Search

Sediment settling velocities are commonly estimated from analytical or process-based approaches. These approaches have theoretical constraints due to the incompletely resolved settling physics. A parametric data-driven approach was recently proposed without theoretical constraints, but it is limited by its mathematical assumptions. To overcome these limitations, this study applies a machine learning algorithm to an aggregated sediment settling experimental database and develops a nonparametric data-driven model to estimate the noncohesive sediment settling velocity in water. A cross-comparison against five process-based equations and a parametric data-driven equation demonstrates the higher accuracy and better consistency of the new model in estimating sediment settling velocities under various physical regimes. The new model also shows an easily implemented self-update capability by assimilating theoretical data derived from the process-based equations. The updated model, incorporating experimental and theoretical data of sediment settling processes, further improves the accuracy and reduces the uncertainty in estimating sediment settling velocities. This study demonstrates the capability of machine learning in sediment transport study and illustrates an alternative framework for other hydraulic engineering challenges. [ABSTRACT FROM AUTHOR]

This paper reviews the application of computational fluid dynamics (CFD) to numerically model the two-phase flow of water and sediment in the complex environment of a stormwater retention pond. The review is intended to draw the attention of the hydraulic engineering community, specifically those involved in pond design, to the recent advancements in computational modeling of sediment transport in ponds. It provides an up-to-date survey of current simulation capability, focusing on the potential of fully three-dimensional methods for solving sediment transport in complex pond flows. An additional goal of this paper is to alert new researchers engaged in stormwater retention pond design to the research opportunities presented by CFD. Even though pond configurations have become more complex to improve their performance, many studies have continued to rely solely on single-phase models. At the present time, unsteady three-dimensional two-phase models are becoming available to study these problems. Of the multiphase models that might be considered, the particle tracking (Eulerian-Lagrangian) method and two-fluid (Eulerian-Eulerian) method both are potentially applicable to modeling sediment transport in pond-type flows. To date, only the particle-tracking method has been applied to stormwater retention ponds. The two-fluid method is capable of simulating sediment transport in retention ponds. It would be advantageous for a simulation of large-scale ponds in which the number of particles required for particle-tracking becomes excessive. Currently, fully three-dimensional CFD methods are being successfully used to model a variety of multiphase flows in mechanical and chemical engineering, as well as some specific applications in hydraulic engineering. Its application to predict sediment transport in a retention pond shows significant promise, especially when the effect of turbulence becomes challenging to model. [ABSTRACT FROM AUTHOR]

One-dimensional (1D) models can be applied, for engineering purposes, to long-term and large-scale morphodynamic simulations of entire river systems only if appropriate simplifications are introduced. This paper proposes an improvement of an existing simplified 1D model based on the local uniform flow hypothesis, coupled with a synthetic description of the transverse profile, which provides the active river width by analyzing the total and the vegetated widths of a watercourse, with assumed variables of the water flow. The overall density of the riparian vegetation, expressed in terms of biological carrying capacity, is predicted as a function of the local climate and some stresses due to interaction between hydrology, morphology, and biology. The constitutive equations have been deduced and the relevant parameters have been calibrated and validated against various hydrological and geometrical data, taken by satellite imagery covering two large watercourses located in tropical and subtropical areas (Parana and Zambezi rivers) and small streams located in temperate zones. The work confirms the opportunity to deal with hydro-morpho-biodynamic river modeling at large spatial and temporal scale through a mixed 1D + quasi-2D approach. The 1D submodel permits long-term computations at watershed scale of the river longitudinal evolution, while the quasi-2D submodel provides the transversal description of the watercourse in terms of vegetated and nonvegetated widths and vegetation density, which in its turn reflects on the 1D computations. [ABSTRACT FROM AUTHOR]

Saltation models provide considerable insight into near-bed sediment transport. This paper outlines a simple, efficient numerical model of stochastic saltation, which is validated against previously published experimental data on saltation in a channel of nearly horizontal bed. Convergence tests are systematically applied to ensure the model is free from statistical errors emanating from the number of particle hops considered. Two criteria for statistical convergence are derived; according to the first criterion, at least 10³ hops appear to be necessary for convergent results, whereas 104 saltations seem to be the minimum required in order to achieve statistical convergence in accordance with the second criterion. Two empirical formulas for lift force are considered: one dependent on the slip (relative) velocity of the particle multiplied by the vertical gradient of the horizontal flow velocity component; the other dependent on the difference between the squares of the slip velocity components at the top and bottom of the particle. The former is found to give more stable results. A parameter study indicates that the saltation length has a minimum value with increasing particle diameter (at D* ~ 12) for a given transport stage. Variations in the friction coefficient and collision line level have a negligible effect on the saltation statistics within the ranges considered. Regression equations are obtained for each of the saltation characteristics. Finally, the model is used to evaluate the bed-load transport rate, which is in satisfactory agreement with common formulas based on flume data, especially when compared against other saltation-derived expressions. [ABSTRACT FROM AUTHOR]

The hydraulic deposition process linked to tailings dams normally presents some technical deficiencies mainly because of the lack of control of hydraulic parameters. Problems of instability in tailings dams usually arise from poor management practices, such as poor decant pond control, in addition to the material being placed randomly. Hydraulic parameters, such as the flow rate and concentration of the slurry, play an important role in the formation of hydraulic fills. Grain size, distribution, segregation, and density, and slope inclination are the main characteristics of tailings dams, which are affected by the hydraulic parameters of the slurry. To investigate these factors, an experimental apparatus [hydraulic deposition simulation test (HDST)] was used to simulate the hydraulic deposition process in the laboratory, where all variables that could affect the phenomenon could be controlled carefully. The HDSTs using different flow rates and concentrations were carried out using the iron waste from the Morro Agudo Mine, Minas Gerais, Brazil (operated by Vale). The results presented in this paper are mainly related to the segregation patterns, mean grain sizes, specific gravities, and densities obtained along the small-scale deposited beach in the HDSTs. The main objective of this investigation was to analyze the influence of hydraulic deposition parameters on the formation process of hydraulic fills, focusing on segregation and its importance to density and porosity values. Moreover, a mathematical model was developed to describe and simulate the mechanism of formation of granular tailings dams based on momentum and continuity equations of the fluid and sediments (quartz and iron). The model takes into account the main external variables (slurry concentration and flow rate) and internal variables (such as mean particle size, grain density, and relative percentage of iron and quartz) related to the slurry mixture. The analytical and numerical results of the model were compared with the deposition profiles obtained by the HDST. [ABSTRACT FROM AUTHOR]

