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Showing papers in "Journal of Hydraulic Engineering in 2002"


Journal ArticleDOI
TL;DR: A new method for detecting spikes in acoustic Doppler velocimeter data sequences is suggested and it is shown to have superior performance to various other methods and it has the added advantage that it requires no parameters.
Abstract: A new method for detecting spikes in acoustic Doppler velocimeter data sequences is suggested. The method combines three concepts: (1) that differentiation enhances the high frequency portion of a signal, (2) that the expected maximum of a random series is given by the Universal threshold, and (3) that good data cluster in a dense cloud in phase space or Poincare maps. These concepts are used to construct an ellipsoid in three-dimensional phase space, then points lying outside the ellipsoid are designated as spikes. The new method is shown to have superior performance to various other methods and it has the added advantage that it requires no parameters. Several methods for replacing sequences of spurious data are presented. A polynomial fitted to good data on either side of the spike event, then interpolated across the event, is preferred by the authors.

1,433 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss the differences between momentum and energy resistances, between point, cross-sectional and reach resistance coefficients, as well as compound/composite channel resistance.
Abstract: In 1965, Rouse critically reviewed hydraulic resistance in open channels on the basis of fluid mechanics. He pointed out the effects of cross-sectional shape, boundary nonuniformity, and flow unsteadiness, in addition to viscosity and wall roughness that are commonly considered. This paper extends that study by discussing the differences between momentum and energy resistances, between point, cross-sectional and reach resistance coefficients, as well as compound/composite channel resistance. Certain resistance phenomena can be explained with the inner and outer laws of boundary layer theory. The issue of linear-separation approach versus nonlinear approach to alluvial channel resistances also is discussed. This review indicates the need for extensive further research on the subject.

520 citations


Journal ArticleDOI
TL;DR: In this article, a large variety of scour elements were considered, ranging from 1 to 60% of the channel width, and flow depths ranging from about 40% of channel width.
Abstract: Scour related to bridge hydraulics received much attention in the past decade, including its relation to flood hydrology and hydraulic processes in addition to steady flow. This paper presents new research on bridge pier and abutment scour based on a large data set collected at ETH Zurich, Switzerland. In total six different sediments were tested, of which three were uniform. Also a large variety of scour elements were considered, from 1 to 60% of the channel width, and flow depths ranging from 1 to about 40% of the channel width. Using similarity arguments and the analogy to flow resistance, an equation for temporal scour evolution is proposed and verified with the available literature data. The agreement of the present scour equation with both the VAW data and the literature data were considered sufficient in terms of river engineering accuracy, provided limitations relating to hydraulic, granulometric, and geometrical parameters are satisfied. These limitations are discussed and refer particularly to e...

385 citations


Journal ArticleDOI
TL;DR: In this paper, a laboratory study on the hydraulics of flow in an open channel with circular cylindrical roughness is presented, and the results show that the flow resistance varies with flow depth, stem concentration, stem length, and stem diameter.
Abstract: A laboratory study on the hydraulics of flow in an open channel with circular cylindrical roughness is presented. The laboratory study consists of an extensive set of flume experiments for flows with emergent and submerged cylindrical stems of various sizes and concentrations. The results show that the flow resistance varies with flow depth, stem concentration, stem length, and stem diameter. The stem resistance experienced by the flow through the vegetation is best expressed in terms of the maximum depth-averaged velocity between the stems. Physically based formulas for flow resistance, the apparent channel velocity, and flow velocities in the roughness and surface layers are developed. The formulas are validated with the flume data from the present study as well as those from past studies. A method for calculating channel hydraulic conditions using these formulas is presented.

379 citations


Journal ArticleDOI
TL;DR: In this paper, an artificial neural model is used to estimate the natural sediment discharge in rivers in terms of sediment concentration, which is achieved by training the network to extrapolate several natural streams data collected from reliable sources.
Abstract: An artificial neural model is used to estimate the natural sediment discharge in rivers in terms of sediment concentration. This is achieved by training the network to extrapolate several natural streams data collected from reliable sources. The selection of water and sediment variables used in the model is based on the prior knowledge of the conventional analyses, based on the dynamic laws of flow and sediment. Choosing an appropriate neural network structure and providing field data to that network for training purpose are addressed by using a constructive back-propagation algorithm. The model parameters, as well as fluvial variables, are extensively investigated in order to get the most accurate results. In verification, the estimated sediment concentration values agree well with the measured ones. The model is evaluated by applying it to other groups of data from different rivers. In general, the new approach gives better results compared to several commonly used formulas of sediment discharge.

