Journal of Hydraulic Engineering

Published by American Society of Civil Engineers
Print ISSN: 0733-9429
The self-aeration of high velocity open-channel flows is attributed to the interaction between the turbulent flow and the liquid free surface. In addition to self-aeration, drops are ejected out of the bulk liquid. It is often proposed that the drops are separated from the bulk by transverse velocity fluctuations. Drops falling back into the liquid later have been suggested to provide a possible mechanism of air entrainment. These ideas have led to the formulation of critical conditions for the inception of self-aeration. It will be shown that the conventional concepts of drop formation are inadequate to explain the ejection of drops to the heights that were observed in experiments. Furthermore, the energy of ejected drops is not sufficiently high for air entrainment. Critical conditions of self-entrainment that were previously derived are, therefore, invalid.
Determination of optimal I from b, Q 0 = 0.7670 kg/s. Solid line shows optimal fit for the given mass rate (based on optimum for b and u c ), while dashed lines shows results when I is chosen ±5, ±10 and ±20% from optimum.  
Determination of optimal I from u c , Q 0 = 0.7670 kg/s. Solid line shows optimal fit for the given mass rate (based on optimum for b and u c ), while dashed lines shows results when I is chosen ±5, ±10 and ±20% from optimum.  
Least square fit for relation between I and Re E . Solid circles show values for I obtained from the experimental data of Milgram (1983) and stars show values for I obtained from experimental data of Fanneløp and Sjøen (1980). Solid line shows the least square fit to a function of the form I = a ln Re E + b.  
Optimal I when λ = 0.5. Solid lines represent the plume width b and dotted lines represent the centerline velocity u c . Compared with experimental data of Milgram (1983) for Q = 0.7670kg/s.  
A phenomenological kinetic energy theory of buoyant multiphase plumes is constructed, being general enough to incorporate the dissolution of the dispersive phase. We consider an axisymmetric plume, and model the dissolution by means of the Ranz-Marshall equation in which there occurs a mass transfer coefficient dependent on the plume properties. Our kinetic energy approach is moreover generalized so as to take into account variable slip velocities. The theoretical model is compared with various experiments, and satisfactory agreement is found. One central ingredient in the model is the turbulent correlation parameter, called I, playing a role analogous to the conventional entrainment coefficient \alpha in the more traditional plume theories. We use experimental data to suggest a relationship between I, the initial gas flux at the source, and the depth of the gas release. This relationship is used to make predictions for five distinct case studies. Comparison with various experimental data shows that the kinetic energy approach built upon use of the parameter I in practice has the order of predictive power as the conventional entrainment-coefficient models. Moreover, an advantage of the present model is that its predictions are very quickly worked out numerically. Finally, we give a sensitivity analysis of the kinetic energy approach. It turns out that the model is relatively stable with respect to most of the input parameters. It is shown that the dissolution is of little influence on the dynamics of the dispersed phase as long as the dissolution is moderate.
INTRODUCTION The study of the catastrophic collapse of a dam is of interest because of the risk to life and property the ensuing flooding may cause. During this century there have been more than 200 failures of dams greater than 15 metres high[1]. They have caused millions of dollars worth of damage and a loss of more than 8,000 lives. These recent disasters have focussed attention on means for assessing public safety and predicting probable damage from the collapse of a dam. Many water authorities are required to assess the risk of failure and develop a flood warning plan for all of their large dams. However, this is not the case for the smaller water supply reservoir which form part of the water reticulation system in many cities. These reservoirs are typically 50 metres in diameter and 10 metres high and contain approximately 20 mega litres of water. They are usually located in elevated positions in residential areas. Due to their proximity to residential areas, water supply r
: A computational algorithm based on the multiquadric, which is a continuously differentiable radial basis function, is devised to solve the shallow-water equations. The numerical solutions are evaluated at scattered collocation points and the spatial partial derivatives are formed directly from partial derivatives of the radial basis function, not by any difference scheme. The method does not require the generation of a grid as in the finite element method and allows easy editing or refinement of the numerical model. To increase the confidence on the multiquadric solution, a sensitivity and convergence analysis is performed using numerical models of a rectangular channel. Applications of the algorithm are made to compute the sea surface elevations and currents in Tolo Harbour, Hong Kong during a typhoon attack. The numerical solution is shown to be robust and free of spurious oscillations. The computed results are compared with the measured data and good agreement is indicated. INTRO...
