Grain-size distribution patterns of suspended sediment in response to hydrodynamics on the Dafeng intertidal flat, Jiangsu, China

Patterns of grain-size distributions of suspended sediment in relation to resuspension, settling, and tidal processes are investigated, based on in situ measurements over the Dafeng intertidal flat, on the Jiangsu coast, in the summer of 2002 and 2003. The suspended sediment here is dominated by fine and very fine silt, with a mean grain-size of 7 - 13 μm. The patterns of the grainsize distributions of suspended sediment during a tidal cycle are characterized by two types： one stable type representing insignificant spatial and temperal variations; and the other bimedal type with significant variations. The main factors influencing the grainsize distributions include resnspension, settling, suspended sediment imported into intertidal flats during the flood phase, and the grain-size distribution of seabed sediment. Resuspension increases the coarse particle content, enhances the mean grain-size of suspended sediment, and results in grain-size distributions for the suspended sediment similar to those of seabed sediment; the settling process has opposite effects on the suspended sediment. When resuspension occurs, the gain-size distributions of suspended sediment in the lower part of water column respond significantly to the current velocity. Where the influence of resuspension and settling processes is weak, the grain-size distributions of suspended sediment appear to be stable and almost identical for the various parts of intertidal flats during different measurement periods. Such distributions are referred to the background grain-size distribution, for which the mean grain-size over the Dafeng intertidal flat is around 7 μm.

Utilizing sediment grain size characteristics to assess the effectiveness of clay–sand barriers in reducing aeolian erosion in Minqin desert area,China

The clay–sand barriers in Minqin desert area,China,represent a pioneering windbreak and sand fixation project with a venerable history of 60 a.However,studies on evaluating the long-term effectiveness of clay–sand barriers against aeolian erosion,particularly from the perspective of surface sediment grain size,are limited and thus insufficient to ascertain the protective impact of these barriers on regional aeolian activities.This study focused on the surface sediments(topsoil of 0–3 cm depth)of clay–sand barriers in Minqin desert area to explain their erosion resistance from the perspective of surface sediment grain size.In March 2023,six clay–sand barrier sampling plots with clay–sand barriers of different deployment durations(1,5,10,20,40,and 60 a)were selected as experimental plots,and one control sampling plot was set in an adjacent mobile sandy area without sand barriers.Surface sediment samples were collected from the topsoil of each sampling plot in the study area in April 2023 and sediment grain size characteristics were analyzed.Results indicated a predominance of fine and medium sands in the surface sediments of the study area.The deployment of clay–sand barriers cultivated a fine quality in grain size composition of the regional surface sediments,increasing the average contents of very fine sand,silt,and clay by 30.82%,417.38%,and 381.52%,respectively.This trend became markedly pronounced a decade after the deployment of clay–sand barriers.The effectiveness of clay–sand barriers in erosion resistance was manifested through reduced wind velocity,the interception of sand flow,and the promotion of fine surface sediment particles.Coarser particles such as medium,coarse,and very coarse sands predominantly accumulated on the external side of the barriers,while finer particles such as fine and very fine sands concentrated in the upwind(northwest)region of the barriers.By contrast,the contents of finest particles such as silt and clay were higher in the downwind(southeast)region of the sampling plots.For the study area,the deployment of clay–sand barriers remains one of the most cost-effective engineering solutions for aeolian erosion control,with sediment grain size parameters serving as quantitative indicators for the assessment of these barriers in combating desertification.The results of this study provide a theoretical foundation for the construction of windbreak and sand fixation systems and the optimization of artificial sand control projects in arid desert areas.