325 citations


Journal ArticleDOI
TL;DR: In this article, a model based on the finite-volume method is developed for unsteady, two-dimensional, shallow-water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession.
Abstract: A model based on the finite-volume method is developed for unsteady, two-dimensional, shallow-water flow over arbitrary topography with moving lateral boundaries caused by flooding or recession. The model uses Roe's approximate Riemann solver to compute fluxes, while the monotone upstream scheme for conservation laws and predictor-corrector time stepping are used to provide a second-order accurate solution that is free from spurious oscillations. A robust, novel procedure is presented to efficiently and accurately simulate the movement of a wet/dry boundary without diffusing it. In addition, a new technique is introduced to prevent numerical truncation errors due to the pressure and bed slope terms from artificially accelerating quiescent water over an arbitrary bed. Model predictions compare favorably with analytical solutions, experimental data, and other numerical solutions for one- and two-dimensional problems.

313 citations


Journal ArticleDOI
TL;DR: In this paper, the Fourier series is used to detect, locate, and quantitatively quantify a 0.1% size leak with respect to the cross-sectional area of a pipeline, and different damping ratios of various Fourier components are used to find the location of a leak.
Abstract: Leaks in pipelines contribute to damping of transient events. That fact leads to a method of finding location and magnitude of leaks. Because the problem of transient flow in pipes is nearly linear, the solution of the governing equations can be expressed in terms of a Fourier series. All Fourier components are damped uniformly by steady pipe friction, but each component is damped differently in the presence of a leak. Thus, overall leak-induced damping can be divided into two parts. The magnitude of the damping indicates the size of a leak, whereas different damping ratios of the various Fourier components are used to find the location of a leak. This method does not require rigorous determination and modeling of boundary conditions and transient behavior in the pipeline. The technique is successful in detecting, locating, and quantifying a 0.1% size leak with respect to the cross-sectional area of a pipeline.

273 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discuss the role of bacteria and microphytobenthians in stabilizing and stabilizing biotic organisms in sediment compaction and sediment stabilization, and show that the formation of faeces and psuedo-faeces can enhance the stability of the sediment.
Abstract: Summary of Stabilizing and Destabilizing Biotic Influenceson Natural Cohesive Sediment STABILIZING DESTABILIZINGEPS secretion : Extracellularpolymeric substances bybacteria and microphytobenthosenhances cohesion, promotesflocculation and hence deposition Blistering : Trapping ofoxygen bubbles in biofilmsincreases buoyancy of thebiofilm to such an extentthat it pulls away fromthe sediment Sediment compaction :Burrowingmacrofauna increasesediment densityand hence stability Pelletization : Theformationof faeces and psuedo-faeces can enhanceerodibility Increased drainage : Burrowand channel formationpromotes dewatering Grazing : Organismsfeedingon intertidal flats causesphysical disturbance andresuspensionof the sediment andreduces the stabilizinginfluence ofmicrophytobenthos Network effects : Filamentous biotaramify through the sediment matrixbinding sediment particles together Burrow cleaning : Somebenthic fauna cleantubes they inhabit inthe sediment giving riseto a localizedbenthic flux Flow effects

265 citations


Journal ArticleDOI
TL;DR: The accuracy, stability, and reliability of a numerical model based on a Godunov-type scheme are verified, through a comparison between calculated results and observed data for the Malpasset dam-break event, which occurred in southern France in 1959.
Abstract: The accuracy, stability, and reliability of a numerical model based on a Godunov-type scheme are verified in this paper, through a comparison between calculated results and observed data for the Malpasset dam-break event, which occurred in southern France in 1959. This event is an unique opportunity for code validation because of the availability of extensive field data on the flooding wave due to the dam failure. In the code the shallow water equations are discretized using the finite volume method, and the numerical model allows second order accuracy, both in space and time. The classical Godunov approach is used. More specifically, the Harten, Lax, and van Leer Riemann solver is applied. The resulting scheme is of high resolution and satisfies the total variation diminishing condition. For the numerical treatment of source terms relative to the friction slope, a semi-implicit technique is used, while for the source terms relative to the bottom slope a new explicit method is developed and tested.

