, suspended sediment concentrations (SSC) increase when the river reaches Sioux City, Iowa. We determined the suspended load concentrations of seven tributaries of the Missouri River entering downstream of the dam. These data were collected from 2012 to 2019 during the summer months of May–July using a depth‐integrated sampler. Sediment rating curves were created based on discharge and SSC. We constructed a simple sediment budget, which indicated that the tributaries located in South Dakota contribute the bulk of the Missouri River's suspended load at ~80%, while the Nebraska tributaries contribute <5%. The remaining sediment is likely supplied by bank and bed erosion. Temporal changes were examined by comparing our recent measurements with historical data from USGS gaging stations on the James River and the Big Sioux River. Suspended sediment and discharge have increased by nearly an order of magnitude, potentially due to increases in precipitation and land use. Sediment budgets are useful resources for informing river management plans on a basin‐wide scale. Given the drastic, long‐term impacts of disruptions to sediment and flow regimes from dams and climate change, this research provides necessary groundwork for remediation efforts and river management.

Study on the influence of ecological vegetation revetment on river flow and sediment environment

AbstractThis paper studied the influence of vegetation cover on the river water flow environment and on sediment suspended load movement environment, closely combining the development and construction of new ecological water conservancy projects such as ecological embankments and ecological wetlands with ecological vegetation revetment cultivated on river bank slopes. The glass flume experiment was carried out in the vegetation-water flow-sediment environment. In the experiment, natural straight holly in the early growth stage was selected as the experimental vegetation, and erect type vegetation with uniform distribution of the upper and lower branches and leaves was simulated, and a total of 14 experimental groups were set in different combinations with fixed bed, movable bed, submerged and non-submerged conditions. The measured data of flow quantity, flow velocity and suspended load concentration were achieved in the experiment. The experimental results show that: (1) as to the influence of vegetation on the water flow environment, the vegetation canopy density directly affects the turbulent environment of the water flow, and the greater the density, the greater the disturbance to the water flow environment, and the flow velocity near the canopy will be decreased sharply; (2) in the fixed bed, under submerged conditions, the maximum turbulence intensity appears near z/h = 0.6; under non-submerged conditions, the turbulence intensity near the water surface is largest. In the movable bed, under submerged conditions, the maximum turbulence intensity reaches the maximum in the top and upper locations of the top of the plant, and the turbulence intensity reaches the maximum at the top of the plant under non-submerged conditions. (3) In terms of the influence of vegetation on the sediment suspended load movement environment, the concentration of suspended sediment decreases with the increase of plant height, the sediment content in the tail of the plant belt is reduced to some degree. When the relative water depth is z/h > 0.5, almost no suspended sediment exists. And the sediment-retaining effect under non-submerged conditions is better than that under submerged conditions.

Modelling hyperconcentrated floods in the Middle Yellow River using an improved river network model

In the section of the Middle Yellow River from Longmen to the Sanmenxia Dam, the prediction to hyperconcentrated flood processes is difficult because of the abrupt change of channel geometry along the river and the high variability of the amount of flood water and sediment load from the main river and tributaries. A river network model based on a Godunov-type FVM scheme is proposed in order to investigate the flow dynamics, sediment transport and bed evolution during hyperconcentrated floods. A quasi 2D algorithm is adopted to calculate the velocity at the junction cell, which is then used for providing the interior boundary conditions. The computation for each reach can be executed simultaneously and the solution procedure is parallelized using OpenMP. The speedup factor compared with a serial program increases linearly in theory with the number of reaches in the river network. Two flood events, featuring significant erosion and deposition respectively, were simulated to validate the model. The calculated water levels, discharges and fractional concentrations of non-uniform suspended load were in agreement with the measurements. A comparison was made between the proposed model and an existing model neglecting the momentum conservation principle at the junction, with the former showing better prediction of the peak water levels near the confluence. Numerical experiments were conducted to analyze the influences of reservoir operation and discharge capacity of the dam on flood routing and bed evolution in the river network. It is demonstrated that decreasing pool level during flood season and increasing discharge capacity are both valid measures to alleviate sedimentation in the Sanmenxia Reservoir, and the former measure is a prerequisite. Therefore, the model presented here can help to enhance the understanding of river network system subject to high sediment input and inspire better strategies on sustainable reservoir management.

