Abstract: divers typically exhibit a tendency for grain size to become finer in the downstream direction. Data for a set of large-scale experiments on the aggradation of heterogeneous gravel have recently become available. These experiments show substantial downstream fining over several tens of meters. Here a decoupled numerical Tiodel for bed aggradation and downstream fining is developed in an attempt to test an existing gravel ransport model against the experimental data. Generally good agreement is found between the predictions and he observations in the absence of all but trivial adjustments to the gravel transport model. The same transport elation does not perform as well for a corresponding case of uniform sediment. In all of the experiments the Froude number was close to unity, a condition which would suggest that a decoupled model might break iown. Coupled and decoupled models for uniform sediment are thus compared for a case with Froude number very close to unity. They are also compared for cases in whic...

Abstract: The control of reservoir sedimentation through hydraulic flushing has been employed in several parts of the world to sustain the useful storage capacity of the reservoirs. However, no comprehensive analysis has been conducted to understand the sediment flushing processes. In this study, laboratory experiments were performed to investigate the flushing processes during drawdown flushing, including outflow sediment discharge, characteristics of the flushing channel and flushing effectiveness. From both laboratory and field data, it is found that outflow sediment discharge can be well related to a hydrauic parameter which is a function of outlet discharge, water-surface gradient and flushing channel width. It is also found that flushing efficiency increases dramatically when retrogressive erosion emerges. A geomorphic relationship is used to estimate the equilibrium width of the flushing channel. A 1-D diffusion model presented herein is employed only to simulate the general trend of bed profile evolution an...

Abstract: This paper presents the results of a laboratory study on the erosion of sand beds by submerged circular impinging vertical turbulent jets of water for the erosion parameter Ec less than 5. The variation of the maximum scour depth with impinging distance was studied and this revealed two major flow regimes referred to as the Strongly Deflected and the Weakly Deflected Jet Regimes. The conditions under which they exist were established. The asymptotic eroded bed profiles were found to be similar except at very low values of the erosion parameter when made non-dimensional using the maximum scour depth as the length scale. Another length scale was introduced to achieve similarity for all values of the erosion parameter. Using results from this study and the literature, semi-empirical equations have been developed for the characteristic lengths of the erosion profiles in the asymptotic state. Equations that may be used for different values of the relative density difference δρ/ρ are proposed for the maximum sc...

Abstract: In modelling rainfall-runoff and flows in drainage systems it can be advantageous to adopt a neural network (NN). Unfortunately traditional NN learning procedures such as back-propagation can be very slow and expensive to carry out. However, if radial basis function (RBF) networks are adopted with radial centres fixed by a suitable data clustering technique then good results may be obtained very much more rapidly. RBF networks are here shown to be very effective in modelling runoff for a large rainfall database and to give broadly comparable results to those obtained by fine-tuning the much slower back-propagation procedure. The specific model is based on the assumption that runoff depends on time, rainfall intensity I, the rate of change of I and the integral of I.

Abstract: Details are given herein of the development and application of a three-dimensional layer-integrated model to predict suspended sediment fluxes in estuarine and coastal waters. The model involves using the finite difference technique to solve the equations of mass and momentum conservation and the transport equation for suspended sediment. The operator splitting technique and a highly accurate finite difference scheme have been used to solve the suspended sediment transport equation. The model has been tested against analytical solutions and laboratory measurements for different flow types and boundary conditions, and has also been applied to predict suspended sediment fluxes in the Humber Estuary, UK.

Abstract: The paper deals with the causes and consequences of urban storm drainage impacts on receiving waters and discusses available methods and tools for implementation of structural as well as non-struct...

Abstract: A two-dimensional numerical model which employs the depth-averaged forms of continuity and momentum equations along with k-e turbulence closure scheme is used to simulate the flow at the open channel divisions. The model is generalised to flows of arbitrary geometries and MacCormack finite volume method is used for solving governing equations. Application of cartesian version of the model to analyse the flow at right-angled junction is presented. The numerical predictions are compared with experimental data of earlier investigators and measurements made as part of the present study. Performance of the model in predicting discharge distribution, surface profiles, separation zone parameters and energy losses is evaluated and discussed in detail. To illustrate the application of the numerical model to analyse the flow in acute angled offtakes and streamlined branch entries, a few computational results are presented.

Abstract: On a stepped channel, two distinct flow regimes may occur : nappe flow for low discharges and flat slopes, andskimming flow for larger flow rates. A simple analytical method to predict the onset of skimming flow is presented.The method is based upon the change of momentum direction at the impact of the jet on the downstreamstep. The results of the analysis are compared with existing experimental data. The onset of skimmingflow is expressed in terms of the initial Froude number and jet angle. The generalisation of the study resultsenables to predict the onset of skimming flow and hence the risk of jet deflection at the first upstream step.

