Distribution Of Suspended Sediment Concentration Research Articles

Measuring and modeling vertical gradients in suspended sediments in the Solimões/Amazon River

AbstractAccurately measuring sediment flux in large rivers remains a challenge due to the spatial and temporal cross‐sectional variability of suspended sediment concentrations in conjunction with sampling procedures that fail to accurately quantify these differences. This study presents a field campaign methodology that can be used to improve the measurement of suspended sediment concentrations in the Amazon River or similarly large rivers. The turbidity signal and Rouse model are together used in this study to define the spatial distribution of suspended sediment concentrations in a river cross‐section, taking into account the different size fractions of the sediment. With this methodology, suspended sediment fluxes corresponding to each sediment class are defined with less uncertainty than with manual samples. This paper presents an application of this methodology during a field campaign at different gauging stations along a 3,000‐km stretch of the Solimões/Amazon River during low water and flood periods. Vertical concentration profiles and Rouse model applications for distinctive sediment sizes are explored to determine concentration gradients throughout a cross‐section of the river. The results show that coupling both turbidity technology and the Rouse model may improve our understanding of the spatial distribution of different sediments fractions sizes in the Solimões/Amazon River. These data are very useful in defining a pertinent monitoring strategy for suspended sediment concentrations in the challenging context of large rivers.

Acoustic measuring techniques for suspended sediment

Acoustic signals can be used in various ways for suspended sediment monitoring. One possibility which lends itself particularly well in the context of hydropower plants (HPPs), is to use installations for acoustic discharge measurement (ADM). Such installations already exist at waterways of many HPPs. Similar to certain turbidimeters, the attenuation of the forward scattered signal travelling through the water-sediment mixture is correlated with suspended sediment concentration (SSC). This correlation can be based on reference SSCs, e.g. from gravimetric analyses of bottle samples. Without the need of additional sensors and practically maintenance-free, this method is used successfully in the HPP Fieschertal to warn the HPP operator of high SSC to prevent excessive turbine abrasion.Acoustic methods and systems that allow for estimating both SSC and particle size distribution (PSD) are under development. The simultaneous determination of SSC and PSD is not possible using a single frequency. Therefore, multi-frequency approaches are investigated for generally scattered signals. When backscattered signals are used, a stronger frequency dependency can be exploited. However, the reliable simultaneous determination of particle size (and distribution) and concentration is still a major challenge due to a low signal-to-noise ratio and an ill- posed problem of estimating concentration and size from recorded signals. The optimal setup configuration (angles, frequencies) for such a system is not unique and further investigations are recommended.

Distribusi Kecepatan dan Konsentrasi Sedimen Suspensi pada Aliran Menikung (Studi Kasus pada Saluran Irigasi Mataram Yogyakarta)

The flow velocity and suspended sediment concentration are important parameters of sediment transport mechanisms, especially for agradation and degradation problems. The centrifugal force at the bend channels will increased flow velocity at the outer bank of the bend. It is of course also affects the distribution of flow velocity toward the outside and the inside of the bend channels. The change of the velocity distribution it is very possible also changes the distribution of suspended sediment concentration. In this paper will discuss the velocity distribution profile and distribution of sediment concentration in the bend flow. This research was conducted at Mataram Irrigation Channel Yogyakarta. The channel rectangular in shape and made of masonry with angle bend 580. Measuring the flow velocity used Propeller currentmeter and sediment concentration used Opcon Probe. Measuring flow velocity and sediment concentration conducted simultaneously for each measurement point.The results showed that due to the centrifugal force in bend flow, flow velocity distribution and sediment concentration distribution undergoing significant change the outside and the inside of the bend. In general, the distribution of flow velocity toward the outerbank of the bend has increased and the distribution suspended sediment concentration has decrease and the opposite occurs innerbank of the bend. A low velocity on the inner bank of the channel bend causes larger grains of sediment that settles and potentially silting.

