Search

Abstract: The regulatory requirements imposed by the Habitats Directive (EU 93/43/EEC) require the Environment Agency for England and Wales (EA) to review consented discharges and determine whether they are compliant with Environmental Quality Standards (EQS). Since the EQS are annual averages, model predictions, and sample comparisons, should be made on an annual average basis. Advection and dispersion of metal contaminants in the Severn Estuary were computed using a coupled 1-D and 2-D hydrodynamic-water quality model. The external inputs of dissolved copper, arsenic, mercury and chromium to the model were from 66 industrial discharges and sewage treatment works and 30 rivers. The annual average predicted concentrations were compared with the annual average dissolved metal concentrations from the 2004 and 2005 monitoring programme, and any discrepancy used to identify the role of additional processes, mainly involving the sediments. This ability to separate anthropogenic inputs from internal estuarine processes contributes to a better understanding of the functioning of the estuary and hence an improved management capability. The paper discusses the approach in designing scenarios and characterising uncertainty, when decision-making in the regulatory context. [Copyright &y& Elsevier]

This paper highlights the increasing concerns relating to hydroenvironmetal issues and cites recent examples of the challenges now being regularly faced by hydroenvironmetal scientists and engineers. The limitations and restrictions of both physical (or laboratory) and numerical (or computer based) hydraulic models used in the planning and management of aquatic basins are discussed. General details are given of numerical models used for flow and water quality concentration predictions in estuarine waters, with particular application to the challenges occurring along the South Wales coast. A highly accurate and non-diffusive finite difference scheme that solves the transport equation for predicting water quality indicators and suspended sediment concentration distributions is also discussed. In particular, details are outlined of the extension of the water quality indicators of faecal coliforms, as required to comply with the EU Bathing Water Directive, to predict health risk assessment, in the form of predicting the risk of gastroenteritis.Three example research projects along the South Wales coast are described; the projects involve the application of two-dimensional and three-dimensional hydroenvironmetal models to predict flow patterns and water quality indicator organism distributions in the coastal receiving waters. These studies include: (i) a curvilinear finite difference approach to modelling flows in the Bristol Channel, (ii) coastal health risk predictions in Swansea Bay using combined water quality and epidemiological models, and (iii) combined sewer overflow discharges into Cardiff Bay. [Copyright &y& Elsevier]

Water quality modeling is a key element for the support of environmental protection and policymaking. The aim of this work is to describe the application of a far-field water quality model for the simulation of marine pollution occurring from heavy metals (cadmium, lead, nickel, copper, and zinc). The highly stressed marine area of the Saronikos Gulf (Aegean Sea, Eastern Mediterranean) was chosen for investigation. Major pollution sources were identified, loads were estimated, and the model was parameterized to reproduce the local seawater conditions. The distribution of the pollutants between the dissolved and particulate phases was examined. The performance of the model set-up was evaluated using field concentration measurements. The described implementation succeeded in reproducing the observed levels of pollution and therefore can be used as a baseline configuration to examine the cumulative impact of future pollution sources; for example, accidental pollution events. [ABSTRACT FROM AUTHOR]

Coastal marinas are particularly susceptible to pollution due to their limited flushing capabilities and ineffective management practices. Therefore, it is necessary to implement measures that promote enhanced sustainability. This study aims to explore the intricate relationship between tidal flushing characteristics and water quality within marinas to foster sustainable development and management practices that mitigate environmental impacts. The research scrutinized seven marinas along the Kuwait coastline, each exhibiting unique hydrodynamic conditions and geometric configurations. Water quality indicators such as BOD, COD, DO, and SO42− were evaluated concerning each marina's flushing efficiency through field assessments and hydrodynamic numerical modeling. An empirical formula was developed to predict and optimize flushing mechanisms, which provided critical insights into the design and management of marinas to enhance water quality. The study revealed significant disparities in water quality across the examined marinas as the hydrodynamic and geometric conditions differed. The empirical formula developed offers a novel approach to quantitatively assessing flushing efficiency, which is valuable for marina designers and managers, facilitating informed decisions, and promoting environmental sustainability. This study underscores the critical importance of integrating hydrodynamic and geometric considerations in the design and management of marinas to improve water quality and sustainability. It advocates for a multifaceted strategy that includes advanced design solutions, rigorous policy implementation, and active community engagement to safeguard coastal marine environments. The findings emphasize the need for comprehensive environmental management plans. [ABSTRACT FROM AUTHOR]