Abstract: A method for predicting the depth-discharge relationship in a compound channel is developed and applied to two different sets of experimental results. The method uses a mixing length formulation to account for the turbulent interaction between the main channel and the floodplain and the resulting momentum exchange. This momentum transfer tends to reduce the discharge in the main channel and increase the discharge on the floodplain. The net effect is a reduction in the overall discharge capacity of the compound channel. As a result, practical methods which can allow for the interaction effect are needed. In this formulation a variation of Prandtl's mixing length hypothesis is applied to calculate the apparent shear stresses, indicative of the turbulent interaction, on the sides of small vertical elements which comprise the compound channel cross-section. The approach suggested is to use the mixing length approximation to calculate the correction for the momentum interaction effects that are neglected when ...

Abstract: Recent developments in urban storm drainage are reviewed starting with drainage impacts on receiving waters, followed by a brief analysis of selected components of urban drainage systems, hydroinformatics. and regulatory programs. Further advancement in drainage planning will require considerations of the catchment. drainage system, groundwater, treatment plant and receiving waters as one entity, and ensuring sustainable integrated development and ecological enhancement of urban streams and corridors. Such processes should be based on comprehensive modelling, which is well advanced for hydrological aspects, but further development is needed in water quality, sediment quality, transport and impacts, and ecological modelling. Mitigation of stormwater impacts is accomplished by best management practices, which form a part of the treatment train, and their sustainability has to be ensured by proper operation and maintenance. Impacts of combined sewer overflow are mitigated either conventionally by storage (an...

Abstract: The unsteady wall shear stress in accelerating and decelerating turbulent flows of water in a smooth pipe was measured using two different approaches simultaneously : a “direct” mechanical approach, and a more conventional “indirect” approach involving measurement of the transient pressure gradient. The measurements covered a Reynolds number range of between 40,000 to 130,000, and values of acceleration parameter (φ) from -2 to 3. The results showed a surprising trend for the unsteady wall friction to increase in decelerating, and decrease in accelerating flows, contradicting all existing observations. It is possible that the phenomenon of relaminarisation occurring during flow acceleration could have accounted for the reduction in wall shear stress. Based on the test measurements, empirical equations for the unsteady friction factor in terms of the acceleration parameter (φ) are derived. Limiting values of (φ) within which the flow may be approximated as being quasi-steady are also proposed.

Abstract: Hydrological studies of rainfall-runoff processes provide the basis for estimating design flows for urban stormwater drainage systems which control floods and the transport of sediments and polluta...

Abstract: The Paper outlines the considerations involved in stormwater hydrological and pollutant mobilisation processes, and the selection of stormwater detention and pollution control Best Management Pract...

Abstract: Infiltrating stormwater locally into the ground instead of discharging to conventional pipe sewers is increasingly considered as a means of controlling urban stormwater runoff. This paper reviews t...

Abstract: Extensive experiments conducted by the writers on fractional bed load transport rates are reported. These data as well as those available from other sources, covering wide range of flow conditions and sediment nonuniformity, have been analysed. Firstly, the semi-theoretical model proposed by Misri et al. (1984) is modified to evolve a method of bed load calculation and finally an empirical relationship is proposed incorporating the several parameters influencing the bed load transport of nonuniform sediments.

Abstract: The application of real time control (RTC) within a wastewater system may be useful if operational problems exist which vary in time and space and if idle capacity in the system is simultaneously a...

Abstract: In this study, a computer program is developed which enables us to design a water distribution system which satisfies all constraints including pipe diameters, low velocities, and nodal pressures with a minimum total cost. The hydraulic analysis of the water distribution system is performed by the Newton-Raphson method. This analysis is coupled with a non-linear optimization technique in order to minimize the design total cost. Accuracy of the developed computer program is approved by applying it to branched water distribution systems for which the optimum design can be calculated analytically in a simple manner. Comparison of the results indicates that the accuracy of the method used in this study is quite satisfactory.

Abstract: The turbulence structure of flows of clay suspensions in smooth-boundary open channels were experimentally studied. Clay suspensions are non-Newtonian fluids. Transition from laminar to turbulent flows occurs when a Reynolds number Rem is between 2,000 and 10.000. Three layers can be identified in transitional flows, i.e. a) laminar sublayer, b) turbulent layer, and c) upper layer. In the upper layer the turbulence intensity is low or even equal to zero. The flow between the turbulent layer and the laminar sublayer is alternatively laminar and turbulent. For various concentrations of clay suspension the mean velocity profiles follow the Coles' velocity formula with negative wake parameter and smaller Karman constant. The distribution of turbulence intensity is far more nonuniform than that of water flow. The probability density and autocorrelation coefficient are discussed and it is concluded that the turbulence in the non-Newtonian flow is produced in the turbulent layer and high frequency turbulence is ...

Abstract: Integrated design of urban drainage systems aims on the abatement of water pollution in the receiving water. This paper outlines the basic approaches in order to formulate and assess appropriate wa...

