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Monitoring the ecological status of water bodies is crucial to guarantee human health and economic development. However, monitoring is often deficient in developing regions due to high installation and maintenance costs, thus it is frequently supported by water quality models, whose results are themselves affected by the lack of detailed input data. A possible solution is to use probabilistic models that consider the inherent uncertainty of the different inputs. In this research, we extended a simple water quality model (QUAL-UFMG, based on Qual2E) through Monte Carlo simulations to generate probabilistic results and applied it to a representative case study in Brazil. Results showed that, depending on the distribution of probabilities and variability of parameters adopted, the outcome of a non-deterministic modelling approach may differ significantly from a deterministic one regarding compliance with water quality standards. Moreover, the probabilistic strategy is more scientifically transparent and robust, as it explicitly communicates the uncertainty in both the measured data and modelling results. We conclude that a probabilistic approach is particularly useful in regions with a low data availability such as developing countries, as uncertainties are high due to insufficient monitoring, and the risk to human health is elevated due to a low prevalence of sanitation. HIGHLIGHTS A deterministic water quality model is expanded through Monte Carlo simulations.; Outcomes of deterministic and probabilistic approaches to water quality modelling are compared for a case study in Brazil.; There may be significant differences in modelling results regarding compliance to water quality standards depending on the approach taken; this is key in data scarce regions with deficient monitoring networks.;

Sand bed braided rivers, such as the Brahmaputra, are highly dynamic in nature. The braided rivers change their course frequently, which causes huge bank erosion and sand bar migration. During the monsoon season the braided river has higher sediment-carrying capacity and the erosion power. A large amount of energy dissipation takes place in terms of river fragmentation and sand bar migration and bar erosion. These are common morphological characteristics within the sand bed braided rivers. The dynamic river bed and planform offer varying resistance to flow based on the hydrologic regime and reach characteristics of the river. Estimation of channel roughness coefficient is important for hydraulic modelling of the river. In this study, roughness characteristics of the Brahmaputra river were estimated using altimetry derived river stage records at different reaches of the river. The estimated Manning's roughness coefficients were incorporated in one-dimensional hydraulic model to perform simulations over the middle reach of the Brahmaputra River. Comparison of seasonal water level differences at different reaches of the river was performed using altimetry retrieved and model simulated water level for 2014 and 2015, respectively. The simulated water levels from altimetry derived Manning's roughness coefficient were found to be in close range with altimetry retrieved water levels for 2014 and 2015. It was found that the spatio-temporal variation of Manning's roughness coefficient proved to be an important parameter for modelling braided river systems such as the Brahmaputra. [ABSTRACT FROM AUTHOR]

This paper shows a detailed, advanced procedure to implement cost–benefit analyses (CBAs) in order to assess the effectiveness of flood mitigation measures. The town of Lodi (North of Italy) has been selected as a case study for the research work, as it was hit by a large flood in 2002 for which several data are available. In order to compute the benefits, in terms of avoided damage with the mitigation measure in place, micro-scale damage models developed within the Flood-IMPAT + project were used. The great amount of input data for such models comes from results of a two-dimensional river modelling, for what concern the hazard parameters, and from open-source database, to evaluate the vulnerability and the exposure of the hit area. The research highlights that technological-advanced, high-performance hydraulic models allow taking into account a variety of hazard scenarios, with reasonable computational time, supporting the proper accounting of the probabilistic nature of risk in CBAs. Nonetheless, such high-resolution tools support the implementation of micro-scale damage assessment models, which can provide information on the distribution of benefits in the investigated area, increasing the effectiveness of CBAs for policy making. [ABSTRACT FROM AUTHOR]

Perfluorooctanoic acid (PFOA) and related chemicals among the per- and polyfluoroalkyl substances are widely distributed in the environment. Adverse health effects may occur even at low exposure levels. A large-scale contamination of drinking water resources, especially the rivers Möhne and Ruhr, was detected in North Rhine-Westphalia, Germany, in summer 2006. As a result, concentration data are available from the water supply stations along these rivers and partly from the water network of areas supplied by them. Measurements started after the contamination's discovery. In addition, there are sparse data from stations in other regions. Further information on the supply structure (river system, station-to-area relations) and expert statements on contamination risks are available. Within the first state-wide environmental-epidemiological study on the general population, these data are temporally and spatially modelled to assign estimated exposure values to the resident population. A generalized linear model with an inverse link offers consistent temporal approaches to model each station's PFOA data along the river Ruhr and copes with a steeply decreasing temporal data pattern at mainly affected locations. The river's segments between the main junctions are the most important factor to explain the spatial structure, besides local effects. Deductions from supply stations to areas and, therefore, to the residents' risk are possible via estimated supply proportions. The resulting potential correlation structure of the supply areas is dominated by the common water supply from the Ruhr. Other areas are often isolated and, therefore, need to be modelled separately. The contamination is homogeneous within most of the areas. [ABSTRACT FROM AUTHOR]

