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Abstract: The mathematical development of a two-dimensional finite volume model for groundwater flow is described. Based on the hydraulic equations for saturated flow, the model deploys an improved least squares gradient reconstruction technique to evaluate the gradient at the control volume face, derived from the application of the finite volume formulation and using a cell-centred structured quadrilateral grid. The model has been compared to a finite difference model with orthogonal grids. The effects of grid non-orthogonality and skewness are investigated. The model was verified by comparison with analytical solutions and the results for a finite difference model. The finite volume model was then applied successfully to an aquifer discharging in a section of the River Tawe, UK, and the results were compared with results from MODFLOW and observed hydraulic heads. Results of the numerical model tests and field exercise showed that the use of finite volume method provides modellers with a consistent substitute for the finite difference methods with the same ease of use and an improved flexibility and accuracy in simulating irregular boundary geometries. [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]

The additional resistance created by mangrove model trees was investigated through experiments in a hydraulic flume and two-dimensional depth-integrated numerical modelling. The numerical model reproduced the influence of the model trees and stilt roots for a range of flow conditions and experimental configurations after including a refined expression for drag on cylinders and the porosity effect. Drag coefficient values obtained from calibrating the hydrodynamic model with the experimental data ranged from 0 to 4.5. The results suggest that the drag coefficient may increase with increasing tree surface, but more data would be required to confirm this relationship. Simultaneous calibration of the drag coefficient and the eddy viscosity coefficient would improve the numerical model further. [Copyright &y& Elsevier]

Abstract: The study investigates the impact that construction of a Severn Barrage in the Severn Estuary, on the west coast of the UK, might have on local wave conditions. Implementation of a barrage will impact on tidal currents and water elevations in the wider region. There is strong tidal modulation of wave conditions under the natural regime and therefore barrage-induced changes to tidal conditions could affect wave modulation in the region. This paper uses Swan, an open source 3rd generation spectral wave model, to investigate the possible impacts of construction of a barrage on tidal modulation of the wave conditions. It is found that current variations, rather than water level variations, are the dominant factor in tidal modulation of wave conditions. Barrage implementation does not substantially change the modulation of the wave period or direction. However, barrage implementation does affect the tidal modulation of wave heights in the area of interest. The tidal modulation of the wave heights is generally reduced compared to the natural case; the peaks in the wave heights on an incoming tide are slightly lowered and there is lesser attenuation in wave heights on the outgoing tide. This modulation leads to net changes in the wave heights over one tidal cycle. For all of the tested wave conditions, this net change is small for the majority of the tested domain, namely to within ±5% of the no barrage case. There are some areas of greater change, most notably larger net increases in the wave heights near the North Somerset coast where the post-construction net wave height increase over a tidal cycle approach 20% of the pre-construction conditions. These changes do not impact coastal flooding because the wave height increase is not co-incident with high tide. Importantly, the maximum wave height is not increased and thus the likelihood of extreme events is not increased. The area of greatest reduction is between Swansea and Porthcawl. Changes over a neap tidal cycle show similar patterns of net change, but the modulation over the tidal cycle is different; primarily the magnitude of modulation is half that for the spring tide case and the shape is altered in some locations. [Copyright &y& Elsevier]

Abstract: The measurement of the bed shear stress along vegetated river beds is essential for accurately predicting the water level, velocity and solute and sediment transport fluxes in computational hydroenvironmental models. Details are given herein of an experimental and theoretical study to determine the bed boundary shear stress along vegetated river beds introducing a novel field measuring method, namely the FliessWasserStammtisch (FST)-hemispheres. Although investigations have been conducted previously for sedimentary channels using the FST-hemispheres, this preliminary study is thought to be the first time that such hemispheres have been used to investigate the bed shear stresses in vegetated channels. FST-hemispheres were first developed by Statzner and Müller [1989. Standard hemispheres as indicators of flow characteristics in lotic benthos research. Freshwater Biology 21, 445–459] to act as an integrated indicator of the gross hydrodynamic stresses present near the bed. Test and validation data were found to be at least of the same order of magnitude for the stresses predicted from literature for sedimentary channels, with this study establishing the commencement of a database of calibrated FST-hemisphere laboratory data for vegetated channel beds. In a series of experiments, depths ranging from 0.1 to 0.28m were considered, equating directly to comparable conditions in small rivers or streams. The results of this study provide a basis for enabling the FST-hemispheres to be used to evaluate the boundary shear stress for a wider range of applications in the future, including vegetated river beds. [Copyright &y& Elsevier]

