EFFECT ON ESTUARINE FINE-SEDIMENT TRANSPORT OF INTERMITTENT PUMP DISCHARGE AT PAGHAM HARBOUR, WEST SUSSEX

Field investigations were undertaken to identify the mechanisms of fine-sediment transport at a landward limit of Pagham Harbour. Which is a semi-enclosed natural harbour in West Sussex, UK. Measurements of water level, velocity, salinity and turbidity were made during three tidal cycles between June and August 2002. Near-bed measurements revealed that, for spring tides, the most significant transport occurs during the flood tide, with smaller turbidity peaks recorded at times of intermittent pumped discharges at low water. Vertical profiling revealed that the timing of these discharges acts as a control on the landward transport of fine sediment by increasing salinity stratification. The resulting graphs show that, while increased near-bed velocity leads to increased turbidity and sediment transport, the degree of vertical salinity gradient is also linked with landward transport of fine sediment. These results help to explain the role of tides and fresh-water flow in controlling the transport of fine sediment in natural harbours, emphasising the importance of taking stratification into account when using 2-D depth-averaged predictive numerical models.     

Observations of turbidity in the Thames Estuary,United Kingdom

Two years of data of water level, salinity and turbidity have been analysed to understand the response of the estuarine turbidity maximum in the Thames to variations in tidal range and freshwater flow. We show the increase in turbidity in spring, together with a sudden decrease in autumn after fluvial flooding. In order to try to understand the mechanisms, we also present data from individual tides. During dry periods, there is a period of slack water around high tide when settling occurs. There is little equivalent settling at low tide, nor is there any significant settling during wet weather periods, pointing to the importance of tidal asymmetry at certain times of year. We also present an empirical relationship between peak tidal water level and turbidity during flood tides, which clearly shows the greater landward transport of sediment under spring tides, although this is moderated by the availability of erodible material.     

Flow measurement with multi‐instrumentation in a tidal‐affected river

Flow measurements in a tidal‐affected river provide important information of cyclic flow pattern characteristics in temporal and spatial variations. Reliability and accuracy of measured flow data can provide for numerical model calibration and verification. In the present study, we measured tidally affected river flow in the Danshui River of northern Taiwan during the 2008 summer and fall. The measured flow data, produced by both state of the art and conventional instruments including particle tracking velocimetry (PTV), acoustic Doppler profiler (ADP), horizontal acoustic Doppler current profiler (H‐ADCP) and Price‐type current metre (PCM) were compared and correlated during several tidal cycles. The mean flows by ADP were similar to that by PCM and highly correlated with those by PTV and H‐ADCP. Index velocity rating between ADP and H‐ADCP separately computed during the flood and ebb tides shows good correlation for the ebb tide and poor correlation for the flood tide due to subsurface maximum velocity in the middle‐ to near‐bottom layers.     

The influence of salting out on the sorption of neutral organic compounds in estuaries

The relative (unsaturated) solubility and sorption of 2,2′,5,5′-tetrachlorobiphenyl have been studied along an estuarine salinity gradient. The aqueous compound was salted out with increasing salinity and an aqueous salting constant of about 0.002 l g⁻¹ was derived. Sorption of the compound to estuarine particles increased with increasing salinity for a range of particle concentrations, but the magnitude of this effect (sorption salting constants of about 0.005–0.01 l g⁻¹) indicated that salting out of the aqueous phase was not solely responsible. It is suggested that the hydrophobicity of sediment organic matter is enhanced by its interaction with seawater ions through a reduction in the charge of the particle surface and, possibly, modification of the structure of the organic matter. Examination of literature data on the sorption of neutral organic compounds to estuarine sediment indicates a general increase in sorption with increasing salinity which can be empirically defined by a salting equation. Although charge reduction of estuarine particles is a general observation, it is not possible to establish the general significance of this effect (or any other form of salting out of sediment organic matter) on the sorption of organic compounds in estuaries because appropriate site- and compound-specific aqueous salting constants are unavailable.

Increased sorption at high salinities has obvious implications for the disposal and transport of organic chemicals in estuaries. However, the inverse dependency of sediment–water partitioning on particle concentration is likely to be of at least equal significance in macrotidal environments where sediment resuspension occurs. An empirical model, combining the effects of salinity and particle concentration, is proposed for deriving first-order estimates of the partitioning of neutral organic compounds in estuaries.     