River model calibration is essential for reliable model prediction. The manual calibration method is laborious and time-consuming and requires expert knowledge. River engineering software is now equipped with more complex tools that require a high number of parameters as input, rendering the task of model calibration even more difficult. This paper presents the calibration tool O.P.P.S. (Optimisation Program for PEST and SRH-2D) and then uses it in multiple calibration scenarios. O.P.P.S. combines PEST, a calibration software and SRH-2D, a bi-dimensional hydraulic and sediment model for river systems, into an easy-to-use set of forms. O.P.P.S is designed to minimise the user’s interaction with the involved program to carry out rapid and functional calibration processes. PEST uses the Gauss–Marquardt–Levenberg algorithm to adjust the model’s parameters by minimising an objective function containing the differences between field observation and model-generated values. The tool is used to conduct multiple calibration series of the modelled Ha! Ha! river in Québec, with varying information content in the observation fields. A sensitivity study is also conducted to assess the behaviour of the calibration process in the presence of erroneous or imprecise measurements. [ABSTRACT FROM AUTHOR]

As opposed to other disciplines, automated calibration procedures are not common practice for full hydrodynamic river models, mainly because of the long computation times impeding the accurate assessment of parameter values. Default or text-book values are therefore often used. This paper introduces a methodology to optimize hydrodynamic model parameter values, based on the use of a surrogate conceptual model. Thanks to the spatial lumping and the explicit calculation schemes of these conceptual models, very short calculation times and a large number of simulation runs can be achieved. The surrogate model is coupled with the Shuffled Complex Evolution Metropolis algorithm of the University of Arizona (SCEM-UA) to identify the optimal parameter sets and their uncertainty. Afterwards, the optimized parameter values are transferred to the full hydrodynamic model. The methodology is demonstrated on a case study of the river Molenbeek in Belgium, using streamflow, water level and gate level observations. Results show a decrease of the hydrodynamic model residuals by about 60 percent. [ABSTRACT FROM AUTHOR]

Lakes influence the regional climate and hydrology in a number of ways and therefore they should be represented in climate models in a realistic manner. Lack of representation of lakes in models can lead to errors in simulated energy and water fluxes, for lake-rich regions. This study focuses on the assessment of the impact of climate change on lakes and hydrology as well as on the influence of lakes on projected changes to regional climate and surface hydrology, particularly streamflows, for Northeast Canada. To this end, transient climate change simulations spanning the 1950-2100 period are performed, with and without lakes, with the fifth generation of the Canadian Regional Climate Model (CRCM5), driven by the Canadian Earth System Model (CanESM2) at the lateral boundaries for Representative Concentration Pathway 8.5. An additional CRCM5 simulation, driven by European Centre for Medium-Range Weather Forecasts Re-Analysis Interim (ERA-Interim) for the 1980-2010 period, is performed in order to assess performance and boundary forcing errors. Performance errors are assessed by comparing the ERA-Interim-driven simulation with available observation datasets, for the 1980-2010 period, for selected variables: 2-m air temperature, total precipitation, snow water equivalent and streamflow. The validation results indicate reasonable model performance over the study region. Boundary forcing errors are studied by comparing ERA-Interim-driven simulation with the one driven by CanESM2 for the current 1980-2010 period, to identify regions and seasons for which projected changes should be interpreted with extra caution. Comparison of projected changes from the CRCM5 simulations with and without lakes suggest that the presence of lakes results in a dampening of projected increases to 2-m air temperature for all seasons almost everywhere in the study domain, with maximum dampening of the order of 2 °C occurring during winter, mostly in the vicinity of the lakes. As for streamflows, projected increases to spring streamflows, based on the simulation with lakes, are found to be smaller than that without lakes and this is due to the storage effect of lakes. Similarly, lower decreases in summer streamflows in future climate are noted in the simulation with lakes due to the gradual release of snowmelt water stored in lakes. An additional CRCM5 transient climate change simulation with lakes and interflow, i.e. lateral flow in the soil layers, is compared with the simulation with lakes, but without interflow, to assess the impact of interflow on projected changes to regional climate and hydrology. Maximum interflow is projected to shift earlier in spring and the maximum interflow rate is expected to decrease by around 25 % in future. Results suggest that the impact of interflow on projected changes to precipitation, soil moisture and humidity are modest, even though the interflow intensity is changing noticeably in future climate. The impact of the interflow on projected changes to streamflows is in the range of ±50 m/s. This study thus for the first time demonstrates the impact of lakes and interflow on projected changes to the regional climate and hydrology for the study region using a single regional modelling system. [ABSTRACT FROM AUTHOR]