257 citations


Journal ArticleDOI
TL;DR: In this paper, a two-dimensional-acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations, discharges, and flume slopes.
Abstract: Understanding of the hydraulics of flow over vegetation is very important to support the management of fluvial processes. In this paper the flow over flexible bottom vegetation is experimentally studied. A two-dimensional-acoustic doppler velocimeter is used to measure the local flow velocities for different vegetation concentrations, discharges, and flume slopes. The influence of vegetation concentration and the depth/vegetation height ratio on the measured velocity profiles is analyzed. All measured velocity distributions are S-shaped and exhibit a three-zone profile. The relationship between the velocity distribution and the turbulence intensity distribution is also analyzed. The characteristics ~inflection point, maximum value, asymptotes ! of the measured velocity distributions and the results of the previous investigators are used to select an analytical expression for the shape of the velocity profile. A theoretical velocity profile is deduced using the classical Prandtl's mixing length approach with a new expression for the mixing length. The deduced four-coefficient profile allows description of the flow both inside and above the vegetation. The physical and geometrical meaning of the four coefficients are also shown. DOI: 10.1061/~ASCE!0733-9429~2002!128:7~664! CE Database keywords: Velocity profile; Vegetation; Channel flow.

231 citations


Journal ArticleDOI
TL;DR: In this paper, the role of near-bed turbulent structures and bed packing density on the commencement of sediment motion is investigated, based on the concept that the particle motion is governed by the intermittent nature of near bed turbulence.
Abstract: Incipient motion criteria based solely on time-averaged bed shear stress may underpredict sediment transport The focus of this study is on the stochastic aspect of the problem of incipient motion Specifically, the role of near-bed turbulent structures and bed packing density on the commencement of sediment motion is investigated The cornerstone of the proposed model is based on the concept that the particle motion is governed by the intermittent nature of near-bed turbulence Based on this mechanism, in this article we provide a quantitative model for predicting the commencement of sediment entrainment for the first time under three representative bed packing densities corresponding to the isolated, wake interference, and skimming flow regimes The performance of the proposed model is compared to published experimental data and the “conventional” approach that is based on the consideration that flow parameters are statistically well represented by a normal distribution

Journal ArticleDOI
TL;DR: In this paper, the pressure within a trapped air pocket in a rapidly filling horizontal pipe is investigated both experimentally and analytically, where the downstream end is either sealed to form a dead end or outfitted with an orifice to study the effects of air leakage on the pressure.
Abstract: The pressure within a trapped air pocket in a rapidly filling horizontal pipe is investigated both experimentally and analytically. The downstream end of the pipe is either sealed to form a dead end or outfitted with an orifice to study the effects of air leakage on the pressure. Three types of pressure oscillation patterns are observed, depending on the size of the orifice. When no air is released or orifice sizes are small, the cushioning effects of the air pocket prevents the water column from impacting on the pipe end and from generating high water hammer pressures. However, the maximum pressure experienced may still be several times the upstream driving pressure. When the orifice size is very large, the air cushioning effect vanishes and the water hammer pressure is dominant. For intermediate orifice sizes, the pressure oscillation pattern consists of both long-period oscillations (while the air pocket persists) followed by short-period pressure oscillations (once water hammer pressures dominate). Air leakage is observed to play a significant role in increasing the magnitude of the observed pressures during rapid filling, resulting in peak pressures up to 15 times the upstream head. An analytical model, capable of calculating the air pocket pressure and the peak pressure when the water column slams into the end of the pipe, is developed and results are compared with those of experiments. The model was successful in determining the amplitude of the peak pressure for the entire orifice range and was able to simulate the pressure oscillation pattern for the case of a negligible water hammer impact effect. Although the model was unable to simulate the pressure oscillation pattern for substantial air release, it was able to predict the type of pressure oscillation behavior and the peak pressure.