Abstract: Meandering channels typically deposit sediments near their inner bank to form point bars Laboratory experiments with narrow sharp bends show that under identical flow conditions the configuration of point bars depends on particle size Explanation to this grain-size effect is found in a three-dimensional particle stability Despite favorable secondary currents, coarse grains tend to move toward the thalweg and coarse-grained point bar deposits are eroded as the side-slope angle approaches the angle of repose of the bed material Calculated results coincide with experimental observations Point bars are considerably smaller for coarse-sand deposits than fine sands

Abstract: A fully conservative Beam and Warming scheme that uses Roe's approximate Jacobian is presented for solving transient open channel flows. A general treatment for satisfying entropy inequality condition is incorporated which always leads to a physically realistic solution. Details of the Beam and Warming scheme, inclusion of the source terms and proposed modifications for achieving full conservation are presented. Improvement in accuracy achieved with the proposed treatment is demonstrated by comparing numerical results by different versions of the scheme with analytical solutions. The applicability of the scheme is examined by comparing numerical results with experimental data and numerical results from existing studies. The scheme's response (o the Courant number and Manning's coefficient is also investigated.

Abstract: The discusser performed a large number of experiments on undular hydraulic jumps (CHANSON 1993, 1995a). Most results were reported in CHANSON and MONTES (1995) and CHANSON (1995b, 1995c). The discusser wishes to stress several aspects of undular jump flows and he will show that the work of REINAUER and HAGER did not bring really new information.

Abstract: A project has recently been undertaken to improve the way in which sewage sludge pipeline systems are designed. A new, more accurate method of calculating pressure losses has been developed which r...

Abstract: A multi-layer water-sediment predictive model has been developed to study the effects of coastline reconfigurations on the three-dimensional (3-D) flow and sediment fields in coastal waters. The model is gridded with finite elements in the horizontal domain for easy adaptation to complex boundary configurations. The non-uniformity of flow and sediment distributions in the water column are represented by multiple vertically averaged layers. The Lax-Wendroff two-step scheme is used for time marching. This allows the flow field and sediment field to be explicitly coupled so that the density of the water-sediment mixture and the flow depth are updated without matrix inversion for the advanced time level. Because of the adoption of the explicit time-marching scheme, the allowed time increment of the present numerical scheme is relatively small. However, this is beneficial to studying short life activities such as sediment entrainment and deposition. The model predicted results were tested against field measure...

Abstract: Recent studies have shown that the trajectories of drogued drifters on the ocean surface have a fractal structure which may be described by fractional Brownian motion. A method is detailed which allows the generation of fractional Brownian motions within a two dimensional particle tracking ocean surface dispersion model. This technique enables the modeller to more accurately mimic particle paths, enhancing the prediction of diffusion and dispersion.

Abstract: Wind/wave interactions in the surf zone were studied using a wave tank and environmental wind tunnel. Waves were modelled at approximately 1/50 scale and broke on a model scale beach of 1/20 slope. The wind was simulated using accelerated growth techniques over a relatively short fetch, and a model scale of roughly 1/100 was achieved. Thus there was some scaling mis-match between wind and wave simulations. Results show that the wind has a significant effect on the breaking of the waves. Both breaker location and breaker type are affected, and the results agree with those of Douglass [10 and 11], The main findings, common to both studies, were that offshore winds promote plunging waves and delay the moment of breaking (reducing surf zone width), whereas onshore winds encourage early wave breaking, generally by spilling. Wave heights at breaking were not generally affected, but due to changes in breaker depth, the height-to-depth ratio is shown to be affected by the wind. Additionally, studies of the motion...

Abstract: Suspension of sediment particles has been found to be in close association with the bursting process in a turbulent wall-layer flow. This mechanism forms the physical basis of the present heuristic turbulent diffusion model for suspended sediment in open channel flows. It is formulated using the bursting intensity and the mean duration of turbulent bursts. The bursting intensity as the fractional vertical turbulence intensity contributed by bursting is determined from its percentage, estimated using existing measured data, among the total vertical turbulence intensity calculated using an analytical solution in the literature. A skewed parabolic profile is obtained for the turbulent diffusion coefficient of suspended sediment. The unique parameter involved in the model is calibrated using measured data spanning wide ranges of suspension indices and sediment concentrations. It is found to increase with particle suspension index, indicating physically that more energetic turbulent bursts with longer duration...

Abstract: This paper reviews the storm water quality regulations of six major industrialized nations: The United States, Canada, United Kingdom, Germany, Australia and Japan, the order being set by the principal authors (both North America) who consider this to be a logical geographical order. The main purpose of the paper is simply to introduce the interested reader to these rules as a matter of broadening his/her knowledge base. Due to space limitations much detail is left out, but hopefully the essence of the laws and regulations are presented. No attempt has been made to compare and contrast these different rules with the objective of determining which are the best rules or what the "best rule" might be. The reader will observe that the differences are great, and to a large degree reflect the culture of the individual country.

Abstract: A theoretical prediction for computing the sequent depth ratio of the hydraulic jump formed in rectangular sloping and roughened stilling basins is developed. It is based on the application of the one-dimensional momentum and continuity equations. The derived equation contains two nondimensional experimental coefficients, one for the effect of slope and the other one for the effect of' bed roughness. When the two coefficients are used together, the combined effect of both slope and roughness on the sequent depth ratio of the hydraulic jump can be computed. Experimental data verify the developed equation reasonably well.