Currently, for modeling two-dimensional (2D) solute transport during pluvial and fluvial floods, the finite volume (FV) models are widely used because of their strong ability to handle steep concentration and velocity gradients from the flow advection term. However, heavy computational requirements are subsequently introduced which limit the numerical efficiency. To further increase numerical efficiency but keep the required accuracy, this study proposes a novel Solute Transport Modeling based on Cellular Automata framework (STMCA) to simulate solute transport due to the flow advection, turbulent diffusion, and material decay mechanisms in several sets of explicit algebraic equations. Four studied cases involving steep gradients of solute concentration and velocities in steady/unsteady violent flow conditions are used to compare the accuracy of the STMCA approach with a Godunov-type FV solute transport approach with a total variation diminishing (TVD) scheme. Then, the performances of the two approaches on water quality modeling are assessed through the E. Coli transport modeling during pluvial/fluvial floods on a real-scale terrain. The proposed STMCA approach is found to achieve almost the same accuracy as the FV approach. As to the numerical efficiency, the STMCA approach is faster than the FV approach by 289.6–328.6%. Hence, the proposed STMCA approach is proven to be an effective tool for simulating solute transport. [ABSTRACT FROM AUTHOR]

Microbial assessments of recreational water have traditionally focused on culturing or DNA‐based approaches of the planktonic water column, omitting influence from microbe–sediment relationships. Sediment (bed and suspended) has been shown to often harbour levels of bacteria higher than the planktonic phase. The fate of suspended sediment (SS) bacteria is extensively related to transport dynamics (e.g., deposition) of the associated sediment/floc. When hydraulic energy allows, SS will settle, introducing new (potentially pathogenic) organisms to the bed. With turbulence, including waves, currents and swimmers, the risk of human ingestion is elevated due to resuspension of bed sediment and associated microbes. This research used multiplex nanofluidic reverse transcriptase quantitative PCR on RNA of bacteria associated with bed and SS to explore the active bacteria in freshwater shorelines. Bacterial genes of human health concern regarding recreational water use were targeted, such as faecal indicator bacteria (FIB), microbial source tracking genes and virulence factors from waterborne pathogens. Results indicate avian sources (i.e., gulls, geese) to be the largest nonpoint source of FIB associated with sediment in Great Lakes shorelines. This research introduces a novel approach to microbial water quality assessments and enhances our understanding of microbe–sediment dynamics and the quality of freshwater beaches. [ABSTRACT FROM AUTHOR]

Residence time is an important parameter linked to the water quality in an estuary. In this paper, we identify and analyze the main processes that affect the residence time of the Caloosahatchee River Estuary, a micro-tidal and mixed diurnal-semidiurnal estuary located in western Florida. Multiyear validated hydrodynamic hindcast results were coupled with an offline particle tracking model to compute the residence time of the estuary, which showed a strong seasonality driven by the river discharge. The residence time reduced with increasing river flow. The wind velocity and direction also affected the residence time. The influence of the wind was dependent on the magnitude of the river discharge. In general, upstream-directed wind increased residence time, while downstream-directed wind decreased residence time. Downstream wind during the dry period reduced residence time on average by a week. Processes such as water density gradient-induced circulation and particle buoyancy also influenced the residence time of the estuary. The outcomes of this study can be used to better understand the influence of the main physical processes affecting the residence time at other similar estuaries and to help in the management of the estuaries to improve their water quality. [ABSTRACT FROM AUTHOR]

The amount of suspended sediment transported from rivers to the ocean fluctuates over time, with a substantial increase occurring during storm events. This surge in sediment poses numerous challenges to coastal areas, highlighting the importance of accurately assessing the sediment load to address these issues. In this study, we developed and experimentally verified a novel method for suspended-sediment-discharge quantification in estuaries and coasts using underwater imaging. Specifically, red clay samples with different particle sizes were introduced into separate tanks containing clean water. After adequate mixing, the concentration, particle size, turbidity, and water quality were measured and analyzed using LISST-200x and EXO2 Multiparameter Sonde sensors. To maintain constant lighting conditions, a camera box was created for filming. Based on the experimental results, a turbidity–concentration relationship formula was derived. The proposed regression equation revealed that the relationship between the turbidity and estimated suspended-sediment concentration was significantly affected by the particle size, and the prediction results were underestimated under high-concentration conditions. Using blue, green, and gray band values, a multiple regression model for estimating suspended-sediment concentrations was developed; its predictions were better than those obtained from the turbidity–concentration relationship. Following efficiency improvements through additional approaches considering underwater-image filming conditions and characteristics of actual streams, estuaries, and coasts, this method could be developed into an easily usable technique for sediment-discharge estimation, helping address sediment-related issues in estuaries and coastal regions. [ABSTRACT FROM AUTHOR]