A hydraulic jump is the sudden transition from a high-velocity to a low-velocity open channel flow. The application of the momentum principle to the hydraulic jump is commonly called the Bélanger equation, but few know that Bélanger's (1828) treatise was focused on the study of gradually varied open channel flows. Further, although Bélanger understood the rapidly-varied nature of the jump flow, he applied incorrectly the Bernoulli principle in 1828, and corrected his approach 10 years later. In 1828, his true originality lay in the successful development of the backwater equation for steady, one-dimensional gradually-varied flows in an open channel, together with the introduction of the step method, distance calculated from depth, and the concept of critical flow conditions.
A 3D numerical model with an orthogonal curvilinear coordinate in the horizontal direction and sigma coordinate in the vertical direction has been developed. This model is based on POM (Princeton Ocean Model). In this model a second moment turbulence closure submodel is embedded and the stratification caused by salinity and temperature is considered. Furthermore, to adapt to estuary locations where the flow pattern is complex, the horizontal time differencing is implicit with the use of a time-splitting method instead of the explicit method in POM. This model is applied to the Pearl River estuary, which is the largest river system in South China, with Hong Kong at the eastern side of its entrance. The computation is verified and calibrated with field measurement data. The computed results mimic the field data well. Author name used in this publication: K. W. Chau KeyWords: BOUNDARY; LAKE; 3D numerical model;
A new set of depth-averaged equations is introduced to study the flow over an arbitrary three-dimensional (3D) surface. These equations are derived based on a generalized curvilinear coordinate system attached to the 3D bed surface, therefore it allows us to include the effect of centrifugal force due to the bottom curvature. These general equations make it possible to analyze flows over complex terrain without the limitation of mild slope assumption used in conventional depth-averaged models. This new model is then applied to calculate the water surface profiles of (1) flow over a cylindrical surface; (2) flow over a circular surface; and (3) flow with an air-core vortex at a vertical intake. A simple hydraulic experiment is conducted in the laboratory to observe the water surface profile of flow over a circular surface. The results obtained from the model are in good agreement with experimental measurements and calculation by an empirical formula. Consequently, it demonstrates the applicability of the model in cases of flow over a highly curved bottom.
The accuracy of cross-channel integrated sediment transport of bed material is determined with an elaborate set of field measurements in the Waal River, The Netherlands. The measurements were done during a discharge wave in the upstream part of the river, which has a bimodal sand-gravel bed. The sampling strategy should take both spatial and temporal aspects into account to obtain maximum accuracy. Presence of moving bedforms, differences in bed-sediment grain size in the cross section, and presence of preferential transport lanes dictate that at least five subsections for sampling in the cross section are necessary. The accuracy of cross channel integrated bedload transport depends mainly on the measurement strategy. An uncertainty of <20% (bedload) and 7% (suspended load) of cross-channel integrated sediment transport is shown to be feasible if 30 samples of bedload and two vertical profiles of suspended bed-material load are taken in one subsection, provided that the cross section of the river is divided into at least five subsections. The samples in one subsection should be distributed over the length of the bed form. Changes of discharge during the measurements cause systematic differences between the subsections. To minimize this uncertainty a compromise between the spatial and temporal accuracy is necessary. Therefore, when only one vessel with instruments is available for doing the measurements, the number of sampling positions and subsections must be reduced if the rate of change of discharge is large, Based on the results a prediction method is given to estimate the feasible accuracy in the planning phase of future campaigns, and the necessary time and financial investment for that accuracy.
Spectral analysis of velocity signals recorded by acoustic-Doppler velocimetry (ADV) and contaminated with intermittent spikes remains a challenging task. In this paper, we propose a new method for reconstructing contaminated time series, which integrates two previously developed techniques for detecting and replacing spurious spikes. The spikes are first detected using a modified version of the Universal Phase-Space-Thresholding technique and subsequently replaced by the last valid data points. The accuracy of the new approach is evaluated by applying it to identify and remove spikes and reconstruct the spectra of two clean data sets which are artificially contaminated with random spikes: (a) high-quality hot-wire measurement; and (b) numerically simulated velocity time series with bi-modal probability density distribution. The technique is also applied to reconstruct the spectra obtained from intentionally contaminated ADV measurements and compare them with ADV spectra at the same point in the flow obtained using proper ADV settings. Special emphasis is placed on testing the ability of the technique to reproduce realistic power spectra in flows with rich coherent dynamics. The results show that the power spectra of the reconstructed time series contain a filtered white noise caused by the steps in the reconstruction technique using the last valid data point. We show that even for a severely contaminated time series, the proposed method can accurately recover the power spectra up to the frequency corresponding to the half the mean sampling rate of the valid data points.