Journal ArticleDOI
TL;DR: In this article, homogeneous small-amplitude embankments were constructed in flumes from a range of uniform noncohesive materials and breached by overtopping flows under constant reservoir level conditions.
Abstract: Homogeneous small-amplitude embankments were constructed in flumes from a range of uniform noncohesive materials and breached by overtopping flows under constant reservoir level conditions. Embankm...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the influence of the volumetric hydraulic radius and the standard deviation of bed surface elevations on the relative roughness of natural alluvial beds, and showed that the (IR\dv/d\dz\N) exponent of power-law flow resistance equations increases from 1/6 to more than 1/2 as bed roughness increases.
Abstract: The definitions of depth and hydraulic radius become ambiguous when bed roughness is large relative to flow depth. Various statistics are currently used to describe bed roughness and many different flow resistance formulas have been developed. The volumetric hydraulic radius \IR\dv\N and the standard deviation of bed surface elevations \Id\dz\N are rational and unambiguous measures suitable for large relative roughness conditions. Their influence on flow resistance is investigated using conceptual models and digital elevation models of natural alluvial beds. The results show that head-losses for large-scale relative roughness beds can be related to (\IR\dv/d\dz\N); the (\IR\dv/d\dz\N) exponent of power-law flow resistance equations increases from 1/6 to more than 1/2 as relative roughness increases, and flow velocity can be determined from boundary topography measures, water level and slope, without any calibrated coefficients. An overlooked form of the log law, using standard deviation \Id\dz\N, performs as well as power laws for predicting flow resistance with high relative roughness and it reverts to the conventional log law when relative roughness is low. A field technique for determining \IR\dv\N and \Id\dz\N is described.

Journal ArticleDOI
TL;DR: In this paper, a three-dimensional numerical model is developed to investigate the open-channel junction flow, which is encountered in many hydraulic structures ranging from wastewater treatment facilities to fish passage conveyance structures.
Abstract: An open-channel junction flow is encountered in many hydraulic structures ranging from wastewater treatment facilities to fish passage conveyance structures. An extensive number of experimental studies have been conducted but a comprehensive three-dimensional numerical study of junction flow characteristics has not been performed and reported. In this paper, a three-dimensional numerical model is developed to investigate the open-channel junction flow. The main objective is to present the validation of a three-dimensional numerical model with high-quality experimental data and compare additional simulations with classical one-dimensional water surface calculations. The three-dimensional model is first validated using the experimental data of a 90° junction flow under two flow conditions. Good agreement is obtained between the model simulation and the experimental measurements. The model is then applied to investigate the effect of the junction angle on the flow characteristics and a discussion of the results is presented.

Journal ArticleDOI
TL;DR: In this paper, a new technique was developed to measure the apparent velocity of bed load using an acoustic Doppler current profiler, which involves estimating the bias in bottom tracking due to a moving bottom.
Abstract: A new technique has been developed to measure the apparent velocity of bed load (\Iυ\da\N) using an acoustic Doppler current profiler. The technique involves estimating the bias in bottom tracking due to a moving bottom. Mean \Iυ\da\N measured at sampling stations in the gravel-bed Fraser River correlated well (\Ir²\N=0.93, \in=9) with mean bed load transport rates measured using conventional samplers. Mean \Iυ\da\N was also correlated (\Ir²\N=0.44, \in=19) with boundary shear stress estimated by a log-law fit to the mean velocity profile. Estimates of \Iυ\da\N from individual 5 s ensemble averages were extremely variable: the coefficient of variation for a sampling station ranged from 1.0 to 6.4, and 25 min of sampling were required to achieve stable estimates of the mean and coefficient of variation (within 5% error). Variance was due to both real temporal variability of transport and measurement error. The mechanisms that produce this variability are discussed and preliminarily quantified.

Journal ArticleDOI
TL;DR: In this article, a series of experiments were conducted in which the volume of the scour hole associated with model spur dikes was measured in a laboratory flume under clear-water overtopping flows.
Abstract: A series of experiments were conducted in which the volume of the scour hole associated with model spur dikes was measured in a laboratory flume under clear-water overtopping flows. Spur dike models were angled at 45, 90, and 135° to the downstream channel sidewall with contraction ratios of 0.125 and 0.250. The main goals of the experiments were to evaluate the effect of the three angles on the volume of scour and potential aquatic habitat and on minimizing erosion adjacent to the streambanks. The experiments showed that of the three angles tested, the least erosion of the bed in the near bank region was associated with the spur dikes with 90° angles, while the greatest volume of the scour hole was associated with the 135° spur dikes. It was concluded that spur dikes with 135$ angles showed the best potential for providing improved aquatic habitats while minimizing the potential for erosion of the channel bank.

