Journal of Hydraulic Engineering

Flow visualization experiments were performed in a glass-walled recirculating flume to observe the fate of sediments released instantaneously in a current. For releases at the surface, criteria were developed to characterize ambient currents as “weak,” “transitional,” or “strong” as a function of particle size. In weak ambient currents, particle clouds were advected downstream with a velocity equal to the ambient current, but otherwise their behavior and structure were similar to those in quiescent conditions. A substantial portion of the mass initially released, up to 30%, was not incorporated into the parent cloud and formed the trailing stem. This percentage was dependent on the initial release variables, with the greatest sensitivity on particle size. The “loss” of sediment during descent, defined as the fraction of mass missing a designated target with a radius equal to the water depth, was quantified and found to increase sharply with current speed. Laws of geometric, kinematic, and dynamic similitude provide a basis for scaling laboratory results to the real world and formulating guidelines to reduce the losses that could result from open-water sediment disposal.

Partially treated wastewater discharge from marine outfall diffusers often contains inorganic and organic solids that may settle close to the source and give rise to sludge banks that affect benthic ecology. An experimental and theoretical investigation of the structure and settling mechanisms of a horizontal sediment momentum jet in stagnant ambient has been carried out. The cross-sectional particle concentration distribution of a horizontal sediment jet is measured for the first time. Bottom deposition measurements are made for a total of 41 experiments of momentum jets laden with sand particles or synthetic spherical glass particles. The sediment jet can be characterised by a sedimentation length scale $l_m$ defined by the jet momentum flux and particle settling velocity. The measured longitudinal sediment deposition rate can be described by a semiempirical log-normal distribution based on $l_m$. In the instantaneous particle distribution, the sediment fallout is concentrated in a central region and settles in a zig-zag trajectory. The time-mean transverse particle concentration shows that the upper half of sediment jet behaves like a pure jet with concentric contours for $x<0.5l_m$. For $0.5l_m<x<l_m$, the sediment cloud starts to depart from the water jet; for $x\gtrsim l_m$, the particle cloud separates significantly from the water jet. For $x<l_m$, the maximum particle concentration $C_m$ is located within the jet region and the decay of $C_m$ closely follows the classical jet theory. For $x\gtrsim l_m$, $C_m$ is significantly less than that given by the jet theory. The time-mean particle concentration distribution across the jet is horseshoe-shaped, with an open end at the bottom due to sedimentation. The concentration distribution is elongated in the vertical direction and shaped like an ellipse. A two-layer Lagrangian jet model is developed to predict the mixing of dilute horizontal sediment jets. The predictions are in excellent agreement with the layer-averaged particle concentrations and bottom deposition rate measurement.

To analyze the spatial variability of two-dimensional dispersion coefficients in meandering channels, an observed dispersion tensor was calculated by applying a theoretical equation to the measured velocity profiles of two laboratory channels. From the observed dispersion tensor, local longitudinal and transverse dispersion coefficients were estimated by the least squares method. In both channels, the spatial variation in the dispersion coefficients was found to be strongly dependent on the specific location within the channel, because alternating bends in channels induces the periodic generation of secondary currents that alter the magnitude of transverse dispersion. Dimensionless transverse dispersion coefficients of each measurement section vary from 0.33 to 1.14 for the M1 channel and from 0.63 to 3.40 in the M2 channel around the entrance and apex of the second bend. The maximum negative correlation occurred near the apex of the channels because of the separation of the point of maximum primary velocity and the center of the circulation cells by the complex flow structure in the meandering channel.

A series of laboratory flume experiments were performed to study the effect of stream barbs on flow field dynamics and sediment erosion in a 135° mobile-bed channel bend. Stream barbs (also known as spur dikes or submerged groynes) are low-profile linear rock features that redirect high velocity flow away from the outer bank of channel bends. Unlike emergent groynes, the submerged nature of these structures creates a unique combination of horizontal shear (plunging type flow) and vertical shear (at the groyne tip). Spatially dense, high frequency velocity data were collected and analyzed to describe the pattern and magnitude of three-dimensional (3D) velocity throughout the bend and in the vicinity of the stream barbs. This paper demonstrates that the outer bank region (particularly between barbs) may still be at risk of erosion (or even increased erosion greater than the same case without barbs) if stream barbs generate excessive secondary velocities (because of their size and layout) that are opposing the primary secondary flow naturally occurring in channel bends. Characterizing the role of flow field dynamics on the pattern of deposition and erosion through experimental measurements provided valuable data about how such flow features contribute to local scour, and about the performance of these structures.

