High Sediment Concentrations Research Articles

Classifications of runoff and sediment data to improve the rating curve method

In this study, data classification method was evaluated to increase accuracy of estimating suspended sediment load. To achieve this objective, suspended sediment in Chehelgazi and Khalifeh-Tarkhan rivers in Kurdistan, Iran, were estimated using Sediment Rating Curve (SRC) method in three different approaches of data classification. At first, measured data were modeled without classification. Then, data based on flow statues were divided into two series as high and low flow. Eventually, based on sediment concentration, the data were divided into low and high sediment concentration. Long-term runoff and sediment data were used to calibrate rating curve model. The estimated values were compared with recorded data and the performances of these models were evaluated using statistical criteria. The results indicated an effective role of data classification to improve estimating sediment transportation by rating curve method. In one of the stations, it was observed that due to classification based on river flow and sediment concentration, model efficiency was increased about 45% and 28%, respectively. Furthermore, in case of improving efficiency of SRC method, classifying data based on flow statues was found to be more effective than sediment concentration. The results of this study can be used to improve the management of the basin by more accurately estimating the amount of suspended sediments transporting in the rivers draining to reservoirs.

Mechanisms of maintaining high suspended sediment concentration over tide-dominated offshore shoals in the southern Yellow Sea

An understanding of the dynamics and behaviors of suspended sediments is vital in analysis of morphological, environmental, and ecological processes occurring in coastal marine environments. To study the mechanisms of maintaining high suspended sediment concentrations (SSCs) on a tide-dominated offshore shoal, we measured water depths, current velocities, SSCs, wave parameters and bottom sediment compositions in the southern Yellow Sea. These data were then used to calculate bottom shear stresses generated by currents (τc), waves (τw), and wave–current interactions (τcw). SSCs time series exhibited strong quarter-diurnal peaks during spring tides, in contrast to the semidiurnal signal during neap tides. A Fourier analysis showed that suspended sediment variations within tidal cycles was mainly controlled by resuspension in most stations. There existed relatively stable background SSCs (maintaining high SSCs among tidal cycles) values at all four stations during both windy (wind speed > 9.0 m/s) and normal weather conditions (wind speed < 3.0 m/s). The background SSCs had strong relationship with spring/neap-averaged τcw, indicating background SSCs were mainly controlled by mean bottom shear stress, with a minimum value of 0.21 N/m2. On account of the strong tidal currents, background SSCs of spring tides were greater than that of neap tides. In addition, on the base of wavelet, statistics analyses and turbulence dissipation parameter, background SSCs during slack tide in the study area may be maintained by intermittent turbulence events induced by a combined tidal current and wave action.

Perfluoroalkyl acids (PFAAs) in sediments from rivers of the Pearl River Delta, southern China.

Having been largely used in industrial and household products, perfluoroalkyl acids (PFAAs) appear in environmental and biological systems with prevalence and persistence and have raised great concern in recent years. The present study is aimed at studying concentrations and composition profiles of 16 PFAAs in surface sediments collected from 51 sampling locations in 4 main rivers of the Pearl River Delta, one of the economy-developed areas in China. The total PFAA concentrations (∑ PFAAs) were determined in a wide range of 1.89-15.1ngg-1 dw (dry weight) with an average concentration to be 3.54ngg-1 dw. Higher ∑ PFAAs were observed in the downstream of Dongjiang River and the Pearl River, possibly due to the discharge of industrial wastewater. Perfluoropentanoic acid (PFPeA) and perfluorooctane sulfonate (PFOS) were the dominant PFAAs, accounting for 51 to 85% of ∑ PFAAs in 27% of the samples. High PFPeA concentrations in sediments of urban river were scarcely observed in previous studies worldwide. The sources of short-chain perfluoroalkyl carboxylic acids (PFCAs) were significantly different from those of other PFAAs. Preliminary hazard assessment proved negligible for PFOS, perfluorooctanoic acid (PFOA), PFPeA, and perfluorohexanoic acid (PFHxA) concentrations in sediments from rivers of the Pearl River Delta.