Journal ArticleDOI
TL;DR: In this paper, the authors used the \ik-ϵ turbulence model to simulate the complex turbulence overflow of the stepped spillway and used the unstructured grid to fit the irregular boundaries and the volume of fluid method was introduced to solve the complex free-surface problem.
Abstract: The stepped spillway has increasingly become and effective energy dissipator. When the hydraulic performance of the overflow is clearly known, the energy dissipation could be increased. However, the study of stepped spillway overflow has been based only on model tests until now. In this paper, the \ik-ϵ turbulence model is used to simulate the complex turbulence overflow. The unstructured grid is used to fit the irregular boundaries and the volume of fluid method is introduced to solve the complex free-surface problem. The free surface, velocities, and pressures on the stepped spillway are obtained by the turbulence numerical simulation. Furthermore, the simulation results compare well with measured data. The study indicates that the turbulence numerical simulation is an efficient and useful method for the complex stepped spillway overflow.

Journal ArticleDOI
TL;DR: In this paper, the authors discuss several common techniques for measuring air-water flows by means of intrusive phase detection probes, and describe a basic data processing method that readily yields expanded information on airwater flow properties.
Abstract: Interest in air-water flows has not diminished in recent years, as evident by the number of associated papers published in the Journal of Hydraulic Engineering and other journals, such as the Journal of Hydraulic Research, the International Journal of Multiphase Flow and the Journal of Fluids Engineering. The writer believes that a particularly important issue is the often inadequate or incomplete interpretation of air-water flow instrumentation by hydraulic engineers and researchers. The present Forum article briefly comments of the several common techniques for measuring air-water flows by means of intrusive phase detection probes, and it describes a basic data processing method that readily yields expanded information on air-water flow properties.

Journal ArticleDOI
TL;DR: In this paper, the results of a laboratory study of hydraulic jumps on corrugated beds are presented, where experiments were performed for a range of Froude numbers from 4 to 10 and three values of the relative roughness t/y 1 of 0.50, 0.43, and 0.25 were studied.
Abstract: The results of a laboratory study of hydraulic jumps on corrugated beds are presented. Experiments were performed for a range of Froude numbers from 4 to 10. Three values of the relative roughness t/ y 1 of 0.50, 0.43, and 0.25 were studied. It was found that the tailwater depth required to form a jump was appreciably smaller than that for the corresponding jumps on smooth beds. Further, the length of the jumps was about half of those on smooth beds. The integrated bed shear stress on the corrugated bed was about 10 times that on smooth beds. The axial velocity profiles at different sections in the jump were found to be similar, with some differences from the profile of the simple plane wall jet. The maximum velocityum at any section in terms of the velocity U1 of the supercritical stream was correlated with the longitudinal distance x in terms of L, which is the distance where um50.5U1 , and this relation was the same as that for jumps on smooth beds with the difference that L/ y 1 was much smaller for jumps on corrugated beds. The normalized boundary layer thickness d/b, where b is the length scale of the velocity profile, was equal to 0.45 for jumps on corrugated beds compared to 0.16 for the simple wall jet. The results of this study show the attractiveness of corrugated beds for energy dissipation below hydraulic structures.

Journal ArticleDOI
TL;DR: In this article, the authors applied deterministic bedload transport predictors to sand-gravel bed rivers and extended them to stochastic predictors for non-uniform sediment.
Abstract: Classical deterministic bedload transport predictors are applied to sand-gravel bed rivers. The turbulent bed shear stress is modeled according to a probability distribution to obtain realistic bedload transport rates at incipient motion. In extending the predictors to stochastic predictors for nonuniform sediment, many parameters that represent near-bed turbulence and the particle size distribution must be chosen. The parameters that give realistic results are chosen by analyzing the results of a new experimental flume dataset with relatively large water depths. Choosing other combinations of parameters may give equal total bedload transport rates, but at the cost of large errors in fractional transport rates. Attention is given to the hiding-exposure phenomenon and a hindrance effect related to nonuni- form sediment. Validation based on two independent field datasets shows that successful predictions of particle sizes near the threshold for motion are feasible using the stochastic approach, while the deterministic approach gives successful predictions well above incipient motion.

Journal ArticleDOI
TL;DR: In this paper, the probability distribution underpinning the velocity distribution and other related variables is resilient, and that the same probability distribution is governing various phenomena observable at a channel section and explains the regularities in open-channel flows.
Abstract: Maximum velocity in a channel section often occurs below the water surface. Its location is linked to the ratio of the mean and maximum velocities, velocity distribution parameter, location of mean velocity, energy and momentum coefficients, and probability density function underpinning a velocity distribution equation derived by applying the probability and entropy concepts. The mean value of the ratio of the mean and maximum velocities at a given channel section is stable and constant, and invariant with time and discharge. Its relationship with the others in turn leads to formation of a network of related constants that represent regularities in open-channel flows and can be used to ease discharge measurements and other tasks in hydraulic engineering. Under the probability concept, the ratio of mean and maximum velocities being constant means that the probability distribution underpinning the velocity distribution and other related variables is resilient, and that the same probability distribution is governing various phenomena observable at a channel section and explains the regularities in open-channel flows.