Sediment dynamics in Rangoon river, Myanmar

The behavior of fine-grained sediment in Rangoon River depends on seasonal variations in freshwater discharge and tidal amplitudes that range from 2 to 5 m. During the monsoon, freshwater with sediment concentrations of 1 g/l, or less, causes unidirectional, seaward flow. In the dry season, salinities reach 20% and sediment concentrations rise to 6 g/l. The saline intrusion advects large quantities of sediment landward from seaward sources. Near-surface sediment concentrations are very low during neap tides, while a layer of 'fluid mud' rests on the bottom. Current speeds greater than 0.2 m/s are needed to entrain sediment into the upper layer. Layered suspensions occur most commonly during decelerating phases of tidal flow and are dispersed by rapidly accelerating flow. When current speeds exceed 0.6 m/s, no 'fluid mud' forms, and sediment concentrations as great as 6-8 g/l extend through the water column.     

海峡科技生态城·竖向标高规划设计探讨

紧密结合海峡科技生态城防洪排涝规划设计,通过园区竖向标高规划设计实践,提出滨海园区竖向规划的一般步骤及技术路线,运用防洪排涝规划分析论证了园区的竖向规划与洪水、涝水、海潮的关系,论述了园区竖向规划确定的思路和办法,如:海堤御潮,高水高排,涝水蓄排兼顾等。     

Impact sédimentaire des travaux d'aménagement de l'estuaire de la Loire

The planning works realized in the Loire estuary (France) during the course of the twentieth century have brought about an important inflow of sea water to this site. The consequences can be observed through important changes in the location of the extreme limits of both the dynamic tide and the salinity front at 0.5‰; the dynamic tide has progressed from 63?km from the river mouth in 1903 to 100?km in 1992 and the salinity front from 38?km in 1948 to 70?km in 1991. Modifications of the hydraulic conditions have also affected the dynamics of the cohesive sediments present in the estuary. The purpose of this study is to determine the impact of the past and future planning works in the Loire estuary on the erosion and deposition of cohesive sediments in relation to hydraulic conditions. The principal sedimentary processes (transportation, deposition, settlement, erosion) are simulated by simplified models from measurements carried out both in situ and in the laboratory. The dynamics of the cohesive sediment in the Loire estuary are linked with the fortnightly cycle of the tide as follows: when the tidal coefficient falls below 70, almost all the suspended matter is quickly deposited and collects near the estuary bed to form a lens-shaped body of fluid mud which consolidates during 6?days of neap tides. Finally, as soon as the tide coefficient rises above 75, this body of fluid mud is taken again into suspension and only the fraction that was highly concentrated in the course of the settlement remains on the bottom. The sediments remaining on the estuary bed in the course of a fortnightly cycle of the tide represent the residual sedimentation rate over this period. Knowledge of the maximum tide current velocities in the estuary permits the determination of the maximum hydrodynamic stress on the bottom and the critical concentration of the mud susceptible to being eroded by this current, taking into account the yield stress of the mud. In other respects, the quantity of mud that is greater than this critical concentration per surface unit and time unit can be calculated according to a theoretical model developed by Sanchez and Grovel. This methodology allows the evaluation of the residual sedimentation rate representing a layer of 0.08?m per year in front of the harbour of Montoir for the hydraulic conditions of 1976, with a maximum current velocity on the surface of 2.40?m?s^–1. Following the dredging works realized between St-Nazaire and Donges after 1976, the level of the bottom has changed from –10.00 to –13.25?m (with respect to the hydrographic datum). These works have brought about a reduction in maximum velocities of 15% and an increase in the residual sedimentation rate of about 100%. This increase is in agreement with the theoretical estimation of this study. This study also describes the high sedimentation rate observed in a locally dredged berth and located in the zone of the estuary where a lens-shaped body of fluid mud is formed during slack tides. The sedimentation rate depends then on the frequency of the dredging works because the dredged zone can be filled up in a few days. Finally, a methodology is developed in order to estimate the erosion rate induced by an increase in current velocities. This methodology takes into account the vertical concentration gradient in the bed resulting from consolidation, the hydrodynamic stress linked to current velocity, the yield stress of sediment which varies with concentration and the critical hydrodynamic stress for erosion estimated from experimental measurements in laboratory. All the methodologies presented in this paper have been applied only to the estuary of the river Loire. Application to any other similar site is possible after laboratory experiments on local sediments in order to adjust the behavioural laws used to evaluate the permeability coefficient, the effective stress and the yield stress. This study shows that knowledge of hydraulic conditions and local sedimentary processes is very important for predicting the impact of planning works in an estuary.     