The lattice Boltzmann method (LBM) is used to simulate the particle resuspension process in a two-dimensional simple shear flow. At first, the lift force on a single disk-shaped particle attached at the channel wall is computed. It is found that when the particle is allowed to freely move in the viscous fluid, the resulting lift force is smaller than that when the particle is constrained to be stationary. The bulk properties of fluids with particles suspended under various concentrations are numerically calculated. The results agree reasonably well with analytical results by Batchelor when the volume fraction is lower than 50%. The resuspension process of a group of particles (up to 500) is simulated at different particle-to-fluid density ratios. It is found that the height and shape of particle bed depend on the particle density ratio and flow conditions. Interactions of groups of particles as well as the final shape of the bedform of the particles were studied during this resuspension process. Finally, the pressure distribution and flow above the bedform of particles was examined. The results obtained agree well with those observed in naturally occurring bedforms of sediments. DOI: 10.1061/(ASCE)0733-9429(2003)129:12(985) CE Database subject headings: Suspended sediments; Sediment transport; Stratified flow; River flow; River beds; Shear flow; Particles.

The experimental study investigates how the application of point suction at different bed locations affects local scour around a cylindrical bridge pier under clear-water conditions. The results show that suction has a profound effect on pier-scour development, and the extent of the influence is related to the location of the suction source. When the suction source is located at or upstream of the pier, the equilibrium scour depth is reduced by up to 50%, with , where and = suction flow rate and undisturbed approach flow rate, respectively. The data also show that for the suction source that is located downstream of the pier, the equilibrium scour depth is reduced by up to 30% with the same suction flow rate. The extent of pier-scour depth reduction at different locations from the suction source is closely associated with changes to the local effective shear and critical shear velocity. Results of this study show that bed suction may be used as an effective pier-scour countermeasure. [ABSTRACT FROM AUTHOR]

Bridge piers having a nonuniform cross section over their height are termed as compound bridge piers. Mostly circular piers resting on large diameter wells or caissons (termed here as a circular compound bridge pier) are adopted for use in the Indian subcontinent for the road and railway bridges. In the present study, a new mathematical model is proposed for computation of temporal variation of scour depth at circular compound bridge piers. Two series of laboratory experiments were conducted to collect data for model application. In the first series of experiments, the data on temporal variation of scour depth were collected, albeit up to the transient (developing) stage of scour, around the circular uniform piers and circular compound piers for the clear-water scour condition. The second series of experiments was carried out to measure the size and hence the area of the principal vortex of the horseshoe vortex system and to determine the bed shear stress at the upstream face of the scour hole around the circular uniform piers and the circular compound piers. The mathematical model proposed in this paper has the capability to compute the temporal variation of scour depth around circular compound piers for all possible cases of footing position with respect to bed level, i.e., footing above the bed level, footing at the bed level, and footing below the bed level. [ABSTRACT FROM AUTHOR]

Information about the grain-size distribution of the surface layer of sediment exposed on riverbeds is often critical in studies of fluvial hydraulics, geomorphology, and ecology. A variety of sampling and analysis techniques are in common usage that produce grain-size distributions that are not directly comparable. This paper seeks to explore the appropriate conversions between different types of surface grain-size sampling methods. This is particularly timely in the light of increasingly widespread use of automatic and semiautomatic image-based measurement methods, the comparability of which with conventional measurement methods is relatively poorly constrained. For conversions between area-by-number (paint-and-pick) and grid-by-number (pebble-count) samples, the empirically derived conversion factor () was found to be greater than that predicted by the Kellerhals and Bray model (), but the errors associated with using the value predicted by the model were small (3.8% in mm). For conversions between areal samples recorded by count and weight, the empirically derived conversion factor was approximately , but the use of the value predicted by the Kellerhals and Bray model () resulted in only small errors (5.2% in mm). Similarly, for conversions between image-based grain-size distributions recorded in area-by-number and grid-by number form, the emipirically derived conversion factor was , but using the model value of resulted in only small errors (4.1% in mm). Although these results are specific to the data sets analyzed, the variety of sedimentary conditions included gives the authors of this study confidence that the results are representative. [ABSTRACT FROM AUTHOR]

A depth-averaged two-dimensional model has been developed in this study to simulate the unsteady flow and noncohesive sediment transport due to embankment break and overtopping breaching. The model adopts the generalized shallow-water equations that consider the effects of sediment transport and bed change on the flow, thus leading to coupled calculations of these processes. It computes the non-equilibrium total-load sediment transport and considers the noncohesive embankment slope avalanching. The model solves the governing equations using an explicit finite-volume method on a rectangular grid, with the Harten, Lax and van Leer (HLL) approximate Riemann solver to handle the mixed-regime flows generated by embankment break/breaching and the monotonic upstream scheme for conservation laws (MUSCL) piecewise reconstruction method to reach second-order accuracy in space. It uses a varying time step length that satisfies both the Courant-Friedrichs-Lewy condition and the limitation that the bed change is less than about ten percent of the local flow depth at each time step. Validations using laboratory and field experiments showed that the developed model generally predicts well the embankment-break wave propagation over movable beds, the induced sediment transport and bed changes, and the temporal evolution of noncohesive embankment breach. [ABSTRACT FROM AUTHOR]