Journal ArticleDOI
TL;DR: In this paper, field measurements during the 1998 flood of the Rhine River in The Netherlands show that both Manning and Darcy-Weisbach friction factors increase with discharge, and the changes in bedform roughness height and friction factors are attributed to the increased dune height during floods.
Abstract: Detailed field measurements during the 1998 flood of the Rhine River in The Netherlands show that both Manning \in and Darcy—Weisbach friction factor \if increase with discharge. The changes in bedform roughness height and friction factors are attributed to the increased dune height during floods. There is a near-peak hysteresis in the dune height measurements. At a given discharge, dunes are significantly larger after than before the peak discharge. The trend is most apparent for the Bovenrijn with weaker variations for the Waal. The methods of Engelund and Vanoni—Hwang provide similar estimates of form drag. When combined with van Rijn’s method to estimate grain resistance, both methods tend to overpredict the measured bed friction factor after the peak discharge. These methods perform best when field bedform measurements are available to estimate form drag. The composite effect of primary and secondary dunes should be considered in the analysis of resistance to flow.

Journal ArticleDOI
TL;DR: In this article, a hybrid approach is proposed, mixing the 1D model for the straight reaches and local 2D models for the bends, which can capture reflection and diffraction processes in such a way that the results are really good in what concerns the water level.
Abstract: In practice, dam-break modeling is generally performed using a one-dimensional (1D) approach for its limited requirements in data and computation. However, for valleys with multiple sharp bends, such a 1D model may fail for predicting as well the maximum water level as the wave arrival time. This paper presents an experimental study of a dam-break flow in an initially dry channel with a 90° bend, with refined measurements of water level and velocity field. The measured data are compared to some numerical results computed with finite-volume schemes associated with Roe-type flux calculation. The 1D approach reveals the expected limits, while a full two-dimensional (2D) approach provides fine level prediction and rather satisfactory information about the arrival time. A hybrid approach is now proposed, mixing the 1D model for the straight reaches and local 2D models for the bends. The compatibility of the Roe fluxes at the interfaces requires a careful formulation, but the resulting scheme seems able to capture reflection and diffraction processes in such a way that the results are really good in what concerns the water level.

Journal ArticleDOI
TL;DR: In this article, the impacts of simplifications in the water-sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes are investigated.
Abstract: Existing numerical river models are mostly built upon asynchronous solution of simplified governing equations. The strong coupling between water flow, sediment transport, and morphological evolution is thus ignored to a certain extent. An earlier study led to the development of a fully coupled model and identified the impacts of simplifications in the water-sediment mixture and global bed material continuity equations as well as of the asynchronous solution procedure for aggradation processes. This paper presents the results of an extended study along this line, highlighting the impacts on both aggradation and degradation processes. Simplifications in the continuity equations for the water-sediment mixture and bed material are found to have negligible effects on degradation. This is, however, in contrast to aggradation processes, in which the errors purely due to simplified continuity equations can be significant transiently. The asynchronous solution procedure is found to entail appreciable inaccuracy for both aggradation and degradation processes. Further, the asynchronous solution procedure can render the physical problem mathematically ill posed by invoking an extra upstream boundary condition in the supercritical flow regime. Finally, the impacts of simplified continuity equations and an asynchronous solution procedure are shown to be comparable with those of largely tuned friction factors, indicating their significance in calibrating numerical river models. It is concluded that the coupled system of complete governing equations needs to be synchronously solved for refined modeling of alluvial rivers.