A study of in-situ sediment flocculation in the turbidity maxima of the Yangtze Estuary

In order to improve our understandings of temporal and vertical variations of sediment flocculation dynamics within the turbidity maxima (TM) of the highly turbid Yangtze Estuary (YE), we deployed LISST-100C, a laser instrument for in-situ monitor of the sizes and concentrations of flocculated particles in a wet season. Field data in terms of vertical profiles of flow velocity, suspended sediment concentration (SSC), salinity, flocculated particle size distribution and volume concentration were obtained, based on field works conducted at consecutive spring, moderate, and neap tides.Data analyses show that the mean floc diameters (DM) were in the range of 14–95 μm, and flocculation exhibited strong temporal and vertical variations within a tidal cycle and between spring-neap cycles. Larger DM were observed during high and low slack waters, and the averaged floc size at neap tide was found 57% larger than at spring tide. Effective density of flocs decreased with the increase of floc size, and fractal dimension of flocs in the YE was mainly between 1.5 and 2.1. We also estimated the settling velocity of flocs by 0.04–0.6 mm s−1 and the largest settling velocity occurred also at slack waters. Moreover, it is found that turbulence plays a dominant role in the flocculation process. Floc size decreases significantly when the shear rate parameter G is > 2-3 s−1, suggesting the turbulence breaking force. Combined effects of fine sediment flocculation, enhanced settling process, and high sediment concentration resulted in a large settling flux around high water, which can in part explain the severe siltation in the TM of the YE, thus shedding lights on the navigation channel management.

Assessment of Surface Inlets Performance on Sediment Transport to Subsurface Drainage System

Abstract. Infield ponding can have detrimental effects on crops and soils and result in reduced yields and increased sedimentation. Surface inlets are commonly used to prevent or reduce incidents of ponding. In this study, the flow and sediment transport characteristics of four surface inlets–the standard Hickenbottom inlet, two inlets (standard and QuickDrain®) designed by Ag-Solutions, and an inlet developed by AgriDrain–were evaluated in both laboratory and field settings with simulation rainfall. The Hickenbottom and QuickDrain® Ag-solutions inlet had higher sediment concentration and sediment load compared to the other inlets. The average sediment concentration and sediment load for Hickenbottom and QuickDrain® Ag-solutions inlets were measured to be 3532.70 mg/L, 64919.05 mg/min, and 3104.31 mg/L, 24880.69 mg/min, respectively. The measured sediment concentration and sediment load for standard Ag-solutions inlet were smaller than Hickenbottom and QuickDrain® Ag-solutions inlets but higher than the AgriDrain inlet. The AgriDrain inlet was the most effective among the four inlets in reducing sediment (66% concentration and 23.2% load compared to Hickenbottom) (p

Influences of retrogressive erosion of reservoir on sedimentation of its downstream river channel—A case study on Sanmenxia Reservoir and the Lower Yellow River

Retrogressive erosion, a widespread phenomenon of sediment transport in reservoirs, often impacts on both the reservoir capacity and the sedimentation in the downstream river channel. Based on field data from the Sanmenxia Reservoir and the Lower Yellow River over the past decades, three courses of retrogressive erosion with distinctive features were analyzed. The results indicate that retrogressive erosion, especially caused by rapid reduction in the water level till the reservoir is empty, often results in the serious siltation of the lower Yellow River and threatens the safety of the flood control in the Lower Yellow River. Unreasonable operation of the reservoir and incoming hyperconcentrated floods accompanied by retrogressive erosion also aggravate the siltation of the main channel of the river. However, a reasonable operation mode of the reservoir so named”storing the clear (low sediment concentration) water in the non–flood season, and sluicing the muddy(high sediment concentration) water in the flood season” was found, which might mitigate the deposition in both the reservoir and the Lower Yellow River. This operation mode provides important experience for the design and operation of large reservoirs in other large rivers carrying huge amounts of sediment.