An understanding of water exchange processes is essential for assessing water quality management issues in coastal bays. This paper evaluates the impact of water exchange processes on pollution persistence in a macro-tidal semi-closed coastal bay through two transport time scales (TTS), namely residence time and exposure time. The numerical model was calibrated against field-measured data for various tidal conditions. Simulated current speeds and directions were shown to agree well with the field data. By considering different release scenarios of a conservative tracer by the refinement of an integrated hydrodynamic and solute transport model (the EFDC), the two TTS were used for interpreting the water exchange processes in a semi-closed system, and for describing the effects of advective and dispersive processes on the transport and fate of pollutants. The results indicate that the magnitudes of river inflows to the bay, tidal ranges, and tracer release times significantly influence the residence and exposure times. Return coefficients were shown to be variable, confirming the different effects of returning water for the different conditions that were studied. For the tested river flow magnitudes and tide conditions, the exposure times were generally higher than the residence times, but particularly so for neap tide conditions. The results, therefore, highlight the risks associated with pollutants leaving a specified domain on an outgoing tide but re-entering on subsequent incoming tides. The spatial distributions of the exposure and residence times across the model domain confirmed that for the case of Dublin Bay, river inputs have a potentially greater impact on water quality on the northern side of the bay. [ABSTRACT FROM AUTHOR]

Beaches represent important economic resources linked to "Sun, Sea and Sand" tourism and, therefore, their water quality constitutes an issue of great relevance especially in developing countries. The main objective of this work was to determine the microbial quality of beach sediments along the Caribbean coast of the Department of Atlántico (Colombia) and its relationships with the existence of local sources of contamination (e.g., streams containing wastewaters), beach exposition to waves, the quantity of beach visitors—which is reflected by beach typology (e.g., urban, rural, etc.), the presence of tourist activities/infrastructures and the beach sand sedimentological characteristics. Along the study area, samples of beach sediments were gathered in beach face and backshore areas at 11 sectors and the microbiological counts of three faecal indicator bacteria, i.e., Escherichia coli, Enterococcus spp. and Clostridium perfringens, were determined. A homogeneous distribution was recorded along the coast of Escherichia coli and Clostridium perfringens in both beach face and backshore sediments, in the order of 5 and 2 log CFU/100 mL, respectively; Enterococcus spp. was, at places, not observed in backshore sediments. No relationships existed between, on one side, the counts of the faecal indicator bacteria considered and, on the other side, the presence of streams and tourist activities/infrastructures, beach typology, exposition to waves and the sedimentological characteristics of beach sands. Such results suggest a chronic contamination of beach face and backshore sediments linked to the heavily polluted sedimentological load of the Magdalena River. [ABSTRACT FROM AUTHOR]

Coastal and transitional waters are often used as bathing waters. In many regions, such activities play an important economic role. According to the European Union Bathing Water Directive (2006/7/EC) (BWD) the concentration of Escherichia coli in bathing water exceeding 500 CFU·100 mL−1 poses a high risk for bathers' health. In order to safeguard public health, microbiological environmental monitoring is carried out, which has recently been supported or replaced by mathematical models detailing the spread of sanitary contamination. This study focuses on the problems and limitations that can be encountered in the process of constructing a mathematical model describing the spread of biological contamination by E. coli bacteria in coastal seawater. This and other studies point to the following problems occurring during the process of building and validating a model: the lack of data on loads of sanitary contamination (often connected with multiple sources of biological contamination inflow) makes the model more complex; E. coli concentrations higher than 250 CFU·100 mL−1 (low hazard for health) are observed very rarely, and are associated with great uncertainty; the impossibility of predicting the time and intensity of precipitation as well as stronger winds and rougher sea, which may be a significant source of E. coli. However, there is universal agreement that such models will be useful in managing bathing water quality and protecting public health, especially during big failures of the wastewater network. [ABSTRACT FROM AUTHOR]

Dalian Jinshitan beach was chosen to evaluate the impact of a typhoon on the bacterial community structure and water quality of a marine bathing beach. The concentration of enterococci was determined by the cultivation method. The bacterial community structure and abundance were analyzed using the 16S rDNA next-generation sequencing and qPCR methods. Results showed that the abundance of cultivable enterococci both in alongshore and offshore seawater increased, while it decreased in dry, wet and submerged sand. The water quality deteriorated immediately after the typhoon, and nearly recovered one month after the typhoon. The typhoon event also decreased the bacterial abundance and changed the bacterial community of the beach. Sphingomonadaceae and Rhodobacteraceae significantly increased in seawater and decreased in dry sand immediately after the typhoon. Human and other fecal taxa increased in water and sand. One month after the typhoon, the diversity and many dominant bacterial taxa nearly recovered in seawater and wet sand. Our work shows that the typhoon changed the bacterial dynamics, deteriorated the water quality and proved the transportation of bacterial taxa and input of fecal pollution between water and beach sand or land. Apart from the impact of the typhoon, the geographical location was another important factor in the changed bacterial community. [ABSTRACT FROM AUTHOR]