Journal ArticleDOI
TL;DR: In this article, the authors developed a method for predicting the longitudinal dispersion coefficient in single-channel natural streams, including straight and meandering ones, using a new channel shape equation for straight channels and a more versatile channel shape or local flow depth equation for natural streams.
Abstract: Using a new channel shape equation for straight channels and a more versatile channel shape or local flow depth equation for natural streams a method is developed for prediction of the longitudinal dispersion coefficient in single-channel natural streams, including straight and meandering ones. The method involves derivation of a new triple integral expression for the longitudinal dispersion coefficient and development of an analytical method for prediction of this coefficient in natural streams. The proposed method is verified using 70 sets of field data collected from 30 streams in the United States ranging from straight manmade canals to sinuous natural rivers. The new method predicts the longitudinal dispersion coefficient, where more than 90% calculated values range from 0.5 to 2 times the observed values. The advantage of the new method is that it is capable of accurately predicting the longitudinal dispersion coefficient in single-channel natural streams without using detailed dye concentration test data. A comparison between the new method and the existing methods shows that the new method significantly improves the prediction of the longitudinal dispersion coefficient.

Journal ArticleDOI
TL;DR: In this paper, a conjunctive two-dimensional surface and three-dimensional subsurface flow model is presented, which uses the noninertia approximation of the Saint-Venant equations for 2D unsteady surface flow and a modified version of the Richards equation for 3D unsaturated and saturated flows.
Abstract: In the rainfall-runoff process, interaction between surface and subsurface flow components plays an important role, especially in rainwater abstraction and overland flow initiation at the early stage of rainfall events. Coupling of surface and subsurface flow submodels, therefore, is necessary for advanced comprehensive and sophisticated rainfall-runoff simulation. This article presents a conjunctive two-dimensional (2D) surface and three-dimensional (3D) subsurface flow model, which uses the noninertia approximation of the Saint-Venant equations for 2D unsteady surface flow and a modified version of the Richards equation for 3D unsteady unsaturated and saturated subsurface flows. The equations are written in the form of 2D and 3D heat diffusion equations, respectively, and solved numerically. The surface and subsurface flow components are coupled interactively using the common boundary condition of infiltration through the ground surface. The conjunctive model is verified with Smith and Woolhiser’s exper...

Journal ArticleDOI
TL;DR: In this paper, bed load discharge formulas have been evaluated by analyzing them in relation to measured Helley-Smith data for the gravel-bedded armored Drau River, Austria, and the choice of formula is made with respect to specific aims: the investigation of individual floods requires a different approach from that of long-term budgets.
Abstract: Bed load discharge formulas have been evaluated by analyzing them in relation to measured Helley-Smith data for the gravel-bedded armored Drau River, Austria. Comparison of calculations with measurements leads to ranking of the formulas that depends on the evaluation parameters. The choice of formula is made with respect to our specific aims: the investigation of individual floods requires a different approach from that of long-term budgets. Formula performance is consistently improved when conditions for the threshold of motion are modified according to data measured up on the initiation of motion. Formulas such as those reported by Parker in 1990, Zanke in 1999, and Sun and Donahue in 2000 are capable of coping with partial transport, which is commonly found in Alpine rivers. These formulas therefore provide encouraging results, particularly after the introduction of modifications. The augmentation of field measurements, even if limited in scope, considerably improves the performance of bed load discharge formulas.

Journal ArticleDOI
TL;DR: In this article, a one-dimensional theoretical model for subcritical flows in combining open channel junctions is developed, which is based on applying the momentum principle in the streamwise direction to two control volumes in the junction together with overall mass conservation.
Abstract: A one-dimensional theoretical model for subcritical flows in combining open channel junctions is developed. Typical examples of these junctions are encountered in urban water treatment plants, irrigation and drainage canals, and natural river systems. The model is based on applying the momentum principle in the streamwise direction to two control volumes in the junction together with overall mass conservation. Given the inflow discharges and the downstream depth, the proposed model solves for each of the upstream depths. The interfacial shear force between the two control volumes, the boundary friction force, and the separation zone shear force downstream of the lateral channel entrance are included. Predictions based on the proposed approach are shown to compare favorably with existing experimental data, previous theories, and conventional junction modeling approaches. The main advantages of the proposed model are that the proposed model does not assume equal upstream depths and that the dynamic treatment of the junction flow is consistent with that of the channel reaches in a network model.

Journal ArticleDOI
TL;DR: In this article, an exponential formula that does not involve the concept of critical shear stress is derived for computing bedload transport rates, which represents well various experimental data sets ranging from the weak transport to high shear conditions.
Abstract: An exponential formula that does not involve the concept of the critical shear stress is derived in this study for computing bedload transport rates. The formula represents well various experimental data sets ranging from the weak transport to high shear conditions. Comparisons of the present study are also made with many previous bedload formulas commonly cited in the literature.