Morphometric and anthropogenic factors of flood risk in the Lower Kura

The morphometric and anthropogenic risk factors of floods in a typical lowland Lower Kura R. are studied. The isolation of the channel from the floodplain is the major cause of floods in the river. The high channel tortuosity makes the flow turbulent. In addition, the high sediment concentration, the turbid and disperse character of the liquid, the gentle bed slope, and the alluvial character of the soil underlying the bed and embankments contribute to the vertical and horizontal dynamics of the channel.

Organophosphate Esters in Sediment of the Great Lakes.

This is the first study on organophosphate ester (OPEs) flame retardants and plasticizers in the sediment of the Great Lakes. Concentrations of 14 OPEs were measured in three sediment cores and 88 Ponar surface grabs collected from Lakes Ontario, Michigan, and Superior of North America. The sum of these OPEs (Σ14OPEs) in Ponar grabs averaged 2.2, 4.7, and 16.6 ng g-1 dw in Lakes Superior, Michigan, and Ontario, respectively. Multiple linear regression analyses demonstrated statistically significant associations between logarithm concentrations of Σ14OPEs as well as selected congeners in surface grab samples and sediment organic carbon content as well as a newly developed urban distance factor. Temporal trends observed in dated sediment cores from Lake Michigan demonstrated that the recent increase in depositional flux to sediment is dominated by chlorinated OPEs, particularly tris(2-chloroisopropyl) phosphate (TCPP), which has a doubling time of about 20 years. Downward diffusion within sediment may have caused vertical fractionation of OPEs over time. Two relatively hydrophilic OPEs including TCPP had much higher concentrations in sediment than estimated based on equilibria between water and sediment organic carbon. Approximately a quarter (17 tonnes) of the estimated total OPE burden (63 tonnes) in Lake Michigan resides in sediment, which may act as a secondary source releasing OPEs to the water column for years to come.

Continuous in situ monitoring of sediment deposition in shallow benthic environments

Sedimentation is considered the most widespread contemporary, human-induced perturbation on reefs, and yet if the problems associated with its estimation using sediment traps are recognized, there have been few reliable measurements made over time frames relevant to the local organisms. This study describes the design, calibration and testing of an in situ optical backscatter sediment deposition sensor capable of measuring sedimentation over intervals of a few hours. The instrument has been reconfigured from an earlier version to include 15 measurement points instead of one, and to have a more rugose measuring surface with a microtopography similar to a coral. Laboratory tests of the instrument with different sediment types, colours, particle sizes and under different flow regimes gave similar accumulation estimates to SedPods, but lower estimates than sediment traps. At higher flow rates (9–17 cm s−1), the deposition sensor and SedPods gave estimates >10× lower than trap accumulation rates. The instrument was deployed for 39 d in a highly turbid inshore area in the Great Barrier Reef. Sediment deposition varied by several orders of magnitude, occurring in either a relatively uniform (constant) pattern or a pulsed pattern characterized by short-term (4–6 h) periods of ‘enhanced’ deposition, occurring daily or twice daily and modulated by the tidal phase. For the whole deployment, which included several very high wind events and suspended sediment concentrations (SSCs) >100 mg L−1, deposition rates averaged 19 ± 16 mg cm−2 d−1. For the first half of the deployment, where SSCs varied from <1 to 28 mg L−1 which is more typical for the study area, the deposition rate averaged only 8 ± 5 mg cm−2 d−1. The capacity to measure sedimentation rates over a few hours is discussed in terms of examining the risk from sediment deposition associated with catchment run-off, natural wind/wave events and dredging activities.