Description of physical aquatic habitat often includes data describing distributions of water depth, velocity, and bed material type. Water depth and velocity in streams deeper than about 1 m may be continuously mapped using an acoustic Doppler current profiler from a moving boat. Herein we examine the potential of using the echo signal strength from the bed as an indicator of bed material type. Mean signal strength from soft muddy beds was consistently 10-20 dB lower than mean signal strength from noncohesive (gravel or sand) beds. Sand beds tended to have larger site-to-site variation (means -30 to -19 dB) than for fines (-43 to -38 dB) or gravel (-23 to -20 dB).
The author provided interesting simple correlations on uniform aerated flows. The writer would like to add some information on the average air concentration and to discuss specific points concerning the bottom air concentration and the mixture flow depth.
In open channel flows an important design parameter is the amount of entrained air. The presence of air within the flow increases the bulk of the flow but also increases the transfer of atmospheric gases (e.g. oxygenation of river). Further aeration of high-velocity flows may prevent or reduce cavitation damage. This paper describes a general method to compute the flow characteristics of self-aerated flows. Firstly the uniform flow characteristics are summarized. Then the basic equations for gradually varied aerated flows are developed using the same method as WOOD (1985). The results are discussed and compared with several experimental data, and practical applications to self-aerated flows and tunnel spillway flow are presented.
The resistance characteristics in terms of power consumption, interpreted in terms of Power number (P-0), of unbaffled surface aeration systems consisting of flat bladed impellers, were studied in two shapes of surface aerations tanks: square and circular. Experiments were conducted in three different sizes in each of the geometrically similar unbaffled square and circular surface aerators. Results have shown that the P-0 cannot be simulated singularly either with Reynolds number R or with Froude number as there are scale effects; hence there appears to be a need for incorporating the effects of both R and F. It is found that P-0 is uniquely related to a parameter X (=(FR1/3)-R-4/3), which is defined as a parameter governing the theoretical power per unit volume for both shapes of aeration tanks; however, such relationships are different for both shapes of aerators. Interestingly P-0 values are always higher in square surface aerators than in circular surface aerators, which suggests that the circular surface aerators require less power input than the square surface aerators. The usefulness of such correlations was demonstrated in estimating the power requirement while achieving a required oxygen transfer coefficient in surface aerators.
The marsh porosity method, a type of thin slot wetting and drying algorithm in a two-dimensional finite element long wave hydrodynamic model, is discussed and analyzed to assess model performance. Tests, including comparisons to simple examples and theoretical calculations, examine the effects of varying the marsh porosity parameters. The findings demonstrate that the wetting and drying concept of marsh porosity, often used in finite element hydrodynamic modeling, can behave in a more complex manner than initially expected.
Benedict Fellowship Program--P. iii. Thesis (Ph. D.)--University of Iowa, 1983. Includes bibliographical references (leaves 159-168).
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.
The hydraulic design of a tilting weir is presented, which allows for periodic exchange of potadromous fish between freshwater ecosystems. The application domain includes inland waters that need to be isolated hydraulically, preserving the existing ecological connection with the surrounding areas as much as possible. In the absence of a hydraulic gradient, the weir is opened in its neutral position and fish can bypass through passages sideways of the weir. When a hydraulic gradient develops in either of two directions, the weir rotates until a new balance of moments of force is reached, while fish can still bypass. Above a threshold value of the hydraulic gradient, the weir falls shut. When the hydraulic gradient returns to zero, the weir reopens, restoring the ecological connection. Four variants of the weir were investigated in the Hydraulics Laboratory at Wageningen University. The versatility of the design is demonstrated by showing that the hydraulic gradients required for closure and reopening can be manipulated largely independently. Patterns of flow velocity and turbulence kinetic energy were analyzed, which suggest that relevant fish species can bypass the weir unimpeded. The effectiveness of the weir will mainly depend on hydrostatic aspects, which determine when the weir is opened and closed, and on the absence of large hydraulic gradients in the migration season.
