Journal of Hydraulic Engineering

The bed morphology of mountain rivers is characterized primarily by the presence of distinguishable isolated roughness elements, such boulders or clasts. The objective of this experimental study was to provide a unique insight into the role of an array of clasts in regulating sand movement over gravel beds for low relative submergence conditions, $H/d_c<1$, and flow depth, $H$, to the diameter of the clast, $d_c$, a process that has not been studied thoroughly. To assess the role of clasts in controlling incoming sand movement, detailed flume experiments were conducted by placing 40 equally spaced clasts atop a well-packed glass bead bed for replicating the isolated roughness flow regime. The experiments were performed for moderate ($\sim 2.50{\tau }_{\mathrm{cr}}^{*}$ where ${\tau }_{\mathrm{cr}}^{*}$ is the critical dimensionless bed shear stress) and high ($\sim 5.50{\tau }_{\mathrm{cr}}^{*}$) applied bed shear stress conditions, representative of gravel bed rivers. For comparison purposes, experiments were also repeated for nearly identical flow conditions but without the presence of clasts to discern the potential effects that clasts may have on sediment movement and hydraulics within the clast array region and also in the upstream section of the clast region where few observations exist. The experimental results revealed the formation of two distinguishable bed morphological features, namely a funnel shaped “sand ridge” upstream from the clast array region and small depositional “sand patches” around individual clasts. The sand patches were formed in the stoss region of the clasts, which contradicted previous observations of depositional patterns around clasts under high relative submergence conditions ($H/d_c>1$) where, in this case, depositional patches were observed to have formed in the clast wake region. Furthermore, most of the incoming sand was found to be intercepted by the evolving sand ridge upstream from the clast array region with implications in the amount of sand entering the clast array region. The exiting bed-load rate was found to be reduced by a factor of $\sim 5.0–20$, depending on the prevailing flow conditions when experiments with and without clasts were compared under nearly identical flow conditions. The findings of this research, although limited to the isolated roughness regime, may have significant ramifications in stream restoration projects for the design of engineered riffle sections, which typically consist of an array of clasts installed to improve degraded waterways and aquatic habitat.

This paper presents the results of an experimental study on stone stability under nonuniform turbulent flow, in particular expanding flow. Detailed measurements of both flow and turbulence and the bed stability are described. Than various manners of quantifying the hydraulic loads exerted on the stones on a bed are extensively reviewed and extended. On the basis of the data, a new relationship between flow parameters and bed damage—expressed as a stone entrainment formula—has been established for nonuniform flow. As the present data is in line with existing data on other flows, the present relation seems applicable for other types of nonuniform flow as well. Such a relationship could provide more consistent design criteria and allow an estimate of the cumulative damage over time, which is important for making decisions regarding maintenance frequency and lifetime analysis of hydraulic structures.

Data obtained from 48 stable reaches of upland rivers in the UK were stratified by stream type to develop regime equations specifically for natural meandering cobble- and gravel-bed rivers: C3 and C4 stream types, according to the Rosgen classification. Multiple regression models were applied to derive equations for reach-averaged values of bankfull width, mean depth, slope, meander arc length and sinuosity in bankfull discharge and associated bed-material load, the caliber of the bed material, bank vegetation density, and valley slope. The equations show that their cross-sectional dimensions are primarily determined by the bankfull discharge, bank vegetation, and bed-material size, whereas their profile and plan form are very strongly influenced by the valley gradient. Although bankfull bed-material load only appears to have a minor influence on channel morphology, its effect is implicit in the value of bankfull discharge because this corresponds to the flow that transports most of the bed-material load. Explanations are given for these results on the basis of processes affecting channel geometry. Comparisons with the regime equations derived more than 20 years ago by Hey and Thorne from the same UK data set indicate that stratification by stream type generates equations that are more consistent; for example, bank vegetation affects all aspects of channel morphology rather than simply channel width, and provides significantly better explanations for channel slope and sinuosity because of the inclusion of valley slope as an independent variable. Their potential for designing river restoration schemes is evaluated against North American data. The equations prove to be comparable to the Hey and Thorne equations for predicting width and depth, but provide a significant improvement for the determination of slope and sinuosity. Although bed-material load was shown, statistically, to influence channel dimensions, numerically its influence is trivial. Removing it from the analysis generates equations that provide the best practical point estimates of channel morphology. Predictions with the simplified regime equations are shown to be comparable to the full equations.