In water treatment facilities, the last step of the treatment process includes disinfectant application to improve the water quality appropriate for a specific end-use purpose. At this step, contact tanks are used to mix water with the disinfectant. Mixing in contact tanks mainly relies on mechanical mixing processes to mix water with the disinfectant to activate the removal process. Thus, mixing efficiency of the contact tank design is critical for the reduction in the amount of disinfectant used to treat a fixed volume of water, to reduce the energy requirements to derive the treated volume of water through the system and to improve other design considerations of the contact tanks. There are numerous design alternatives reported in the literature that do achieve some of these purposes to a certain extent. Among the recent and more successful designs, one can cite the slot-baffle, the perforated-baffle, and the porous-baffle designs. Although these designs provide important improvements to the mixing process, the studies in which these concepts are reported did not provide an optimal design for the baffle geometry used in the design that would include other important considerations beyond the baffle geometry. In this paper, a new optimal design concept is introduced where important design considerations that are not considered in earlier studies are included in the analysis. The results show that new baffle geometries are possible for the optimal design of contact tanks when these innovative design criteria are included in the analysis. [ABSTRACT FROM AUTHOR]

The degradation of wetlands has caused regional environment and climate problems in the Sanjiang Plain. To provide a reference for wetland protection and restoration, two artificial water replenishment schemes were designed and four indicators—water quantity, ammonia nitrogen, total nitrogen and total phosphorus—were chosen to analyse results simulated by an environmental fluid dynamics code model. Simulation results showed that the wetlands receive a suitable amount of water and reach a normal water elevation, and the concentration of most water quality indicators decreased. In addition, a fuzzy analytic hierarchy process was used to select the four indicators and 30 different combinations were designed. Following the fuzzy calculation, the comprehensive scores of 29 combinations showed that a scheme involving multiple replenishments is better than a scheme of a single replenishment. This study indicates that an effective method for restoring wetlands near or surrounding irrigation areas is rational allocation of water resources. [ABSTRACT FROM AUTHOR]

The study provides an assessment of sand dredging activities from the bottom of the sea during 2016 in the Kingdom of Bahrain. Total Suspended Solids were analyzed from 2010 until 2016 in the northern and eastern locations according to the Manual of oceanographic observations and pollutant analyses methods. Fifty five percent of sand dredging companies complied with some legislation such as air quality and occupational health. Almost all lacked any compliancy evidence supporting environmental protection. Only 9% of these sand companies use siltation processes to the dredged materials. Siltation is an important step to avoid dispersion of sand into the marine environment. Ambient Total Suspended Solids was around 6.1 mgl−1 ± Standard Error and the study recommends 10 mgl−1 level as an accepted concentration in samples taken from 500 meters away from the dredgers and 100 mgl−1 in samples taken from the middle of the generated silt plumes. The effect of climatic temperatures, dust storms and rain levels on seawater Total Suspended Solids concentration has been briefly discussed. The study concludes no significance seasonal or spatial variation on the ambient Total Suspended Solids concentration. It recommends coupling remote sensing with the conventional data collection and integration of modelling efforts for effective cost benefit monitoring and management of the coastal waters. [ABSTRACT FROM AUTHOR]

Lowland river basins are characterised by complex hydrologic and hydraulic interactions between the different subsystems (aerated zone, groundwater, surface water), which may require physically-based dynamically-coupled surface water and groundwater hydrological models to reliably describe these processes. Exemplarily, for a typical north-eastern Germany lowland catchment (Tollense river with about 400 km²), an integrated hydrological model, MIKE SHE, coupled with a hydrodynamic model, MIKE 11, was developed and assessed. Hydrological and hydraulic processes were simulated from 2010 to 2018, covering strongly varying meteorological conditions. To achieve a highly reliable model, the calibration was performed in parallel for groundwater levels and river flows at the available monitoring sites in the defined catchment. Based on sensitivity analysis, saturated hydraulic conductivity, leakage coefficients, Manning's roughness, and boundary conditions (BCs) were used as main calibration parameters. Despite the extreme soil heterogeneity of the glacial terrain, the model performance was quite reasonable in the different sub-catchments with an error of less than 2% for water balance estimation. The resulted water balance showed a strong dependency on land use intensity and meteorological conditions. During relatively dry hydrological years, actual evapotranspiration (ETa) becomes the main water loss component, with an average of 60%–65% of total precipitation and decreases to 55%–60% during comparatively wet hydrological years during the simulation period. Base flow via subsurface and drainage flow accounts for an approximate average of 30%–35% during wet years and rises up to 35%–45% of the total water budget during the dry hydrological years. This means, groundwater is in lowland river systems the decisive compensator of varying meteorological conditions. The coupled hydrologic and hydraulic model is valuable for detailed water balance estimation and seasonal dynamics of groundwater levels and surface water discharges, and, due to its physical foundation, can be extrapolated to analyse meteorological and land use scenarios. Future work will focus on coupling with nutrient transport and river water quality models. [ABSTRACT FROM AUTHOR]

