Journal of Hydraulic Engineering

This editorial is the occasion for me to introduce the Journal’s new Editor, to take a brief moment to summarize the state of the Journal, and to offer sincere thanks to many people who have assisted me during my term as Editor. It also is an occasion to introduce two new Associate Editors, and to mention an Associate Editor continuing on for a second term.

In 1986 the trashracks on the intake to the outlet works at Dillon Dam in Colorado were damaged due to filling the intake tunnel too rapidly. As the air from the tunnel was discharged through the intake structure, high velocities displaced two horizontal trashracks and removed one vertical trashrack from its guides. This damage was discovered through an underwater inspection in 1996. The addition of an air vent and the establishment of a filling procedure provided a solution to the problem. The quantity of air in the intake tunnel was reduced through the installation of a 102 mm (4 in.) diam air valve and 63.5 mm $\left(2\frac{1}{2} \mathrm{in}\text{.}\right)$ vent hole in the crown of the intake tunnel at the control tower. Since the vent could not remove all the air in the tunnel, the tunnel was filled by opening the emergency gate 7.9 mm $(\frac{5}{16}$ in.) and letting the conduit fill over a 12 h period.

Field observations of the Ipanema Beach, Rio de Janeiro, Brazil, ocean sewage outfall were obtained by adding dye tracers to the effluent and simultaneously measuring oceanographic conditions. Four experiments were performed, two during unstratified conditions, and two during stratified conditions. When stratified, the plume was trapped below the thermocline with low dilution, around 35 to 1, when unstratified, the plume surfaced and the dilution increased to more than 100 to 1. The results were compared with predictions of some commonly used near field plume mathematical models: UM3, RSB, and CORMIX. With suitable assumptions, all the models reasonably predict near field dilution. RSB predicts near field results directly; for UM3 and CORMIX, it was assumed that the end of the near field occurs when the plume reaches its terminal rise height or impacts the free surface. Different assumptions about the shape of the density profiles in CORMIX resulted in widely differing predictions of dilution. While the gross properties of the plume can be reasonably predicted by plume models, there remain many aspects which cannot be, particularly the patchy nature of the wastefield that has been observed here and in other field tests.

The results of a laboratory investigation on the characteristics of a circular three-dimensional turbulent wall jet are presented. Measurements were performed up to 50 nozzle diameters using a combined Particle Image Velocimetry and Planar Laser Induced Fluorescence approach that captured simultaneously the planar velocity and concentration fields. Both the velocity and concentration profiles exhibited similarity in the streamwise and spanwise directions after sufficient distance from the nozzle. The existence of a secondary mean motion is shown to be responsible for the far greater lateral spread compared to the normal spread for both the momentum and scalar mixing. Using curve fitting, the mean properties of the three-dimensional wall jet are approximated. The consistency of the relationships is further examined based on mass conservation and momentum balance.

A closed-form solution for transient flow rates across the wellbore in a confined aquifer is derived from a two-zone radial ground-water flow equation subject to the boundary condition of keeping a constant head at the well radius. An aquifer may be considered as a two-zone system if the formation properties near the wellbore are significantly changed due to the well construction and/or well development. An efficient numerical approach is used to evaluate this newly derived solution. Values of the transient flow rate are provided in a tabular form and compared with those obtained by numerical inversion for the Laplace-domain solution. The results show that the two solutions are in good agreement. This newly derived solution can be used not only for predicting the transient flow rate across the wellbore but also for identifying the effects of a skin with a finite thickness on the estimation of transient flow rates in a ground-water system with two different formation properties.