Abstract: A new EU Bathing Water Directive was implemented in March 2006, which sets a series of stringent microbiological standards. One of the main requirements of the new Directive is to provide the public with information on conditions likely to lead to short-term coastal pollution. The paper describes how numerical models have been combined with Artificial Neural Networks (ANNs) to develop an accurate and rapid tool for assessing the bathing water status of the Ribble Estuary, UK. Faecal coliform was used as the water quality indicator. In order to provide enough data for training and testing the neural networks, a calibrated hydrodynamic and water quality model was run for various river flow and tidal conditions. In developing the neural network model a novel data analysis tool called WinGamma was used in the model identification process. WinGamma is capable of determining the data noise level, even with the underlying function unknown, and whether or not a smooth model can be developed. Model predictions based on this technique show a good generalisation ability of the neural networks. Details are given of a series of experiments being undertaken to test the ANN model performance for different numbers of input parameters. The main focus has been to quantify the impact of including time series inputs of faecal coliform on the neural network performance. The response time of the receiving water quality to the river boundary conditions, obtained from the hydrodynamic model, has been shown to provide valuable knowledge for developing accurate and efficient neural networks. [Copyright &y& Elsevier]

Abstract: Pollution loads from land sources and their impact on the receiving waters can be predicted by using land-use and surface water quality models, respectively. In this paper details are given of the development of an integrated modelling system for managing water quality in coastal basins. The system includes a model linking the pollution input loads to land-use and a model for simulating surface flow and chemical and biological processes. The land-use model consists of two main components: a database and a model base. It uses a GIS system, namely ArcGIS, as the model platform. The database, built in the Geo-database format, includes six data sets containing information on social, economical, bathymetrical and hydrological aspects of a study area. The model base includes a series of transfer functions that link the pollution loads to key sources, including those from: industrial, domestic and agricultural inputs, and fish and animal farming. The water quality model is a numerical model which solves the governing equations representing the physical, chemical and biological processes in coastal waters. The modelling system was set up for Bohai Bay in China, with the land-use model being used to provide nutrient loadings from individual inputs and the water quality model used to predict the impact of these inputs on the receiving waters. Model simulations were also undertaken to predict the water quality conditions for various development and management scenarios. [Copyright &y& Elsevier]

Abstract: This paper outlines a numerical modelling study to predict the average residence time of a conservative tracer in a macro-tidal estuary, namely the Mersey Estuary, UK. An integrated hydrodynamic-dispersion model was used to predict the average residence time in the estuary for various tidal level and freshwater discharge conditions. The numerical model was verified against six sets of field measured hydrodynamic data, with the model-predicted water elevations and salinity levels generally agreeing well with the field measurements. The numerical model results show that in the Mersey Estuary both the tidal level and river discharge affect significantly the predicted average residence time. The value of the average residence time is also shown to be closely linked to the intensity of the residual tidal current. This is due to the fact that a large proportion of the Upper and Inner Estuary dries out during low tides, thus a significant amount of the tracer material is transported through the deep channels. An increase in the freshwater discharge causes a considerable increase in the intensity of the residual current along the main channels and thus a reduction in the average residence time. The predicted overall tracer residence time for the whole estuary is relatively short for a relatively large estuary, ranging from less than 1 day to 4 days for various tidal level and freshwater flow combinations. When the tidal range and freshwater discharge are both small, then the local tracer residence time in the upper part of the estuary can be significantly longer than the values predicted for the middle and lower reaches of the estuary. [Copyright &y& Elsevier]

Abstract: The paper describes a modelling study of near-shore coastal waters, undertaken to assess the impact of various bacterial input loads on the receiving waters in a coastal basin in the UK. Total and faecal coliforms, used as the indicators for bathing water quality under the European Union (EU) Bathing Water Directive, were numerically modelled using a 2D depth integrated hydro-environmental model. Details are given of the governing equations and solution methods used in the numerical model, together with a discussion of the recent development in faecal bacterial indicator modelling. Details are also given of a field data collection exercise, which involved initially collecting existing information on effluent input loads and followed by an intensive field survey. Using the water quality model, the mortality rate of the pathogen bacteria was investigated. Three methods were used to represent the relationship between the decay rate and the level of solar radiation including: a constant decay rate, day- and night-time decay rates and a solar radiation related time varying decay rate. Relatively close agreement between model predicted and measured total and faecal coliform concentration distributions were obtained for different day- and night-time decay rates and time varying decay rates. No significant differences were found in the optimum decay rates for total and faecal coliform levels. Finally, the impact of the individual inputs on the bathing water quality of the basin was also statistically and numerically investigated. Results showed that the River Irvine was the most significant input during high river flows, and that under these conditions the bathing waters were likely to fail to comply with the European Union Bathing Water Directive. For base river flow conditions the Meadowhead effluent input was found to be critical for both total and faecal coliform level predictions. [Copyright &y& Elsevier]

