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Effects of bed material and downstream flow depth on bed evolution in a right-angled channel confluence were studied through laboratory experiments. Velocity field, water surface elevation, and bed profile were measured intermittently until the flow attained equilibrium. Sediment discharges at various locations of the confluence were estimated from bed levels. Six prominent bedforms were identified, and their characteristics were quantified. The sediment discharges from different channels were initially high but decreased to approximately zero as the flow attained equilibrium. Downstream flow depth influenced overall sediment transport in the system, including the main features of bed morphology. Overall erosion in the confluence reduced as the particle size of the bed material increased. In addition, the maximum scour depth occurred at the confluence edge, and, due to the sharp corner of the confluence, its location did not change with time. Results from the present experimental study can help validate numerical models and assist in the design of a right-angled confluence. This study is related to the hydraulics of man-made confluences with mobile beds and can be useful in the following practical applications. More accurate numerical models to predict maximum scour, bed morphodynamics, and sediment transport in man-made confluences can be developed using the detailed bed profile measurements at different time instants presented in this study. Note that available numerical models use sediment discharge formulas (e.g., Meyer-Peter-Muller, Van Rijn), which are for sediment flows in straight channels. The interplay between the three-dimensional flow field, developed bed shear stress, and sediment discharge can be explored. In addition, A man-made confluence with the mobile bed can be designed with findings from the present study. The bedforms corresponding to equilibrium flow depend on discharge ratio, confluence angle, flow conditions at the exit channel, and bed material characteristics. The major bedforms can be incorporated into the confluence geometry. [ABSTRACT FROM AUTHOR]

The piano key weir is a unique new geometric type that can have a linear (rectangular or trapezoidal) or arc (trapezoidal) layout. Depending on the flow hydraulics and the bed type, different shapes of scour holes can form downstream of these weirs. Two types of piano key weirs—rectangular, and trapezoidal with an arced plan—were built to investigate the sediment transport patterns. The bed material comprised sand (d50=1.25 mm) and gravel (d50=8.9 mm). The results revealed that the scour hole dimensions and bed topography patterns depend on hydraulic conditions, crest geometry, and bed material gradation. Analysis of the data suggested that local scour depths behind a piano key weir with a rectangular crest might be as much as 12% larger than those for other configurations in sand or gravel. [ABSTRACT FROM AUTHOR]

Suspended sediment concentration is critical for many aspects of water resources management, such as sedimentation prevention in irrigation channels. Samplers from the Federal Interagency Sedimentation Project (FISP) are widely used for suspended sediment measurement. There is a need to evaluate their accuracy. This paper reports the use of a three-dimensional (3D) computational fluid dynamics (CFD) model to make such evaluation. Two selected depth-integrating samplers, D95 and D96, were studied, with the focus on the intrusion effect of the samplers. Suspended sediment transport was simulated to capture the entrainment, transport and deposition processes. The turbulence was simulated using a Reynolds-averaged Navier-Stokes (RANS) k-ω model. The samplers were placed at three different vertical locations in an open channel. The simulation results showed that the surrounding flow was disturbed by the sediment samplers. However, regardless of the vertical location of the samplers, they had a negligible effect on the sediment concentration at the inlet nozzle. The main reason is that the inlet nozzles of both samplers had enough protrusion upstream such that the intake was not affected by the sampler bodies. The results did not show significant vorticity at the inlet nozzle either, which in the past was suspected of imparting centrifugal force on sediment particles and thus having selective sampling efficiency depending on sediment sizes. [ABSTRACT FROM AUTHOR]

The rheological behavior of soil–water mixtures can affect the flow dynamics of natural processes such as flow-type landslides and sediment transport. In this study, an experimental investigation was carried out on soil–water mixtures containing particles up to 0.425 mm with volumetric solid concentrations of 0.05≤CV≤0.35 using a wide-gap rotational viscometer, and the contributions of particle–fluid, collisional, and colloidal interactions to their rheological behavior were evaluated thoroughly. The torque-scaling method was applied to identify the flow regime and extract the effective rheological parameters from turbulent flows. A transition between dilute and concentrated mixtures can be identified based on their sediment type, CV , and the predominance of particle–fluid and interparticle interactions. For dilute mixtures (CV<0.25–0.28) the particle-fluid interaction is dominant. The colloidal interactions induce another force scale that is independent of the shear rate. Thus, the Bingham model can be applied to such mixtures (debris or mud flood). For concentrated mixtures (CV>0.25–0.28), the shear-thickening rheology can be applied for granular mixtures (debris flows), because the collisional interactions are dominant, whereas shear-thinning rheology can be applied for fine-grained mixtures (mudflows), because colloidal interactions are dominant. [ABSTRACT FROM AUTHOR]