The grain-size distribution of the suspended particulate matter in the Huanghe Estuary and its adjacent sea area in winter

The grain-size of suspended particulate matter （SPM） in the Huanghe Estuary and its adjacent sea area was investigated with an in situ laser particle size analyzer （LISST-100） in November 2006.The spatial distribution of the grain-size parameters was very complicated.The results show that （1） the mean particle size of SPM ranged from 3.00Φ to 6.41Φ,with an average value of 4.66Φ;（2） the frequency distribution patterns of the SPM grain-size showed three different types,which were mono-mode,dual-mode and tri-mode,respectively;（3） C-M chart suggested that the transportation-processes of the SPM not only included suspended mode,but also the bed load transportation mode.The bed load transportation mode mainly occurred at the bottom layer.The characteristics and space distribution of SPM grain-size might be mainly controlled by sediment discharge of the Huanghe River,hydrodynamics condition,surface sediment types,and biological process within the study area.

Laboratory Application of Laser Grain-Size Analyzer in Determining Suspended Sediment Concentration

Suspended sediment concentration(SSC) is an important parameter in marine sedimentology. With the development of technology, many acoustic and optical devices, such as the Laser In-Situ Scattering and Transmissometry, have been designed to measure in situ SSC and grain size distribution. But due to fund or other restrictions, many experiments were only conducted in laboratory, using an indoor laser grain-size analyzer and gravimetric method to measure grain size distribution and concentration, respectively. In this study the laboratory experiment is simplified by omitting the tiring step of gravimetric method. The connections between SSC and other parameters(obscuration, D50 and sorting index) were investigated based on 124 surface sediment samples collected from different offshore areas. A new method is developed for determining SSC in laboratory using a laser grain-size analyzer.

Improvement and Application of Grain Size Distribution Characteristics Calculation of Bed Material

Grain size distribution of bed material is an important characteristic for studying evolution of natural river channel by means of experimental ways and numerical modeling of flow and sediment process.In this study,the fractal characteristic of sediment particle has been defined by means of fractal theory based on ana- lyzing the property of grain size distribution of bed material in the river channel.Furthennore,the fractal prop- erty of sediment particle has been applied to judge the process of armorin...

The spatial distribution of major and trace elements of surface sediments in the northeastern Beibu Gulf of the South China Sea

A multi-index analysis including grain size, major and trace elements is performed on the surface sediments from the northeastern Beibu Gulf to trace the sources of the sediments and to understand the controlling factors for elements distribution. The mean grain size exhibits a wide variation ranging from 0.09Φ to 8.05Φ with an average value of 5.33Φ. The average contents of major elements descend in an order of c(SiO_2)>c(Al_2O_3)>c(Fe_2O_3)>c(CaO)>c(MgO)>c(K_2O)>c(Na_2O)>c(TiO_2)>c(P_2O_5)>c(MnO), while those of trace elements exhibit a descending order of c(Sr)>c(Rb)>c(V)>c(Zn)>c(Cr)>c(Pb)>c(Ni)>c(Cu)>c(As). On the basis of elementary distribution characteristics and statistical analyses, the study area is divided into the four zones: Zone I is located in the northeastern coastal area of the gulf, which receives large amount of fluvial materials from local rivers in Guangxi and Guangdong, China, and the Qiongzhou Strait; Zone Ⅱ is located in the center of the study area, where surface sediments exhibits a multiple source; Zone Ⅲ is located in the Qiongzhou Strait, where surface sediments are dominated by materials from the Zhujiang River and Hainan; Zone IV is located in the southwest of the study area, where surface sediments are mainly originated from the Red River and Hainan. The statistical analyses of sediment geochemical characteristics reveal that the grain size, which is mainly influenced by hydrodynamics and mineral composition of terrigenous materials, is the leading factor controlling the elementary distribution.Meanwhile, impacts from anthropogenic activities and marine biogenic process will also be taken into consideration.