Typescript (photocopy). Thesis (Ph. D.)--University of Iowa, 1987. Bibliography: leaves 119-133.
Surge flow phenomena. e.g.. as a consequence of a dam failure or a flash flood, represent free boundary problems. ne extending computational domain together with the discontinuities involved renders their numerical solution a cumbersome procedure. This contribution proposes an analytical solution to the problem, It is based on the slightly modified zero-inertia (ZI) differential equations for nonprismatic channels and uses exclusively physical parameters. Employing the concept of a momentum-representative cross section of the moving water body together with a specific relationship for describing the cross sectional geometry leads, after considerable mathematical calculus. to the analytical solution. The hydrodynamic analytical model is free of numerical troubles, easy to run, computationally efficient. and fully satisfies the law of volume conservation. In a first test series, the hydrodynamic analytical ZI model compares very favorably with a full hydrodynamic numerical model in respect to published results of surge flow simulations in different types of prismatic channels. In order to extend these considerations to natural rivers, the accuracy of the analytical model in describing an irregular cross section is investigated and tested successfully. A sensitivity and error analysis reveals the important impact of the hydraulic radius on the velocity of the surge, and this underlines the importance of an adequate description of the topography, The new approach is finally applied to simulate a surge propagating down the irregularly shaped Isar Valley in the Bavarian Alps after a hypothetical dam failure. The straightforward and fully stable computation of the flood hydrograph along the Isar Valley clearly reflects the impact of the strongly varying topographic characteristics on the How phenomenon. Apart from treating surge flow phenomena as a whole, the analytical solution also offers a rigorous alternative to both (a) the approximate Whitham solution, for generating initial values, and (b) the rough volume balance techniques used to model the wave tip in numerical surge flow computations.
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.
In open channels, the transition from supercritical to subcritical flows is called a hydraulic jump. For low upstream Froude numbers, free-surface undulations develop downstream of the jump and the hydraulic jump is called an undular jump. New experiments on undular hydraulic jumps were performed in a rectangular channel in which the upstream flows were fully developed turbulent shear flows. In this paper, the main flow patterns are described. Visual and photographic observations indicate five types of undular jumps. One of the main flow characteristics is the presence of lateral shock waves for Froude numbers larger than 1.2. The results show that the disappearance of undular jump occurs for Froude numbers ranging from 1.5 to 2.9 and that the wave length and amplitude of the free-surface undulations are functions of the upstream Froude number and the aspect ratio yc/W.
A simple method is presented for evaluating wall shear stresses from known flow histories in unsteady pipe flows. The method builds on previous work by Trikha, but has two important differences. One of these enables the method to be used with much larger integration time steps than are acceptable with Trikha's method. The other, a general procedure for determining approximations to weighting functions, enables it to be used at indefinitely small times (high frequencies). The method is applicable to both laminar and turbulent flows.
Theoretical predictions of wall shear stresses in unsteady turbulent flows in pipes are developed for all flow conditions from fully smooth to fully rough and for Reynolds numbers from 103 to 108. A weighting function approach is used, based on a two-region viscosity distribution in the pipe cross section that is consistent with the Colebrook–White expression for steady-state wall friction. The basic model is developed in an analytical form and the resulting weighting function is then approximated as a sum of exponentials using a modified form of an approximation due to Trikha. A straightforward method is presented for the determination of appropriate values of coefficients for any particular Reynolds number and pipe roughness ratio. The end result is a method that can be used relatively easily by analysts seeking to model unsteady flows in pipes and ducts.
Previous studies on tidal water table dynamics in unconfined coastal aquifers have focused on the inland propagation of oceanic tides in the cross-shore direction based on the assumption of a straight coastline. Here, two-dimensional analytical solutions are derived to study the effects of rhythmic coastlines on tidal water table fluctuations. The computational results demonstrate that the alongshore variations of the coastline can affect the water table behavior significantly, especially in areas near the centers of the headland and embayment. With the coastline shape effects ignored, traditional analytical solutions may lead to large errors in predicting coastal water table fluctuations or in estimating the aquifer's properties based on these signals. The conditions under which the coastline shape needs to be considered are derived from the new analytical solution.