Turbidity maximum formation and its seasonal variations in the Zhujiang (Pearl River) Estuary, southern China

Real-time observations in the field and numerical simulations (with Delft3D) were combined to study the formation, distribution and the relevant influencing factors of turbidity maximum (TM) in the Zhujiang (Pearl River) Estuary (ZE). The spatial distribution pattern of the TM varies with the longitudinal distributions of salinity and suspended sediment concentration (SSC). The SSC is enhanced and the TM is intensified during dry seasons, whereas the center of the TM moves upstream by a distance of 10 km during wet seasons. The formation of the TM is influenced by a complex combination of numerous factors, including tides, river discharges and topography, wherein sediment resuspension and vertical circulation dominate the formations and variability of the TM.

A multiple-state discrete-time Markov chain model for estimating suspended sediment concentrations in open channel flow

Transport processes of uniform size sediment particles in steady and uniform flow are described by a multi-state discrete-time Markov chain. The multi-state discrete-time Markov chain is employed to estimate the suspended sediment concentration distribution versus water depth for various steady and uniform flow conditions. Model results are validated against available measurement data and the Rouse profile. Moreover, the proposed model is used to quantify the average time required to reach dynamic equilibrium of particle deposition and entrainment processes. Firstly, suspended sediment concentrations under three different flow conditions are discussed. As the Rouse parameter decreases, the difference between the suspended sediment concentration estimated by the Markov chain model and the Rouse profile becomes more significant, and is larger for higher relative height from the bed. It is speculated that the use of the terminal settling velocity in the transport process can lead to underestimation of the residence probability and overestimation of the deposition probability. Secondly, laboratory experiments are used to validate the proposed model. It is observed that as the Rouse parameter decreases, more time is required for the sediment concentration to reach a dynamic equilibrium. The flow depth is found to have an impact on the time spent to reach the concentration dynamic equilibrium. It is recognized that the performance of the proposed model relies heavily on the knowledge of the vertical distribution of the turbulence intensity. Also, for lower Rouse parameters, concentrations estimated by the Markov chain model exhibit larger variation compared to those estimated by the Rouse profile.

Remote sensing observations and numerical studies of a super typhoon-induced suspended sediment concentration variation in the East China Sea

By integrating remote sensing observations and a numerical modeling technique, we studied the influences of super Typhoon Saomai on the suspended sediment concentration (SSC) in the Yangtze River estuary and its adjacent coastal areas in the East China Sea. First, three consecutive Moderate Resolution Imaging Spectroradiometer (MODIS) images acquired during the post-typhoon stage were used to estimate the SSC. Then, we implemented a hydrodynamic model, including a sediment transport module, based on Delft3D to simulate the sediment erosion, re-suspension, transport and deposition processes in the study area during the passage of Typhoon Saomai. The model-simulated water level was validated against the in situ station data to show the feasibility of the model. The simulated SSC results agree reasonably well with the satellite observations. Time series of the simulation results showed that the model revealed the whole SSC variations during this extreme weather event and made up for the scarcity of in-situ and satellite observations. SSC significantly increased during the passage of the typhoon and decreased gradually during the post-typhoon stage. Modeled results also reveal that the spring-neap tidal effect significantly controlled the distribution and variation of SSC in the shallower coastal water (<20–30m in depth) and the typhoon-induced re-suspension is evident in most of the study area, especially in the coastal waters near the Yangtze River estuary and Hangzhou Bay during the passage of the typhoon. Finally, based on the simulation results, we discuss the dynamic mechanisms including turbulent energy, bed shear stress and vertical mixing that caused the SSC variation.

Distribution of suspended sediment concentration in wide sediment‐laden streams: A novel power‐law theory

AbstractThe diffusion equation of suspended sediment concentration in a wide sediment‐laden stream flow is dependent on the vertical gradient of streamwise velocity and the sediment diffusivity. This study aims at investigating the influence of the streamwise velocity laws on the suspended sediment concentration distributions, resulting from the solution of the diffusion equation. Firstly, the sediment concentration distributions are obtained numerically from the solution of the diffusion equation using different velocity laws and compared with the experimental data. It is found that the power‐law approximation produces good computational results for the concentration distributions. The accuracy of using a power‐law velocity model is comparable with the results obtained from other classical velocity laws, namely log‐law, log wake‐law and stratified log‐law. Secondly, a novel analytical solution is proposed for the determination of sediment concentration distribution, where a power‐law, wall‐concentration profile is coupled with a concentration wake function. The power‐law model (for velocity and concentration) is calibrated using the experimental data, and then a generalized wake function is obtained by choosing a suitable law. The developed power‐law model involving the wake function adjusted by an exponent predicts the sediment concentration distributions quite satisfactorily. Finally, a new explicit formula for the suspended‐load transport rate is derived from the proposed theory, where numerical computation of integrals, as needed in the Einstein theory, is avoided.