Lakes affect regional climate by modulating surface albedo, surface energy, and moisture budgets. This is especially important for regions such as Northeast Canada with approximately 10 % of the landmass covered by lakes, wetlands and rivers. From the regional hydrology perspective, interactions between lakes and rivers are important as streamflow patterns can be significantly modified by lake storage, and similarly lake levels can be modified by streamflows. In this study, using a suite of experiments performed with the fifth generation Canadian Regional Climate Model (CRCM5) driven by the European Centre for Medium range Weather Forecasting ERA40 reanalysis data at the lateral boundaries for the 1979-2010 period, lake-river-atmosphere interactions and their impact on the regional climate/hydrology of north-east Canada are assessed. In these CRCM5 simulations, a one-dimensional lake model represents lakes, while the rivers are modeled using a distributed routing scheme, and one of the simulations includes interflow, i.e. lateral flow of water in the soil layers. Comparison of CRCM5 simulations with and without lakes suggests significant differences in winter/summer precipitation and winter temperature for the study region. CRCM5 simulations performed with and without lake-river interactions suggest improved representation of streamflows when lake storage and routing are taken into account. Adding the interflow process leads to increased streamflows during summer and fall seasons for the majority of the rivers, causing modest changes to land-atmosphere interactions via modified soil moisture. The impact of interflow on streamflow, obtained in this study, is comparable to the impact of lake-atmosphere interactions on streamflows. This study clearly demonstrates the need for realistic representation of lake-river interactions in regional climate models for realistic simulation of regional hydrology, particularly streamflows. [ABSTRACT FROM AUTHOR]

The planning of the correct channel reconstruction is a priority in the rehabilitation of regulated surface streams. The present study examines the most important morphological and ecohydrological factors of a highly modified watercourse. A comparative analysis was performed among modelled and measured morphological, river geometrical, hydraulic, and vegetation status indicators. Reduction of data redundancy and examination of the relationships was done by factor analysis. This was found during the data reduction to six or seven attributes (component) and it was sufficient for imaging the original information content. There are mathematically derived hydrological background variables that are extremely significant in characterizing the watercourses, for example; the Reynolds number, Froude number, ratio of slope Froude-number, speed-to-depth ratio, depth-to-width ratio, etc. The partially regulated and artificial river sections were numerically separated from each other in the analysis. The functional aquatic plant habitats and Manning’s n Roughness have got a higher factor weight in the less regulated river section, than in artificial stage. The weakest factor weights were those status indicators which were most changed by the regulations. The results provide support for defining and monitoring the required environmental geometric riverbed interventions. [ABSTRACT FROM AUTHOR]

Aquatic habitat assessment and river restoration design require geospatially explicit maps of hydraulic conditions. Diverse mechanistic ecohydraulic models compute spatially explicit depth and velocity results to evaluate habitat suitability spatially as a function of these abiotic conditions. This study compared depth and velocity results from two-dimensional (2D) and one-dimensional (1D) hydraulic models with algorithms that laterally discretize 1D velocity and interpolate depth and velocity spatially based on the Laplacian heat mapping approach. These 'conveyance distributed' methods constitute 'best 1D modelling practice' and were compared with 2D results for the first time. The 1D and 2D models were applied to three morphologically distinct reaches (leveed, meandering, and anastomosing) for three flows (base, bankfull, and flood flows) of the partially regulated, gravel/cobble lower Yuba River in north-central California. The test metrics were the coefficient of determination ( R2) and the median absolute residual ( [ABSTRACT FROM AUTHOR]