ADCP measurements of suspended sediment flux at the entrance to Jiaozhou Bay, western Yellow Sea

The purpose of the present contribution is to explore the technique to use Acoustic Doppler Current Pro- filers （ADCPs） for suspended sediment flux measurements, which may be applied to coastal embayment environments such as estuaries and tidal inlets for sediment exchange and budget studies. Based on tidal cycle measurements from the entrance of ]iaozhou Bay, Shandong Peninsula, eastern China, statistical rela- tionships between the suspended sediment concentration （SSC） and ADCP echo intensity output are estab- lished. Echo intensity data obtained during an ADCP survey along two cross-sections during a spring tidal phase were transformed into SSC data. The ADCP current velocity and SSC data were then used to calculate the flux of fine-grained sediment. The results show that net sediment transport at the entrance is directed towards the open sea, with an order of magnitude of 103 t per spring tidal cycle; hence, although Jiaozhou Bay is a low SSC environment, the tidally induced suspended sediment transport can be intense.

Dynamic release process of pollutants during suspended sediment transport in aquatic system

Pollutants release is highly consistent with suspended sediment concentration （SSC） in water column, especially during re-suspension and transport events. The present research focuses on pollutant dynamic release from re-suspended sediment, especially the vertical distribution relationship between them. The sediment erosion experiments on a series of uniform flow are conducted in a circulate flume. Reactive tracer （phosphorus） is used as the contaminant in fine-grained sediments to identify the release characteristic length and time. Experimental results show that the flow condition near-bed depends on the sediment surface roughness. The region with high turbulent intensities corresponds to a high concentration sediment layer. In addition, the SSC decreases with the distance, water depth, and particle grain size. The sediment in a smaller grain size takes much more time to reach equilibrium concentration. Total phosphorus （TP） concentration changes along the water depth as SSC in the initial re-suspension stage, appearing in two obvious concentration regimes： the upper low-concentration layer and the high-concentration near-bottom layer. This layered phenomenon remains for about 3 hours until SSC distri- bution tends to be uniform. Longitudinal desorption plays an important role in long-way transport to reduce the amount of suspended sediment in water column.

Assessment of Sediment and Benthic Macrofauna Distribution at Dar es Salaam Harbour Channel

Sediment and macrobenthic fauna distribution at Dar es Salaam harbour channel were investigated to attest the influence of sediment grain size distribution and total organic carbon contents on benthic macrofauna dominance and diversity. Sampling campaign was conducted from January to April, 2019 in 25 sampling stations along the channel. Sediment grain sizes ranged between 0.7405 and 0.00273 mm with an average of 0.0804 mm classified as medium silt. Sediment distribution showed an onshore-offshore pattern consisting of fine dark clay-silt sediments in the southern part of the harbour close to Mwalimu Nyerere Bridge, medium (sandy) at the harbour and coarse sandy offshore. Five classes of macrofauna were identified with sedentary Polychaetes (Diopatra cuprea) found in tubes and free forms being dominant in most of the sediment types, however more abundant in clay-silt. High species diversity index values were encountered in sediments with medium total organic carbon (TOC) and sediment grain sizes (sand-silt). Apparently, low species similarity indices were observed in all sediment type indicating significant dissimilarities in species composition among sediment grain sizes. Thus, the distribution of benthic macrofauna species along Dar es Salaam harbour channel is strongly influenced by the sediment grain sizes and organic carbon contents in sediments.

Sediment distribution characteristics and environment evolution within 100 years in western Laizhou Bay,Bohai Sea,China

This study is about the reconstruction of fluvial origins based on the grain size distribution of sediment deposits in the western Laizhou Bay,Bohai Sea,China.Thirteen sediment cores were selected to research sediment characteristics using the Sahu discriminant formula,C-M diagram,and Folk method.The results showed:(1)Bounded by the Guangli River estuary,the north sediment was affected by the water and sand flowing from the Yellow River during different periods.The south sediment came from multi-source rivers under the influence of the Xiaoqing River,Mihe River,and other coastal rivers;(2)the deposited sediments were dated by a clear historical record of the branched channel oscillation combined with the characteristics of the diversion channel,erosion,and regression.The subaqueous delta overlapped during several Yellow River channel runs(1897–1904,1929–1934,1938–1947,1947–1953,1976–1996)and the deposited sediment facies changed(the north tidal flat-abandoned subaqueous delta-lateral delta-delta front);(3)the deposited sediment characteristics can be revealed by studying the branched diversions of the Yellow River and coastal multi-rivers of the past one hundred years.