Seasonal transportation and deposition of the suspended sediments in the Bohai Sea and Yellow Sea and the related mechanisms

The Yellow River is well known for high concentration of suspended particulate matter (SPM), which is one of the most important SPM sources in the Bohai Sea and Yellow Sea, China. The mechanisms of long-distance transport and deposition of the Yellow River sediment discharges are hot topics. Based on field observations in four different seasons of 2010–2011 and 15 numerical experiments, this work studied the seasonal sediment transportation and deposition in the Bohai and Yellow Seas. Results show that the horizontal distribution of suspended sediment concentration in the Bohai Sea and Yellow Sea is neither closely related to the Yellow River discharge in flood and dry seasons nor to the temperature and salinity distributions in winter and summer because most of the Yellow River-discharged sediments deposited near the river mouth. However, the winter northerly wind events, especially the winter storm events with high waves, are the major factors inducing the long-distance transport of the sediments from the Bohai Sea to the Yellow Sea. The net SPMs are transported to the Yellow Sea from the Bohai Sea in both winter and summer. The net SPM flux at the Bohai Strait is 14.0 Mt/year by the combined effects of tides, wind, and waves. The SPM is transported to the Shandong Peninsula in the Yellow Sea for the generation of the mud wedge off the peninsula. The northern part of the mud wedge is related to the southerly wind in summer, and the southeastern part resulted from the winter northerly wind, especially the strong wind.

Using GOCI Retrieval Data to Initialize and Validate a Sediment Transport Model for Monitoring Diurnal Variation of SSC in Hangzhou Bay, China

The diurnal variation of the suspended sediment concentration (SSC) in Hangzhou Bay, China has been investigated using remotely-sensed SSC derived from the Geostationary Ocean Color Imager (GOCI) in combination with a coupled hydrodynamic-ecological model for regional and shelf seas (COHERENS). The SSC maps were inferred through a UV-AC atmospheric correction algorithm and an empirical inversion algorithm from the GOCI Level-1B data. The sediment transport model was initialized from maps of the GOCI-derived SSC and the model results were validated through a comparison with remotely-sensed data. The comparison demonstrated that the model results agreed well with the observations. The relationship between SSC distribution and hydrodynamic conditions was analyzed to investigate the sediment transport dynamics. The model’s results indicate that the action of tidal currents dominate the sediment deposition and re-suspension in the coastal waters of the East China Sea. This is especially the case in Hangzhou Bay where the tidal currents are strongest. The satellite-derived sediment data product can not only dramatically improve the specification of the initial conditions for the sediment model, but can also provide valuable information for the model validation, thereby improving the model’s overall performance.

水位低下による土砂スルーシング時の超音波を用いた SS 濃度と粒度分布の連続計測

In recent years, ultrasonic attenuation spectroscopy has been frequently used for the measurement of suspended sediment concentration and particle size distribution. Sediments are derived from the rock masses at the upper basin and transported downstream owing to floods, and then deposited in the reservoir. The reservoir sediments affect the entire river system because the sediment transport is blocked by dams. For this reason, sediment sluicing has been performed in several rivers. In such cases, it is important to monitor the suspended sediment concentration and particle size distribution. Therefore, we have measured the suspended sediment concentration and particle size distribution using an ultrasonic spectrometer during sediment sluicing by drawdown operation. The applicability of our measurement technology using ultrasonic attenuation spectroscopy for monitoring of suspended sediment concentration and particle size distribution was verified.

Parameterization of Time-Averaged Suspended Sediment Concentration in the Nearshore

To quantify the effect of wave breaking turbulence on sediment transport in the nearshore, the vertical distribution of time-averaged suspended sediment concentration (SSC) in the surf zone was parameterized in terms of the turbulent kinetic energy (TKE) at different cross-shore locations, including the bar crest, bar trough, and inner surf zone. Using data from a large-scale laboratory experiment, a simple relationship was developed between the time-averaged SSC and the time-averaged TKE. The vertical variation of the time-averaged SSC was fitted to an equation analogous to the turbulent dissipation rate term. At the bar crest, the proposed equation was slightly modified to incorporate the effect of near-bed sediment processes and yielded reasonable agreement. This parameterization yielded the best agreement at the bar trough, with a coefficient of determination R2 ≥ 0.72 above the bottom boundary layer. The time-averaged SSC in the inner surf zone showed good agreement near the bed but poor agreement near the water surface, suggesting that there is a different sedimentation mechanism that controls the SSC in the inner surf zone.