Scour hole monitoring is widely used by engineers in reaction to bridge scour. Current monitoring methods lack the ability to observe wide areas on operational time scales. It is imperative that wide areas be observed after channel bed armoring countermeasures are taken because the armoring occupies an area larger than can be observed by traditional single-point scour monitors. The present bridge piers within the Indian River Inlet, Delaware, are adjacent to deep scour holes that threaten the bridge. A new scour monitoring system (SM) using two three-dimensional profiling sonars was installed on the Indian River Inlet Bridge to observe more than 19,000 m2 of bathymetry daily. The system components, configuration, and operation are described and example data are presented. Bathymetric data collected by the SM compare favorably with historic high-quality multibeam data from the U.S. Army Corps of Engineers. Quantitative correlations with temporally consistent data from a single-beam personal watercraft survey vessel yield an r2 correlation coefficient of 0.84 with 93% of the absolute value of elevation differences between the two data sets less than 3 m. [ABSTRACT FROM AUTHOR]

By applying the incomplete self-similarity argument, this study presents a structural analysis of models for predicting bed-material load discharge, which can be formulated consistently according to the number of independent variables considered. The coefficients involved in the proposed models are calibrated with published laboratory and field data (comprising almost 6,600 records). In comparison with the six bed-material formulas that are recommended in the recently updated ASCE manual on sedimentation engineering, the proposed models show significant improvements on the prediction of bed-material load discharge. This study also implies that the model developed, based on regular regression analysis, can be enhanced by considering interaction terms of independent variables. [ABSTRACT FROM AUTHOR]

The development of sand dunes in an erodible bed exposed to flowing water is considered using a numerical flow model. The bed is initially given a small perturbation, which is followed in the time domain. Examples are given where a sinusoidal perturbation reaches the fully developed steady equilibrium shape. The flow modeling is based on a k-ω turbulence closure. The sediment transport is assumed to be bed-load only, with an avalanche-like movement on the steep dune front. The model is also found capable of predicting the growth in wavelength if the initially prescribed wavelength is sufficiently short. Results of the dune development are presented for different initial wavelengths. It is demonstrated that an equilibrium shape is developed for a range of wavelength-depth ratios as long as this ratio is sufficiently small. [ABSTRACT FROM AUTHOR]

The changes in channel geometry downstream of Hapcheon Dam, South Korea, are closely examined. Daily pulses of water from peak hydropower generation and from sudden sluice gate operations affect the 45-km reach of the Hwang River between the Hapcheon Reregulation Dam and the Nakdong River. From 1983 to 2003, the median bed-material size, d50, increased from 1.0 to 5.7 mm, and the bed slope of the reach decreased from 94 to 85 cm/km. The vertical riverbed degradation averaged 2.6 m for a distance of 20 km below the reregulation dam. A simple analytical model is developed to predict the increase in sediment transport and the river bed adjustments from flow pulses in comparison with steady flow discharges. Numerical model simulations confirm the theoretical prediction that sediment transport rates from daily pulses are 21% higher than for steady flow discharges. Unsteady sediment transport simulations indicate that the channel bed degradation should extend mostly 20-25 km below the reregulation dam and should not change much after 2013. [ABSTRACT FROM AUTHOR]

The article reviews the article "Sediment Transport Modeling Review-Current and Future Developments," by M. Elhakeem and colleagues, published in the January 2008 issue of the journal.

The Santa Fe River Watershed in Santa Fe County, New Mexico was identified as one of the top five high risk nonpoint source pollution areas out in the Rio Grande Basin. This watershed was selected to demonstrate the use of hydrologic modeling as a powerful tool for assessing the impacts of land management practices on erosion and sediment control at the watershed level. A method based on the Hydrologic Simulation Program-Fortran was used to address the local nonpoint sediment pollution concerns. The model was modified to reflect predicted future land uses related to expected urban expansion in the watershed. Six scenarios were created and the costs and benefits of each were weighed. The total estimated costs ranged from under $1 million to over $66 million. Total average annual sediment yields at the watershed outlet ranged from 3,441 to 4,111 tonnes/year, depending on management practices employed. These results indicate the magnitude of expected sediment reductions under various management strategies. Additionally, they provide an indication of the magnitude of expected sediment reductions in the Santa Fe Watershed and the estimated cost of each management practice. [ABSTRACT FROM AUTHOR]

Detailed knowledge of the flow and boundary shear stress fields near the banks of natural channels is essential for making accurate calculations of rates of near-bank sediment transport and geomorphic adjustment. This paper presents a high-resolution laboratory data set of velocity and boundary shear stress measurements and uses it to test a relatively simple, fully predictive, numerical method for determining these distributions across the cross-section of a straight channel. The measurements are made in a flume with a fairly complex cross-section that includes a simulated, cobble-roughened floodplain. The method tested is that reported by Kean and Smith in Riparian Vegetation and Fluvial Geomorphology in 2004, which is modified here to include the effects of drag on clasts located in the channel. The calculated patterns of velocity and boundary shear stress are shown to be in reasonable agreement with the measurements. The principal differences between the measured and calculated fields are the result of secondary circulations, which are not included in the calculation. Better agreement with the structure of the measured streamwise velocity field is obtained by distorting the calculated flow field with the measured secondary flow. Calculations for a variety of narrower and wider configurations of the original flume geometry are used to show how the width-to-depth ratio affects the distribution of velocity and boundary shear stress across the channel. [ABSTRACT FROM AUTHOR]