In bed-load sediment transport, the lifting force plays an important role in reducing the friction between sediment particles and the bed surface, and it makes particle transportation by the shear force easier. Because the lifting force is related to vorticity, a three-dimensional (3D) numerical model incorporating large eddy simulations was applied to simulate the vorticity field in a channel bend. The results show that the distribution of vorticity is highly nonuniform, and it can lead to significant variations in lifting force and bed-load sediment transport per unit width in a channel bend. Relevant theories are modified on the basis of physical reasoning and then incorporated into numerical models to investigate the lifting-force effects on the bed topography and bed-surface sediment size gradation in a channel bend. With the lifting-force effects considered, it is shown that the errors in simulated bed topography can be reduced by approximately 40% and in bed-surface sediment size by 50%.

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.

On the basis of a Strouhal number and the definition of the control factor, $m$, a new routing to calculate the energy slope in the lower and upper alluvial regimes is proposed. The control factor, $m$, representing the interactions in alluvial rivers, is reckoned as a bed-form index: while the flow evolves through transition, the control factor, $m$, decreases from $m=2$, associated with two-dimensional fully developed dunes, to $m=1$, associated primarily with in-phase waves. The way to predict the value of the control factor, $m$, is drawn from a previously published criterion for delineating the upper regime and is calibrated with experimental data. On several data from flumes and rivers, the routing is tested and compared with other methods from the literature. It appears that the new routing is the most robust because it allows researchers to obtain low averages of the discrepancy ratio for a wide range of ratios between the water depth and the median sediment diameter. On a selection of contrasted freshet events, the new routing allows for the capture of the primary dynamic of the flow resistance decrease.

This experimental study is devoted to quantification of the near-bed turbulence characteristics at an entrainment threshold of noncohesive sediments. Near the bed, the departure in the distributions of the observed time-averaged streamwise velocity from the logarithmic law is more for immobile beds than for entrainment-threshold beds. In the Reynolds shear stress distributions, a damping that occurs near the bed for sediment entrainment is higher than that for immobile beds. Quadrant analysis reveals that in the near-bed flow zone, ejections and sweeps on immobile beds cancel each other, giving rise to the outward interactions, whereas sweeps are the dominant mechanism toward sediment entrainment. The bursting duration for entrainment-threshold beds is smaller than that for immobile beds. On the other hand, the bursting frequency for entrainment-threshold beds is larger than that for immobile beds. The third-order correlations indicate that during sediment entrainment, a streamwise acceleration associated with a downward flux and advection of streamwise Reynolds normal stress is prevalent. The streamwise and the downward vertical fluxes of turbulent kinetic energy (TKE) increase with sediment entrainment. The TKE budget proves that for sediment entrainment, the pressure energy diffusion changes drastically to a negative magnitude, indicating a gain in turbulence production.

This paper describes the implementation of a new dispersion relation and energy-dissipation equation obtained from a viscous two-layer model schematization in the state-of-the-art wave forecasting model SWAN to simulate wave damping in coastal areas by fluid mud deposits. This new dispersion relation is derived for a nonviscous, nonhydrostatic upper layer and a viscous, hydrostatic lower layer, covering most conditions encountered in nature. An algorithm is developed for a robust numerical solution of this new implicit dispersion relation through proper starting values in the iteration procedure. The implementation is tested against a series of analytical solutions and three schematic test cases. Next, four dispersion relations published in the literature are evaluated and compared with the new dispersion relation. The solution of the dispersion relations forms a multidimensional space. Comparison of the various model solutions through one-dimensional graphs can therefore become quite misleading, as shown in the discussion of a two-dimensional representation of the solution space, explaining for instance the variation in ambient conditions at which maximum wave damping is to be expected. The various models have been developed for a variety of conditions, such as shallow and deep water and shallow and thick mud layers; the various models agree well in their domain of applicability, but they show significant deviations when used outside their domain. Because the ambient and mud conditions may vary considerable in space and time at a particular site, the use of the new model is advocated because it covers most water depths and fluid mud thicknesses encountered in nature. The strength of the new SWAN-mud model lies in its large-scale applicability, assessing the two-dimensional evolution of wave fields in coastal areas. Therefore, the new implementation is evaluated with respect to the behavior of waves on a sloping seabed, representing real-world coasts. In all cases, the new SWAN-mud model behaves satisfactorily; a critical remaining issue, though, is the assessment of the relevant fluid mud parameters.

Various hydrodynamic and sediment deposition experiments were conducted on a purpose-built, wide, shallow water table using a range of incoming flow and bed roughness conditions, including five flow rates, different inflow sediment concentrations, and different artificial roughness coefficients generated by four transverse string intervals. A recirculation zone was created behind a 0.5-m-wide backward-facing step on the left side of the table. Surface velocities, sediment concentrations, and processes and features of sediment deposition in recirculation zones were measured. Experimental results indicate that (1) as the value of the shallow stability parameter increased from 0.033 to 0.47, the length of the recirculation zone decreased to less than half, but the corresponding area and volume of sediment deposition increased about four times, and (2) it is the strength of the mixing layer rather than the size of the recirculation zone that dominates the process of sediment deposition as well as the final deposition feature.