Natural and anthropogenic inputs of hydrocarbons to the Strait of Georgia

Sediment cores from the Fraser estuary, Vancouver Harbour and Strait of Georgia, suspended sediment samples from the Fraser River and sediment grabs from Vancouver Harbour have been analyzed for alkanes and parent and alkyl PAHs (polycyclic aromatic hydrocarbons). Principal components analysis (PCA) clearly distinguishes mixed sources by separating parent PAHs according to molecular size, and separating alkyl substituted PAHs from higher plant PAHs. We find the Fraser River to be the predominant source for natural and anthropogenic hydrocarbons to the Strait of Georgia. The natural hydrocarbon burden from the Fraser River is augmented principally by petroleum hydrocarbons and combustion PAHs from Vancouver. Contaminated sediments from Vancouver Harbour very likely have also been transported to a major ocean disposal site off the Fraser estuary. Petroleum alkanes, which dominate Fraser River suspended sediment samples, are lost by processes such as dissolution or microbial degradation during transport and sedimentation, while PAHs from the river are delivered essentially unchanged to sediments in the strait. Hydrocarbon composition undergoes little change with depth at a reference location in the Strait of Georgia, indicating that PAH inputs have changed very little since the early part of this century. In Vancouver Harbour the low rate of sediment accumulation coupled with surface mixing has led to the retention of contaminant PAHs within the surface mixed layer, while the rapid delivery of sediments from the Fraser River has buried contaminant PAHs from historical ocean disposal in the Strait of Georgia.     

Modelling diagnosis of heavy metal (copper) transport in an estuary

A vertical (laterally-averaged) two-dimensional heavy metal transport model was developed to simulate the fluxes of copper in the Danshuei River estuarine system. The toxic model was incorporated into the hydrodynamic, the salt transport and the sediment transport modules. The model has been validated with observed time series data of water surface elevation, current, salinity, and suspended sediment concentrations in 2001 and 2002. An exponential relationship was established to relate variation in partition coefficient of copper to salinity and suspended sediment concentrations in the Danshuei River estuary. Comparisons of the total, dissolved, and particulate copper concentrations calculated by the numerical model and field data along the Danshuei River-Tahan Stream show good agreement. It is noteworthy that the model requires a point source of total copper with the strength of 250 kg/day to account for the observed persistently high total copper concentration near Hsin-Hai Bridge in the Tahan Stream, about 24 km upriver from the river mouth. The huge garbage dump site near the Hsin-Hai Bridge is likely the source of heavy metal pollution. The validated model was then applied to investigate the tidally averaged salinity distributions, residual circulation, suspended sediment, and total copper concentrations under low flow condition. The residual circulation is characterized by the upriver movement of denser saline water in the lower layer and the downriver movement of fresher water in the upper layer. The circulation pattern is driven by the longitudinal gradient of salinity distribution. The residual circulation occurs in the deep channel of Kuan-Du Bridge and Taipei Bridge. Under low flow condition, the limits of salt intrusion are located at Hsin-Hai Bridge. The tidally-averaged sediment concentration distribution exhibits a local maximum concentration around the null point in the Danshuei River-Tahan Stream. A local maximum of total copper concentration, which is nearly as high as that near the point source, occurs around the null point, which is potentially a hot spot of heavy metal accumulation.     