Abstract: Details are given of the development and application of a numerical model for predicting free-surface flows in estuarine and coastal basins using the finite volume method. Both second- and third-order accurate and oscillation free explicit numerical schemes have been used to solve the shallow water equations. The model deploys an unstructured triangular mesh and incorporates two types of mesh layouts, namely the ‘cell centred’ and ‘mesh vertex’ layouts, and provides a powerful mesh generator in which a user can adjust the mesh-size distribution interactively to create a desirable mesh. The quality of mesh has been shown to have a major impact on the overall performance of the numerical model. The model has been applied to simulate two-dimensional dam break flows for which transient water level distributions measured within a laboratory flume were available. In total 12 model runs were undertaken to test the model for various flow conditions. These conditions include: (1) different bed slopes (ranging from zero to 0.8%), (2) different upstream and downstream water level conditions, and (3) initially wet and dry bed conditions, downstream of the dam. Detailed comparisons have been made between model predicted and measured water levels and good agreement achieved between both sets of results. The model was then used to predict water level and velocity distributions in a real estuary, i.e. the Ribble Estuary, where the bed level varies rapidly at certain locations. In order to model the whole estuary, a 1-D numerical model has also been used to model the upper part of the estuary and this model was linked dynamically to the 2-D model. Findings from this application are given in detail. [Copyright &y& Elsevier]

Abstract: Intestinal enterococci are the principal ‘health-evidence-based’ parameter recommended by WHO for the assessment of marine recreational water compliance. Understanding the survival characteristics of these organisms in nearshore waters is central to public health protection using robust modelling to effect real-time prediction of water quality at recreation sites as recently suggested by WHO and the Commission of the European Communities Previous models have more often focused on the coliform parameters and assumed two static day-time and night-time T 90 values to characterise the decay process. The principal driver for enterococci survival is the received dose of irradiance from sunlight. In the water column, transmission of irradiance is determined by turbidity produced by suspended material. This paper reports the results of irradiated microcosm experiments using simulated sunlight to investigate the decay of intestinal enterococci in relatively turbid estuarine and coastal waters collected from the Severn Estuary and Bristol Channel, UK. High-turbidity estuarine waters produced a T 90 value of 39.5h. Low-turbidity coastal waters produced a much shorter T 90 value of 6.6h. In experiments receiving no irradiation, high-turbidity estuarine waters also produced a longer T 90 of 65.1h compared with corresponding low-turbidity coastal waters, T 90 24.8h. Irradiated T 90 values were correlated with salinity, turbidity and suspended solids (, ). The results suggest that enterococci decay in irradiated experiments with turbidity >200 NTU is similar to decay observed under dark conditions. Most significantly, these results suggest that modelling turbidity and or suspended solids offers a potential means of predicting T 90 values in ‘real-time’ for discrete cells of a hydrodynamic model. [Copyright &y& Elsevier]

At present, very little information is available about the design and maintenance of ‘natural’ river restoration schemes, combining hydraulic and ecological conditions. This field and numerical modelling study sought to redress this situation. A unique data set, containing hydraulic, substrate, and ecological parameters was collected over a three-year period for a 3 km meandering section of the Afon Morlais, a small river in West Wales, UK. The reach was investigated commencing immediately after it had been reinstated over a disused opencast coal mine, with the aim being to evaluate the overall success of the restoration scheme and for calibration and validation of the ecohydraulics model developed in this study. Surveying results showed that the river bed was stable and chemical data analysis indicated that the water quality was good. Macroinvertebrates were collected and taxa also showed good water quality. A computer modelling tool was used and further developed to investigate the dependence of habitat creation on hydrodynamic factors. The two-dimensional finite difference model Depth Integrated Velocitiy and Solute Transport (DIVAST) was applied to several meanders, taking account of the cross-sectional velocity and depth distributions. A curvilinear computational mesh was applied. DIVAST was then linked with the stream ecology; through macroinvertebrate suitability and two-dimensional velocity, bed shear stress and the consequential habitat distributions of two macroinverbrate species were predicted. The integrated modelling tool enabled habitat predictions to be made and addressed current design guidelines for enhanced recolonisation processes in river regeneration projects. [Copyright &y& Elsevier]

This article first details the development of an integrated modelling system faster (Flow And Solute Transport in Estuaries and Rivers), which is capable of predicting water elevations, velocities and solute and sediment concentration distributions in well-mixed rivers or narrow estuaries. The model comprises hydrodynamic and solute transport solvers, a user-friendly graphical interface—including data management and storage tools—and graphic and tabular reporting facilities. The faster program, initially written in Fortran, is a numerical modelling program which deploys highly accurate numerical schemes to solve the hydrodynamic and solute transport equations. This model has recently been modified to include a graphical user interface based on an object-oriented methodology, and implemented using the Visual Basic programming language. Details are given herein of the procedures used to combine the Fortran program with a Windows-based programming language, namely Visual Basic. Particular emphasis has been focused on the construction of the interface for unsteady free-surface flow problems. An example application of the model is cited to illustrate the data management capabilities and accuracy of the model when applied to real hydroenvironmental projects. [Copyright &y& Elsevier]

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]