The impact of urban water fluxes on the river system outflow of the Grote Nete catchment (Belgium) was studied. First the impact of the Waste Water Treatment Plant (WWTP) and the Combined Sewer Overflow (CSO) outflows on the river system for the current climatic conditions was determined by simulating the urban fluxes as point sources in a detailed, hydrodynamic river model. Comparison was made of the simulation results on peak flow extremes with and without the urban point sources. In a second step, the impact of climate change scenarios on the urban fluxes and the consequent impacts on the river flow extremes were studied. It is shown that the change in the 10-year return period hourly peak flow discharge due to climate change (-14% to þ45%) was in the same order of magnitude as the change due to the urban fluxes (þ5%) in current climate conditions. Different climate change scenarios do not change the impact of the urban fluxes much except for the climate scenario that involves a strong increase in rainfall extremes in summer. This scenario leads to a strong increase of the impact of the urban fluxes on the river system. [ABSTRACT FROM AUTHOR]

Hydrodynamic river models are applied to design and evaluate measures for purposes such as safety against flooding. The modelling of river processes involves numerous uncertainties, resulting in uncertain model results. Knowledge of the type and magnitude of these uncertainties is crucial for a meaningful interpretation of the model results. Uncertainty in the hydraulic roughness due to bed forms is one of the main contributors to the uncertainty in the modelled water levels. The aim of this study was to quantify the uncertainty in the bed form roughness under design conditions and quantify the effect on the design water levels in the Dutch river Waal. Five roughness models that predict bed form roughness based on measured bed form and flow characteristics were extrapolated to design conditions. The results show that the 95% confidence interval of the predicted Nikuradse roughness values under design conditions ranges from 0.32 to 1.03 m. This uncertainty was propagated through the two-dimensional hydrodynamic model, WAQUA, by means of a Monte Carlo simulation for an idealized schematization of the Dutch river Waal. The uncertain bed form roughness results in an uncertainty in the design water levels, with a 95% confidence interval of 0.53 m, which is significant for Dutch river management practice. The uncertainty in the bed form roughness was mainly caused by a lack of knowledge about the physical process of bed form evolution that causes roughness. An improved estimation of bed form roughness can significantly reduce the uncertainty in the design water levels. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Hydrodynamic river models are applied to design and evaluate measures for purposes such as safety against flooding. The modelling of river processes involves numerous uncertainties, resulting in uncertain model outcomes. Knowledge of the type and magnitude of uncertainties is crucial for a meaningful interpretation of the model results and the usefulness of results in decision making processes. The aim of this study is to identify the sources of uncertainty that contribute most to the uncertainties in the model outcomes and quantify their contribution to the uncertainty in the model outcomes. Experts have been selected based on an objective Pedigree analysis. The selected experts are asked to quantify the most important uncertainties for two situations: (1) the computation of design water levels and (2) the computation of the hydraulic effect of a change in the river bed. For the computation of the design water level, the uncertainties are dominated by the sources that do not change between the calibration and the prediction. The experts state that the upstream discharge and the empirical roughness equation for the main channel have the largest influence on the uncertainty in the modeled water levels. For effect studies, the floodplain bathymetry, weir formulation and discretization of floodplain topography contribute most to the uncertainties in model outcomes. Finally, the contribution of the uncertainties to the model outcomes show that the uncertainties have a significant effect on the predicted water levels, especially under design conditions. [ABSTRACT FROM AUTHOR]

River hydraulic models have successfully identified the weaknesses and areas for improvement with respect to flooding in the Sarawak River system, and can also be used to support decisions on flood management measures. Often, the big question is 'how'. This paper demonstrates a theoretical flood management framework inferred from Sarawak River modelling outputs. The river model simulates the movement of flood waters through river reaches. Information on flood levels and overtopping of embankments is used to guide a flood early warning system. The above-mentioned elements were combined in a logical framework that showed logic sequences and impact indicators for improved flood relief activities in the city of Kuching, Malaysia. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents the analytical properties of the solutions of the sensitivity equations for steady-state, two-dimensional shallow water flow. These analytical properties are used to provide guidelines for model calibration and validation. The sensitivity of the water depth/level and that of the longitudinal unit discharge are shown to contain redundant information. Under subcritical conditions, the sensitivities of the flow variables are shown to obey an anisotropic elliptic equation. The main directions of the contour lines for water depth and the longitudinal unit discharge sensitivity are parallel and perpendicular to the flow, while they are diagonal to the flow for the transverse unit discharge sensitivity. Moreover, the sensitivity for all three variables extends farther in the transverse direction than in the longitudinal direction, the anisotropy ratio being a function of the sole Froude number. For supercritical flow, the sensitivity obeys an anisotropic hyperbolic equation. These findings are confirmed by application examples on idealized and real-world simulations. The sensitivities to the geometry, friction coefficient or model boundary conditions are shown to behave in different ways, thus providing different types of information for model calibration and validation. [Copyright &y& Elsevier]