Prediction of the Suspended Transport Rate of River Reach

A new suspended transport rate equation using field measurements that apply to the Euphrates River’s reach in the upstream direction from the Ramadi barrage in Iraq was developed via multiple linear regression. The governing parameters were carefully chosen based on dimensional analysis and grouped into four parameters: shields, transport, mobility, and particles. The ability of the suspended transport rate equations of Karim-Kennedy and van Rijn were tested. A total of 25 series of field data for which the concentration of suspended load, average flow depth, sediment particle size, flow velocity, and the width of the water surface were applied. A comparison of the suspended transfer rates in the river reach and the calculated transport rates in the modified equation showed good coincidence. The evaluation results showed that the new equation performed better than the three equations used. The performance of the new equation was determined utilizing three statistical criteria (the coefficient of determination, discrepancy ratio and relative error). The computed suspended transport rates were found within a discrepancy ratio of 1.02 for the measured values and a relative error of 13.4%. The performance of the Van Rijn formula performed better, with a discrepancy ratio of 1.26 for the measured values and a relative error 39%, than the other two equations. The percentage of data that ranged between 0.5–2.0 of the discrepancy ratio varied between 72–100% for the three equations and the new equation.

Morphodynamic Responses to the Hong Kong–Zhuhai–Macao Bridge in the Pearl River Estuary, China

Li, M.; Li, W.; Xie, M., and Xu, T., 2021. Morphodynamic responses to the Hong Kong–Zhuhai–Macao Bridge in the Pearl River estuary, China. Journal of Coastal Research, 37(1), 168–178. Coconut Creek (Florida), ISSN 0749-0208.Human activities such as constructing large bridges, performing land reclamation, and creating harbors in complex tidal estuaries can result in severe and undesirable morphodynamic responses. This study investigates morphodynamic responses to the construction of the Hong Kong–Zhuhai–Macao Bridge (HZMB) in Lingdingyang Bay of the Pearl River estuary (LBPRE). The LBPRE in China is an important estuary with unique geomorphic features, complex hydrodynamic sediment conditions, dense shipping routes, high ship density, and a high navigation grade. The HZMB, a major sea-crossing transportation project consisting of bridges, a tunnel, and man-made islands, is being designed to cross the LBPRE. The morphodynamic responses resulting from the HZMB are likely to be significant. Therefore, it is necessary to carry out studies to optimize the HZMB design to minimize its impacts on hydrodynamics, sediment environment, harbors, and navigational channels as much as possible. In this article, the natural hydrodynamic and sediment conditions are first analyzed on the basis of in situ data. Next, a numerical model of tidal current, sediment movement, and seabed deformation based on TK-2D software is set up with an irregular triangular grid. The model is calibrated with in situ data, and the results show that the calculated tidal levels, tidal currents, suspended load concentrations, and seabed deformations are all in good agreement with field data. The model is then applied to carry out high-resolution simulations for design optimization of the HZMB from the perspective of its impacts on morphodynamics and hydrodynamics, as well as on harbors and channels. The study shows that the proposed HZMB design is feasible in terms of the morphodynamic responses. The conclusions provide an important foundation for the construction of the HZMB project.

KORELASI ANTARA DEBIT ALIRAN DAN SEDIMEN MELAYANG (SUPENDED LOAD) DI SUNGAI DATA’ KABUPATEN PINRANG

The hydrological process that occurs in a watershed is related to erosion process, sediment transport and downstream deposition. Land use changes and watershed management practices will also affect erosion and sedimentation. The purpose of this study was to determine the magnitude of flowrate, suspended load concentration (suspended load), and floating sediment discharge and correlation of floated sediment discharge and flowrate at the Data’ River. Measuring river characteristics is done by measuring river water flow and river slope. Sediment collection floated with EWI (equal with incerentment) method. Laboratory analysis was carried out by calculating the amount of flow discharge, sediment concentration, and sediment discharge. The results showed the lowest amount of flow discharge occurred on 17/12/2016 with a value of 0.271 m3/s with a floating sediment concentration of 17.167 mg / L, and the sediment discharge floated at 0.402 tons/day. The correlation between flow discharge and floating sediment discharge using a sccatter diagram shows that the determination value R2 is 0.9754 with the equation y = 0.1x + 0.4355.

A 3-D finite volume model for sediment transport in coastal waters

A 3-D model has been developed to simulate sediment transport and bed change induced by currents and waves in coastal waters. The currents are calculated with the 3-D phase-averaged shallow water flow equations, the wave characteristics are determined with a horizontal 2-D wave spectral transformation model, and multiple-sized non-cohesive suspended load and bed load are simulated using a non-equilibrium transport model. The classical mixing length model is modified to determine the horizontal and vertical eddy viscosity considering the effects of current, waves, and wave breaking. A new approach is proposed in the present 3-D model framework to calculate the bed grain shear stress, which is applied to determine the equilibrium bed-load transport rate and near-bed suspended-load concentration. The flow and sediment transport equations are numerically solved using an implicit finite volume method on a hexahedral mesh constructed with horizontal telescoping (quadtree) rectangular cells and vertical sigma coordinate. The difference in the near-bed cells for flow and suspended load calculations is avoided by adding the bed load to the suspended load in the first flow cell above the bed. The developed model has been tested in four laboratory and field cases. It reasonably well reproduces the measured water levels, flow velocities, sediment concentrations, and bed changes.