Partitioning and analyzing temporal variability of wash and bed material loads in a forest watershed in Iran

The amount of transported material from a hillslope or channel, mirrors the watershed health, which needs to be quantified. However, the contribution of different sediment sources to sediment load has not been adequately studied. In this study, 24 samples of suspended load, bed load and channel material were taken bi-weekly for a period of one year from the Kojour River of the Educational and Research Forest Watershed of Tarbiat Modares University in Iran. The suspended sediment concentration and particle-size distribution were determined. The total sediment load was then partitioned into bed load, wash load and suspended bed material load based on three criteria: (i) the upper limit of 63 micron, (ii) the Einstein method, and (iii) the lower limit of sediment particles in the channel material. The results suggested a significant contribution of wash load compared to suspended bed material and bed loads ratio of 96.8, 2.65 and 0.55%, respectively. The ratio of suspended bed material load to wash load varied from 13.12% (the maximum) in winter to 11.02, 2.70 and 0.91% in autumn, spring and summer, respectively. The results also showed the effects of flow discharge on different components of sediment loads. While, the flow discharge significantly affected bed load and wash load with respective correlation coefficients (r) of 0.520 and 0.464 < r < 0.535 for three methods with significant level (p) between 0.007 and 0.022. It had little influence on suspended bed material load (–0.243 < r < 0.277 with 0.190 < p < 0.253).

Physical processes and influencing factors of contaminants release due to resuspended sediments in water environment

Strong interaction exists in water flow, sediment movement and pollutants migration, resulting in an integrated environmental system of close contact with each other. Impact of sediment and suspended sediment on the water environment appears a combined dynamic coupling effect by complex hydrodynamic conditions. Three main ways of the pollutants entering water are studied by flume experiments. These three physical processes may be the static diffusion through sediment-water interface, the release due to sediment resuspension and the release of suspended sediment by turbulence. The results show that the sediment can be divided into two distinct muddy and sandy matters based on surface characteristics. Sediment grain size, porosity and initial contaminant amount are the main factors to determine static release of contaminants at the sediment-water interface. The pollutant quantity attenuation formula in sediment was established thereby, indicating that the contaminated attenuation time are proportional to the sediment thickness, density and distribution coefficient. The contaminant release process due to suspended sediment can be broadly divided into three stages: the initial stage, the alternating stage between suspension and settlement and the balance stage. The ratio of the solid/liquid distribution in the water body increases firstly and then decreases in the later two stages. Pollutants emission amount equations is derived based on the mass conservation law, and its contract with experimental results shows that the nature of the adsorption and desorption of contaminants to some extent alleviate the rate of its release. Water pollutant concentration distribution and velocity distribution as well as suspended sediment concentration distribution are closely related, showing the same variation. Vertical distribution difference of sediment contaminants becomes larger with the increase of flow velocity. The larger the initial sediment concentration is, the more uniform the distribution of sediment contaminants tends to be. The time to reach a uniform vertical concentration distribution takes more for sediment with smaller particle size.

Hydrology, sediment circulation and long-term morphological changes in highly urbanized Shenzhen River estuary, China: A combined field experimental and modeling approach

