Scaling dispersion model for pollutant transport in rivers

This communication presents a scale-dependent model, called Scaling Dispersion (SD) Model, for simulating solute dispersion and transport in rivers without using a user-specified residence time distribution function. The SD model consists of (1) the advection dispersion equation with a transient storage term which is characterized by a variable residence time, (2) a new method for estimation of the longitudinal Fickian dispersion coefficient involved in the model, and (3) a split-operator method for numerical solution of the equations involved in the model. Comparisons between the SD model and the most widely used transient storage model against tracer test data observed in three US rivers show that the SD model is capable of simulating different types of residence time distributions commonly observed in streams with an accuracy higher than or at least comparable with existing solute transport models, demonstrating the efficacy of the SD model. The SD model unifies the residence time distributions observed in natural rivers within a single modelling framework for the first time. The SD model provides an efficient and cost effective tool for predicting solute dispersion and transport in streams and rivers.     

ANFIS-based approach for predicting sediment transport in clean sewer

The necessity of sewers to carry sediment has been recognized for many years. Typically, old sewage systems were designated based on self-cleansing concept where there is no deposition in sewer. These codes were applicable to non-cohesive sediments (typically storm sewers). This study presents adaptive neuro-fuzzy inference system (ANFIS), which is a combination of neural network and fuzzy logic, as an alternative approach to predict the functional relationships of sediment transport in sewer pipe systems. The proposed relationship can be applied to different boundaries with partially full flow. The present ANFIS approach gives satisfactory results (r² = 0.98 and RMSE = 0.002431) compared to the existing predictor.     

Sediment transport phenomenon in rivers: an alternative perspective

During the last century, a great deal of research has been devoted to modeling the dynamics of sediment transport phenomenon. In spite of the progress achieved, our understanding of the sediment transport phenomenon is far from complete, as there is no generally accepted relationship between the components involved, e.g. water discharge, suspended sediment concentration and bed load. Also, any error (e.g. measurement error) in one component of the system (e.g. discharge) could eventually lead to an inaccurate outcome in deriving either another component or relationships between the components. One possible way to avoid these problems is by modeling the component of interest (e.g. bed load) using a time series of the same component itself. Such an approach may also be able to represent the dynamics of the entire system. In this regard, the concept of phase-space reconstruction, i.e. reconstruction of a single-variable series in a multi-dimensional phase-space, and the related ideas of chaos theory could be useful. This study investigates the possible use of such an approach for understanding bed load dynamics. The approach is employed for predicting the bed load dynamics in the Mississippi River basin in USA. The predictions are made using a local approximation method. The results indicate very good agreement between the predicted and the observed bed load values. The near-accurate predictions indicate the appropriateness of phase-space reconstruction and local approximation prediction for understanding the bed load dynamics. The results also reveal that the bed load dynamics are dominantly influenced by three variables, suggesting that the dynamics could be understood from a low-dimensional chaotic dynamical perspective.     

Kernel ridge regression model for sediment transport in open channel flow

Neural Computing and Applications - Sediment transport modeling is of primary importance for the determination of channel design velocity in lined channels. This study proposes to model sediment...     

Extreme learning machine assessment for estimating sediment transport in open channels

The minimum velocity required to prevent sediment deposition in open channels is examined in this study. The parameters affecting transport are first determined and then categorized into different dimensionless groups, including “movement,” “transport,” “sediment,” “transport mode,” and “flow resistance.” Six different models are presented to identify the effect of each of these parameters. The feed-forward neural network (FFNN) is used to predict the densimetric Froude number (Fr) and the extreme learning machine (ELM) algorithm is utilized to train it. The results of this algorithm are compared with back propagation (BP), genetic programming (GP) and existing sediment transport equations. The results indicate that FFNN-ELM produced better results than FNN-BP, GP and existing sediment transport methods in both training (RMSE = 0.26 and MARE = 0.052) and testing (RMSE = 0.121 and MARE = 0.023). Moreover, the performance of FFNN-ELM is examined for different pipe diameters.     