黄河二氧化碳逸出时空变化及其影响因素——以头道拐水文站为例

PDF HTML阅读 XML下载 导出引用 引用提醒 黄河二氧化碳逸出时空变化及其影响因素——以头道拐水文站为例 DOI: 10.5846/stxb201609091833 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（91547110，51469018）；水利部公益性行业科研专项（20150104） Spatial-temporal variations and influencing factors of carbon dioxide evasion from the Yellow River:An example of the Toudaoguai Gauging Station Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:河流连接着海洋碳库和陆地碳库，河流碳逸出是全球碳收支的重要组成部分。本文以黄河上游和中游分界点-内蒙古段头道拐断面为研究对象，采用Li-7000静态箱法监测了断面4个采样点在2013-2015年期间四季的CO2逸出通量（FCO2），并分析了FCO2时空变化规律。基于研究断面主要水文和水化学指标的野外监测和室内分析结果，探讨了FCO2的主要影响因素。结果表明断面FCO2介于14-186 mol m-2 a-1，平均值为84 mol m-2 a-1；水体CO2分压（pCO2）介于467-2101 μatm，平均值为995 μatm；DOC浓度介于2.7-13 mg/L。FCO2季节性差异明显：夏季FCO2为全年最大456 mmol m-2 d-1，冬季最小33 mmol m-2 d-1。FCO2在4个采样点的空间差异显著：河道右岸S4点处最大为392 mmol m-2 d-1；河道中部S2和S3点基本相同；河道左岸S1点最小为86 mmol m-2 d-1。FCO2与河道流速呈现较好的正相关关系，与pCO2中等相关，与pH负相关，与风速的相关性不明显，说明对于该研究断面河道流速较pCO2对FCO2的贡献更大。本研究较为精细地探讨了头道拐断面的水体CO2逸出规律，表明即使在同一河道断面，FCO2也可能存在较大空间差异，流速较大处的FCO2较大，因此在野外监测FCO2时需要在河道断面选取具有代表性的采样点，特别是较大的河流。研究结果为黄河中上游CO2逸出量评价和河道断面FCO2监测点的布设提供了科学依据。 Abstract:The oceanic carbon pool and terrestrial carbon pool are connected by rivers. Carbon dioxide (CO2) evasion from rivers to the atmosphere represents a substantial flux in the global carbon cycle. The CO2 efflux (FCO2) and CO2 partial pressure (pCO2) in large rivers have been widely evaluated. Most studies concerning CO2 emission from the Yellow River, a typical river containing high sediment concentrations, focused on the lower reach and its estuary, but less is known about its upper and middle reaches. In this study, a river cross-section at the Toudaoguai Gauging Station in Inner Mongolia, the dividing point between the upper and middle reaches of the Yellow River was chosen as a study site. Evasion of CO2 was measured four times each year using Li-7000 static chamber method from 2013 to 2015 at four sampling points in a river cross-section. The spatial and temporal variations of FCO2 were analyzed. The relevant hydrological indexes, including water temperature, pH,and wind velocity as well as current velocity were measured at the four sampling points. The hydrochemical indicators, including ALK and DOC in water samples, were analyzed in the laboratory and pCO2 was estimated. The possible influential factors of FCO2 were further discussed using correlation analysis. The CO2 evasion from the river cross-section ranged from 14 to 186 mol m-2 a-1 and its average was 84 mol m-2 a-1. The pCO2 in the Yellow River at the Toudaoguai Gauging Station was within the range of 467-2101 μatm and the average value was 995 μatm. The concentration of DOC ranged from 2 to 13 mg/L. The FCO2 exhibited obvious seasonal variations, with the maximum FCO2 of 456 mmol m-2 d-1 occurring in summer and the minimum of 33 mmol m-2 d-1 occurring in winter. The FCO2 values were markedly different at sampling points, with the maximum value of 392 mmol m-2 d-1 at S4 near the right bank, similar values at S2 and S3 in the middle of the river section, and the minimum of 86 mmol m-2 d-1 at S1 near the left bank. The analysis of factors influencing FCO2 indicated that FCO2 was positively correlated with current velocity and pCO2, and negatively correlated with pH. There was no obvious correlation between FCO2 and wind speed. Results also showed that current velocity contributed more to FCO2 than to pCO2 in the river cross-section. In this study, evasion of CO2 from the Toudaoguai cross-section was determined on a relatively fine scale. The results suggested that a distinct spatial variation in FCO2 exists even at the level of river cross-section, with the maximum FCO2 found at the point with the highest current velocity. Thus, typical sampling points in a river cross-section should be chosen for FCO2 measurement. The study provided a scientific reference for both FCO2 evaluation in the upper and middle reaches of the Yellow River and FCO2 sampling in a river cross-section. 参考文献 相似文献 引证文献