Selenium and trace element mobility affected by periodic displacement of stratification in the Great Salt Lake, Utah

The Great Salt Lake (GSL) is a unique ecosystem in which trace element activity cannot be characterized by standard geochemical parameters due to the high salinity. Movement of selenium and other trace elements present in the lake bed sediments of GSL may occur due to periodic stratification displacement events or lake bed exposure. The water column of GSL is complicated by the presence of a chemocline persistent over annual to decadal time scales. The water below the chemocline is referred to as the deep brine layer (DBL), has a high salinity (16.5 to 22.9%) and is anoxic. The upper brine layer (UBL) resides above the chemocline, has lower salinity (12.6 to 14.7%) and is oxic. Displacement of the DBL may involve trace element movement within the water column due to changes in redox potential. Evidence of stratification displacement in the water column has been observed at two fixed stations on the lake by monitoring vertical water temperature profiles with horizontal and vertical velocity profiles. Stratification displacement events occur over periods of 12 to 24 h and are associated with strong wind events that can produce seiches within the water column. In addition to displacement events, the DBL shrinks and expands in response to changes in the lake surface area over a period of months. Laboratory tests simulating the observed sediment re-suspension were conducted over daily, weekly and monthly time scales to understand the effect of placing anoxic bottom sediments in contact with oxic water, and the associated effect of trace element desorption and (or) dissolution. Results from the laboratory simulations indicate that a small percentage (1%) of selenium associated with anoxic bottom sediments is periodically solubilized into the UBL where it potentially can be incorporated into the biota utilizing the oxic part of GSL.     

Soil erosion by rainfall and runoff—state of the art

The processes of soil detachment and sediment transport by rainfall and overland flow and resulting sediment transport are described. The results of past research on the role of raindrop impact in detaching soil, experimental studies of erosion, and erosion modelling are presented. Studies of soil loss from experimental field plots led to the development of the Universal Soil Loss Equation and to its subsequent modification for use in quantifying erosion by individual storms. Systems to produce rainfall for erosion studies in the laboratory are described. A system which is currently being calibrated and used for erosion control system testing at Drexel University's Geosynthetic Research Institute (GRI) is described. Preliminary spatial rainfall distributions and runoff measurements are presented. Experimental results obtained by others on the performance of natural and geosynthetic erosion control systems are discussed along with a proposed experimental program for the GRI system.     

Parameter estimation for suspended sediment transport processes under random waves

This paper presents a parameter estimation method for suspended sediment transport processes subject to random wave environments. An objective function was constructed based on measurements of suspended sediment concentration profiles and the governing equation of sediment transport. The Chebyshev least square method was employed to approximate the process parameters, i.e. vertical eddy diffusivity (epsilon) and net vertical velocity (w). The objective function of sediment transport processes with Chebyshev's parameters is well posed and does not require boundary conditions. First, second, and third order epsilon and w Chebyshev orthogonal functions were determined for monochromatic (MONO), narrow-banded (NBR) and broad-banded (BBR) random wave conditions. In the BBR and NBR conditions, the best fit Chebyshev approximations of epsilon and w were 2nd degree, while the best approximations in the MONO condition were 2nd degree for epsilon and 1st degree for w. The Chebyshev method provides a quick, accurate and direct estimation of two prime parameters in sediment transport dynamics.     

A study of the cycling of manganese and other elements in a seasonally anoxic lake, Rostherne Mere, U.K.

The vertical distribution of sulphate, dissolved sulphide, alkalinity, pH, total iron and manganese, Fe(II) and Mn(II) and humic substances was monitored for a year in a seasonally anoxic lake, Rostherne Mere, U.K. During summer stratification Mn(II), probably of sediment origin, accumulated in the hypolimnetic bottom waters to a concentration of 50μm. Release occurred in two stages and appeared to be related to the supply of organic material to the sediment. No ferrous iron or dissolved sulphide were detected in the water column, although they were measured in the interstitial waters of the sediment. Ferrous sulphide formation in the sediment controls the iron(II) and dissolved sulphide concentrations and so minimises the concentration gradients at the sediment-water interface. Electron acceptors other than oxygen are capable of oxidising ferrous and sulphide ions in the water column. pH and alkalinity were the only other chemical components to show appreciable variation with depth, reflecting the biological processes of photosynthesis, respiration and decomposition. Iron and humic substances simultaneously increased in the surface waters after a major flood indicating that they are both present in the solution in contact with the soils of the catchment.     