Spectral element modeling of sediment transport in shear flows

Climate change and accelerated sea level rise coupled with increased human activities in coastal regions have resulted in severe land loss globally. Mitigating coastal erosion requires better understanding and improved capability of modeling sediment transport. This paper presents the methodology and simulation results of a new mathematical model, Virtual Identity Particles, using a spectral/hp element method for sediment transport driven by shear flows. Assimilated the advantages of Eulerian and Lagrangian methods, this model is capable of modeling each individual grain as well as a bulk of numerous grains where frequent collisions between particles and with walls are characterized by the Speed Proportional Collisions. Besides, this model maintains an excellent balance of accuracy and efficiency through its economical considerations in the formulation, allowing modeling a large number of sediment particles. Simulation results demonstrate that this model holds promising potential for investigating sediment transport and the associated land erosion problems.     

An integrated model suite for sediment and pollutant transport in shallow lakes

To assess effectively the impact of sediments and pollutants input to a water body, it is necessary to predict their spatial and temporal distributions in the water column and in the sediment substrate, resulting from physico-chemical processes such as advection, dispersion, aggregation, deposition, erosion and adsorption. Physical or mathematical representation of these processes requires a good estimate of the velocity field and circulation patterns induced by hydrodynamic forcing functions. The modeling strategy adopted was to link similarly structured two-dimensional, vertically averaged finite element models for hydrodynamics and sediment-pollutant transport. To enhance model use and interaction, these models were interfaced with pre- and post-processing modules. Using the same spatial grid and temporal scale, dynamic simulations were performed to investigate mercury pollution in a shallow lake. Results show that the integrated model suite provided a reasonable representation of the hydrodynamics and its influence on sediment and mercury transport processes.     

Numerical simulation-aided MODIS capture of sediment transport for the Bohai Sea in China

Traditionally, the establishment of a remote-sensing retrieval model depends on in situ data acquired by expensive and considerably labour-intensive field surveys, but now we can benefit from numerical simulation. In this study, after considering the advantages of numerical simulation in extending the spatial and temporal suspended sediment concentration (SSC), we propose an approach to establish an SSC retrieval model from remotely sensed images with the aid of a numerical model for the Bohai Sea in China. First, significant correlation, between simulated SSC and atmosphere-corrected water-leaving reflectance derived from Moderate Resolution Imaging Spectroradiometer (MODIS) band-1 images, was investigated to demonstrate a novel SSC retrieval model. The synchronous data from remote sensing and numerical simulations enabled the removal of spatial and temporal differences between satellite and in situ measurements. Based on this retrieval model, the SSC distribution pattern was simulated in two scenarios to separate river sediment discharge from the overall process of resuspension. The results indicate that the distribution pattern of the simulated surface SSC without sediment discharge from the Yellow River in most study areas generally matched that derived from MODIS images, except for the estuarine area. The surface SSC 30–40 km away from the estuaries are dominated by sediment discharge from rivers. The proposed method, the numerical simulation-aided SSC retrieval MODIS model, can efficiently capture the sediment transport in the Bohai Sea, which is helpful for operational monitoring of the water environment in estuary and coastal waters.     

Stretched Eulerian coordinate model of coastal sediment transport

A one-dimensional vertical model of sediment and dissolved material transport in a coupled, vertically resolved benthic-pelagic system has been developed. An apparently unique feature of the model is that the governing equations are first formulated in a time-varying Eulerian frame and then solved numerically, which provides a consistent approach for incorporating resuspension/deposition, swelling/consolidation, and biodiffusion processes within a single modelling framework. Numerical experiments were carried out with varying grids to test diffusive properties of the model. A stretched numerical grid that maintains high vertical resolution of the top sediments and constrains numerical diffusion in deep layers is an integral part of the model. The developed model provides a test bed for testing scientific hypothesis pertaining to coastal sediment transport. The model can also be used to support biogeochemical studies in a coupled benthic-pelagic system.     