The three-dimensional (3D) numerical simulation of a steady, shallow turbulent flow around a groyne in a rectangular channel is presented. A method used to track a moving surface boundary and to follow its evolution, using a one-phase 3D Reynolds solver with rigid grids, by means of a transient fraction of fluid or "porosity" field is applied. Some results are compared with experimental data, such as the isolines of water depths and the mean velocity field. A comparison of the reattachment length prediction using the free-surface model and the rigid-lid assumption is given. Other results concerning the pressure field, turbulence, or shear stress distribution are presented and analyzed.
This paper describes a numerical model developed to simulate flow and bed deformation around river hydraulic structures. The model solved the fully three-dimensional, Reynolds-averaged Navier-Stokes equation expressed in a moving boundary-fitted coordinate system to calculate the flow field with water and bed surfaces varying in time. A nonlinear k-epsilon turbulence model was employed in order to predict flow near the structure where three-dimensional flow is dominant. The temporal change in bed topography was calculated by coupling a stochastic model for sediment pickup and deposition using a momentum equation of sediment particles ill order to account for the effect of nonequilibrium sediment transport. In validating the numerical model, a spur dike and a bridge pier, which are considered to be typical river-engineering structures, were selected. By comparing the numerical results with observed laboratory experimental data, the model was found to reproduce flow and scour geometry around these structures with sufficient accuracy.
The work of Auguste Graeff is rarely acknowledged for his true contribution to hydraulic engineering and structures. Herein further information on Graeff and his co-worker Emile Delocre are presented together with the influence of their work in France and overseas, and several curved gravity dams built around Saint-Etienne based upon the Gouffre d'Enfer dam design. Altogether Auguste Graeff and Emile Delocre had a significant influence on gravity dam design in France and overseas.
Since the early European settlements, Australia's economy has been highly dependent upon its water supply, although limited because of the dry climate. Today, the Australian continent is equipped with a large number of hydraulic structures per capita, and hydraulic engineering expertise is critical to future developments. In the universities, the civil engineering and environmental engineering undergraduate courses include a significant number of fluid mechanics and hydraulics subjects, including an introduction to hydraulic design. At the University of Queensland, the teaching of hydraulic design is focused on the sound application of the basic principles of fluid mechanics. Basic applications include the hydraulic design of spillways and culverts. Each type of design is supported by a series of lectures and a case study involving homework, a field visit, and a series of tutorials. Practical classes (laboratory and field visit) are an indispensable complement of the lectures. The subject assessment is based upon a combination of homework, practicals, and end-of-semester examination grades.
Comparison of different models for the propagation of a sinusoidal hydrograph on a 10 km long river with α = 3.0 m 2−3β s β , β = 1.5 and Q = 1.5 m 3 /s.
Fit coefficient γ for the propagation of a sinusoidal hydrograph on a river of length L = 10 km represented by the nonlinear KWE with α = 3 m 2−3β s β , β = 0.3 and β = 1.5.
Variation of the time delay along time T (L, t) for daily input discharge of the Schuylkill river at Norristown
This discussion raises questions about the new method proposed by the authors in their paper.
In the steady flow computation of water surface profiles with one-dimensional models, bridges across floodplains require special attention. Accurate prediction of energy losses in the reaches upstream and downstream of the bridge requires accurate evaluation of four parameters: the expansion reach length, the contraction reach length, the expansion coefficient, and the contraction coefficient. This study investigated these four parameters through the use of field data, two-dimensional hydraulic modeling, and one-dimensional modeling. In this paper, the findings of the study with regard to the transition reach lengths are presented. The traditional rule, which recommends an expansion rate of one unit outward for every four units downstream from a bridge, overestimates the reach length in many cases. The standard rule regarding contraction reach lengths, which assumes a one-to-one rate of contraction, was not refuted by this study, but more refined estimates are reported.
Definition sketch of flow and topography in open-channel bends
Hydraulic Conditions in A21 Experiment without Footing and B4 Experiment with Footing
River bank protection is a costly but essential component in river management. Outer banks in river bends are most vulnerable to scour and erosion. Previous laboratory experiments illustrated that a well-designed horizontal foundation of a vertical outer bank protruding into the cross section, called a footing, can reduce the scour depth and thereby protect the bank. This paper provides detailed experimental data in a reference experiment without footing and an experiment with footing carried out under similar hydraulic conditions, which suggest a delicate interaction between bed topography, downstream and cross-stream velocity, and to lesser extent turbulence. The presence of the outer bank footing modifies this delicate interaction and results in a more favorable configuration with respect to bank stability including: reduced maximum scour depth, more uniformly distributed downstream velocity, and weaker cross-stream circulation cells.