Effective discharge (Qe) is an important design variable used in stream restoration design. Qe of a stream reach is affected by both the hydrological characteristics of the upstream watershed and the sediment-transport characteristics of the stream reach. This study identified the most critical hydrological and sediment-transport characteristics affecting Qe of small urban streams in southern Ontario. Continuous simulation of hypothetical watersheds was conducted to generate hourly streamflow data. Qe and other related variables of interest were determined based on simulated streamflow series and randomly generated sediment-transport rating curve parameters. Global sensitivity analysis using samples of input and output data indicated that Qe is highly sensitive to, first, the exponent of the sediment rating curve (β); second, the watershed storage coefficient reflecting the storage characteristics of a watershed; and third, the time of concentration of a watershed. Further, this study showed that only when β values are within a specific range, Qe and the discharge corresponding to a particular return period are close to each other. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to develop an unsteady 2D depth-averaged model for nonuniform sediment transport in alluvial channels. In this model, the orthogonal curvilinear coordinate system is adopted; the transport mechanisms of cohesive and noncohesive sediment are both embedded; the suspended load and bed load are treated separately. In addition, the processes of hydraulic sorting, armoring, and bed consolidation are also included in the model. The implicit two-step split-operator approach is used to solve the flow governing equations and the coupling approach with iterative method are used to solve the mass-conservation equation of suspended sediment, mass-conservation equation of active-layer sediment, and global mass-conservation equation for bed sediment simultaneously. Three sets of data, including suspension transport, degradation and aggradation cases for noncohesive sediment, and aggradation, degradation, and consolidation cases for cohesive sediment, have been demonstrated to show the rationality and accuracy of the model. Finally, the model is applied to evaluate the desilting efficiency for Ah Gong Diann Reservoir located in Taiwan to show its applicability. [ABSTRACT FROM AUTHOR]

This paper concerns the quantitative evaluation of the time of bed development of alluvial meandering streams. In agreement with the prevailing approach, it is assumed that the stream centerline follows a sine-generated curve; the banks are rigid. The flow is turbulent and subcritical, and the flow width is much larger than the flow depth. The movable bed is flat at time t=0; at t=Tb, the bed reaches its equilibrium or developed state. With the aid of dimensional and physical considerations, an expression is found for the duration of bed development Tb. According to this expression, Tb is proportional to the square of the flow width B and inversely proportional to the specific volumetric bed-load rate corresponding to the channel-averaged flow. The proportionality factor is found to be a function of the initial deflection angle θ0 alone. The form of this function is investigated on the basis of a series of experimental runs carried out by the writers in a sine-generated channel having an intermediate value of θ0 (i.e., an intermediate value of sinuosity), as well as data available in the literature. [ABSTRACT FROM AUTHOR]

The Lorenz curve and the Gini index are statistical tools that have been widely used to quantify nonuniformity in economics, ecology, and medicine, but have apparently not been previously applied in hydraulic engineering. In this work, the Lorenz curve was applied to the analysis of sediment transport data from several experiments with natural and lightweight solid particles. The distributions of instantaneous sediment transport rate data have been analyzed, leading to some interesting observations: (1) the values are quite nonuniformly distributed, with a significant proportion of zero values at the lowest sediment transport rates; and (2) the distributions of the values considering only samples with nonzero values are still quite nonuniform; yet the variability of the Gini index with the average sediment transport rate is much smaller than that obtained for the complete data samples, indicating a major role of intermittency in determining the nonuniformity of sediment transport. [ABSTRACT FROM AUTHOR]

Confluence zones in rivers are common occurrences in natural rivers, and their flow structures have a great impact on sediment transport and pollutant dispersion in confluence regions. Previous studies mainly focused on two-dimensional properties of the separation zone, and the studies of the variation of the separation zone from the water surface to the bottom are limited. Based on the confluence experiments carried out in a junction flume, the detailed characteristics of the separation zone were analyzed by using the commonly used streamline and the velocity isoline first proposed in this study, respectively. The velocity isoline method is conducted by the longitudinal velocity streamline considering its great impact on flow structure. Based on the analysis of the selected data from experiments, the geometry and the tendency of the separation zone present different forms with variations of distance to the flume bottom. Further, the discharge ratio also influences the separation zone from bed bottom to surface. [ABSTRACT FROM AUTHOR]

Global positioning system (GPS) data are used to measure boat velocity during acoustic Doppler current profiler (ADCP) discharge measurements, particularly when bottom tracking (BT) is biased by moving bed. A Kalman filter is developed to improve the velocity reference used by the ADCP under such conditions. Kalman filtering is a recursive statistical technique that estimates the current state of a process, given various inputs and their variance. In the case of data obtained by ADCP, the availability of two independent velocity measurements and a position measurement makes this method particularly attractive. The new Kalman filter combines raw inputs for GPS position (GGA) and Doppler velocity (VTG) with BT data in real time to produce best estimates of velocity. The technique is evaluated and calibrated using various accuracies of GPS data collected simultaneously along with unbiased BT data at two different sites. On the Gatineau River, real-time kinematic and wide area augmentation system corrections were used for this study. On the Saint Mary’s River, nondifferential GPS was collected. To examine the conditions under which such a system would be required, synthetic data for a moving bed contamination of BT were created. In all moving bed conditions evaluated, the Kalman filter estimates of reference velocity were superior to raw inputs. [ABSTRACT FROM AUTHOR]

Experiments were conducted over uniform gravel bed materials to obtain 143 friction factor values under bed-load equilibrium flow conditions in an attempt to add to the scarce data available on slopes between 1 and 9% for Shields numbers between 0.08 and 0.29. Analyses showed that when only flows over flat beds are considered, a distinction must be made between flows with and without bed load. More particularly, fitting flow resistance equations indicated that the roughness parameter increases by a factor of 2.5 from clear water flow to intense bed-load transport. Between these two states, the flow resistance can be approximated by a constant for a given slope. [ABSTRACT FROM AUTHOR]

A two-dimensional depth-averaged model was used for the simulation of scour and deposition in sand-bed meandering channels with fixed banks. The model employs unstructured meshes based on triangular elements and incorporates the effects of curvature-induced helical flow and transverse bed slope in the direction of bed-load sediment transport. The model was tested using experimental data from a well-known laboratory curved channel and a full scale meandering river. The numerical results agreed well with observed data, demonstrating that the model can reproduce the main features of bed profiles along meandering rivers, such as the formation of point bars and pools. [ABSTRACT FROM AUTHOR]