Forecasting the effects of polluting discharges on natural waters—II

A brief account is given of the present state of development of methods for forecasting the effects of pollution on estuaries and coastal waters. In the case of vertically homogeneous estuaries the concentration of given pollutants at a chosen state of tide and given freshwater flow can be determined by means of a one‐dimensional steady‐state mathematical model in which use is made of observations of the distribution of salinity to calculate the rate of dispersion of the pollutants. An example is given of the application of such a model to the prediction of the concentration of dissolved oxygen, ammonia and oxidized nitrogen in the Thames Estuary. This type of approach has been extended to allow approximate estimates to be made of the variation of concentration of pollutants during a tidal cycle, and of the steady‐state concentrations in vertically stratified estuaries. A somewhat different type of model is used for predicting the effects of polluting discharges on coastal waters and in this case dispersion characteristics are determined with the aid of radio isotopes. An example is given of the application of one type of model to the prediction of the contamination of coastal waters by coliform bacteria resulting from discharge of sewage from a submerged pipeline.     

Neural network modeling of salinity variation in Apalachicola River.

Salinity is an important indicator for water quality and aquatic ecosystem in tidal rivers. The increase of salinity intrusion in a river may have an adverse effect on the aquatic environment system. This study presents an application of the artificial neural network (ANN) to assess salinity variation responding to the multiple forcing functions of freshwater input, tide, and wind in Apalachicola River, Florida. Parameters in the neural network model were trained until the model predictions of salinity matched well with the observations. Then, the trained model was validated by applying the model to another independent data set. The results indicate that the ANN model is capable of correlating the non-linear time series of salinity to the multiple forcing signals of wind, tides. and freshwater input in the Apalachicola River. This study suggests that the ANN model is an easy-to-use modeling tool for engineers and water resource managers to obtain a quick preliminary assessment of salinity variation in response to the engineering modifications to the river system.     

Agricultural sediment reduction using natural herbaceous buffer strips: a case study of the east African highland

Buffer strips are permanently vegetated areas situated immediately adjacent to streams and provide an efficient and economical way to reduce nutrient loads from agricultural areas, but no studies exist of their effectiveness from the East African highlands. We thus evaluated the sediment filtering capabilities of natural herbaceous buffer strips under tropical highland climatic conditions. Overland flow samples were collected at field edges and at various positions in herbaceous buffers and tested for total suspended sediment, nitrate‐nitrogen and total phosphorus. There was a significant effect (P < 0.05) of distance from field edge on the mean values of nutrients. On average, a 10.0 m herbaceous buffer reduced the total phosphorus by 99%, total suspended sediment by 94% and nitrate‐nitrogen by 85%. Altogether, the results suggest that herbaceous buffer strips are important to include in watershed management in agriculturally dominated tropical highlands in order to control sediment loss, stream siltation and the washout of nutrients.     

River flow and associated transport of sediments and solutes through a highly urbanised catchment, Bradford, West Yorkshire

The hydrological characteristics of catchments become drastically modified in response to urbanisation. The total contributions and dynamics of runoff, suspended sediment and solutes may change significantly and have important implications downstream where they may affect flooding, instream ecological habitat, water quality and siltation of river channels and lakes. Although an appreciation of the likely hydrological changes is crucial for effective catchment management they are still poorly understood. In this paper we present data from a network of river monitoring stations throughout the heavily urbanised Bradford catchment, West Yorkshire. Sites are upstream, within and downstream of the highly urbanised central part of the catchment. Flow, turbidity (calibrated to suspended sediment concentration) and specific conductance (surrogate for solute concentration), logged at 15-min intervals, are presented for a 12-month period (June 2000 to June 2001). The total amounts and dynamics of flow, solute and suspended sediment transport were investigated. Estimated total flow and suspended sediment transport for the monitoring period were found to be high in response to the high total rainfall. Flow and sediment transport regimes were extremely 'flashy' throughout the catchment and became increasingly flashy in a downstream direction. Suspended sediment discharged from the Bradford subcatchment makes an important contribution to downstream sediment transport on the river Aire at Beal. Data suggest that the urbanised part of the Bradford catchment is extremely important in contributing solutes to the Beck (river). Although flow and sediment are also contributed to the Bradford Beck in the urbanised part of the catchment the data suggest that significant amounts may enter the combined sewer system and bypass the river. Understanding the spatial and temporal variations of flow and the transport of suspended sediment and solutes in rivers in urbanized subcatchments is crucial to their effective management and monitoring. Furthermore, this knowledge may be extremely important to the management and monitoring of downstream rivers in large scale mixed catchments.     