Essential strategy for urban seasonal-river restoration

Recently, many urban rivers are being restored due to positive environmental effects while debris flow may occur in seasonal-rivers of cities in arid regions. Therefore, as a part of river restoration studies, the impacts of debris flow on an urban seasonal-river (Vardavard River, Tehran) were analysed based on field investigations and hydrologic, hydraulic and sediment analyses. The results show that high-concentration of sediments in debris flow increases peak flow and hydraulic roughness, resulting in river flooding. The steep slope of the river basin increases the debris flow peak up to 1.2 times more than an ordinary flood peak with the similar return period. Hence, designing a slit dam before the river enters the city is suggested as an essential strategy to control the debris flow and improve safety of the downstream urban areas. The proposed approach, with enforced watershed management schemes, can be implemented to restore other urban seasonal-rivers and to prevent probable debris flow in arid regions.

Essential strategy for urban seasonal-river restoration

Recently, many urban rivers are being restored due to positive environmental effects while debris flow may occur in seasonal-rivers of cities in arid regions. Therefore, as a part of river restoration studies, the impacts of debris flow on an urban seasonal-river (Vardavard River, Tehran) were analysed based on field investigations and hydrologic, hydraulic and sediment analyses. The results show that high-concentration of sediments in debris flow increases peak flow and hydraulic roughness, resulting in river flooding. The steep slope of the river basin increases the debris flow peak up to 1.2 times more than an ordinary flood peak with the similar return period. Hence, designing a slit dam before the river enters the city is suggested as an essential strategy to control the debris flow and improve safety of the downstream urban areas. The proposed approach, with enforced watershed management schemes, can be implemented to restore other urban seasonal-rivers and to prevent probable debris flow in arid regions.

Measurements of suspended sediment transport and turbulent coherent structures induced by breaking waves using two-phase volumetric three-component velocimetry

Sediment suspension and transport under plunging regular waves was investigated in a laboratory surf zone using the volumetric three-component velocimetry technique. The two-phase flow measurements captured the motions of sediment particles simultaneously with the three-component, three-dimensional velocity fields of turbulent coherent structures (large eddies) induced by plunging breakers. Sediment particles were separated from fluid tracers based on a combination of particle spot size and brightness in the two-phase flow images. The interactions between the large eddies and bottom sediment were investigated in the outer surf zone. The measured data showed that breaker vortices impinging on the bottom was the primary mechanism that lifted sediment particles into suspension. High suspended sediment concentrations were found in the wall-jet region where the impinging flow was deflected outward and upward. Sediment particles were also trapped by counter-rotating vortices behind the down flow. Suspended sediment concentrations were significantly lower in the impingement zone where the fluid velocities were downward, even though the turbulent kinetic energy in the down flow was very high. Suspended sediment concentration was well correlated with vertical velocity and apparent shear stresses in the deflected flow, and with vorticity magnitude in the counter-rotating vortices. A linear relationship was found between net sediment flux and net turbulent kinetic energy flux over one wave cycle. It was found that a strong deflected flow in front of the impingement zone enhanced onshore sediment transport compared to a more symmetrical flow pattern, while counter-rotating vortices kept sediment particles in suspension for transport offshore after flow reversal. Onshore sediment transport was observed in less than 20% of the breaking waves. In most wave cycles, net sediment flux was directed offshore due to advection by predominantly offshore flow velocities.

Effects of different operation scenarios on sedimentation in irrigation canals of the Gezira Scheme, Sudan

Sediment and water management are key issues in irrigation schemes that suffer from accumulation of sediment along canals. This accumulation creates problems with adequate water supply and may lead to water shortage. The aim of this study was to analyse improvement options for operation and maintenance in order to achieve better sediment and water management in irrigation canals. A model has been developed to simulate cohesive sediment transport in irrigation canals. The model is a useful tool to predict cohesive sediment deposition under different operation and maintenance scenarios. It has been calibrated and validated by using field data of the Gezira Scheme in Sudan and has been applied for different options of operation. The best operation scenario was found when the scheme was operated based on the crop water requirement during the period of high sediment concentration. When the inflow was reduced by 51% during this period in 2011, the reduction in deposition was 48%. Such types of adaptation will significantly reduce deposition and improve sediment and water management in irrigation canals. Copyright © 2016 John Wiley & Sons, Ltd.