This paper presents a numerical analysis of river channel processes with bank erosion. The model can be used for investigating both bed-deformation and bankline shifting in 2D plan form. The basic equations are used in a moving boundary fitted-coordinate system, and a new formulation of nonequilibrium sediment transport is introduced to reproduce the channel processes. The model was applied to examine the morphological behavior of experimental channels. Temporal changes in the plan form in a meandering channel can be classified into two patterns: meander developing and meander straightening. Comparison of the observed and calculated results indicates that the model is applicable to both channel changes under various hydraulic conditions. On the basis of the numerical findings, the paper clarifies the influence of hydraulic variables on the location of bank erosion and bed scouring. The model also was used to investigate the effect of alternate bars on bank erosion and to investigate the development of channel meandering from an initially straight channel.
Model studies have been undertaken to study the spatial and temporal development of a brackish pool within an impoundment supplied by a freshwater inflow and bounded by an impermeable barrier that is overtopped periodically by a tidally generated saline water inflow. The results demonstrate the relative influence of the freshwater inflow and downstream tidal conditions in controlling the temporal development of this pool. In particular, the experimental data illustrate that the dimensions of the brackish pool reach equilibrium after a specific number of tidal cycles, with the normalized thickness of the pool being dependent primarily on the strength of the freshwater inflow. The density structure of the water within the impoundment is interpreted in terms of two contributory processes, namely, (1) turbulent entrainment of fresh receiving water into the saline intrusion; and (2) shear-induced interfacial erosion of the brackish water by the overriding fresh water during receding tidal conditions. A scaling analysis shows that the temporal growth of the brackish pool thickness can be parameterized successfully in terms of a volume ratio representing the dilution capacity of the freshwater stored in the impoundment during the saline intrusion phase.
Energy dissipation systems such as single fall-stilling basin and single chute bucket have been used in the design and construction of large dams. In the case of high head structures, however, due to the high flow velocity, these systems suffer from problems such as cavitation, vibration, and abrasion. As an alternative, a cascade system could be used, which is a cascade of falls and stilling basins below each fall. A procedure has been developed for optimum design of cascade stilling basins using dynamic programming as an optimization technique to minimize the excavation and concrete-work costs with given geometric parameters of the system. Based on this procedure, a computer model was developed and examined in the design of the Tehri Dam in India as a case study. Evaluation of the model results and comparing them with those obtained by a model not using an optimization tool shows 31% of improv6ement with regard to the minimization of concrete and excavation volumes and consequently construction costs.
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 nonuniform 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.
The writer wishes to congratulate the authors for their excellent paper. He would like to discuss some possible drag reduction effects.
Attention is given to the properties of sediment beds over the full range of conditions silts to gravel, in particular the effect of fine silt on the bed composition and on initiation of motion critical conditions is discussed. High-quality bed-load transport data sets are identified and analyzed, showing that the bed-load transport in the sand range is related to velocity to power 2.5. The bed-load transport is not much affected by particle size. The prediction of bed roughness is addressed and the prediction of bed-load transport in steady river flow is extended to coastal flow applying an intrawave approach. Simplified bed-load transport formulas are presented, which can be used to obtain a quick estimate of bed-load transport in river and coastal flows. It is shown that the sediment transport of fine silts to coarse sand can be described in a unified model framework using fairly simple expressions. The proposed model is fully predictive in the sense that only the basic hydrodynamic parameters depth, current velocity, wave height, wave period, etc. and the basic sediment characteristics d10, d50, d90, water temperature, and salinity need to be known. The prediction of the effective bed roughness is an integral part of the model.
Full-text of this article is not available in this e-prints service. This article was originally published following peer-review in the Journal of Hydraulic Engineering, published by and copyright American Society of Civil Engineers. Dam-break flows in general geometries with complex bed topography are simulated numerically using a high-resolution Godunov-type cut cell method. The model is based on the shallow water equations with appropriate source terms. A vertical step in the bed is treated efficiently and accurately with the surface gradient method. For dam-break flows occurring in complicated geometries, the Cartesian cut cell method together with transmissive boundary conditions is incorporated. Verification of the method is carried out by predicting dam-break flows typical of practical situations, i.e., dam-break flows over a vertical step into bent channels and a dam-break flow over a bump in a bed with both transmissive and reflective boundary conditions at the channel end. The results are compared with experimental data showing good agreement. The method is simple, efficient, and conservative. It shows promise for handling a wide range of dam-break flows.