Summary The Shenzhen River estuary is a small estuary in highly urbanized regions between Shenzhen and Hong Kong, China. An increasing amount of sediment has been observed to accumulate in the estuary, imposing a severe impact on the ecological environment. In this study we utilized a series of hydrographic and bathymetry surveys to study the hydrology, sediment transport and morphological processes in the estuary. Flow and sediment circulation patterns in different seasons were inferred using current velocity, salinity and suspended sediment concentration (SSC) time series collected in the hydrographic surveys in conjunction with fathometer profiles in bathymetry surveys. Historical time series at two stations were also analyzed by Mann–Kendall test for possible trends of the driving forces for estuarine morphological processes. The two-dimensional depth-averaged DELFT numerical model was employed to simulate the flow, salinity and SSC fields during the synchronous surveys and to predict the long-term morphological processes in the estuary. A bimodal SSC distribution was observed with two high-SSC zones separated by a low-SSC zone near the central bay, which cannot be explained by the conventional nongravitational transport theory of Postma (1967). It is hypothesized that sediment circulation in the estuary can be separated into two different systems: the “tidal zone” is under the influence of marine sediment from the Pearl River estuary, whereas the “fluvial zone” is mainly affected by terrestrial sediment from the river. Sediment mass exchange between the two systems is limited due to the presence of the low-SSC zone, the location of which could vary with the relative strengths of river flow and tides. The trend analysis of historical time series shows that the river discharge and the mean sea level are increasing and the flood tide range and the ebb tide range are decreasing. These trends are closely related to the intense human activities in the urbanization of Shenzhen. The long-term simulations show depositional trends for the inner bay and the coastline of the outer bay, which could be further aggravated by the detected trends of the driving forces.

Remote sensing of spatial-temporal distribution of suspended sediment and analysis of related environmental factors in Hangzhou Bay, China

In this study, a total of 37 images of Landsat Operational Land Imager/Thematic Mapper/Enhanced Thematic Mapper plus were adopted to delineate the qualitative changes of Suspended Sediment Concentration (SSC) in Hangzhou Bay, China. Combined with in-situ SSC, remote sensing reflectance of the water (Rrs), water depth and simulated currents, the influence of both seabed topography and tidal currents on the SSC distribution was analysed. The results showed: (1) four High SSC Areas (HSA) and two Low SSC areas (LSA) in Hangzhou Bay. (2) SSC has a negative correlation with bathymetry, which is especially obvious during mid to late period of flood tide. HSAs appear in the shallow water (3–7 m depth) area, while the LSAs distribute in the deep water area (10–15 m depth). (3) The surface SSC distribution during the mid to late period of flood tide can help us estimate the topography information. The results of this paper can be used to other coastal embayments similar to Hangzhou Bay.

THE INFLUENCE OF HYDRODYNAMIC FACTORS ON CHARACTERISTICS OF SUSPENDED SEDIMENT DISTRIBUTION IN THE MEKONG RIVER MOUTH AREA

This paper presents some research results on the distribution characteristics of suspended sediment in coastal waters of Mekong river under the influence of hydrodynamic factors by using numerical model. The model was built on unstructured grid and calibrated with observed data to verify water levels at My Thanh, Thuan An stations. The calculated results showed the role of wind, wave, river discharges during both the rainy and dry seasons, and water level fluctuation to the distribution characteristics of suspended sediment in coastal waters of Mekong river mouth area. Accordingly, under the influence of waves, wind, the concentration of suspended sediment in the flood tidal phase was enhanced from the bottom floor to the surface, and a significant increase in turbidity occurred off Mekong River mouth. On the other hand, the distributions of suspended sediment concentration in tributaries were different, and depended on the tidal fluctuations.

An optimal model for estimating suspended sediment concentration from Landsat TM images in the Caofeidian coastal waters

Suspended sediment concentration (SSC) is one of the most critical parameters in water quality and environmental evaluations. Remote sensing has the potential for monitoring the dynamics and spatial distribution of SSC efficiently. The primary objective of this study is to develop retrieval models that are reliable and sensitive to SSC levels in the Caofeidian area, a new seaport in northeast China, based on Landsat-5 Thematic Mapper (TM) images and a set of in situ data sets, including spectral reflectance data and water quality data. The study finds that the band reflectance ratio and binary combination factor (i.e. the ratio of the reflectance to the particle size) are more effective than single band reflectance, and a non-linear model is more potent than a linear model for predicting SSC in the Caofeidian waters. A quadratic polynomial regression model of the RTM3/RTM2 ratio is proposed as the optimal retrieval model after evaluating various models with respect to different sensitive factors. The accuracy of the model is acceptable with a relative error and a root mean square error of 25.35% and 7.22 mg l–1, respectively; the correlation coefficient between the observed and estimated SSCs is 0.986. This study also indicates that the band reflectance ratio and binary combination factor are effective in weakening and even partially eliminating the effects of the changes in the sediment type (i.e. particle size and refractive index). And the band reflectance ratio is more efficient. Using the proposed model and TM data, SSC levels for the entire region were estimated. Such results can serve as a baseline for future environmental monitoring efforts.