Experiments were conducted in a laboratory flume channel to evaluate the effects of increasing amounts of sand on its transport over and through an immobile coarse gravel bed. Detailed measurements of sand transport rate, bed texture, and bed topography were collected for four different discharges at approximately the same flow depth of 0.2 m for 11 different elevations of sand in the gravel bed. Sand transport was measured using both physical samples and a density cell. For a given flow rate, increases in the elevation of sand relative to gravel resulted in decreases of bed shear stress from 32–44% and increases in sand transport by three orders of magnitude. For the highest two discharges, the sand merged into a small number of long and low bed forms that translated through and over the gravel bed. A collapse of the transport data was accomplished by relating the sand transport rate to the bed shear stress scaled by the cumulative probability distribution function of the gravel surface evaluated at the height of the mean sand bed.

Experimental measurements of the reach-averaged bed-load particle velocity $V_p$ on smooth and rough plane surfaces were analyzed for particles of different shape, size $d_s$, and density $G$. Particle types included natural quartz particles ($1.2\mathrm{mm}<d_s<13.6\mathrm{mm}$ at $G=2.65$), spherical glass marbles ($14.5\mathrm{mm}<d_s<29.3\mathrm{mm}$ at $G=2.6$), and spherical steel ball bearings ($1.6\mathrm{mm}<d_s<19\mathrm{mm}$ at $G=8.02$). The velocity of 9,739 individual bed load particles continuously rolling on aluminum plates coated with a layer of sand/gravel (roughness $0<k_s<3.4\mathrm{mm}$) was measured for 356 different conditions. For each flow condition, the reach-averaged particle velocity measurements over a 2 m test reach were repeated at least 15 times to provide mean values and standard deviations. For bed load particles rolling on smooth surfaces ($k_s=0$), it was concluded that (1) $V_p$ is within $\pm 30\%$ of the calculated flow velocity from the vertical velocity profile at the top of the particle; (2) $V_p$ for spheres does not vary much with particle density; and (3) $V_p$ increases slightly with particle size $d_s$, up to approximately $20u_{*}$. On rough surfaces ($k_s>0$), for particles of diameter $d_s$ continuously rolling on a stationary bed of roughness $k_s$, it was concluded that (1) bed load particles roll in continuous motion in the range $2.5<V_p/u_{*}<12.5$; (2) steel particles are much slower than spherical marbles ($G=2.6$); and (3) the particle velocity increases primarily with a new parameter ${\tau }_{*ks}=R_h{S}_f/(G-1)k_s$ in the range $0.008<{\tau }_{*ks}<0.2$ up to a maximum $V_p\approx 12u_{*}$. Spherical particles roll slightly faster than natural particles. In a comparison with a large data set that included 1,018 measurements, the analysis of discrepancy ratios showed that the proposed formula was in good agreement with other measurements from the literature.

This work deals with the evaluation of the most suitable expression for the motion resistance of a debris flow. In particular, it focuses on inertial debris flows, i.e., granular-fluid mixtures in which the particle inertia dominates both the fluid viscous force and turbulence; it provides, through an order-of-magnitude analysis, the criterion to be satisfied for a debris flow to be considered inertial and shows that most of real-scale debris flows match this description. The analytical relation between flow depth, depth-averaged velocity, and tangent of the angle of inclination of the free surface is then used in steady, uniform flow conditions to approximate the flow resistance in depth-averaged mathematical models of debris flows. That resistance formula is tested against experimental results on the longitudinal profile of steady, fully saturated waves of water and gravel over both rigid and erodible beds, and against field measurements of real events. The notable agreement, especially in comparison with the results obtained using other resistance formulas for debris flows proposed in the literature, assesses the validity of the theory.

Physical and numerical simulations of open channel flow over a heterogeneously roughened bed are examined. The velocity field is mapped at four different cross sections by using an acoustic Doppler velocimeter and the boundary shear stress obtained from both the velocity data and application of a Preston tube. These data illustrate that in the current arrangement the roughness elements dominate the physics of the flow and act as a source of vorticity, which is initially manifested as local boundary shear stress and, in turn, affects the secondary flow structures and momentum transfer in the channel. This paper presents the first attempt at using the Shiono–Knight method to model velocity and boundary shear stress distributions in a heterogeneous open channel. Appropriate advice concerning values of calibration parameters and discretization of the cross section is given. The combined physical/numerical approach provides an insight into the changing properties of the flow structure within a nonuniform roughness environment and will be of use to environmental regulators and river managers and academics working in the area.