Sedimentation in a drain system has been recognized as one of the major causes of nuisance flooding produced by localized storms in Southeast Texas. The objective of the study is to assess the sediment load from runoff under different hydrological and road conditions to implement design guidance for a proper self-cleaning drain system. A diffusion wave model is developed to simulate runoff hydrodynamics on the roadway with curb inlets. An empirical sediment load equation is developed as a function of rainfall intensities, road conditions, and field sediment characteristics. The required flow velocity to erode the cohesive deposited sediment, and transport the deposited sediment incorporating the sediment from runoff in the drainpipe has been investigated to implement design guidance for a self-cleaning drain system. Regional hydrological conditions and field sediment characteristics are critical to design an effective drainage system for improving coastal resilience under severe weather conditions. [ABSTRACT FROM AUTHOR]

Accurate flow rate prediction is essential to analyze flood control, sediment transport, riverbank protection, and so forth. The flow rate distribution becomes even more complicated in compound channels due to the momentum transfer between different subsections across the width of the channel. Conventional channel division methods estimate flow distribution at the main channel and floodplains by assuming a division line with zero apparent shear stress. The article attempts to develop a model to calculate the percentage of discharge in the main channel (%Qmc) using techniques such as Group Method of Data Handling—Neural Network (GMDH-NN) and gene-expression programming (GEP) by incorporating the effects of various geometric and hydraulic parameters. The paper proposes a modified channel division method with a variable-inclined interface, with zero apparent shear force distribution at the channel subsections according to the statistical indices employed to assess these models' performance in predicting %Qmc. This variable-inclined interface changes its slope according to the channel parameters. The model's effectiveness is verified by validating with experimental observations by conventional analytical methods. [ABSTRACT FROM AUTHOR]

An accurate prediction of scour depth around bridge piers is crucial for economical and safe design of bridge pier foundations. The main objective of the present study is to identify the influencing cohesive parameters and their effects on the local scour processes around bridge piers, depending on various proportions of clay–sand–gravel mixtures. Twenty experimental tests were performed in a channel 25 m long and 1.0 m wide for this purpose. Runs lasted from 16 to 40 h. It was noted from the experimental work that an increment of clay fraction significantly reduces the scour depth around bridge piers. It was also observed that the initiation of scour occurred at the sides of the pier where separation of flow occurred. Typically, the maximum scour depth at the equilibrium stage was still observed at the sides of the pier. A dimensional analysis was used to propose mathematical relationships assessing the temporal scour depth variation at the wake and sides of the pier. The developed relationships yielded reasonable results with maximum error of two folds for 95.22% of total data sets for scour depth at the wake and 92.57% of the total data sets for scour depth at the sides of the pier. [ABSTRACT FROM AUTHOR]

The current state of the art on how the circular cross-section shape of a rigid boundary channel affects the incipience of sediment entrainment is not well investigated in the literature. Moreover, the incipience of sediment entrainment studies via artificial intelligence is very limited so far. The studies for rigid boundary channels to date have yielded different incipient motion data depending on the cross-sectional shape. Also, most of the existing works were proposed for rectangular cross-sectional channels. Conversely, this study investigated the effects induced by a circular cross-sectional shape on critical dimensionless shear stress by experimental procedures under smooth flow conditions. It was found that the circular cross-sectional channel shape significantly altered the conditions in favor of reducing the critical shear stress for the incipient sediment entrainment. This implies that the circular cross-sectional channel shape exhibits the advantage of self-cleansing open channel design. For a circular cross-sectional channel and smooth flow conditions, a new critical shear stress formula is proposed based on the obtained experimental data. Ninety-seven experimental observations were performed under hydraulically transitional flow conditions with a grain shear Reynolds number (Re*) range of 5.2–41.17. Most of the experiments were performed with Re*>10. The new proposed equation is an empirical approach to express the governing equations of incipient motion in rigid boundary channels. Furthermore, a novel hybrid-geno-fuzzy inference system (GENOFIS) and the adaptive neural fuzzy inference system (ANFIS) approaches were developed using experimentally obtained data to predict the incipient motion of sediment entrainment. The performance of the quantitative results of the novel GENOFIS, ANFIS, and empirical equations were evaluated via the root mean square error (RMSE), F -test, and the coefficient of efficient (CE) model evaluation criteria. The GENOFIS is a novel attempt to revolutionize the prediction of complicated nonlinear phenomena such as incipient motion. The results show that prediction of the incipient motion of sediment via the GENOFIS approach yielded more accurate results than those of ANFIS for hydraulically transitional flow conditions. [ABSTRACT FROM AUTHOR]