Co-genetic, cohesive and non-cohesive delta front facies: A case study of flow transformation in a lacustrine setting, Camaquã Basin, southernmost Brazil

Sediment gravity flows comprise gravity-driven underflows with a large concentration of suspended load. Along the downslope transport, flow transformations from laminar to turbulent conditions or vice-versa can take place due to several factors, including the incorporation and segregation of clay into, or from the flow. These flow changes may produce hybrid behavior and resulting hybrid event beds. Flow transformation and hybrid events are widely discussed in marine settings, but studies on lacustrine environments are rare. The Ediacaran Western Santa Bárbara Rift represents one stage of the development of the Camaquã Basin and includes both cohesive (debrites) and non-cohesive (turbidites) gravity flow deposits associated with braidplain deltas deposited in shallow lake. A range of cohesive and non-cohesive density flow facies is here discussed in terms of triggering mechanism, genetic processes and related flow transformations. The analysis of aerial images combined with outcrop descriptions allowed the identification and mapping of key stratigraphic surfaces and therefore associated systems tracts. Sedimentological and gamma-ray logs, sampling and laboratory analyses (optical microscopy, X-ray diffraction –XRD - and Scanning Electron Microscopy – SEM) were performed to define facies and facies associations. Microscopy was useful to identify vermiculite as an important matrix component. The position of distinct facies within the genetic stratigraphic framework allowed the construction of a generalized facies tract model. The basinward shift of facies indicates three flow transformations, in addition to hybrid flows. Substrate erosion, and ensuing incorporation and fragmentation of mud clasts into turbulent flows caused changes from fluidal to plastic flow rheology. Generalized facies tracts suggest fluvial floods (and resulting hyperpycnal flows) as the triggering mechanism for the subaqueous density flows herein described.

Simplified Entropic Model for the Evaluation of Suspended Load Concentration

Suspended sediment concentration is a key aspect in the forecasting of river evolution dynamics, as well as in water quality assessment, evaluation of reservoir impacts, and management of water resources. The estimation of suspended load often relies on empirical models, of which efficiency is limited by their analytic structure or by the need for calibration parameters. The present work deals with a simplified fully-analytical formulation of the so-called entropic model in order to reproduce the vertical distribution of sediment concentration. The simplification consists in the leading order expansion of the generalized spatial coordinate of the entropic velocity profile that, strictly speaking, applies to the near-bed region, but that provides acceptable results also near the free surface. The proposed closed-form solution, which highlights the interplay among channel morphology, stream power, secondary flows, and suspended transport features, allows reducing the needed number of field measurements and, therefore, the time of field activities. Its accuracy and robustness were successfully tested based on the comparison with laboratory data reported in literature.

Multibeam Bathymetric Investigations of the Morphology and Associated Bedforms, Sulina Channel, Danube Delta

In the Danube Delta, on the Sulina branch, the morphology, sediment, and bedform characteristics were investigated. Three-dimensional (3D) bathymetry, flow velocity, suspended-load concentration, and liquid and solid discharge data were acquired throughout several cross sections along the Sulina channel, in order to investigate the distribution of water and sediment discharges and their influence against the river bed. A single observation (in February 2007) was made regarding the geometry, sediment composition, and hydraulic conditions under which the dunes grew and degenerated. The investigation focuses here mostly on the geometrical parameters of these bedforms, such as height, length, as well as grain size characteristic of the sediment and water dynamics. Based on in-site measurements, different hydraulic parameters were calculated, such as bed shear stresses and Reynolds number. During the field campaign, the measured water mean velocity was from v = 0.22–1.13 m∙s−1. At the same time, the measured range of shear stresses within the dune field formation was from τ0 = 2.86 N·m−2 (on the cutoffs) to 8.62 N·m−2 (on the main channel). It was found that the correlation between height (H) and length (L) of the Sulina branch dunes describes the formula: H = 0.093L0.5268. The bedforms of the Sulina channel are, in general, developed in fine sand (D50 between 0.06 and 0.35 mm).

