Journal of Hydraulic Engineering

South Florida has a complex regional hydrologic system that consists of thousands of miles of networked canals, sloughs, highly pervious aquifers, open areas subjected to overland flow and sheet flow, agricultural areas and rapidly growing urban areas. This region faces equally complex problems related to water supply, flood control, and water quality management. Advanced computational methods and super fast computers alone have limited success in solving modern day problems such as these because the challenge is to model the complexity of the hydrologic system, while maintaining computational efficiency and acceptable levels of numerical errors. A new, physically based hydrologic model for South Florida called the regional simulation model (RSM) is presented here. The RSM is based on object oriented design methods, advanced computational techniques, extensible markup language, and geographic information system. The RSM uses a finite volume method to simulate two-dimensional (2D) surface and groundwater flow. It is capable of working with unstructured triangular and rectangular mesh discretizations. The discretized control volumes for 2D flow, canal flow and lake flow are treated as abstract “water bodies” that are connected by abstract “water movers.” The numerical procedure is designed to work with these and many other abstractions. An object oriented code design is used to provide robust and highly extensible software architecture. A weighted implicit numerical method is used to keep the model fully integrated and stable. A limited error analysis was carried out and the results were compared with analytical error estimates. The paper describes an application of the model to the L-8 basin in South Florida and the strength of this approach in developing models over complex areas.

The proper timing, duration, and direction of wind events interacting with the geometry of an estuarine system can control the intensity of stratification. A three-dimensional, time-dependent hydrodynamic model was used to examine this process. Intense mixing is closely tied with wind-generated internal velocity shear. A south wind generates up-estuary directed surface currents, which eventually leads to downwelling movements of water. This downwelling process in the upper bay region accelerates the bottom current in a down-estuary direction. A vertical instability occurs, especially in the upper bay region, due to the generation of shear across the pycnocline, causing mixing sufficient to destratify the entire water column. On the other hand, strong stratification occurs when a north wind advects fresher upper bay surface water into the lower bay. A downwelling movement of water is produced, which in turn drives bottom saline water in the up-estuary direction.

This paper presents direct measurements of multiphase plumes in stratification and correlates characteristic plume properties with the nondimensional slip velocity $U_N$ . $U_N$ is defined as the ratio of the bubble slip velocity $u_s$ to a characteristic plume fluid rise velocity ${\left(BN\right)}^{1∕4}$ ; $B$ is the total kinematic buoyancy flux, and $N$ is the buoyancy frequency. $U_N$ is derived by dimensional analysis and is compared to other nondimensional parameters for multiphase plumes in the literature. To investigate correlations of the nondimensional numbers with plume properties, laboratory experiments were conducted in linear stratification using dispersed phases of air, oil, and glass beads (creating an inverted plume). A new type of plume behavior is identified, called Type $1^{*}$ , in which the horizontal motion in the first detrainment event disperses the relatively weak bubbles, creating a diffuse bubble plume that forms out of the intrusion. Measurements from these and previous experiments for type behavior, trap height, and intrusion layer flux are presented. Measurements are also presented for the new parameters peel height, mass fraction of passive tracer peeled, and bubble spreading ratio. The results show that correlations with the single parameter $U_N$ , which replaces other two-parameter models, are successful.

A numerical model of turbidity currents with a deforming bottom boundary has been developed. The model predicts the vertical structure of the flow velocity and concentration as well as change in the bed level due to erosion and deposition of suspended sediment. The Reynolds-averaged Navier–Stokes equations for dilute suspension have been solved using a finite volume method. The bottom boundary and the grid system are allowed to adjust in response to sediment deposition and entrainment during the computation. The model has been applied to simulate the evolution of a conservative saline density current and turbidity currents along an $11.6\mathrm{m}$ long flume that includes a slope followed by a horizontal bed. The model successfully simulates the evolution of the currents. Model results have been compared with the experimental data. Good similarity profiles of velocity and excess density or suspended sediment concentration are obtained at both the upstream supercritical and the downstream subcritical flow regions. A turbulent Schmidt number larger than one has been found to be appropriate for providing a good match with the experimental data. Changes in bed level predicted by the model have also been found to be in agreement with the experiment data.