Abstract: The deterministic Riverstrahler model of river functioning is applied for the first time to sub-arctic catchments. Seasonal nutrient (N, P, Si) deliveries to the coastal zone are simulated, and nutrient annual fluxes are established for the nearly pristine river Kalix (hereafter called Kalixälven) and the heavily dammed river Lule, (hereafter called Luleälven) both located in Northern Sweden and draining into the Bothnian Bay, Baltic Sea. For Kalixälven simulations are performed with a runoff calculated from precipitation, evapo-transpiration and temperature data for the period 1990–1999, using a hydrological model calibrated on observed monthly discharges at the river outlet. The same hydrological parameters are used to calculate specific runoff for the Luleälven basin in absence of dam regulation. Reservoir filling and emptying are simulated using a simplified representation of their management rules. Diffuse sources of nutrient are evaluated according to land cover of the catchment. The simulated seasonal trends are within the range of the observed data, in particular for discharge, dissolved silica, total phosphorus, inorganic nitrogen and total organic carbon. Specific runoff is 50% higher in the Luleälven than in the Kalixälven watershed due to higher altitudes and precipitations. Average silica, nitrate and phosphorus concentrations are much lower in Luleälven than in Kalixälven. Comparison of model results for the Luleälven with and without dams shows a reduction of respectively 25% and 30% in silica and phosphorus fluxes delivered at the outlet, while nitrogen delivery is increased by 10% in the dammed vs. undammed river system. The model allows assessing the respective role of reservoir trapping of nutrient in the reservoir through algal uptake and sedimentation, and of changes in the vegetation induced by flooding the valley formerly covered by forests and wetlands. [Copyright &y& Elsevier]

Abstract: A total variation diminishing (TVD) modification of the MacCormack scheme is developed for simulating shallow water dynamics on a uniform Cartesian grid. Results obtained using conventional and deviatoric forms of the conservative non-linear shallow water equations (SWEs) are compared for cases where the bed has a varying topography. The comparisons demonstrate that the deviatoric form of the SWEs gives more accurate results than the conventional form, in the absence of numerical balancing of the flux-gradient and source terms. A further comparison is undertaken between the TVD-MacCormack model and an alternating direction implicit (ADI) model for cases involving steep-fronted shallow flows. It is demonstrated that the ADI model is unable to predict trans-critical flows correctly, and artificial viscosity has to be introduced to remove spurious oscillations. The TVD-MacCormack model reproduces all flow regimes accurately. Finally, the TVD-MacCormack model is used to predict a laboratory-scale dyke break undertaken at Delft University of Technology. The predictions agree closely with the experimental data, and are in excellent agreement with results from an alternative Godunov-type model. [Copyright &y& Elsevier]

Abstract: The transferability of a water quality model, WASP5, to different reaches of a large river, which vary in both quantity and quality of the surface water is tested. The transferability is set in a theoretical framework based on a hypothesis proposed by Snowling and Kramer (Snowling, S.D., Kramer, J.R., 2001. Evaluating modelling uncertainty for model selection, Ecol. Model. 138, 17–30) stating that as a model becomes more complex in process description, the error between simulations and measurements decreases and the overall model sensitivity increases. This hypothesis is extended to include model transferability by observing the behaviour of the complexity versus uncertainty curves when a model is transferred from one area to another. An overall increase in model error and a decrease in parameter sensitivity are indicative of lack of model transferability. Data from the Saale River, Germany, was used to test the extended hypothesis. The constituents modelled are suspended sediments, chloride and two heavy metals, copper and zinc. The parameters describing sorption of heavy metals to suspended solids or particulate organic carbon proved to be very sensitive to simulation results, hence different complexity levels of the sorption process were implemented. The model was first calibrated and then validated separately for the middle and lower courses of the river. The complexity versus the model error and parameter sensitivities was plotted for the two river courses. Juxtaposition of the two sets of curves shows that the model is transferable between the two reaches when simulating heavy metal transport. Some difficulty arose in capturing a peak of suspended sediments, which is due to exuberant phytoplankton growth. A model restructuring is suggested for simulating the middle course of the Saale River to include the storage (dead) zones in this part of the river, which are havens for phytoplankton growth and potential inoculants of large amounts of algae in the main stem of the river. [Copyright &y& Elsevier]