During summer 2017, two parallel trenches were excavated in the Sagavanirktok River (located in northern Alaska, United States) to acquire construction material for roadwork on the Dalton Highway nearby. A study to estimate the time it would take for the trenches to fill with the upstream sediment was needed. In undertaking this study, we used three bed sediment transport equations for gravel-bed rivers available in the Sedimentation and River Hydraulics—Two-Dimensional model, with three hydrograph input scenarios: (1) normal cumulative volumetric flow; (2) maximum discharge; and (3) maximum cumulative volumetric flow. These scenarios, coupled with the three sediment transport equations, produced a total of nine simulations. Scenario 1 predicted a time to refill of 1–3.75 years based on the sediment transport equations used. Scenarios 2 and 3 predicted shorter times to refill. All three sediment transport equations predicted that sustained high flows are capable of refilling the trenches in 1 year. This is the first time that calculations have been made to estimate the refilling time of an extraction site on the Sagavanirktok River. These calculations could expedite the permitting process, eliminating the need for a new extraction site by returning to a site that has refilled with sediment. An indirect benefit of these calculations is that they provide information for fisheries biologists working in northern regions. [ABSTRACT FROM AUTHOR]

This study evaluates sediment gradation effects on clear-water scour at bridge piers. By considering the average erosion and deposition rates in a pier-scour hole, the normalized equilibrium scour depth is theoretically shown to be a cubic function of the densimetric Froude number. Comparisons with experimental data demonstrate that the cubic law achieves its best fit when the representative particle size is taken to be d84. The present prediction equation, which is founded on rational theoretical principles, provides an improved approach to evaluating sediment gradation effects on clear-water scour around bridge piers apart for pure empiricism. [ABSTRACT FROM AUTHOR]

The purpose of the study is to reveal changes of the hydrodynamics and sediment transport induced into the river channel by the operation of small hydropower plants (SHPs). A 36-km reach of the upper Prahova River in Romania has been chosen, along which 10 run-ofriver developments are built. A 1D modeling software was used to compute hydrodynamic parameters over the selected reach. Two discharge scenarios were considered into the channel: (1) mean annual flow (for the natural regime, without SHPs), and (2) the minimum discharge (worst case scenario of SHP operation for the environment). Results of the second scenario show that ecologically relevant hydraulic parameters in the channel are approaching the thresholds of endangering the fish habitat. On average, depth and shear stress drop by 50%, mean velocity by 40%, and flow area by 75%. Comparison between computed nondimensional shear stress and its corresponding critical value indicates that minimum discharge can only transport finer particles than average from the bed surface, thus leading to potential filling of fish spawning areas with sand. [ABSTRACT FROM AUTHOR]

A mechanistic-cum-stochastic theory describing the sediment transport phenomenon from the particle scale of entrainment to the continuum scale of bedload flux under a steady unidirectional flow over a compact sediment bed is developed. The sediment particles, considered as discrete spherical particles, are subjected to hydraulically smooth, transitional, and rough wall-shear flows. At the particle scale, the hydrodynamic forces acting on a sediment particle resting over three closely packed bed particles are analyzed. The criteria for entrainment threshold in rolling, sliding, and lifting modes are determined introducing the velocity fluctuations. Comparison of the computed threshold curves with the experimental data reveals that the entrainment threshold primarily belongs to the transition of the sliding to the lifting modes. Then, at the particle scale, the entrainment probabilities in rolling, sliding, and lifting modes for a given median size of sediment particles are obtained. The rolling and sliding probabilities increase with an increase in Shields parameter, and after attaining their individual peak values, they decrease, while the lifting probability increases. Finally, the bedload flux, in a continuum scale, is obtained using the lifting probability. [ABSTRACT FROM AUTHOR]