Phosphorus in lake sediments of Poland – Results of monitoring research

Abstract In 2010-2013, 528 samples of surface sediments were collected from the profundal zone of lakes to determine concentrations of phosphorus, Al, Ca, Fe, K, Mn, Na and S, as well as trace elements (As, Ba, Cd, Co, Cr, Cu, Mo, Ni, Pb, Sn, Sr, Ti, V and Zn) using the ICP-OES method. Additionally, Hg concentration (by the TMA method) and organic carbon concentration (using the coulometric titration method) were also determined. Phosphorus concentration was found to range from 0.005 to 1.925% (0.109% on average). High phosphorus concentrations in sediments were reported in lakes located within and around urban areas, in lakes on which recreation centres and leisure facilities are situated, and in lakes adjoining special protection areas of birds. The phosphorus concentration in sediments shows a clear correlation with the contents of Al, Fe, Mn, S and TOC, which indicates the presence of phosphorus in both organic and inorganic forms. It also correlates with the contents of most of the trace elements examined for this study, including Zn, Hg and Pb. A certain regional variability was found; water sediments of lakes in the Masurian and Pomeranian lakelands, located in the area covered by the Pomeranian phase ice sheet, are characterised by a slightly higher phosphorus concentration compared with those from the Greater Poland Lakeland situated in the area of the Poznań phase glaciation.

Optimization of hydropower plants with respect to fine sediment focusing on turbine switch-offs during floods

At medium- and high-head hydropower plants (HPPs) on sediment-laden rivers, hydro-abrasive erosion in turbines is an important economic issue. In HPPs with headwater storage, reservoir sedimentation is another problem related to fine sediment. On the one hand, turbine erosion is mitigated by reducing the sediment load in power waterways. On the other hand, reservoir sedimentation may be mitigated by conveying more fine sediment through power waterways to downstream river reaches. To optimize the operation of HPP schemes on the long-term, it is recommended to find a balance between these options based on real-time data using available monitoring techniques.An operational measure to mitigate turbine erosion is to close intakes and switch-off turbines in periods of high suspended sediment concentration (SSC) and coarse particles, typically during floods. Prerequisites for such operation are (i) there is no obligation to generate electricity, (ii) real-time SSC measurements are available, and (iii) the value of the ‘switch-off SSC’ is known. In a case study at the high-head HPP Fieschertal, a switch-off SSC of 10 g/l was estimated. The economic analysis showed that it would have been clearly profitable to practice such a switch-off during the major flood in 2012 which had an SSC peak of 50 g/l.

Metais potencialmente tóxicos em rios a montante do Pantanal Norte

Os rios Cuiabá (CBA) e São Lourenço (SL) são considerados estratégicos por integrar regiões de grande relevância econômica, social e ambiental para o Brasil e o mundo. Porém, diversas atividades nas bacias destes rios podem representar fontes de metais potencialmente tóxicos e comprometer a sua qualidade ambiental. Neste trabalho foi avaliada a variabilidade espacial e temporal da concentração de metais nestas bacias e a sua relação com parâmetros de qualidade da água. Foram coletadas mensalmente, de agosto/2012 a julho/2013, 15 amostras de água superficial e 9 amostras de sedimento de fundo, nos rios CBA e SL. As concentrações de Cr, Cu, Fe, Mn, Pb e Zn nas amostras de água foram determinadas por espectrometria de emissão óptica com plasma acoplado indutivamente, e nas amostras de sedimento de leito, por espectrometria de absorção atômica com atomização em chama. Os elementos Fe, Mn, Pb e Cr apresentaram elevadas concentrações nas amostras de água e sedimento, porém apenas Pb e Cr representam potencial risco ambiental. As concentrações de Fe e Mn foram mais elevadas na parte alta do rio SL enquanto as concentrações de Cu e Pb ocorreram na área dos centros urbanos. Temporalmente, os metais estiveram associados ao regime pluviométrico. A correlação observada entre metais indica uma fonte comum. Desta maneira, a ocorrência e concentração de metais nos rios CBA e SL mostram contribuição de origem natural, reflexo do tipo de solo associado ao regime pluviométrico da região, bem como contribuição antrópica devido às atividades agropecuárias e ao lançamento de efluentes urbanos não tratados.