SEDIMENT TRANSPORT IN YALU RIVER ESTUARY

Tidal cycle measurements of tidal currents, salinity and water tempe rature, and suspended sediment concentrations were measured at four stations, to gether with surveys along two profiles short core collection within the Yalu Riv er estuary. Grain size analysis of the three core sediment showed that: 1) the s ediment from B1 to B3 became finer, worse sorting and positively skewed; 2) the diversification of matter origin became more and more evident from east to west; 3) the sediments over the region were of the same origin, as indicated by their similar colors and grain sizes. The data indicated that stratification occurred in the flood season, from upstream to downstream, and a salt wedge was formed. The water column was well mixed, but the longitudinal gradient of the salinity w as larger on spring tide. The results also showed that the dominating mechanism of suspended sediment transport in the Yalu River estuary was T1, T2, T3 and T5. The non-tidal steady advection transport was restricted by the net transport o f suspended sediment induced by mass Stoked drift directed to landwards, then th e net sediment transport rate were decreased and the turbidity maxima was also f avored to forming and extending.

A method for simulating sediment incipient motion varying with time and space in an ocean model(FVCOM):development and validation

We modified the sediment incipient motion in a numerical model and evaluated the impact of this modification using a study case of the coastal area around Weihai, China. The modified and unmodified versions of the model were validated by comparing simulated and observed data of currents, waves, and suspended sediment concentrations(SSC) measured from July 25^(th) to July 26^(th), 2006. A fitted Shields diagram was introduced into the sediment model so that the critical erosional shear stress could vary with time. Thus, the simulated SSC patterns were improved to more closely reflect the observed values, so that the relative error of the variation range decreased by up to 34.5% and the relative error of simulated temporally averaged SSC decreased by up to 36%. In the modified model, the critical shear stress values of the simulated silt with a diameter of 0.035 mm and mud with a diameter of 0.004 mm varied from 0.05 to 0.13 N/m^2, and from 0.05 to 0.14 N/m^2, respectively, instead of remaining constant in the unmodified model. Besides, a method of applying spatially varying fractions of the mixed grain size sediment improved the simulated SSC distribution to fit better to the remote sensing map and reproduced the zonal area with high SSC between Heini Bay and the erosion groove in the modified model. The Relative Mean Absolute Error was reduced by between 6% and 79%, depending on the regional attributes when we used the modified method to simulate incipient sediment motion. But the modification achieved the higher accuracy in this study at a cost of computation speed decreasing by 1.52%.

福宁湾及附近海域悬沙粒度与影响因素

基于闽北福宁湾及附近海域冬、夏两季水文泥沙实测数据,分析了不同时间尺度下悬沙的粒度特征,探讨了影响悬沙粒度季节差异的主要因素以及悬沙粒度与浓度的关系。结果表明:正常天气下,研究区悬沙中值粒径普遍大于6.5Φ。悬沙粒度具有“冬细夏粗”的季节分布特征;受潮动力影响,悬沙粒度大小潮变化明显;潮周期内悬沙粒径变化规律不明显。悬沙粒级-标准偏差曲线显示两种主要的敏感粒级分布范围为2.8~3.4μm和21.1~25.1μm。悬沙粒度“冬细夏粗”的季节差异主要受底质再悬浮和泥沙来源的影响。冬季悬沙粒径与浓度的相关性不明显,夏季两者存在显著的线性关系,悬沙粒径随悬沙浓度的增加而减小,这种季节差异可能与悬沙来源和混合作用有关。夏季悬沙粒径的粗化可能与细颗粒发生絮凝沉降有关。