Self-cleaning in an estuarine area formerly affected by 226Ra anthropogenic enhancements: numerical simulations

A numerical model of the Odiel-Tinto estuary (Spain) has been developed to study the self-cleaning process that was evidenced from 226Ra measurements in water and sediments collected in the period 1999-2002, after direct releases from a fertilizer complex ceased (in 1998). The hydrodynamic model is first calibrated, and standard tidal analysis is carried out to calculate tidal constants required by the dispersion code to determine instantaneous water currents and elevations over the estuary. In this way, long-term simulations may be carried out. The dispersion code includes advective/diffusive transport of radionuclides plus exchanges with bottom sediments described through a kinetic approach. The dispersion model is first tested by comparing computed and measured 226Ra concentrations over the estuary resulting after releases in the Odiel and Tinto rivers. Next, it is applied to simulate the self-cleaning process of the estuary. The time evolution of radium concentrations in bed sediments is in generally good agreement with observations. The computed sediment halving time of the estuary is 510 days, which also is in good agreement with that estimated from measurements.     

Three-dimensional modelling of mercury cycling in the Gulf of Trieste

The Gulf of Trieste (Northern Adriatic) is subject to mercury pollution from a former mercury mine in Idrija, located along a river which transports mercury-contaminated sediments into the Gulf. Concentrations in suspended and bottom sediments are up to two orders of magnitude higher than in the central and southern Adriatic. Extensive research has been carried out on measurements and modelling of the transport and fate of mercury in the Gulf. Two- and three-dimensional models have been developed to include the influence of the significant advective transport due to currents. Wind, thermohaline forcing, and the Soca river momentum are the most important forcing factors. A two-dimensional model simulated the transport of non-methylated and methylated mercury in dissolved, particulate and plankton fractions. Mercury processes included the input of atmospheric mercury, sedimentation, reduction, methylation and demethylation. The model simulations gave basically what were proper trends of the phenomena; quantitatively the measured and computed results are mainly within a factor of three. To simulate the non-uniform distribution of parameters over the depth, an existing three-dimensional (3D) hydrodynamic and transport-dispersion (TD) model, PCFLOW3D, was adapted and applied. As it was found that most mercury transport is related to suspended sediment particles, a new 3D sediment transport module was also developed and included in the model. Three cases are presented: one describing the simulation of TD of dissolved total mercury; another the simulation of the TD of particulate mercury in the Gulf during a river flood; and the third simulating sediment transport in the Gulf during a period of strong ENE wind. Comparison with measurements was only partly possible, but mainly the computed and measured results were within a factor of two and proper trends of the phenomena were obtained by the simulations. The combination of modelling and measurements has resulted in some interesting conclusions about the phenomenon of the transport and fate of mercury in a coastal sea.     

Carcinogenic and genotoxic activity of extracts from contaminated sediments in western Lake Ontario

In order to investigate the putative association between chemical contamination in western Lake Ontario and high prevalences of fish tumors, sediments from Hamilton Harbour and Oakville Creek in Lake Ontario and reference sites in non-polluted areas of Ontario, Canada were collected and extracted for organic contaminants. Sediment extracts from Hamilton Harbour had the highest concentrations of polychlorinated biphenyls and organochlorine insecticides (ppb) and contained very high concentrations of polynuclear aromatic hydrocarbons (ppm); although the levels of these compounds varied widely with sampling location in the harbor. A sediment extract from Hamilton Harbour was mutagenic in the Ames bacterial assay, both with and without microsomal activation. High levels of aromatic DNA adducts were induced in cultured mouse C3H1OT1/2 cells after in vitro exposure to Hamilton Harbour sediment extract. In two separate carcinogenicity experiments involving a sac fry microinjection assay with rainbow trout (Oncorhynchus mykiss), Hamilton Harbour sediment extract induced hepatocellular carcinomas in fish. No hepatic neoplasms were observed in fish that had been treated with sediment extract from Oakville Creek, or with extract from a reference sediment. The significance of these results is discussed in relation to the distribution of neoplasms in feral fish within western Lake Ontario.