River water quality models usually apply the Fischer equation to determine the longitudinal dispersion coefficient (Dx) in solving the advection–dispersion equation (ADE). Recently, more accurate formulas have been introduced to determine Dx in rivers, which could strongly affect the accuracy of the ADE results. A numerical modelling-based approach is presented to evaluate the performance of various Dx formulas using the ADE. This approach consists of a finite difference approximation of the ADE, a MATLAB code and a MS Excel interface; it was tested against the analytical ADE solution and demonstrated using eight well-known Dx formulas and tracer study data for the Chattahoochee River (USA), the Severn (UK) and the Athabasca (Canada). The results show that Dx has an important effect on tracer concentrations simulated with the ADE. Comparison between the simulated and measured concentrations confirms the appropriate performance of Zeng and Huai's formula for Dx estimation. Use of the newly proposed equations for Dx estimation could enhance the accuracy of solving the ADE. [ABSTRACT FROM AUTHOR]

Purpose Finer sediment particles (silt and clay) transported by rivers carry the major part of nutrient loads by absorption; thus, sediment settling can remove nutrients from the water column. The purpose of this paper is to analyze the relation between reservoir sedimentation and water quality by assessing the reservoir sedimentation process and the sediments’ characteristics.Design/methodology/approach Bathymetric surveys from 2004 to 2014 were analyzed to assess the sedimentation process. Core samples provided information on a layer-by-layer basis of the sediment deposits, and water samples near the surface and near the bottom provided information on sediment concentration, and adsorbed and dissolved nutrients.Findings The upstream region of a reservoir is already silted. From 2004 to 2014, the delta evoluted approximately 500 m downstream and the deposits were mainly composed of clay. An area of approximately 1,000 m between the delta and the dam should still be able to continue allowing sediment deposition in the coming years. Most of the nutrients were absorbed into the sediment particles, except for the nitrogen measured in the dry season.Research limitations/implications Although analyses of the full cycle of the nutrients were not carried out, the constant sediment trapping of finer sediments and the high rate of absorbed nutrients in the suspended sediment support the hypothesis that the reservoir has removed nutrients from aqueous media by adsorption into sediments.Practical implications In the studied case, reservoir sedimentation has led to better water quality downstream.Originality/value It is shown in this study that reservoir sedimentation may have positive effects on river water quality. [ABSTRACT FROM AUTHOR]

The MARS-3D model in conjunction with the particle tracking module Ichthyop is used to study circulation and tracer dynamics under a variety of forcing conditions in the eastern English Channel, and in the Boulogne-sur-Mer harbour (referred to hereafter as BLH). Results of hydrodynamic modelling are validated against the tidal gauge data, VHF radar surface velocities and ADCP measurements. Lagrangian tracking experiments are performed with passive particles to study tracer dispersal along the northern French coast, with special emphasis on the BLH. Simulations revealed an anticyclonic eddy generated in the harbour at rising tide. Tracers, released during flood tide at the Liane river mouth, move northward with powerful clockwise rotating current. After the high water, the current direction changes to westward, and tracers leave the harbour through the open boundary. During ebb tide, currents convergence along the western open boundary but no eddy is formed, surface currents inside the harbour are much weaker and the tracer excursion length is small. After the current reversal at low water, particles are advected shoreward resulting in a significant increase of the residence time of tracers released during ebb tide. The effect of wind on particle dispersion was found to be particularly strong. Under strong SW wind, the residence time of particles released during flood tide increases from 1.5 to 6 days. For release during ebb tide, SW wind weakens the southward tidally induced drift and thus the residence time decreases. Similar effects are observed when the freshwater inflow to the harbour is increased from 2 to 10 m 3/s during the ebb tide flow. For flood tide conditions, the effect of freshwater inflow is less significant. We also demonstrate an example of innovative coastal management targeted at the reduction of the residence time of the pathogenic material accidentally released in the harbour. [ABSTRACT FROM AUTHOR]