In the rainfall-runoff process, interaction between surface and subsurface flow components plays an important role, especially in rainwater abstraction and overland flow initiation at the early stage of rainfall events. Coupling of surface and subsurface flow submodels, therefore, is necessary for advanced comprehensive and sophisticated rainfall-runoff simulation. This article presents a conjunctive two-dimensional (2D) surface and three-dimensional (3D) subsurface flow model, which uses the noninertia approximation of the Saint-Venant equations for 2D unsteady surface flow and a modified version of the Richards equation for 3D unsteady unsaturated and saturated subsurface flows. The equations are written in the form of 2D and 3D heat diffusion equations, respectively, and solved numerically. The surface and subsurface flow components are coupled interactively using the common boundary condition of infiltration through the ground surface. The conjunctive model is verified with Smith and Woolhiser’s experimental data (reported in 1971) of initially dry and initially wet soil. Subsequently the model is applied to a hypothetical soil plot of clay or sand to simulate the overland flow, infiltration, and subsurface flow for four different rainfalls. The conjunctive model contributes as a tool for improved detailed simulation of 2D surface and 3D subsurface flows and their interaction.

Numerous three-dimensional models that solve the shallow water equations have been proposed to describe the processes of circulation and mixing in large bodies of water. The utility of those models is often demonstrated by comparison of computed variables with field observations. However, both the hydrodynamic data and the boundary conditions that drive the model have unknown measurement uncertainties and a limited spatial coverage, which limit the validity of this approach. A series of simple benchmark problems with analytical solutions is proposed to evaluate a particular model’s suitability to efficiently and accurately reproduce a wide range of characteristic hydrodynamic phenomena in natural lakes. The test problems focus on the representation of free and forced oscillations in homogeneous water bodies (barotropic response). This is not intended as a substitute for model validation against field data but, rather, as a necessary step in the initial model testing and selection. To illustrate this approach, the proposed test problems are used to compare a finite-element and a finite-difference free-surface hydrostatic model.

A complex problem of turbulent-sediment interactions in an open-channel flow is approached experimentally, using specially designed field experiments in an irrigation canal. The experimental design included synchronous measurements of instantaneous three-dimensional (3D) velocities and suspended sediment concentration using acoustic Doppler velocimeters (ADV) and a water sampling system. Various statistical measures of sediment concentration fluctuations, turbulent sediment fluxes, and diffusion coefficients for fluid momentum and sediment are considered. Statistics, fractal behavior, and contributions of bursting events to vertical fluxes of fluid momentum and sediment are evaluated using quadrant analysis. It has been found that both turbulence and sediment events are organized in fractal clusters which introduce additional characteristic time and spatial scales into the problem and should be further explored. It is also shown that Barenblatt’s theory of sediment-laden flows appears to be a good approximation of experimental data.

The performance characteristics of a centrifugal slurry pump has been evaluated at three rotational speeds with water as well as solid-liquid mixtures of two materials to establish the applicability of affinity relations to these pumps. Measurements have shown that the standard affinity relations are applicable to these pumps under special conditions only. The relations for head and capacity are found to be applicable only at low solid concentrations, whereas application of affinity relation for input power gives significant errors, both with water and slurry, for substantial changes in the pump speed.

A rectangular slit weir is designed for measurement of small (<0.005 m³/s) discharges. The discharge coefficient is determined experimentally using the measured discharges and the corresponding heads over the weir. The relationship between the discharge coefficient and all relevant dimensionless parameters is investigated. It is concluded that the discharge coefficient can be represented solely as a function of Reynolds number.

This paper presents results of an experimental and theoretical study on the use of a high density polyethylene (HDPE) additional pipe inserted downstream of a pump in a hydraulic network as a surge suppressor. The experiments consistently show a reduction of the oscillations with respect to the case without a HDPE device, while in the case of a single pumping pipeline the oscillations can be amplified for small volumes of the additional pipe. Previously calibrated mechanical parameters are considered in the mathematical models whose results are compared with experimental results. Both linear elastic and Kelvin-Voigt viscoelastic behavior of the pipe material and both one-dimensional (1D) and quasi-2D flow models are taken into account. The numerical results show that the viscoelastic model better describes the phenomenon, but the elastic model adequately estimates the maximum and minimum oscillations. Furthermore, the results of the quasi-2D model are in better agreement with the experimental maximum and minimum oscillations than those of the 1D model, but the differences are less important than in the case of networks without a HDPE device.