Semianalytical equations were derived to evaluate the mean boundary shear stress in smooth trapezoidal open channels using conformal mapping techniques. This process tends to a complicated function that should be simplified based on numerical integration. Also, based on a mathematical analysis, an approach that divides the flow area into subsections corresponding to the channel bed and sidewalls is presented. In particular, the hydraulic aspects of the best hydraulic trapezoidal sections were characterized to estimate the boundary shear stress distribution based on the exact form of the interface between adjacent subsections. To validate this approach, the analytical results were compared with the results of model experimentation performed in the present study. The analytical results agree well with the experimental measurements and the results of former investigations.

Archimedes screws have become increasingly popular throughout Europe to drive hydropower plants using residual flow from a stream or river. This heightened usage of such screws during the past few years is attributable to their robustness, simplicity, and fish friendliness. Presently the dimensioning of a hydropower site equipped with an Archimedes screw is dependent mainly on the experience of the design engineer. This is so because there is no appropriate theory for the optimal hydraulic design of screws used at hydropower sites, especially for the water-inflow conditions. In this paper, a new analytical model for the water inflow is derived, and the optimal values of the inflow parameters are determined to achieve a planned inflow to the screw.

A hydraulic jump is a common phenomenon that can be observed in open channel flows such as rivers and spillways. It can cause damage of the downstream bed and bank of the channel due to the process of continuous erosion and degradation. In order to reduce the hydraulic jump destruction, the energy in the hydraulic jump must be dissipated as much as possible. One method to increase dissipation of energy is using a corrugated bed. In order to know the effect of a corrugated bed on the hydraulic jump, a smoothed particle hydrodynamics (SPH) model is applied to investigate the characteristics of hydraulic jumps in various corrugated beds. A variety of corrugated beds that are smooth, triangular, trapezoidal, and sinusoidal are considered. The opening of a gate is changed to adjust the hydraulic jump. The conjugate depth ratio, the jump length, the bottom shear stress distribution, and the energy dissipation are reported. The results of the present study are in a good agreement with previous studies. Energy dissipation is compared among corrugated beds and a smooth bed. It is found that the sinusoidal bed can dissipate more energy than other beds. As a result, corrugated beds can be used to enhance energy dissipation of hydraulic jump in the open channel. In general, the proposed SPH model is capable of simulating the effect of corrugated beds on hydraulic jump characteristics.

This paper focuses on the analysis of unsteady pipe flows caused by a pump trip in a water pipeline system. Field experiments have been carried out to collect transient pressure and steady-state flow rate data in the Prado–Instituto Politécnico da Guarda (IPG) pumping system located in Guarda, Portugal. Observed transient pressures were compared with numerical results. Results obtained were excellent both in terms of damping and phase shift of the transient pressure signal, provided that unsteady friction effects were taken into account and an appropriate downstream end boundary condition was considered. The downstream end boundary condition was described by small tanks with variable level and with free discharge into the storage tank; the variation of water level in these small tanks results in the relief of extreme transient pressures (conversely to what is observed in the line-packing effect) and changes the shape of transient pressure waves. This analysis has shown that classical water hammer theory (neglecting unsteady friction) and the consideration of a constant-level reservoir at the downstream end do not accurately describe the observed transient behavior of pressurized pipe systems.

In urbanized areas, flood flows constitute a hazard to populations and infrastructure, as illustrated during major floods in 2011. During the 2011 Brisbane River flood, some turbulent velocity data were collected using acoustic Doppler velocimetry in an inundated street. The field deployment showed some unusual features of flood flow in the urban environment. That is, the water elevations and velocities fluctuated with distinctive periods between 50 and 100 s linked with some local topographic effects. The instantaneous velocity data were analyzed using a triple decomposition. The velocity fluctuations included a large energy component in the slow fluctuation range, whereas the turbulent motion components were much smaller. The suspended sediment data showed some significant longitudinal flux. Altogether, the results highlighted that the triple decomposition approach originally developed for periodic flows is well-suited to complicated flows in an inundated urban environment.