Real-time prediction of bathing water quality is suggested as an appropriate regulatory approach in recent WHO Guidelines and new European Union (EU) standards for bathing water quality. The Scottish Environment Protection Agency (SEPA) has developed the first EU real-time bathing water quality predictions at 10 sites throughout Scotland since 2004. This paper covers two stages in the evolution of modelling tools which inform these predictions based on antecedent rainfall and river flow, using four sites as examples. These tools, together with associated advisory systems, demonstrate the potential to minimise public exposure to adverse water quality where this occurs in discrete episodes after rainfall events. In addition, they allow an effective prediction and communication system to provide significant compliance benefits as samples taken during periods when bathing is not advised are disregarded for classification purposes. [ABSTRACT FROM AUTHOR]

The main objective of the present investigation is to predict longitudinal dispersion coefficient ( Kx) in natural streams using artificial neural network (ANN) technique based on most famous training functions such as Trainlm, Trainrp, Trainscg, Trainoss, and so on. To achieve the goal, hydraulic and geometric data (shear velocity, channel width, local flow depth, and mean longitudinal velocity) that are easily obtained in natural streams are used. First, we have tried to review the most well-known of published work in the field due to find out deficiencies of them. Second, new approach of ANN model based on the famous training functions is applied for predicting Kx in natural streams and then the best architectures for each training functions is selected by trial and error. Finally, Levenberg-Marquardt training function (Trainlm) is selected as the best choice for training the network parameters. Determination coefficient ( R2) and mean absolute error for ANN (Trainrp) model were equal to 0.94 and 33 in the training and 0.95 and 30 in the testing steps, respectively. It is hoped that the presented methodology in the research, can be useful in river water quality management studies. © 2010 American Institute of Chemical Engineers Environ Prog, 2011. [ABSTRACT FROM AUTHOR]

Surface aerators have often been introduced in urban ponds for esthetics, but their roles in remediating water quality are less understood. Effects of surface aerators on controlling eutrophication were examined in two urban ponds, in which anaerobic odors and cyanobacterial blooms had occurred and several aerators had been installed. In one of the ponds, a dramatic improvement in dissolved oxygen (DO) (from 1.8 to 8.1 mg L−1) and total phosphorus (TP) (from 1.6 to 0.4 mg L−1) was evident based on the comparison before and after the aeration. Although cyano-bloom did not occur, phytoplankton was dominated by cyanobacteria Microcystis species in both periods. Chlorophyll a (Chl-a) increased (from 29 to 51 μg L−1) and water transparency decreased (from 81 to 27 cm) after the aeration. In the other pond with an irregular shape, water quality was monitored two years after the installation to examine seasonal variation in trophic state and its spatial variation associated with aerator distribution. The water was mixed vertically well for the whole pond, as indicated by small surface-to-bottom differences in temperature. DO decreased in summer after rainfall but was always >5.7 mg L−1. Total nitrogen (TN) and TP were 0.8–2.3 and 0.03–0.07 mg L−1, respectively, and no cyano-blooms were observed across sites throughout the year. Phytoplankton was dominated by green algae and diatom species, which may be favored by the lower phosphorus level of the pond. Chl-a was higher and transparency was lower in the north side, which had more aerators and less shade from trees and buildings. These results suggest that surface aerators increased DO by vertical and horizontal mixing of water, reduced phosphorus release from sediment, and prevented cyano-bloom occurrence, but they did not improve Chl-a level and transparency. Rather, aeration can promote algal growth, and thus, additional purifying measures such as filtration and contact oxidation are required to further improve the trophic state of these ponds. [ABSTRACT FROM AUTHOR]

Parallel policy developments driven in the USA by the Clean Water Act and in Europe by the Water Framework Directive have focused attention on the need for quantitative information on the fluxes of faecal indicator bacteria in catchment systems. Data are required on point and diffuse source loadings, fate and transport of these non-conservative parameters, on the land surface, within soil systems, in groundwater, streams, impoundments and nearshore waters. This new information is needed by regulators to inform Total Maximum Daily Load estimates in the USA and Programmes of Measures in Europe both designed to prevent impairment of water quality at locations where compliance is assessed against health-based standards for drinking, bathing or shellfish harvesting. In the UK, the majority of catchment-scale activity in this field has been undertaken by physical geographers although microbial flux analysis and modelling has received much less attention from the research and policy communities than, for example, the nutrient parameters. This paper charts the policy drivers now operative and assesses the evidence base to support current policy questions. Finally, gaps and priority research questions are identified. [ABSTRACT FROM AUTHOR]