Dramatic sediment load changes and sedimentation characteristics upstream of the Three Gorges Dam due to the large reservoirs construction

After the construction of cascade reservoirs in the upper reaches of the Three Gorges Reservoir(TGR),the sediment load outflow of the upper Yangtze River Basin(YRB)has been significantly altered,decreasing from 491.8 Mt/yr(1956–2002)to 36.1 Mt/yr(2003–2017)at Yichang station.This has widely affected river hydrology,suspended sediment grain size distribution,and channel morphology.This study analyzed hydrological variations in water discharge and sediment load of the upper YRB over the past 62 years(1956–2017)by employing a double mass curve.The variations in the source areas of sediment yielding for the upper YRB were quantified,and field measurement data of the cross-channel profile were collected to investigate the sedimentation process in the TGR from 2003 to 2017.More than 90%of the sediment load reduction in the upper YRB may be explained by human activities.The Jinshajiang River was no longer the largest sediment source area for the Zhutuo station(accounting for 5.23%)in the 2013–2017 time span,and the sediment rating rates for the inflow and outflow of the TGR shifted to negatively correlated.A longitudinal fining trend was revealed in the suspended sediment size.Still,the mean median grain size of suspended sediment in the TGR had an increasing trend in the 2013–2017 period.This result may be closely related to sediment regulation in reservoirs and incoming sediment load reduction.Sedimentation in the TGR decreased sharply from 299.8 Mt/yr in 2003–2012 to 47.2 Mt/yr in 2013–2017,but the sedimentation rate of the TGR remained at>80%annually.Moreover,some cross sections in the fluctuating backwater zone experienced scouring.

ADCP在长江口悬沙输运观测中的应用

声学多普勒流速剖面仪 (ADCP)是近年来发展起来的一种用于测量流速的声学仪器 ,同时还可以通过建立回声强度和现场取得水样的回归关系式而获得悬沙浓度的数据。本文利用在长江口两个站位的高频观测数据 ,对现场取得的悬沙作粒度分析 ,在此基础上对枯季长江口地区悬沙输送机制和悬沙粒度对水动力的响应进行了分析和探讨。结果表明 :平均流输运在整个悬沙输送中占主导地位 ,同时潮扩散和垂向扩散作用也是引起两站悬沙输运的重要因子 ;不同层次和不同时刻的悬沙粒度参数的变化 ,既和海 陆转换有关 ,也和潮相变化密切相关。

长江口表层沉积物粒度时空分布特征

结合近期长江口558个表层沉积物采样资料,分析了长江口表层沉积物时空分布特性,得到了近期长江口表层沉积物中值粒径和沉积物类型分布特征。横沙以上海域表层沉积物粒径洪枯季变化较小;浑浊带海域洪季粗,枯季细;口外海域则枯季粗,洪季细。横沙以上和口外海域沉积物类型洪枯季变化较小,浑浊带海域沉积物类型变化较复杂。无论洪枯季北港表层沉积物最粗,北槽次之,南槽最小。表层沉积物大小潮变化较小,两次采样平均差别为9.7%;沉积物年际变化随大通流量和输沙量的变化而变化。近十五年来,长江口表层沉积物类型变化较大的区域主要是北支上段、南北港分流口、北槽和南槽浑浊带海域,主要与河槽的自然演变和人类活动有关。结合Pejrup新三角图对长江口各沉积动力环境进行分区,对比各沉积环境亚区的粒度特征,并对黄河口、长江口、珠江口表层沉积物粒度参数进行对比。