Spectral irradiance profiles of suspended marine clay for the estimation of suspended sediment concentration in tropical waters

Reflectance spectra of water containing varying concentrations of organic and inorganic sediments isolated from the coastal waters of Singapore were measured using a portable spectroradiometer under controlled experimental conditions and natural sunlight. The effect of different sizes of sediments on the spectral profile of water was also investigated. In the presence of organic sediments, maximum reflectance of water was observed over a broad band between 440-580 nm, with a peak reflectance at about 550 nm, followed by two smaller peaks at 600-645 nm and 665-690 nm. In contrast, inorganic sediments produced a distinct band peak between 595 and 690 nm. For both sediment types, characteristic features in the infra-red region include a reflectance trough at 754 nm and peak at 814 nm. The empirical colour ratios, OD550-OD754 and OD 595-OD754, were used to estimate the organic and inorganic sediment concentrations respectively. In the case of organic sediments, a power function was found to fit the data well ( R 2 =0.89-0.98), whereas a linear fit was found for inorganic sediments ( R 2 =0.53-0.86). In general, decreases in particle size resulted in overall increases in spectral reflectance.     

A practical approach to formulate stage–discharge relationship in natural rivers

This study proposes a new formulation technique for modeling stage–discharge relationship, as an alternative approach to standard regression techniques. An explicit neural network formulation (ENNF) is derived by using data obtained from United States Geological Survey data base. The neural network model is trained and tested using time series of daily stage and discharge data from two stations in Pennsylvania, USA. The model is compared with the standard rating curve (SRC) technique. Statistical parameters such as average, standard deviation, minimum, and maximum values, as well as criteria such as root mean square error, the efficiency coefficient (E), and determination coefficient (R ²) are used to measure the performance of the ENNF. Considerably, well performance is achieved in modeling streamflow by using ENNF. The comparison results reveal that the suggested formulations perform better than the conventional SRC.     

Mathematical modeling of sediment transport in the coastal zone of shallow reservoirs

A nonstationary spatial two-dimensional model of sediment transport in the coastal zone of water reservoirs is considered, taking into account the following physical parameters and processes: the porosity of soil, the critical shear stress at which sediment begins moving, turbulent exchange, the dynamically changing geometry and function of the bottom elevation level, as well as wind currents and friction on the bottom. The hydrodynamic spatial two-dimensional model of sediment transport in the coastal zone of the reservoirs is also considered. For the proposed mathematical models their discretization has been fulfilled. Based on the developed algorithms a complex of programs has been built and the results of numerical experiments are presented.     

Development of a landslide component for a sediment budget model

Most erosion models focus on overland-flow erosion with fewer incorporating landslide erosion although it is common on hillslopes. Landslide models are typically dynamic, spatially distributed simulations with large data requirements for parameterisation and are often computationally intensive. The Australian SedNet model represents a middle ground between process-based and empirical models and is being modified for New Zealand conditions by incorporating shallow landsliding.We describe a method for implementing a model within SedNetNZ to provide the long-term annual average sediment contribution from shallow landsliding and its spatial distribution. The mass of soil eroded over a defined period is calculated from the landslide probability for each slope class, slope class area, failure depth, soil bulk density, and sediment delivery ratio. Landslide probability is derived from mapping a time series of landslides intersected with DEM-derived slope. The conceptual approach and methodology for parameterisation are suitable for landslide modelling where rainfall-triggered shallow landslides occur.     