In recent years, there has been a growing concern worldwide about climate change and the corresponding apparent increase in the risk and frequency of flooding and about the implications for a wide range of river basin management issues. This paper describes the United Kingdom government's approach to implementing Catchment Flood Management Plans (CFMPs), which will provide a large-scale strategic planning framework for the integrated management of flood risk to people and the development of the natural environment in a sustainable manner This unified approach is to be adopted across England and Wales, with a view to establishing a unified framework to study flood management in each major catchment. Following on from this introduction to the U.K. approach to high-level flood management, details are given of a study where better water quality management during flood flow conditions has been shown to require a catchment-wide approach to reducing diffuse source pollution from agricultural regions. This study also shows that without this holistic approach to water management, a major cause of non-compliance with an EU Directive would not have been established for this river basin. [ABSTRACT FROM AUTHOR]

Drinking water storage tanks are used to respond to fluctuating demand and to maintain water pressure in the distribution network. In drinking water plants, they are also used for disinfection. In both cases, a good knowledge of the residence time distribution (RTD) is important. An easy way to obtain the water RTD in a drinking water tank is to perform a tracer study. Nevertheless, "classical" tracing techniques can only be used under steady flow conditions. To cope with that, this study proposes a new approach to extend the application of tracer tests to unsteady flow conditions. This new approach is based on signal processing. It has been tested numerically and on a pilot scale model. The numerical tests have shown that this technique can be used for determining the RTD twice more rapidly than the "classical" methods. Thus, this technique allows to approach the knowledge of the RTD under unsteady flow conditions. Pilot scale tests have shown the need for other improvements to bring the quality of the results obtained to the same level of goodness as those obtained from a theorical example.Key words: drinking water, storage tanks, water quality, tracer study, residence time distribution, signal processing, unsteady flow.Les réservoirs d'eau potable sont utilisés pour répondre à la demande et maintenir la pression en réseau. Dans les usines de traitement de l'eau potable, ils sont utilisés comme bassins de stockage et de désinfection. Dans ces deux cas, une bonne connaissance de la distribution des temps de séjour (DTS) est importante. Une façon simple de déterminer la DTS est d'effectuer un essai de traçage. Toutefois, un essai de traçage n'est réalisable seulement qu'en régime permanent. La présente étude propose des améliorations à cette technique afin de permettre son utilisation en régime non permanent. Cette nouvelle méthode, basée sur des techniques du traitement du signal, a été validée numériquement et à l'échelle d'un bassin pilote. Les essais numériques ont montré que cette technique permet de déterminer la DTS dans les réservoirs plus rapidement que la méthode usuelle, permettant d'approcher la connaissance de la DTS en régime non permanent. L'essai pilote a montré que cette méthode nécessite des améliorations afin d'atteindre une qualité de résultat comparable à ceux obtenus numériquement.Mots clés : réservoir, eau potable, qualité de l'eau, essai de traçage, distribution des temps de séjour, traitement du signal, régime non permanent. [ABSTRACT FROM AUTHOR]

In recent years, considerable investment has been committed to sewerage infrastructure and new sewage treatment plants in the catchment surrounding an estuarine basin along the north-west coast of England. Although this capital investment has resulted in a marked reduction in the input of bacterial loads, relatively high counts of faecal indicator organisms are still being encountered in the coastal receiving waters, and the local bathing waters continue to fail on occasions to comply with the European Community (EC) Bathing Water Directive (1976) mandatory standards. Details are given herein of a comprehensive modelling study aimed at quantifying the impact of various bacterial inputs into the estuary and surrounding coastal waters on the bathing water quality. The model domain includes the coastal area and the entire estuary (namely the Ribble) up to the tidal limits of its tributaries. Faecal coliforms have been used as the main water quality indicator organisms. The numerical model developed for this study combines a depth integrated two-dimensional coastal model and a cross-sectionally integrated one-dimensional river model, and is capable of predicting water surface elevations, velocity fields and faecal coliform concentration distributions across the entire model domain. The hydrodynamic model was calibrated using water level and velocity measurements from three surveys and then validated against measured data from three other surveys. In order to predict the faecal coliform concentration distributions, variable faecal coliform decay rates were used, i.e. different values of decay rates were applied to the coastal and riverine waters, for day- and nighttime, and for wet and dry weather conditions. The maximum and minimum decay rates used were 2.32/day and 0.71/day for the dry and wet weather surveys, respectively. The model was then applied to (i) assess the impact of previous discharge strategies and investigate the effectiveness of future capital investment works and (ii) predict the impact of a range of strategic options, including: the effects of adding UV treatment, constructing storm water storage tanks and incorporating various combined sewer overflow (CSO) discharge scenarios for different weather conditions. [Copyright &y& Elsevier]