Knowing the flow field characteristics of pavement rainfall runoff is essential for highway drainage design and skid management. This paper presents an innovative approach to characterize the flow field properties of pavement rainfall runoff under natural rainfall events. The approach is based on two-dimensional shallow water equations with porosity to encounter pavement topography, including highway alignment, the obstructive effect of pavement surface macrotexture, and side drainage types. The model is verified with a classical dambreaking model, and compared well with field monitoring results of water film thickness on existing expressway pavement. The capabilities of the approach to predict the flow field characteristics in temporal and spatial dimension make it useful in highway geometry and drainage design, and can also be potentially incorporated into skid and hydroplaning risk management. [ABSTRACT FROM AUTHOR]

This paper describes the development and multistep validation of a one-dimensional, large strain consolidation coupled contaminant transport model with nonlinear and nonequilibrium sorption kinetics. The RCM-XPORT2K model uses the CS2 large strain consolidation approach for modeling the deforming saturated porous medium consolidating under a surcharge stress, coupled with reactive advective/dispersive solute transport through the medium, capped with a thin-layered reactive sequestering geocomposite known as a reactive core mat (RCM). In addition to assumptions made in previously developed, one-dimensional consolidation coupled contaminant transport model RCM-XPORT2, the RCM-XPORT2K model accounts for sediment- and sorbent-specific sorption kinetics to model nonlinear, and nonequilibrium sorption behavior. Validation of the model is presented by simulating: (1) sorption kinetics tests performed on sediment sampled from Neponset River, Milton, Massachusetts, USA and a commercial product, CETCO Organoclay PM-199; (2) solute transport from the large strain consolidation coupled contaminant transport tests with Br- and Cl- using a high water content inert silt sample (New York Silt); and (3) the naphthalene transport and breakthrough times observed in upflow column tests with Neponset River sediment with various overlying cap layers. [ABSTRACT FROM AUTHOR]

Most of the models developed to simulate the cohesive sediment transport processes refer to estuary or marine environments and are generally not developed for the specific characteristics of irrigation schemes provided with the different types of hydraulic structures. The aim of this study is to simulate the cohesive sediment transport in irrigation canals. The fine sediment transport (FSEDT) model was developed using a software program to estimate the sediment transport and deposition rates of cohesive sediments in irrigation canals. The model has been applied in the Gezira Scheme in Sudan, which is threatened by high sediment supply from the Blue Nile River. The model was calibrated and validated using the field data selected during the flood seasons in 2011 and 2012. The hydrodynamic part of the model was verified by comparing the water surface profile obtained by the developed model and by using a microcomputer program for simulating one-dimensional steady/unsteady flow in open canals. The results of the two models show good agreement. The sensitivity of different parameters to the deposition was tested. The model is a useful tool that can be applied to study the mechanism of sediment transport under different operation and maintenance scenarios not only in the Gezira Scheme but also in similar cases. [ABSTRACT FROM AUTHOR]

This study presents a scaling analysis of the time development of clear-water scour depth at bridge piers. It shows that the widely-used exponential formula can be theoretically derived with scaling arguments. The derivation provides connections between the physical pier-scouring process and two empirical constants used in the formula. The dependence of the two constants on sediment coarseness is calibrated using published laboratory data with scour duration ranging from 49 to 1094 h. The analysis presented is restricted to conditions, including steady flow, clear-water scour, narrow circular cylindrical pier, and uniform sediment with low coarseness. [ABSTRACT FROM AUTHOR]