Towards an establishment of a rating curve for suspended sediment transport by means of ADCP measurements

This study presents a series of acoustic current Doppler profiler (ADCP) measurements, which are converted into suspended load concentrations (SSC). Depending on the particle size distribution (PSD), the sound backscatter and its attenuation are used to determine a theoretical minimal and physical upper limit of the SSC. The SSC are displayed over time and compared with the evolution of the water level during the same time interval. The present study shows that it is possible to have continuous measurements of SSC and water level with a horizontally installed two beam equipped ADCP and discusses the potential of such a continuing times series measurement for application in hydraulic engineering and research. However, the presented data set shows also that the calibration and the filtering of the raw data has to be improved and that further investigations are needed. After data verification, it will be possible to calculate the yearly sediment load and investigate physical behaviour of SSC concentration as a function of water level and discharge.

Bed Load Pickup Rate and Flow Resistance for Turbid Flow on a Movable Plane Bed

This study investigates bed load transport and flow resistance in alluvial channels that contain fine suspended sediment. In all, 123 samples were run in a laboratory flume over uniform bed materials. Different hydraulic conditions were considered in an 8.0 m-long, 0.255 m-wide, and 0.6 m-deep tilting flume. Unit flow discharge ranged from 3.176 × 10−3 to 18.640 × 10−3 m2 s−1, and the slope gradient varied from 2% to 5%. Two sediment-size classes (median diameter, d50, of 1.7 and 3.29 mm) and five suspended load concentrations (10, 20, 30, 40, and 50 g/L) were used. A preliminary analysis showed that the bed load pickup rate increases with an increase in the concentration of suspended particles. Dimensional analysis, which was performed satisfactorily on the bed load transport data, indicated that shear stress is the dominant parameter in bed load pickup. Moreover, the resistance of turbid flow in a channel with an erodible bed was studied. The net results were found to be an increase in the flow resistance over a movable plain bed by increasing suspended load concentration. In other words, increasing suspended particles increased the mobility of bed material and led to a higher friction factor. Special attention was paid to the separation of the friction coefficient between boundary resistance and mobile-bed resistance caused by the mobility of bed materials. The results showed that the damping effect of suspended sediment caused lower boundary resistance with increasing suspended load concentration. On the other hand, suspended particles increased the mobility of bed materials and led to a higher mobile-bed resistance. Analysis indicates that the relative importance of mobile-bed resistance is more than the boundary friction for the high bed load transport rate. Therefore, the damping effect of the suspended sediment on boundary friction can only be observed for low sediment transport or a fixed bed.

The formation of single-channel and multiple-channel rivers on large slopes

We investigated the formation of different types of rivers depending on slope, total discharge, and grain size. Calculations were performed using numerical package CCHE2D, developed by the National Center for Computational Hydroscience and Engineering. The model is based on the Navier-Stokes equations for depth-integrated two-dimensional turbulent flow and the three-dimensional convection-diffusion equation of sediment transport. For each model we use the same river geometry, suspended load concentration, and bedload transport rate. We distinguish three types of rivers using two methods for classification (single-channel, multiple-channels and transitional). We found that the trend line for transitional rivers is an increasing function of Q in space (Q, d) and that for large S the number of multichannel rivers decreases.

BARRAGEM DE PORTO PRIMAVERA E O TRANSPORTE FLUVIAL NA SEÇÃO DE PORTO SÃO JOSÉ, RIO PARANÁ

The Porto Primavera Dam caused the decrease of the concentration of suspended load and reduction of the size of the bed forms of Parana River, but the effects of the construction on fluvial transport have not yet been quantified. In order to do that, this paper aims to evaluate the influence of the dam on the sediment transport in the section of Porto Sao Jose. Thus, data of Porto Sao Jose Fluviometric Station, field and orbital images information available in literature were used. The data were analyzed by linear regression to obtain significant correlation between sediment transport and river discharge. The equations with significant coefficient of determination were used to estimate the annual average transport for different time periods. The suspended transport before construction was 214.1 kg/s, increased to 222.2 kg/s during construction and decreased to 56.4 kg/s after completion of the dam. The bed load transport was 99.7 kg/s during the construction, decreased to 86.2 kg/s during 1999 and 2000 and to 41.2 kg/s after 2001. In the same period the total transport decreased from 321.9 kg/s to 177.8 and finally to 91.2 kg/s. These results indicated that the Porto Primavera Dam reduced 74.6% of the suspended transport, 58.7% of the bed load transport, 71.7% of the total transport and increased the proportion of the bed load of 33, 9% to 44.5% of total.