A new instrument built to directly measure the bottom shear stress under different conditions of periodic waves is presented. Similar to classical Taylor’s cylindrical viscosimeter, the instrument is formed by two concentric cylinders, and the space between them is filled with water. The internal cylinder is fixed whereas the external cylinder, with a specific roughness, rotates following a given unsteady velocity time history. The shear stress at the outer cylinder wall is measured by using a torque meter. Both monochromatic and sawtooth-shaped waves have been tested, and the experimental shear stress time histories were compared with the results obtained from a numerical model.

The resistance induced by simulated emergent vegetation in open-channel flows has been interpreted differently in the literature, largely attributable to inconsistent uses of velocity and length scales in the definition of friction factor or drag coefficient and Reynolds number. By drawing analogies between pipe flows and vegetated channel flows, this study proposes a new friction function with the Reynolds number that is redefined by using a vegetation-related hydraulic radius. The new relationship is useful for consolidating various experimental data across a wide range of vegetation density. The results clearly show a monotonic decrease of the drag coefficient with the new Reynolds number, which is qualitatively comparable to other drag coefficient relationships for nonvegetated flows. This study also proposes a procedure for correcting sidewall and bed effects in the evaluation of vegetation drag.

This technical paper presents the development and application of a pseudo-transient continuation (PTC)– inspired flow model for the simulation of dam and levee failure. The unstructured, implicit, Petrov-Galerkin finite-element model relies on computed residuals to automatically adjust the time-step size. The implicit time integration, together with the automatic time-step size selection through PTC, makes the model computationally efficient. The model is verified and applied to several analytic and real-world test cases that exercise model behavior and accuracy for several critical, transcritical, and subcritical flows. The result is an efficient and accurate prediction of both the speed and depth of shock waves as the dam-break flow passes over initially dry and wet land.

Experimental analysis concerning supercritical flow over a dentated sill in nonsubmerged conditions and the local scour downstream of this sill is presented. In this case, the energy dissipation is incomplete so that a scour control downstream of the hydraulic structure could be required. The use of this type of dissipation device could be needed in cases where the maximum flow depth upstream of the sill must be limited to satisfy physical or structural conditions. This could happen, for instance, in the restoration of stilling basin in gravity dams and at the outlet of diversion systems. Experimental and theoretical results, useful in the design of this type of stilling basin and scour control, are presented in the paper, with an application to the case of the Molato Dam in Italy.

Physical model tests were conducted of the mixing of heated water from a proposed thermal diffuser. Dilutions were measured and flows imaged by a three-dimensional laser-induced fluorescence system that provides vastly more data than conventional thermocouple techniques. The flows were quite three-dimensional. For zero current speed, the effluent mixed over the water depth, but only in a limited region, and a two-layer stratified flow developed toward the edges of the effluent field and farther downstream. For zero and slow currents, the lowest surface dilution occurred where the jet centerline intersected the water surface and could be reasonably predicted by simple free-jet calculations. The prediction of an entrainment model, UM3, was close to the observed results because the flow is three-dimensional and the entraining water can be supplied from the ends. CORMIX considerably underestimated the observed dilution because it uses a two-dimensional analysis and neglects the effect of source momentum flux. Two-dimensional analyses and sectional physical models of diffusers with finite lengths should be used with caution until their limitations are better known.

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 $19,000{\mathrm{m}}^2$ 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 $r^2$ correlation coefficient of 0.84 with 93% of the absolute value of elevation differences between the two data sets less than 3 m.

Recently, the modified instantaneous acceleration-based (MIAB) model has been improved by the authors by using position-dependent coefficients found from investigation of the convolution-based (CB) model. Although this improvement is not proven general by any means, the fit with experimental results is very good. The three existing classes of one-dimensional models for the water-hammer transient that are applicable from an engineering point of view are the two models mentioned previously and the extended irreversible thermodynamics (EIT) model, which uses a coefficient found from thermodynamical considerations. This paper seeks the equivalent coefficients for the EIT model corresponding to the position-dependent coefficient the MIAB model to investigate the implications to the EIT model by using these coefficients. This is interesting because the EIT model is based on physical considerations using irreversible thermodynamics, and conclusions can possibly be drawn from this approach. The EIT coefficients found based on the position-dependent coefficients are used in simulations, and the results show an improvement compared to classical constant-coefficient EIT simulations. Based on this and discussion of water-hammer transient phenomena, it is suggested that limitations in the original EIT model regarding the coefficients might not be just and may be a possible limitation to the EIT model’s performance.