Development of design principles for automated systems in transport control

This article reports the results of a qualitative study investigating attitudes towards and opinions of an advanced automation system currently used in UK rail signalling. In-depth interviews were held with 10 users, key issues associated with automation were identified and the automation's impact on the signalling task investigated. The interview data highlighted the importance of the signallers' understanding of the automation and their (in)ability to predict its outputs. The interviews also covered the methods used by signallers to interact with and control the automation, and the perceived effects on their workload. The results indicate that despite a generally low level of understanding and ability to predict the actions of the automation system, signallers have developed largely successful coping mechanisms that enable them to use the technology effectively. These findings, along with parallel work identifying desirable attributes of automation from the literature in the area, were used to develop 12 principles of automation which can be used to help design new systems which better facilitate cooperative working. PRACTITIONER SUMMARY: The work reported in this article was completed with the active involvement of operational rail staff who regularly use automated systems in rail signalling. The outcomes are currently being used to inform decisions on the extent and type of automation and user interfaces in future generations of rail control systems.     

Extension of ENO and WENO schemes to one-dimensional sediment transport equations

Essentially nonoscillatory and weighted essentially nonoscillatory schemes are high order resolution schemes constructed for the hyperbolic conservation laws. In this paper we extend these schemes to the one-dimensional bed-load sediment transport equations. The difficulties that arise in the numerical modelling come from the fact that a nonconservative product is present in the system. Our specific numerical approximations for the nonconservative product are based on two ideas. First is to include the influence of that term in the system upwinding and the second is to define the numerical approximation in such a way that the obtained scheme solves the system for the quiescent flow case exactly. As a consequence, the resulting schemes give excellent results, as it can be seen from the numerical tests we present. On the opposite, the numerical results obtained by applying the pointwise evaluation of nonconservative product on the same tests present unacceptably large numerical errors.     

OpenMI-based integrated sediment transport modelling of the river Zenne,Belgium

Recent observations show that the river Zenne (Belgium) remains well below the water quality goals stated by the European Union Water Framework Directive. An interuniversity, multidisciplinary research project was therefore launched to evaluate the effects of wastewater management plans on the ecological functioning of the river. To this end, different water quantity and quality processes had to be considered and modelled, e.g., the hydrology in the river basin, hydraulics in the river and sewers, erosion and sediment transport, faecal bacteria transport and decay. This paper considers the development of an Open Modelling Interface (OpenMI) based integrated model for the purpose of simulating the river's sediment dynamics. We used the Soil and Water Assessment Tool (SWAT) to model water and sediment fluxes from rural areas. The Storm Water Management Model (SWMM) was used to simulate the hydraulics of the river, canal, and sewer systems in urban catchments. New model codes for sediment transport and stream water temperature were developed to complement SWMM. The results show that the integrated sediment transport model reproduced the sediment concentrations in the river Zenne with ‘good’ to ‘satisfactory’ accuracy. We may therefore conclude that the OpenMI has been successfully implemented to integrate water quality models into a hydraulic one. While the OpenMI run-time data communication inflicted calculation time overhead, we found that the overhead was not significant with respect to the total run-time of the integrated model.     

Terrace erosion and sediment transport model: a new tool for soil conservation planning in bench-terraced steeplands

Despite widespread bench-terracing soil erosion remains a major problem in Java’s uplands. To elucidate the causes for this lack of impact, runoff and erosion processes were studied at a variety of spatial scales within a volcanic catchment in West Java. Research indicated that soil loss occurs via rain splash and wash of rainfall-detached sediment by shallow overland flow from the terrace riser and bed, and via runoff entrainment of sediment deposited in the central terrace toe drain. The terrace erosion and sediment transport mode (TEST) was developed to physically describe these processes, as a function of vegetation and soil surface cover where appropriate, yet use as few parameters as possible. Runoff generation was described by the spatially variable infiltration model (SVIM) and a two parameter rainfall depth-intensity distribution was assumed to derive a simple analytical expression for storm runoff depth. In a similar manner expressions were derived for effective rainfall kinetic energy to predict rainfall-driven transport using a newly developed model, and for effective runoff rate to predict flow-driven transport using GUEST model theory. The model and its components were tested using measured runoff and soil loss from 31 sections of terrace beds or risers and from six terrace units during two seasons. The model generally performed satisfactorily and provides a useful new tool for assessing the impacts of soil conservation measures on bench terrace runoff and soil loss.