The performance of four sedimentation basins (SBs) at a Pennsylvania Department of Transportation I-99 highway construction site was evaluated based on their particle removal ability. Suspended solids data from the basins indicated poor particle removal, peaks in suspended solid concentration that correlated with rainfall peaks and possibility of sediment resuspension. The current Pennsylvania Department of Environmental Protection basis for basin design is the allocation of 28 m3(1,000 ft3) of sediment storage zone and 140 m3(5,000 ft3) of drainage zone per disturbed acre of the drainage basin. Overflow rate, which is a scientific basis for particle removal, is currently not considered in the design of basins. This paper presents a methodology for developing an integrated design for SBs, applying rainfall probability plots to determine an appropriate basin settling volume. The revised universal soil loss equation is used to identify sediment zone volume, and an overflow rate is determined to design basin surface area. The method presented is a comprehensive procedure for designing SBs with flexibility to choose the extent of particle removal and runoff capture, and to vary construction costs. [ABSTRACT FROM AUTHOR]

This study presents a novel, simple, but rather accurate approximation of the eigenvalues of the system formed by the Saint-Venant–Exner equations, based on the comparison between eigenvalues for the complete system and eigenvalues for the water phase only. Moreover, a strategy is proposed to compute efficiently the intercell fluxes by properly adapting a Harten, Lax, and van Leer scheme for each equation. Two examples of transient transcritical flows are developed: the erosive migration of a knickpoint induced by an increase in the bed slope, and the evolution of a hydraulic jump over a mobile bed. [ABSTRACT FROM AUTHOR]

This paper describes the flow structures that occur in a 90° junction of four open channels with supercritical flow in two orthogonal inlet channels. An experimental facility was constructed to permit the measurement of flow rates, water depths, and the positions of hydraulic jumps in the channels. The various flow patterns which appear depend on the characteristics of the incoming flows and can be classified into three main types, depending on the location and shape of the hydraulic jumps that develop. These jumps can either be normal to the flow and located in the upstream channels, or can be oblique and confined within the junction. The explanation for the existence of various flow patterns is derived from previous studies of the rapid deflection of supercritical flow. A detailed description of each flow regime is provided, with information on the surface elevations, the behavior of the hydraulic jumps, the deflections of the incoming flows, and the formation and characteristics of recirculation zones. [ABSTRACT FROM AUTHOR]

A robust computational model for simulating the long-term evolution of incised and restored or rehabilitated stream corridors is presented. The physically based model simulates the three main processes that shape incised streams: hydraulics, sediment transport, and streambed and bank adjustments. A generalized implicit Preissmann scheme is used for the spatial and temporal discretization of the flow governing equations to accommodate large time steps and cross sections spaced at irregular intervals. The solution method introduces several enhancements that increase its robustness, specifically to simulate flashy flows. Transport of cohesive or cohesionless graded bed material is based on a total-load concept, and suspended and bed load transport modes are accounted for through nonequilibrium effects. The model simulates channel width adjustment by hydraulic erosion and gravitational mass failure of heterogeneous bank material. The present paper focuses mainly on the treatment of streamflow hydraulics and evolution of graded streambeds, and reports simulations of published experiments on degrading and aggrading channels with graded bed material. Description and validation of the model’s streambank erosion component and the application of the model to incised stream systems are presented elsewhere. [ABSTRACT FROM AUTHOR]

In March of 2003, the 43 m wide, 2.2 m high St. Johns Dam (Sandusky River, Ohio) was breached to lower the water level in the reservoir. In November of the same year, the dam was removed in an effort to restore aquatic habitat and connectivity in the river. During both the breach and the dam removal, high resolution time series of discharge and suspended sediment concentrations were monitored 200 m downstream of the dam. Discharge and suspended sediment during the breach were not discernible from background values. In contrast, the dam removal resulted in a peak suspended sediment concentration of 59 mg/L and a peak discharge of 33.5 m3/s, which returned to background levels of 19 mg/L and 1.5 m3/s, respectively, approximately 8 h after the removal. The floodwave during the removal attenuated by 50% at the City of Fremont, 53 km downstream, illustrating the diffusive nature of the channel and the limited risk of flooding downstream. Levels of suspended sediment and discharge during the removal were comparable to subsequent discharge events. Spatial distributions of turbidity in and upstream of the dam pool and archived turbidity data from the City of Tiffin, 13 km downstream of the dam, suggest that sediments stored in the impoundment did not statistically enhance turbidity up to 2 years after the removal. Generally, the removal had a minor impact on water quality and posed no risk to public safety or to downstream aquatic habitats. [ABSTRACT FROM AUTHOR]

Experiments on clear-water scour below underwater pipelines (initially laid on the sediment bed) in uniform and nonuniform sediments under steady flow were conducted. Equilibrium scour profiles were modeled by a cubic polynomial. The experimental results are examined to describe the influence of various parameters on equilibrium scour depth. The equilibrium scour depth ds increases with increase in approach flow depth h for shallow flow depths, becoming independent of higher flow depths when h/b>5, where b=pipe diameter. However, the curves of scour depth versus sediment size d and Froude number Fb have a maximum value of ds/b=1.65 at b/d=27 and Fb=0.6. The influence of sediment gradation on scour depth is prominent for nonuniform sediments, which reduce scour depth to a large extent due to the formation of armor layer within the scour hole. The influence of different shaped cross sections of pipes on the scour depth was investigated, where the shape factors for circular, 45° (diagonal facing) and 90° (side facing) square pipes obtained as 1, 1.29, and 1.91, respectively. Using the data of scour depths at different times, the time variation of scour depth is scaled by an exponential law, where the nondimensional time scale increases sharply with increase in Froude number characterized by the pipe diameter. In addition, clear-water scour below circular pipelines laid on a thinly armored sand bed (the sand bed is overlain by a thin armor layer of gravels) was experimentally studied. Depending on the pipe diameter, armor gravel, and bed-sand sizes, three cases of scour holes were recognized. The comparison of the experimental data reveals that the scour depth below a pipeline with an armor layer under limiting stability of the surface particles (approach flow velocity nearly equaling critical velocity for surface particles) is greater than that without armor layer for the same sand bed, if the secondary armoring formed within the scour hole is scattered. In contrast, the scour depth with an armor layer is less than that without armor layer for the same sand bed, when the scour hole is shielded by the secondary armor layer. [ABSTRACT FROM AUTHOR]