This study derives a semianalytical solution for drawdown distribution during a constant-head test at a partially penetrating well in an unconfined aquifer. The constant-head condition is used to describe the boundary along the screen. In addition, a free-surface condition is used to delineate the upper boundary of the unconfined aquifer. The Laplace-domain solution is then derived using separation of variables and Laplace transform. This solution can be used to identify the aquifer parameters from the data of the constant-head test when integrated with an optimization scheme or to investigate the effects of vertical flow caused by the partially penetrating well and free-surface boundary in an unconfined aquifer.

Detailed mapping of bathymetry and apparent bed load velocity using a boat-mounted acoustic Doppler current profiler (ADCP) was carried out along a 388-m section of the lower Missouri River near Columbia, Missouri. Sampling transects (moving boat) were completed at 5- and 20-m spacing along the study section. Stationary (fixed-boat) measurements were made by maintaining constant boat position over a target point where the position of the boat did not deviate more than 3 m in any direction. For each transect and stationary measurement, apparent bed load velocity ($v_b$) was estimated using ADCP bottom tracking data and high precision real-time kinematic (RTK) global positioning system (GPS). The principal objectives of this research are to (1) determine whether boat motion introduces a bias in apparent bed load velocity measurements; and (2) evaluate the reliability of ADCP bed velocity measurements for a range of sediment transport environments. Results indicate that both high transport (${\overline{v}}_b>0.6\mathrm{m}/\mathrm{s}$) and moving-boat conditions (for both high and low transport environments) increase the relative variability in estimates of mean bed velocity. Despite this, the spatially dense single-transect measurements were capable of producing detailed bed velocity maps that correspond closely with the expected pattern of sediment transport over large dunes.

The models for flood propagation in an open channel are governed by Saint-Venant’s equations or by their simplified forms. Assuming the full form of hyperbolic type nonlinear expressions, the complete or dynamic wave model is obtained. Hence, after first-order linearization procedure, the dispersion relation is obtained by using the classical Fourier analysis. From this expression, the phase and group speed and the variations of the amplitude of the waves are defined and investigated. Adopting Manning’s resistance formula, the effects of the variations of the Froude number, Courant number, and friction parameter are examined in the wave number domain for progressive and regressive waves. For small and high wave numbers, the simplified kinematic and gravity wave models are recovered, respectively. Moreover, the analysis confirms, according to the Vedernikov criterion, the Froude number value corresponding to the stability condition to contrast the development of roll waves. In addition, for stable flow on the group speed versus wave number curves, the results show critical points, maximum and minimum for progressive and regressive waves, respectively.

A theoretical method was used to derive an equation for the discharge coefficient of sluice gates in rectangular channels under orifice-flow (both free and submerged) conditions. The proposed equation allows for the effects of energy dissipation between the upstream section of the gate and the vena contracta. The hydraulic energy loss in the upstream pool is attributable to the induced turbulence by the recirculating region and to the growth of bottom boundary layer. For the submerged-flow condition, turbulent shear-layer entrainment is also responsible for the energy loss. This energy loss is introduced into the equations through a coefficient $k$ that has been conventionally assumed to be negligible. Experimental data from the literature were used to validate the equation, which showed good agreement with the measured values. It is also shown that the magnitude of the energy-loss factor is a function of the geometry of the gate and can modify the discharge coefficient. An equation for the distinguishing condition between free and submerged flows is also presented. The new equations can be used to predict the performance of sluice gates with different edge shapes under free- and submerged-flow situations.

Supercritical flow below chute piers generates an aerated flow known as rooster tail. Their behavior varies along the spillway or chute for different Froude numbers. This paper aims to analyze the effect of various parameters including the Froude number, approach flow depth, chute pier width, and presence of a deflector ramp on the rooster tail geometry. Aerator systems, which generally include deflectors in chutes, are effective in the generation of rooster tails. The interaction between a deflector and supercritical flow of chutes causes a higher rooster tail. New equations define the rooster tail geometry in the presence of a deflector. The air concentration profile was measured and the effects of deflectors on the air entrainment were studied.

Using data from six very long experiments on local scour at single cylindrical piers, some of the existing equilibrium criteria found in the literature are assessed. It is found that common criteria, which consider scour depth increments in 24 h or the observation of horizontal plateaux in records of scour depth time evolution, can incur important errors on the equilibrium scour depth. Using some of the expressions for time evolution found in the literature to fit the experimental data and infer equilibrium scour depth through extrapolation to infinite time, it is found that the equilibrium scour depth cannot be specified, in general, for experiments shorter than one to two weeks.