A new distributed periphytic model has been developed and implemented in the hydro-biological river model ProSe, which models the biogeochemical processes in rivers. The transient periods, like floods, are taken into account, and periphyton scouring is represented in an original way. A validation step shows agreement between field data (carbon and nitrogen) concerning either the water column or the periphyton and outputs of the model. The first results have shown that the decreases of ammonium concentrations along the modeled stretch (40 km) are mostly driven by nitrification in the periphyton, the other processes being of smaller importance on the ammonium balance. Then, the model was used to extrapolate the punctual benthic estimations to the whole river and to determine carbon fluxes at the scale of the studied stretch. The carbon biomass, which is fixed on the bottom of the stretch, can reach several tons depending on the development stage of the periphyton. In case of flood, the exported flux of this biomass can reach 1.4 t C day-1 during the summer of 2001. This value is widely predominant compared to the human contribution on this river stretch, which is only 130 kg C day-1. Finally, the most important impact of periphyton on the water column is due to DOM dynamic, which is the most reactive form of the organic matter. [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]

Approaches to the modelling of long-term, large-scale (1–100 year and drainage basin to coastal zone) behaviour are outlined for the catchments of the Humber and Tamar estuaries, UK, and San Francisco Bay, USA. The estuarine environment is particularly difficult to model. Once fluvial materials enter an estuary, sharp chemical gradients and complex physical and biochemical dynamics can result in large changes to the amount, chemical nature and timing of the flux of nutrients and other materials that are transported to the coastal zone. Examples are given both of catchment models for the three systems and of an estuarine model that has been used to estimate contemporary fluxes of some nitrogen species from the Humber catchment to the North Sea, in an attempt to forecast the possible effects associated with climate change. Other applications of long-term models are discussed, including predictions of oxygen isotope ratio distributions in San Francisco Bay, which are of value to palaeo studies, and the dependence of salt intrusion on rising sea level and drought conditions there. Some of the more difficult modelling problems involve the determination of estuarine sediment transport and its consequences. A problem which has received little attention up to now, but which is becoming a very active area of research, is the influence of biota on sediment transport. Long-term modelling of fine sediment transport and its application to contaminant (including radionuclide) transport and dispersion to the coastal zone are discussed for the Tamar Estuary. Other long-term estuarine problems that are discussed include the modelling of seasonal heat fluxes from the Tamar to its coastal zone, and the dispersion of tracers within the coastal zone using three-dimensional simulations of heat, salinity and flow. The article is mainly concerned with simulations that require only reasonably short amounts of time to run on a PC and with models that are not intended to give solutions of great temporal or spatial resolution. Generally, they are intended to provide insights into phenomena and systems. To achieve this, a common feature of the long-term models has been their parameterisation of some intratidal processes, such as sediment resuspension and deposition, or tidal mixing. Provided the parameterisations are physically based and lead to good comparisons with available data, when these exist, then the approach would appear to be a valid ‘use’ rather than an invalid ‘abuse’ of models. [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]

For an accurate assessment of the toxic effects of chemicals during their life cycle, LCA developers try more and more to include chemical fate into the life-cycle impact assessment (LCIA) procedure. In this study the application of multi-media partitioning models within LCIA is discussed. With the case of textile chemicals as an example, USES-LCA and a simple river model (box approach) are compared according to their practicability and the value added to the assessment results. It is shown that emissions from the supply and use of energy still dominate the LCIA results even if ecotoxicity is assessed with a rather complex fate model such as USES-LCA. Second, the treatment of modelling results is addressed for persistent substances with low or unknown toxicity. A possible approach to include such chemicals into valuation is to define an exposure-based impact category additionally to the existing effect-oriented ones (toxicity scores) or a combination of different methods. A combined presentation of results from complementary tools is proposed, providing a more detailed background for decision making while avoiding aggregation and leaving the final weighting between the categories to the user. [ABSTRACT FROM AUTHOR]