Degradation of water quality in recreational areas can be a substantial public health concern. Models can help beach managers make contemporaneous decisions to protect public health at recreational areas, via the use of microbial fate and transport simulation. Approaches to modeling microbial fate and transport vary widely in response to local hydrometeorological contexts, but many parameterizations include terms for base mortality, solar inactivation, and sedimentation of microbial contaminants. Models using these parameterizations can predict up to 87% of variation in observed microbial concentrations in nearshore water, with root mean squared errors ranging from 0.41 to 5.37 log10 Colony Forming Units (CFU) 100 mL−1. This indicates that some models predict microbial fate and transport more reliably than others and that there remains room for model improvement across the board. Model refinement will be integral to microbial fate and transport simulation in the face of less readily observable processes affecting water quality in nearshore areas. Management of contamination phenomena such as the release of storm-associated river plumes and the exchange of contaminants between water and sand at the beach can benefit greatly from optimized fate and transport modeling in the absence of directly observable data. [ABSTRACT FROM AUTHOR]

Numerical models are useful tools to analyze water quality by computing the concentration of physical, chemical and biological parameters. The present work introduces a two-dimensional depth-averaged model that computes the most relevant and frequent parameters used to evaluate water quality. High performance computing (HPC) techniques based on graphic processing unit (GPU) parallelization have been applied to improve the efficiency of the package, providing speed-ups of two orders of magnitude in a standard PC. Several test cases were analyzed to show the capabilities and efficiency of the model to evaluate the environmental status of rivers and non-stratified estuaries. IberWQ will be freely available through the package Iber. [ABSTRACT FROM AUTHOR]

Understanding the impact of various hydraulic structures, such as coastal reservoirs and tidal range impoundments, has been one of the key challenges of hydro–environmental engineering in recent years. Over the last half-century, several proposals for tidal range schemes in the UK have been scrutinised and then abandoned due to the uncertainty over the environmental footprint and/or the cost of electricity. Therefore, it is essential to understand the fundamental assumptions for reliable hydrodynamic analysis of these projects. This study examined the impact of the fully conserved momentum through tidal structures using a novel approach. The method was applied to 2D and 3D versions of the regional model of Swansea Bay tidal lagoon, examining two different types of velocity distribution at turbine exit. A simplified distribution significantly increased the velocity and length of the jet exiting the turbines during power generation. A realistic distribution gave more accurate results, with jet velocities more closely resembling the situation without including the momentum. The 3D model with realistic distribution has markedly improved the resulting vertical velocity profile. The value of the improved methodology for momentum conservation has proved to be particularly useful in local-scale studies. It can be applied to other similar hydraulic structures and used for the analysis of sediment transport, water quality, etc. [ABSTRACT FROM AUTHOR]

Artificial structures installed in rivers can change the natural physical, physiochemical, and biological characteristics of the rivers. Coliform bacteria are important water quality indicators, related to human health. This study investigated the relationship between coliform bacteria and water quality factors at eight weir stations constructed in the Nakdong River, a major river in South Korea. Fifteen water quality factors were analyzed at these sites from 2012 to 2016 using correlation and multiple regression analyses. The results for all stations confirmed the analytical validity, with high adjusted R2 values of approximately 0.6 and 0.8 on average for total and fecal coliforms, respectively. The results showed influential water quality factors affecting the concentration of coliform bacteria at weir stations. Specifically, total coliforms were mostly affected by organic matter and fecal coliforms were mostly affected by phosphate phosphorus and suspended solids. Rainfall was the most influential factor affecting both coliforms. Further, both coliforms were negatively affected by organic matter below the Dalseong weir in the mid- to downstream area of the Nakdong River. A positive relationship with phosphate phosphorus was indicated at all weir stations. To the authors' knowledge, this kind of study has never been attempted so far. Thus, the study results can provide important information on influential water quality factors related to coliform bacteria, especially in the Nakdong River, creating a foundation for future water quality management. [ABSTRACT FROM AUTHOR]

In this paper, a study of the potential causes of the occurrence of high concentration of Enterococcus Faecalis in surface water within urban areas in dry-weather conditions (DWCs) is presented. Two hypotheses were formulated: (1) undersized sewer system; and (2) groundwater infiltration into damaged sewer pipes. In both cases, more frequent combined sewer overflows (CSOs) may occur discharging untreated sewage into surface water. To evaluate the first hypothesis, a hydraulic model of a sewer was developed assuming a water-tight system. The simulation results show that CSOs never occur in DWCs but a rain event of intensity equal to 1/3 of one-year return period may trigger them. To evaluate the second hypothesis, a model combining sewer failure with groundwater level was developed to identify the sections of damaged sewer below the water table and, therefore, potentially affected by infiltration. The risk of infiltration exceeds 50% in almost half of the entire network even at the lowest calculated water table. Considering 50% of infiltration distributed throughout that part of the network, CSOs can occur also in DWCs. [ABSTRACT FROM AUTHOR]