This paper presents the results of a laboratory study of the structure of flow in a diversion structure with a vertical angled wedge-wire fish screen. This screen had a $10\times 25\mathrm{mm}$ mesh and was tested at three angles of 10.4, 17.5, and 26.8°, to the direction of the approaching flow, for two mean velocities of 0.5 and $0.8\mathrm{m}∕\mathrm{s}$ , with a depth of flow of about $0.75\mathrm{m}$ . In this water and fish diversion (channel or) structure, it was found that the depth of flow at any section is approximately constant with a drop at the screen on the side of the canal and decreased towards the bypass located at the downstream end. The distribution of the velocity component $u$ in the direction of the approaching flow as well as the perpendicular component $w$ and the resultant velocity $V$ was uniform in the vertical direction. The depth averaged mean velocity $\overline{V}$ for different verticals at any section in the diversion structure increased with the longitudinal distance $x$ and was correlated with the relative width, $b_s∕b$ (in the diversion structure) for all five experiments. Correlations have been found for the depth averaged transport velocity $\overline{u^{\prime }}$ and the impinging velocity on the screen $\overline{w^{\prime }}$ in terms of the approach velocity $U$ . A general relation has also been developed for the attack angle of the flow on the screen. The downstream part of the screen carried more flow into the canal compared to the upstream part as a result of the uniform mesh size used in this study. The results of this hydraulic study should be useful, particularly for freshwater adult fish, in designing screens in irrigation canals and for micro-hydro sites that use diversion canals.

Pipe transitions frequently occur in piping networks such as a water distribution system, or piping in a chemical engineering plant. Whereas the contraction transitions involve less head loss, the expansion transitions involve a sizable head loss. Considerable energy savings can be achieved if the transitions are designed by minimizing the head loss. The conservation of energy will be significant if the transition is meant for a steel-lined power tunnel where the flow velocities are high. Similarly, in a system having frequent occurrence of transitions, such as a high-rise building or plan of a city, the optimum transition profile can be used most effectively. This paper uses optimal control theory to develop a methodology for optimal design of expansion pipe transitions. Analyzing a large number of designed optimal transitions; empirical design equations for the pipe diameter profile are obtained.

New data are presented describing the retention time and longitudinal dispersion of a solute tracer across circular surcharged manhole structures of different diameters. The variations with both discharge and surcharge level are described and the relationships quantified. The variation of the longitudinal dispersion coefficient exhibits poorly defined trends, however using an aggregated dead zone technique both the reach time delay and travel time show clear variations. A surcharge threshold level for these parameters is evident at the larger manhole diameters and this is explained in relation to jet theory. The variation of the surcharge mean time delay and postthreshold mean travel time are quantified, while the prethreshold travel times are shown to be dependent on both discharge and surcharge. The relationships allow for inclusion in sewer water quality modeling and provide a method for improving predictive techniques.

A simplified model for the computation of boundary shear stress distributions acting on the flow perimeter of closed ducts is presented. The model assumes that the surplus energy within any control volume in a three-dimensional flow will be transferred towards the nearest boundary to be dissipated. Based on this model, the flow cross sectional area in the closed duct is divided into subflow regions corresponding to the side walls and bed, and the shear distributions over the wetted perimeter within each subflow area are assessed. Analytical equations, valid for all channel aspect ratios, for the prediction of local and mean shear stresses along the bed and side walls in smooth rectangular duct flow are derived. The formulae give good predictions of the shear stress distributions when compared with existing experimental data in the literature. The possible applications of the model to nonrectangular duct flows are also discussed.

A new methodology to predict local scour depth at a complex pier is presented herein that combines existing expressions for scouring respectively at uniform piers, caisson-founded piers, pile groups with debris rafts, and pile groups alone. The method recognises the relative scouring potentials of the components of complex piers and the transition of scouring processes occurring for varying pile-cap elevation. The validity of the method is confirmed herein using the present and also historical measurements of local scour at complex piers. The proposed methodology has the advantages of being conceptually consistent with observed scour behaviours, relatively simple to apply, applicable to wide ranges of flow and sediment conditions (through incorporation into a more general analysis framework), and applicable over the entire range of possible pile-cap elevations. For design purposes, the present method highlights respective pile-cap elevations that maximize (i.e., to be avoided over the pier life) and minimize local scour at complex piers. The present method reinforces that where the pile-cap elevation relative to the bed can vary with time at a bridge site, potential local-scour depths need to be assessed over the range of possible pile-cap elevations for the pier.