This paper develops a numerical model for the analysis of sediment transport in irrigated channels. The overland flow equation considers infiltration into the subsurface. The model solves Saint Venant and sediment continuity equations to analyze overland flow and sediment transport, while Richard's equation is used to analyze subsurface flow. Saint Venant and sediment continuity equations are solved using MacCormack-scheme-based finite-difference method and Richard's equation is solved using a mass conservative fully implicit finite-difference method. The model is validated by comparing model-predicted aggradation with experimental observations. The model is used to study the effect of infiltration on aggradation of a channel bed during sediment-laden flows. It was observed that infiltration significantly affects and alters the aggradation phenomenon and aggradation considering infiltration is found to be higher than that without considering infiltration. Among the different unsaturated soil parameters, the saturated hydraulic conductivity and initial dryness of the soil were found to be the main factors affecting the sediment transport in irrigated channels. [ABSTRACT FROM AUTHOR]

Construction activities require contractors to install, continuously monitor, and maintain controls to minimize erosion and sediment transport. Construction sites discharge up to 100 times more sediment per acre than agriculture land activities because of mechanized compaction of bare soils that decreases infiltration capacity, increases runoff volumes, and increases erosion potential. Silt fence perimeter controls are widely used by the construction industry to intercept and impound stormwater runoff sheet flow, forming large impoundment areas ideal for sedimentation. Ditch checks are often used to minimize channel erosion and promote sedimentation in conveyance channels through runoff impoundment. Structural failures of silt fence have caused many state agencies to exclude their use in concentrated flows. Researchers at the Auburn University-Erosion and Sediment Control Testing Facility (AU-ESCTF) have evaluated the use of wire backed, nonwoven geotextile silt fence as ditch checks using large-scale testing techniques. This research has shown that silt fence, properly installed, can be used as a ditch check successfully. A longevity test of an enhanced silt fence ditch check installation resulted in sediment retention of 91.2% by volume. [ABSTRACT FROM AUTHOR]

Ship-generated waves and return currents are capable of resuspending significant quantities of bottom and bank sediments. However, most of the previous studies done on the subject do not show how and where sediment is resuspended by the wakes and the directions of net transport. In this paper, a three-dimensional (3D) numerical model based on hydrosedimentary coupling is presented to search the relationship between the sediment movement and the pattern of ship-generated waves around and far away from the vessel and the return currents around the ships. The hydrodynamic model is based on 3D Navier-Stokes equations, including the standard model for turbulence processes, and the sediment transport model is based on a 3D equation for the resuspended sediment transport. The computation results show that the areas of sediment concentration and transport (whether by resuspension or by the bedload) depend mainly on the position, the speed of the ship in the waterways, the kinematics of ship-generated waves, and the return flows. Thus, a map of sediment distribution and the modes of sediment transport generated by the passage of the ship are presented. [ABSTRACT FROM AUTHOR]

Numerical simulations of free-surface flows are important to provide a prediction tool for the optimal management of irrigation canals. Here, we consider an alternative to solving the shallow-water equations. We propose a free-surface model in which the vertical component of the water current is fully resolved. We believe that such a detailed description can be useful to model the flow around gates or in other situations where the vertical structure of the flow will be important such as in the case of sediment transport and deposition. Our approach is based on a two-fluid lattice Boltzmann model. We compare the predictions obtained from numerical simulation and experiments performed on a laboratory microcanal facility. [ABSTRACT FROM AUTHOR]

Side weirs, also known as lateral weirs, are flow diversion devices widely used in irrigation as a head regulator of distributaries and escapes, land drainage, and urban sewage systems. The studies on the subject have been generally focused on rectangular and triangular side weirs located on a straight channel. However, the same is not true for labyrinth side weirs. The current studies deal with sediment transport and scour problems around side weirs and lateral structures. The investigation of the hydraulic effects of labyrinth side weirs to increase discharge capacity of them has been studied in this particular work. In the study, 2,830 laboratory tests were conducted for determining discharge coefficient of labyrinth side weirs, and results were analyzed to find the influence of the dimensionless weir length L/b, the dimensionless effective length L/ℓ, the dimensionless weir height p/h1, triangular labyrinth side weir included angle θ, and upstream Froude number F1 on the discharge coefficient, water surface profile and velocities in the channel along the side weir. It has been found that discharge coefficient of labyrinth side weirs gives pretty higher coefficient value compare to that of classical side weirs and a reliable equation for discharge coefficient of labyrinth weirs is presented. Discharge coefficient of the labyrinth side weir is 1.5–4.5 times higher than rectangular side weir. [ABSTRACT FROM AUTHOR]