An investigation of spatial variation of suspended sediment concentration induced by a bay bridge based on Landsat TM and OLI data

This study investigates the spatial variation of suspended sediment concentration (SSC) induced by Hangzhou Bay Bridge (HBB) in the coastal waters of the East China Sea. Based on Landsat Thematic Mapper (TM), Operational Land Imager (OLI) data and in-situ measurements, spectral characteristics of waters in Hangzhou Bay and SSC retrieved from near infrared single band have been analyzed. The results revealed significant difference of SSC in the water on two sides of HBB. SSC increases downstream of the bridge under conditions of low turbidity (SSC<300mgl−1) upstream water, while SSC decreases when high turbidity water (SSC>400mgl−1) upstream. This study shows that the interaction of bridge piers and currents has important influences on SSC distribution by inducing hydrodynamic factors and by changing suspended sediment transport. Remotely sensed data with high spatial resolution as TM and OLI can be applied to investigate SSC variations induced by a bridge in the bay area.

The impact of channel deepening and dredging on estuarine sediment concentration

Many estuaries worldwide are becoming more urbanised with heavier traffic in the waterways, requiring continuous channel deepening and larger ports, and increasing suspended sediment concentration (SSC). An example of a heavily impacted estuary where SSC levels are rising is the Ems Estuary, located between the Netherlands and Germany. In order to provide larger and larger ships access to three ports and a shipyard, the tidal channels in the Ems Estuary have been substantially deepened by dredging over the past decades. This has led to tidal amplification and hyper concentrated sediment conditions in the upstream tidal river. In the middle and outer reaches of the Ems Estuary, the tidal amplification is limited, and mechanisms responsible for increasing SSC are poorly understood. Most likely, channel and port deepening lead to larger SSC levels because of resulting enhanced siltation rates and therefore an increase in maintenance dredging. Additionally, channel deepening may increase up-estuary suspended sediment transport due to enhanced salinity-induced estuarine circulation.The effect of channel deepening and port construction on SSC levels is investigated using a numerical model of suspended sediment transport forced by tides, waves and salinity. The model satisfactorily reproduces observed water levels, velocity, sediment concentration and port deposition in the estuary, and therefore is subsequently applied to test the impact of channel deepening, historical dredging strategy and port construction on SSCs in the Estuary. These model scenarios suggest that: (1) channel deepening appears to be a main factor for enhancing the transport of sediments up-estuary, due to increased salinity-driven estuarine circulation; (2) sediment extraction strategies from the ports have a large impact on estuarine SSC; and (3) maintenance dredging and disposal influences the spatial distribution of SSC but has a limited effect on average SSC levels.

SSC Analysis of South Maharashtra Coast: A Case Study from Vengurla Coastal Region

Suspended sediment transport plays a major role in many coastal, estuarine and offshore engineering applications. The transport of suspended sediment influences the constructions of harbours, constructions of coastal power stations and refineries, safety of offshore platforms and pipelines, erosion and accretion of beaches, quality of the water and many other applications. To understand the suspended sediment transport pattern along South Maharashtra coastal region, a case study was conducted at Vengurla coastal waters. In order to do that, the sea water samples at 6 transects (18 stations) were collected for analysis of suspended sediment concentration (SSC) during pre-monsoon and post-monsoon periods. The results showed that during post monsoon, the SSC pattern at surface, mid and bottom layers having 10-20mg/l, 10-19mg/l and 50-60mg/l respectively. But during the pre-monsoon, the respective layers show 5-20mg/l, 4-15mg/l and 70mg/l of SSC concentration. In addition, Ocean Colour Monitor (OCM) satellite images were analyzed in the same study area to know the SSC distribution pattern. In Vengurla, post-monsoon, the SSC values of surface coastal waters ranging from 5-15mg/l from OCM satellite images and also SSC is compared with OBS 5+ profiles. In this paper, the SSC distribution pattern of both seasons is narrated and the validations of SSC using OCM satellite data are also discussed.