长江口悬浮体粒度特征及其季节性差异

1998年 1 1月和 1 999年 5月长江口悬浮体样品的激光粒度仪分析结果表明 ,长江口悬浮体粒度较细 ,分选较差 ,偏态和峰态偏小 ,粒度组成以粉砂为主 ;粘土含量次之 ,基本不含砂或砂含量很小 ,由陆向海平均粒径有由粗到细的变化趋势。粒度分布呈典型的非正态分布 ,存在“双峰”和“三峰”两种形式 ,表层样品以“双峰”分布为主 ,底层“三峰”或“双峰”并存。标准偏差 -粒度曲线上多峰出现 ,反映了长江口悬浮体组成的复杂性。长江口悬浮体粒度特征有较大的季节变化。悬浮体粒度变化的影响因素包括泥沙来源、底质再悬浮、生物作用和絮凝作用 ,粒度特征的季节差异是这些因素综合作用的结果。

鸭绿江河口地区沉积物特征及悬沙输送

根据鸭绿江河口区 4 个站位的潮周期测量数据和 3 个柱状样的粒度数据，对悬沙的输送规律以及口门地区最大浑浊带的形成机制、悬沙输送方向以及物质来源和动力条件进行了分析。计算分析表明，鸭绿江是一条落潮流占优势的河流，平均流作用、斯托克斯漂移效应以及水深与悬沙浓度的潮变化引起的悬沙输送是其河口区最主要的悬沙输送机制。3 个柱状样粒度参数自东向西的变化反映了鸭绿江口西侧沿岸地区动力条件和沉积环境的变化：沉积物的平均粒径变小，分选变差，并且更正偏，物源的多元化特征逐渐增强。物源和河口区沿岸沉积动力环境的差异以及潮相的周期变化使 3 个柱状样中的环境敏感粒度组分对应着不同的粒径分布区间。

中国北方部分地区黄土、沙漠沙、湖泊、河流细粒沉积物粒度多组分分布特征研究

通过对我国北方部分地区的黄土、沙漠沙、湖泊、河流细粒沉积物的粒度多组分分布特征系统研究后总结了其粒度分布特征及组分间差异,并提出了风成、水成沉积物成因类型的判别依据。认为:1)细粒沉积物粒度一般由多个组分叠加构成,表现为多组分粒度分布特征。2)黄土粉尘粒径以<70μm的悬浮颗粒为主,粒度由粗、中、细三个组分构成。粗粒组分含量最高,其中值粒径与源区距离呈负相关,中粒组分百分含量与源区距离呈正相关。3)沙漠沙粒度由一个极其明显的粗粒跳跃组分构成,中值粒径一般位于100～300μm,分选性极好。4)湖泊沉积物粒度分布最多可有6个组分(中值粒径:<1μm,2～10μm,10～70μm,70～150μm,150～700μm,>700μm),前4个组分属悬浮组分,⑤为跳跃组分,⑥为滚动组分,分选性差。5)河流沉积物粒度分布曲线较复杂,其分布特征蕴含了水动力强弱信息。6)沙漠沙→黄土与河流沙→湖泊沉积物其优势组分的粒径均逐渐变细,但水成相对应组分比风成组分粒径要粗。

东海陆架北部泥质区表层沉积物碳酸盐粒级分布与物源分析

对取自东海陆架北部表层沉积物及黄河、长江河道沉积物样品按 1/ 4Ф或 1/ 2Ф的间隔筛分 ,分别测定不同粒级中碳酸盐的含量 ,结果表明东海陆架表层沉积物碳酸盐含量都较高 ,且在砂、砾级中异常富集 ,碳酸盐颗粒分布具有分散、多峰的特点 ;黄河沉积物碳酸盐含量较高 ,主要分布于细粒级部分 ,并在细粒部分富集 ;长江沉积物碳酸盐含量明显低于黄河 ,分布较均匀 ,但是由于有淡水钙质生物碎屑的混入导致粗粒级中碳酸盐较为富集。依据沉积物中碳酸盐含量、分布及富集特征 ,结合沉积作用分析 ,表明济州岛西南泥质区沉积物为黄河、长江物质以及泥质区周边的再悬浮物质三部分的混合产物。