Soil erosion from agricultural areas continues to be problematic in terms of both financial and environmental measures. Ephemeral gullies contribute to the soil loss both by the volume of sediment eroded from the gullies and because they act as delivery channels for surface erosion. High resolution aerial imagery was used to quantify the amounts and locations of ephemeral gullies in the subbasins of the Potlatch River system. Areal ephemeral gully erosion rates varied from 33.6 mt/km2 (0.15 U.S. t/acre) in the Big Bear Creek Subbasin to 88.4 mt/km2 (0.39 U.S. t/acre) in the Middle Potlatch Creek Subbasin representing 2.3–7.7% of the total surface sediment load. An erosion potential index was proposed to assist resource managers predict gully locations at the watershed scale using readily available remote sensing and geographic information system layers. [ABSTRACT FROM AUTHOR]

This paper reports an experimental investigation on the velocity and turbulence characteristics in an evolving scour hole downstream of an apron due to submerged jets issuing from a sluice opening detected by an acoustic Doppler velocimeter. Experiments were carried out for the conditions of submerged jets, having submergence factors from 0.96 to 1.85 and jet Froude numbers from 2.58 to 4.87, over sediment beds downstream of a rigid apron. The distributions of time-averaged velocity vectors, turbulence intensities, and Reynolds stress at different streamwise distances are plotted for the conditions of initial flat bed, intermediate scour holes, and equilibrium scour hole downstream of an apron. Vector plots of the flow field show that the rate of decay of the submerged jet velocity increases with an increase in scour hole dimension. The bed-shear stresses are determined from the Reynolds stress distributions. The flow characteristics in evolving scour holes are analyzed in the context of self-preservation, growth of the length scale, and decay of the velocity and turbulence characteristics scales. The most significant observation is that the flow in the scour holes (intermediate and equilibrium) is found to be plausibly self-preserving. [ABSTRACT FROM AUTHOR]

A stochastic partial differential equation-based model has been derived based on the law of mass conservation and the Langevin equation of particle displacement to simulate suspended sediment transport in open-channel flows. In this model, the movement of any suspended sediment particle in turbulent flows is modeled as a stochastic diffusion process, which is composed of a drift term and a random term. The stochastic formula of fluid velocity is then substituted into the advection-diffusion (AD) equation to obtain the stochastic partial differential equation (SPDE) for suspended sediment transport. The lattice approximation is applied to solve the SPDE of suspended sediment transport in open channel flow. The proposed model, explicitly expressing the randomness of sediment concentration, has the advantage of capturing any randomly selected scenarios of particle movement and thus a more comprehensive quantitative description of sediment concentrations compared with the deterministic AD equation. As a result, the probability distribution of the sediment transport rate can be characterized based on a number of realizations obtained in the numerical experiments. It is found from the numerical experiments of particle trajectory that the transport of sediment particles is in the form of fully suspended load when the Rouse number is less than one. The ensemble mean sediment concentration of the proposed SPDE, obtained by the Monte Carlo simulation, agrees well with that of the deterministic AD equation. [ABSTRACT FROM AUTHOR]

In this article, we quantify the effects of a standing ice cover on the hydrodynamics of a mesotidal estuary. The Portneuf Estuary, Québec, is 5.9 km in length and has a 3-m-deep thalweg. According to our numerical model simulations (using an adapted version of Environment Canada’s ONE-D model) and field measurements, the midwinter 50-cm-thick ice cover produced an attenuation of the neap tidal range (1.9 m) and spring tidal range (4.0 m) of 17 and 37%, respectively, near the upstream end of the estuary. The arrival of low water was also delayed by about 90 min at this location. At the mouth, the cover attenuated peak ebb tide flow (200 m3/s) and flood tide flow (500 m3/s) by approximately 18 and 13%, respectively. Here the peak flood flow was normally delayed by 41 min, while the ebb tide was usually advanced by 8 min. In general, the ice cover attenuated peak velocities by 12 to 20%, although at certain times and locations the ice cover could induce higher velocities than would be present under open water conditions. The ice cover also retarded and diminished the salt wedge intrusion and is expected to dramatically reduce the sediment transport processes, although its presence could cause some sporadic local increases in erosion. [ABSTRACT FROM AUTHOR]