The relative magnitudes of the celerities at which disturbances on the water surface and the bed are propagated play a key role in the mathematical modeling of mobile bed flow. Earlier analyses assumed that the solids concentration of the flow was negligible. This assumption is inappropriate both for some natural streams and for many aqueous mine-waste disposal applications. Here, the relative celerities of mobile bed flow are determined for flows with finite solids concentrations. The solids concentration is assumed to be a function of the velocity and depth of flow. The analysis confirms and extends the results of earlier analyses. It is shown that the movement of the sediment and the water can be considered to be mathematically independent of each other only within very limited ranges of solids concentration and Froude number. This severely constrains the application of numerous existing mathematical models to mobile bed flows with relatively high solids concentrations.
Open-channel beds show variations in the transverse direction due to the interaction between downstream flow, cross-stream flow, and bed topography, which may reduce the navigable width or endanger the foundations of structures. The reported preliminary laboratory study shows that a bubble screen can generate cross-stream circulation that redistributes velocities and hence, would modify the topography. In straight flow, the bubble-generated cross-stream circulation cell covers a spanwise extent of about four times the water depth and has maximum transverse velocities of about 0.2 ms¿1. In sharply curved flow, it is slightly weaker and narrower with a spanwise extent of about three times the flow depth. It shifts the counter-rotating curvature-induced cross-stream circulation cell in the inwards direction. Maximum bubble-generated cross-stream circulation velocities are of a similar order of magnitude to typical curvature-induced cross-stream circulation velocities in natural open-channel bends. The bubble screen technique is adjustable, reversible, and ecologically favorable. Detailed data on the 3D flow field in open-channel bends is provided, which can be useful for validation of numerical models
Described is a method for channel erosion control and habitat rehabilitation featuring intermittent placement of structures made of large woody debris. This method is expressly tailored to address severe problems typical of incised channels with little sediment coarser than sand. In these types of environments, buoyancy forces are typically more important factors in woody debris stability than fluid drag. Buoyant forces are counteracted by the weight of the structure, earth anchors, and sediment deposits. Design concepts were tested in a demonstration project constructed along 2 km of channel draining a 37-km2 watershed. Large woody debris structures reduced velocities in the region adjacent to the bank toe and induced sediment deposition and retention. Construction costs per unit channel length were 23-58% of costs for recent stone bank stabilization projects within the same region. During the second year following construction, 31% of the structures failed during high flows, probably due to inadequate anchoring.
Thesis (M.S.)--University of Minnesota, 1983. Includes bibliographical references (leaves 127-128).
The processes involved in bed-load sediment transport are complex and difficult to quantify. Field measurements provide insight and a chance to improve predictive methods. A comprehensive database is described that contains more than 15,000 observations from nearly 500 data sets of bed-load sediment transport. Observations are compiled from published sources, author responses to queries, and personal visits to offices. Each entry has been checked twice for accuracy against the original data and converted to a common set of units. The database contains sections for sample descriptions, discharge and transport data, channel and bankfull characteristics, surface and subsurface grain size distributions, and, where possible, stream classification descriptors. Discharges range from far below to several times bankfull values. The database is freely available to the public and may be accessed via direct download and through WaterML based web services from the BYU World Water Data Sediment Transport Database portal at The intent of this database is to provide useful data to researchers as they continue to investigate bed-load transport processes. Data can be added to the database by contacting the authors.
Publicación ISI Email :;; Sediment management in reservoirs with the help of water jets has motivated this work. Erosion caused by single and multiple submerged circular turbulent wall jets on a noncohesive sediment bed of finite thickness lying on a fixed boundary was studied with the help of laboratory experiments. Different combinations of jet diameter, jet separation, and sediment thickness to jet diameter ratio were tested. Results show a relation between dimensionless parameters characterizing the steady state bed profile and the densimetric particle Froude number F-0 given by the velocity at the nozzle and the effective diameter and submerged specific density of the sediment. Evolution of scour with time confirms previous studies where the erosion was found to initially grow with the logarithm of time up to a certain reference time t*. This time, made dimensionless with a time scale t(c), involving the volume of sediment scoured and the rate of erosion, was also related to the densimetric Fronde number. A comparison with studies regarding erosion of a semiinfinite layer of sediment is also presented.
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