Persistent Organic Pollutants in sediment and fish in the River Thames Catchment (UK)

Some organic pollutants including polychlorinated biphenyls (PCBs), polybrominated diphenylethers (PBDEs) and hexachlorobenzene (HCB) have been banned from production and use in the UK for >30years but due to their toxicity and persistence are still of concern. However, due to their hydrophobicity they are present at very low concentrations and are difficult to measure in water, and so other matrices need to be sampled in order to best assess contamination. This study measured concentrations of ΣICES 7 PCBs (PCB congeners 28, 52, 101, 118, 138, 153 and 180) and Σ6 PBDEs (PBDE congeners 28, 47, 99, 100, 153, 154) and HCB in both bed-sediments and wild roach (a common pelagic fish) in the Thames Basin. The highest sediment concentrations were detected in an urbanised tributary of the Thames, The Cut at Bracknell (HCB: 0.03–0.40μg/kg dw; ICES 7 PCBs: 4.83–7.42μg/kg dw; 6 BDEs: 5.82–23.10μg/kg dw). When concentrations were expressed on a dry weight basis, the fish were much more contaminated than the sediments, but when sediment concentrations were normalised to organic carbon concentration they were comparable to the fish lipid normalised concentrations. Thus, despite the variability in the system, both sediments and wild fish can be considered suitable for representing the level of POPs contamination of the river system given sufficient sample numbers.

Transport Capacity of Overland Flow for Sediment Mixtures

AbstractSediment transport capacity of overland flows is crucial to understanding and modeling the erosion and deposition processes. The transport capacity for sediment mixtures is particularly complex because of the need for an algorithm to allocate the total available shear stress or stream power to individual size classes. The transport capacity for sediment mixtures may not even be unique, depending on whether the flow is eroding or depositing sediments unless all sediments are of a single size class. Using data from a set of flume experiments involving steep slopes and high sediment concentrations, a formula was proposed for the sediment transport capacity limited by available stream power and available accommodation space for sediments. Sediments used for the experiment were further sieved into five distinct size classes. The sediment transport capacity was measured for 25 flow-slope combinations to validate a new formula for individual size classes, and to propose and test a method to compute the s...

Mudflat Morphodynamics and the Impact of Sea Level Rise in South San Francisco Bay

Estuarine tidal mudflats form unique habitats and maintain valuable ecosystems. Historic measurements of a mudflat in San Fancsico Bay over the past 150 years suggest the development of a rather stable mudflat profile. This raises questions on its origin and governing processes as well as on the mudflats’ fate under scenarios of sea level rise and decreasing sediment supply. We developed a 1D morphodynamic profile model (Delft3D) that is able to reproduce the 2011 measured mudflat profile. The main, schematised, forcings of the model are a constant tidal cycle and constant wave action. The model shows that wave action suspends sediment that is transported landward during flood. A depositional front moves landward until landward bed levels are high enough to carry an equal amount of sediment back during ebb. This implies that, similar to observations, the critical shear stress for erosion is regularly exceeded during the tidal cycle and that modelled equilibrium conditions include high suspended sediment concentrations at the mudflat. Shear stresses are highest during low water, while shear stresses are lower than critical (and highest at the landward end) along the mudflat during high water. Scenarios of sea level rise and decreasing sediment supply drown the mudflat. In addition, the mudflat becomes more prone to channel incision because landward accumulation is hampered. This research suggests that sea level rise is a serious threat to the presence of many estuarine intertidal mudflats, adjacent salt marshes and their associated ecological values.