Previous studies assessing the accuracy of bed-load transport equations have considered equation performance statistically based on paired observations of measured and predicted bed-load transport rates. However, transport measurements were typically taken during low flows, biasing the assessment of equation performance toward low discharges, and because equation performance can vary with discharge, it is unclear whether previous assessments of performance apply to higher, geomorphically significant flows (e.g., the bankfull or effective discharges). Nor is it clear whether these equations can predict the effective discharge, which depends on the accuracy of the bed-load transport equation across a range of flows. Prediction of the effective discharge is particularly important in stream restoration projects, as it is frequently used as an index value for scaling channel dimensions and for designing dynamically stable channels. In this study, we consider the geomorphic performance of five bed-load transport equations at 22 gravel-bed rivers in mountain basins of the western United States. Performance is assessed in terms of the accuracy with which the equations are able to predict the effective discharge and its bed-load transport rate. We find that the median error in predicting effective discharge is near zero for all equations, indicating that effective discharge predictions may not be particularly sensitive to one’s choice of bed-load transport equation. However, the standard deviation of the prediction error differs between equations (ranging from 10% to 60%), as does their ability to predict the transport rate at the effective discharge (median errors of less than 1 to almost 2.5 orders of magnitude). A framework is presented for standardizing the transport equations to explain observed differences in performance and to explore sensitivity of effective discharge predictions. [ABSTRACT FROM AUTHOR]

Transient bed sediment waves in alluvial rivers have been described using a multitude of hydraulic formulations. These formulations are based on some form of the St. Venant equations and conservation of mass of sediment in suspension and in bed. Depending on the assumptions employed, a hierarchy of formulations is expressed. These formulations in the literature employ uncoupled, semicoupled, or fully coupled transport models treating the sediment waves as either hyperbolic (dynamic wave) or parabolic (diffusion wave). It is, however, hypothesized that the movement of bed sediment waves in alluvial rivers can be described as a kinematic wave. Kinematic wave theory employs a functional relation between sediment transport rate and concentration and a relation between flow velocity and depth. This study summarizes the hierarchy of the formulations while emphasizing the kinematic wave theory for describing transient bed sediment waves. The applicability of the theory is shown for laboratory flume data and hypothetical cases. [ABSTRACT FROM AUTHOR]

Bed-load transport is commonly evaluated in the condition of a hydrostatic pressure distribution of the flow field; while this condition is reasonable for quasi-steady, quasi-uniform rectilinear flows, it cannot be satisfied in a large variety of flow conditions, i.e., near an obstacle as in the case of a bridge pier. The dimensionless Shields number, which contains the assumption of a hydrostatic pressure distribution in its denominator, therefore cannot be strictly applied to evaluate bed-load transport in all the configurations where nonhydrostatic pressure distributions are observed. In the present work, a generalization of the Shields number is proposed for the case of nonhydrostatic pressure distribution produced by groundwater flow. Experiments showing the effects of vertical groundwater flow on the bed morphodynamics are presented. The comparison between the experimental observations and numerical results, obtained by means of a morphodynamic model which employs the new formulation of the Shields number, suggests that the proposed generalization of the Shields number is able to account the effect of the nonhydrostatic pressure distribution on the bed-load transport. [ABSTRACT FROM AUTHOR]

Tidal current and wave forces are the primary factors causing agitation, suspension, and transport of littoral materials in a bay. This paper presents a study of the circulation patterns of the water and sediment fluxes in a real bay during ordinary natural weather conditions. A coupled hydrodynamic and wave model is developed to support the research. A two-dimensional parallel advanced circulation hydrodynamic model with an extended transport module is used to calculate the water circulation within the bay, while the simulating wave nearshore model is implemented to provide the wave parameter data. The month of March 2003 is selected to represent the test case for the sediment transport model in Matagorda Bay, Tex. The presence of wave action significantly, increases the amount of suspended sediment, and consequently, more deposited sediments occur around the ship channel, where shallow shoals are located. Comparison of the simulated deposited sediments in the Matagorda ship channel with the two selected points of historical dredging data of the bay gives a maximum difference of 22%. This result suggests the need for an extensive comparison study. [ABSTRACT FROM AUTHOR]

Stochastic bed load transport formulas for nonuniform sediment exist, but most of them do not account for the composition of surface material to predict fractional transport rate. This study transformed a surface-based bed-load transport predictor to a stochastic one by approximating the fluctuation of bed-shear stress with a standard log-normal distribution. The deterministic predictor underpredicts fractional transport rate at low values of bed-shear stress and Reynolds number. The modified stochastic predictor predicts fractional transport rate more accurately and converges to the deterministic one at high shear stresses. [ABSTRACT FROM AUTHOR]