This paper presents an investigation of the performance of the hydraulic and sediment removal of a flushing system in a detention basin. A hydraulic criterion for the design of the flushing system is proposed. An equation for the maximum height of the flushing wave front as a function of the distance from the gate, the initial water depth in the chamber, and the chamber length is proposed. The Lauber and Hager equation for the maximum velocity of a flushing wave is also verified. Effective removal of sediment particles on the bed is a direct function of the bed shear stress generated by the flushing flow. This study reveals that the bed shear stress on the channel bed induced by the flushing flow can be attributed to the hydrostatic pressure, the flow acceleration, and the convection-induced momentum. The shear stress associated with fluid distortion and the turbulent viscosity may be neglected. Significant error would occur if the hydrostatic pressure component were used as an estimate of the bed shear stress on a mild slope channel. The energy slope method may provide an overestimate of the bed shear stress. Finally, an appropriate equation to evaluate the maximum bed shear stress is proposed. [ABSTRACT FROM AUTHOR]

An analytical model is presented to determine the threshold bed shear stress for noncohesive sediment motion subject to upward seepage on horizontal sedimentary bed under a stream flow. Hydrodynamic, seepage, and micromechanical forces acting on a solitary sediment particle, resting over a sedimentary bed under slip-spinning condition, are analyzed. The correlation coefficient between the results obtained using the present model and the experimental data of threshold bed shear stress with upward seepage on the horizontal bed is 0.767. It indicates that the model predicts satisfactorily the threshold bed shear stress with upward seepage. [ABSTRACT FROM AUTHOR]

A model is presented to determine the critical shear stress for the incipient motion of bivalve shells on a horizontal sand bed, under a unidirectional flow of water. Hydrodynamic forces on a solitary bivalve shell, resting over a sand bed, are analyzed for the condition of incipient motion including the effect of turbulent fluctuations. Hydrodynamic forces such as drag and lift are taken into consideration. Three types of bivalve shells, namely Coquina Clam, Cross-barred Chione and Ponderous Ark, were tested experimentally for the condition of incipient motion. The shape parameter of bivalve shells is defined appropriately. Experiments were conducted in a flume with a horizontal bed, and the critical shear stresses were computed using Vanoni's side-wall correction. The experimental data are used to calibrate the model making lift coefficient a free parameter. The results obtained using the present model agree satisfactorily with the experimental data. [ABSTRACT FROM AUTHOR]

Presents a study which examined the parameterization problems of sediment entrainment equations in overland flow areas. Use of a process-based erosion model to provide information on the amount and sources of sediment production and transport on watersheds; Methodology; Results and discussion.

Deals with a study which measured the mean and turbulence characteristics in a non-uniform open-channel flows using a three-dimensional acoustic Doppler velocimeter. Flow equilibrium condition; Horizontal velocity distribution; Reynolds stress distribution.

Presents information on a study that proposed a method for estimating rates of sediment transport in ice-covered channels. Flume experiments at the Iowa Institute of Hydraulic Research in Iowa; Limitations of the proposed method; Conclusions.

Presents a study which investigated the noncohesive sediment threshold under a unidirectional steady uniform stream flow on streamwise sloping sedimentary beds. Determination of threshold shear stress; Experimental procedure; Results and discussion; Conclusion.

Determines the effect of irrigation methods and spatial variability of saturated hydraulic conductivity on solute transfer. Utilization of two-dimensional deterministic solute transport model and stochastic parameter generator; Spatial variability versus infiltration rate; Susceptibility of sprinkler irrigation versus furrow irrigation in causing ground-water contamination.

Investigates the effect of water table depth and rainfall timing on bromide and nitrate transport using large undisturbed columns obtained from Rossburg silt loam and Clermont silt loam soils. Water table treatments and time delays; Cumulative nitrate-N recovery and bromide recovery; Pedon properties of the soil.

Supplements the reported result of the study 'Stability and Mobility of Sand-Bed Channels Affected by Seepage' with reference to the problem of sediment transport. Discussion on the incipient motion without seepage on plane and nontransporting beds; Calculation of the critical shear velocity with zero sheepage.