Modelling river physical processes is of critical importance for flood protection, river management and restoration of riverine environments. Developments in algorithms and computational power have led to a wider spread of river simulation tools. However, the use of two-dimensional models can still be hindered by complexity in the setup and the high computational costs. Here we present the freeware basement version 3, a flexible tool for two-dimensional river simulations that bundles solvers for hydrodynamic, morphodynamic and scalar advection-diffusion processes. basement leverages different computational platforms (multi-core CPUs and graphics processing units GPUs) to enable the simulation of large domains and long-term river processes. The adoption of a fully costless workflow and a light GUI facilitate its broad utilization. We test its robustness and efficiency in a selection of benchmarks. Results confirm that basement could be an efficient and versatile tool for research, engineering practice and education in river modelling. • Basement v3 simulates different 2D river physical processes. • A suite of test cases proves the tool's robustness and validity. • Modularization and parallelization enable efficient large domain applications. • Multiple computational backends readily available. • Graphical User Interface available for simulation setup. [ABSTRACT FROM AUTHOR]

• We analyzed hydraulic data from 1327 reaches in France and New Zealand. • We developed hydraulic geometry models based on catchment physical characteristics. • General intercontinental models perform as well as country-specific ones. • Our models will be useful for physical and ecological catchment models. Hydraulic geometry is used to describe spatio-temporal variations in wetted width, mean depth and mean velocity with discharge in stream reaches. Models describing downstream (spatial variations) and at-a-station (temporal variations) hydraulic geometry are required for efficient and effective management of flow regimes, sediment and nutrient transport, and physical habitats at catchment to global scales. Data describing observed hydraulic conditions at 1327 stream reaches in France and New Zealand were compiled alongside reach descriptors and upstream catchments extracted from available GIS databases with nationwide coverage. Three contrasting empirical methods were developed to predict hydraulic geometry at unvisited sites. The first method applied basic models in which downstream hydraulic geometry parameters depend on discharge only. The second method applied separate country-specific models whose predictors were selected from the available nationwide GIS data from country. The third method applied an intercontinental model in which all observed hydraulic data were lumped together and predictors were selected from those available across both countries. Flexible regression models that account for interactions were used to parameterize second and third methods. Cross-validation tests showed that downstream parameters were well predicted for independent sites regardless of country. Model performance was higher for width than for depth. At-a-station parameters were less well predicted than downstream parameters, but the models provided satisfactory predictions of observed reach hydraulics. Importantly, the lumped intercontinental model performance was comparable to that of the country-specific models. This suggests that our approach can be applied in other regions where similar explanatory environmental variables are available. [ABSTRACT FROM AUTHOR]

Flood-plain wetlands are the seasonal water bodies formed along a river. These wetlands become active during the monsoon season, which frequently grow in size with seasonal floods and eventually dry up during the non-monsoon season. The flow interaction between flood-plain wetlands and the river sometimes vary over a very short period in response to rapid rise in the river water level due to high precipitation in its upstream catchment. Understanding the complex flow interactions between the river and its associated flood-plain wetlands with field-based measurements of wetland hydrologic characteristics is always a challenging task. To overcome these challenges, an attempt has been made to utilise Topex/Poseidon satellite altimetry-derived water levels into a hydrodynamic model (HEC-RAS) to study river and wetland flow interactions in the lower reach of the Kosi river in India. The satellite altimetry-derived water levels and Landsat satellite images on the Kosi wetlands are used to develop volume-elevation relation. HEC-RAS is setup over the study area and calibrated for different values of manning's roughness coefficient (n) for the river bank and the main channel of the river for the period of 1993–1996. Unsteady flow simulations are carried out for different monsoon seasons to simulate daily river flow interaction (inflow/outflow) between river and wetlands. Statistical analysis is performed between the altimetry-derived and the model-simulated water levels. It is found that simulated water levels are in good agreement ( R 2 = 0.87 , root mean square error of 0.84 m and Nash–Sutcliffe efficiency coefficient of 0.85) with altimetry-derived water levels. The analysis of simulations indicates that interactions between the wetland and the river are bidirectional with most of the flow coming out from the river during the month of August and leaving out from the wetlands during the month of September. The wetlands respond in three different ways, i.e., (i) gaining stage, (ii) wetland and river in equilibrium and (iii) loosing stage, which is reflected on water levels of the river and wetland. This study demonstrates complex interaction processes happening between the Kosi river and its surrounding wetlands. [ABSTRACT FROM AUTHOR]