The paper presents the application of a two-dimensional depth-averaged numerical model to simulate the lateral migration processes of a meandering reach in the West Jordan River in the state of Utah. A new bank erosion model was developed and then integrated with a depth-averaged two-dimensional hydrodynamic model. The rate of bank erosion is determined by bed degradation, lateral erosion, and bank failure. Because bank material in the West Jordan River is stratified with layers of cohesive and noncohesive materials, a specific bank erosion model was developed to consider stratified layers in the bank surface. This bank erosion model distinguishes itself from other models by relating bank erosion rate with not only flow but also sediment transport near the bank. Additionally, bank height, slope, and thickness of two layers in the bank surface were considered when calculating the rate of bank erosion. The developed model was then applied to simulate the processes of meandering migration in the study reach from 1981 to 1992. Historical real-time hydrographic data, as well as field survey data of channel geometry and bed and bank materials, were used as the input data. Simulated cross-sectional geometries after this 12-year period agreed with field measurements, and the R2 value for predicting thalweg elevation and bank shift are 0.881 and 0.706, respectively. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive analysis of suspended sediment transport in open channels under various flow conditions through a kinetic-model-based simulation. The kinetic model, accounting for both sediment-turbulence and sediment-sediment interactions, successfully represents experimentally observed diffusion and transport characteristics of suspended sediments with different densities and sizes. Without tuning any model coefficients, the nonmonotonic concentration distribution and the noticeable lag velocity with a negative value close to the wall are reasonably reproduced. Examination of flow conditions typical of suspension dominated rivers shows that the conventional method may overestimate or underestimate unit suspended-sediment discharge, depending on the Rouse number, sediment size, as well as shear velocity. The error may be less than 20% for dp<0.5 mm and might exceed 60% for dp>1.0 mm under typical flow conditions where shear velocity ranges from 1.0 to 12.5 cm/s and flow depth ranges from 1.0 to 5.0 m. [ABSTRACT FROM AUTHOR]

In the saltation regime where bed-shear stress is low, bed load moves by sliding, rolling, and saltating along the bed, while in the sheet-flow regime where bed-shear stress is high, it travels by a combination of saltation and sheet flow. In this paper a theoretical model is developed for predicting the onset of the sheet-flow regime as shear stress increases. This model is based on a new variable Pb representing the proportion of grains on the bed that are entrained as bed load. The model yields the equation Pb=2.56θG3 in which G=1-θc/θ, θ=dimensionless bed-shear stress; and θc=critical value of θ at which grains begin to move. The equation shows that θt, which is the value of θ at the onset of the sheet-flow regime and is assumed to occur when Pb=1, is around 0.5 with the exact value controlled by θc. For example, when θc=0.045, θt=0.52. The theoretical model is verified by performing a nonlinear regression analysis on data from 285 flume experiments. Additional flume experiments with a high-speed video (HSV) system result in consistent values of θ for the onset of the sheet-flow regime, which support the theoretical model. The HSV images further reveal that: (1) the sheet-flow regime is characterized by granular sheets or laminations; and (2) a zone of mixed saltation and rolling grains exists not only in the saltation regime but also in the sheet-flow regime. [ABSTRACT FROM AUTHOR]

The assessment of sediment transport in rivers is of vital importance in design and management of hydraulic structures such as dams, diversions, hydro-power projects, river training works, bridges, etc. Previously reported studies have shown that data driven techniques such as the artificial neural network (ANN) can give better results in modeling stage-discharge relations than the conventional rating curves. In view of the complexities of rating relationships, compound rating curves are frequently used in place of a single rating curve. Accordingly, this paper investigates the abilities of compound neural networks (CNNs) to model integrated stage-discharge-suspended sediment rating relationship. Using the data of two stations on the Mississippi River and one station on Conococheague Creek, CNNs were trained. A comparison of the results of applying a single ANN and a CNN shows that the estimates of CNN are closer to the observed values than those of single ANN. [ABSTRACT FROM AUTHOR]

Results of an experimental study on clear-water scour at submerged cylindrical obstacles (circular cylinders) in uniform bed sediments under steady flow are presented. The scour depths at submerged circular cylinders are compared with the scour depths at corresponding unsubmerged cylinders (extended above the free surface of flow) of the same diameters under similar flow and bed sediment conditions. The scour depth decreases with an increase in submergence ratio. A submergence factor is introduced to determine the scour depth at a submerged cylinder from the information of the scour depth at an unsubmerged cylinder of the same diameter. In addition, the flow fields along the upstream vertical plane of symmetry of unsubmerged and submerged cylinders are presented through vector plots, which reveal that the dimension and strength of the horseshoe vortex decreases with an increase in submergence ratio. The horseshoe vortex circulations, which decrease with an increase in submergence ratio, are computed from the vorticity contours by using the Stokes theorem. [ABSTRACT FROM AUTHOR]

A negative bias in discharge measurements made with an acoustic Doppler current profiler (ADCP) is attributed to the movement of sediment on or near the streambed, and is an issue widely acknowledged by the scientific community. The integration of a differentially corrected global positioning system (DGPS) to track the movement of the ADCP can be used to avoid the systematic bias associated with a moving bed. DGPS, however, cannot provide consistently accurate positions because of multipath errors and satellite signal reception problems on waterways with dense tree canopy along the banks, in deep valleys or canyons, and near bridges. An alternative method of correcting for the moving-bed bias, based on the closure error resulting from a two-way crossing of the river, is presented. The uncertainty in the mean moving-bed velocity measured by the loop method is shown to be approximately 0.6 cm/s. For the 13 field measurements presented, the loop method resulted in corrected discharges that were within 5% of discharges measured utilizing DGPS to compensate for moving-bed conditions. [ABSTRACT FROM AUTHOR]

Technical note discusses a detailed approach to dimensional analysis for the bridge pier scour phenomenon and the introduction of flow intensity. It demonstrates the dependence of critical upstream velocity on the rest of the parameters describing the process and its implications on dimensional analysis. Assuming that the viscous effects are negligible in the local scour phenomenon, it is concluded that the flow intensity of the approaching undisturbed flow is not an adequate parameter to describe the process in usual laboratory conditions. A new proposal is established. [ABSTRACT FROM AUTHOR]

Existing bed-load transport formulas may overestimate the transport rate in mountain rivers by two orders of magnitude or more. Recently published field data sets provide an opportunity to take a fresh look at the bed-load transport relationship and it is hypothesized that the overestimate is due to a failure to account for the effect of a coarse surface layer of bed material inhibiting the release of fine subsurface material. Bed-load transport is determined as gs=aρ(q-qc) where q=water discharge per unit width; qc=critical value for initiation of bed material movement; ρ=water density; and a=coefficient. The gs/q relationship is typically piecewise linear, characterized by two transport phases with, respectively, low and high rates of change. Twenty-one flume and 25 field data sets were used to quantify the relationship for Phase 2. The flume data confirm the dependence of a on S1.5, where S=channel slope, in agreement with earlier studies. The field data additionally show that a varies inversely with the degree of bed armoring, given by the ratio of surface to subsurface bed material size. The finding is consistent with the hypothesis and suggests the need to account for the bed material supply limitation in the bed-load transport formula. However, the available data are not entirely sufficient to rule out an alternative dependency, or codependency, on flow resistance. The critical conditions for initiation of Phase 2 transport are also quantified as a function of bed material size and channel slope. The resulting set of equations allows a more accurate estimation of Phase 2 bed-load transport rates. However, the equations are empirical and should be restricted for use within the range of conditions used in their development, to determine mean rather than instantaneous transport rates and to determine bulk transport rates, not transport by size fraction. [ABSTRACT FROM AUTHOR]

The results of an experimental investigation of riprap stability at wing-wall abutments are reported. The aim of the experiments was the determination of the size of riprap stones necessary to resist shear failure by the flow. The results, which were obtained under a wide range of mobile-bed conditions, are compared with predictions of riprap stone size given by existing equations. Two existing methods, with the addition of suitable factors of safety, are shown to give stable stone size for riprap layers at wing-wall abutments under mobile-bed conditions. It is noted that consideration needs also to be given to filter protection, edge effects, and the effects of bed-form undermining in the design of such riprap layers. [ABSTRACT FROM AUTHOR]

The development of a fully three-dimensional finite volume morphodynamic model, for simulating fluid and sediment transport in curved open channels with rigid walls, is described. For flow field simulation, the Reynolds-averaged Navier–Stokes equations are solved numerically, without reliance on the assumption of hydrostatic pressure distribution, in a curvilinear nonorthogonal coordinate system. Turbulence closure is provided by either a low-Reynolds number k-ω turbulence model or the standard k-[variant_greek_epsilon] turbulence model, both of which apply a Boussinesq eddy viscosity. The sediment concentration distribution is obtained using the convection-diffusion equation and the sediment continuity equation is applied to calculate channel bed evolution, based on consideration of both bed load and suspended sediment load. The governing equations are solved in a collocated grid system. Experimental data obtained from a laboratory study of flow in an S-shaped channel are utilized to check the accuracy of the model’s hydrodynamic computations. Also, data from a different laboratory study, of equilibrium bed morphology associated with flow through 90° and 135° channel bends, are used to validate the model’s simulated bed evolution. The numerically-modeled fluid and sediment transportation show generally good agreement with the measured data. The calculated results with both turbulence models show that the low-Reynolds k-ω model better predicts flow and sediment transport through channel bends than the standard k-[variant_greek_epsilon] model. [ABSTRACT FROM AUTHOR]

The interactions between acid mine drainage (AMD) and three tropical clayey soils have been studied through hydraulic conductivity and batch sorption/dissolution testing. After 19–24 pore volumes of AMD flow through the soils, the measured final hydraulic conductivity ranged between 1.1×10-11 and 3.3×10-11 m/s. The pH, electrical conductivity, and solute breakthrough curves obtained suggested the soils had low acid-buffering capacities. Also, several chemical species were released from the soils due to AMD attack of soil grains and mineral. The batch tests revealed high dissolution of species such as sodium, cobalt, and sulfate from the soils by AMD. The results also indicated dissolution of metals from soil constituents, desorption of chemical species, and transformation and dissolution of soil minerals due to AMD attack. The results of the study showed that, in general, the soils were not effective in attenuating contaminants present in the AMD. Thus, they may not be used alone to construct liners for acid-generating waste mine containment facilities. [ABSTRACT FROM AUTHOR]

This note presents an experimental study of seepage effects on the dimensions of a dune: its height, length and lee-side slope. The critical slope of a cohesionless material was found to be related to the ratio of the hydraulic gradient of seepage to its critical value under the quick condition. The theoretical relationship is successfully used to predict seepage effects on the lee-side slope of dunes. Measured laboratory data support the assumption that the effect of seepage on the lee-side slope of dunes is the same as that on the critical slope of the sediment. The data reveal that the slope is reduced and increased with injection and suction, respectively. Additionally, the study explores seepage effects on the development of dune height and length. Experimental results show that suction and injection increase and decrease the equilibrium height of dunes by 25 and 40%, respectively. On the other hand, the dune length is found to increase by approximately 30% and decrease by 20% under the influence of suction and injection, respectively. [ABSTRACT FROM AUTHOR]

A low-risk, stream restoration design includes methods that validate design assumptions, incorporate uncertainty in the decision-making process during the project design phase, and reduce uncertainty by checking the final design. A two-step method of incorporating uncertainty and risk in stream restoration design has been developed as a combination of design failure modes and effects analysis (DFMEA) and risk quantification. As a first step, DFMEA is applied to identify risk in terms of ratings with respect to consequence of failure, the likelihood of occurrence of a failure, and the ability to detect a failure. Due to its evolutionary nature, the DFMEA can be revised to account for design modifications and relative ratings are reevaluated to examine reductions in uncertainty, and thereby, risk. The second step of the method is quantifying risk using initial and expected failure costs. The two-step, risk-based method is illustrated through application to a stream relocation project in Pennsylvania. Both sediment transport capacity and supply analysis and alluvial channel modeling design methods were shown to reduce uncertainty and risk by detecting design deficiencies that the initial design using incipient motion tests overlooked. However, the alluvial channel model method was favored due to its ability to simulate the combined effects of flow hydraulics, sediment transport, and river channel adjustment. [ABSTRACT FROM AUTHOR]

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 F0 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 tc involving the volume of sediment scoured and the rate of erosion, was also related to the densimetric Froude number. A comparison with studies regarding erosion of a semiinfinite layer of sediment is also presented. [ABSTRACT FROM AUTHOR]