Journal of Hydraulic Engineering

The micromodel is an extremely small physical river model having a movable bed, varying discharge, and numerous innovations to achieve quick answers to river engineering problems. In addition to its size being as small as $4\mathrm{cm}$ in channel width, the vertical scale distortion up to 20, Froude number exaggeration up to 3.7, and no correspondence of stage in model and prototype, place the micromodel in a category by itself. The writer was assigned to evaluate the micromodel’s capabilities and limitations to ensure proper application. A portion of this evaluation documents the deviation of the micromodel from similarity considerations used in previous movable bed models. The primary basis for this evaluation is the comparison of the micromodel to the prototype. The writer looked for comparisons that had (1) a reasonable calibration of the micromodel and (2) about the same river engineering structures constructed in the prototype that were tested in the micromodel and (3) a prediction by the micromodel of the approximate trends in the prototype. Evaluation of these comparisons shows a lack of predictive capability by the micromodel. Differences in micromodel and prototype likely result from uncertainty in prototype data and the large relaxations in similitude. Based on the lack of predictive evidence, the micromodel should be limited to demonstration, education, and communication for which it has been useful and should be of value to the profession.

Riprap of bridge piers is placed to prevent scour and to secure the pier from failure. Riprap is therefore an addition to a pier to increase its performance against scour. The present research intends to present three basic scour mechanisms associated with circular-shaped bridge piers in rivers first, to introduce then a number of selected experiments for a range of hydraulic, geometric, and sedimentologic conditions, and finally to describe a novel procedure for assessing the safety of these river elements against failure. This procedure is based on the Shields diagram relating to sediment entrainment in a uniform and flat sediment bed subjected by a water flow. The Shields approach is extended for the presence of a circular-shaped pier that is protected by a circular-arranged riprap layer of equal size elements. The design procedure presented in the following thus reduces to the entrainment condition of a pier for equal riprap and the sediment sizes and to the Shields entrainment condition when the pier diameter degenerates to 0.

The entrainment properties of plane surface-jets in shallow moving water were studied. The jet entrainment characteristics were determined from laser doppler velocimetry measurements of longitudinal velocity. The entrainment constant $\beta$ was found to be 0.064 within the range of ambient cocurrent studied $(0.12<U_{a0}^{\prime }<0.22)$ . The experimental data also suggested that the total entrainment coefficient ${\alpha }_T$ approached a constant value of 0.033 in the far field. In contrast, the vertical entrainment coefficient ${\alpha }_V$ was noticeably more sensitive to the strength of the ambient current. Predictions of entrainment models for surface jets in deep and shallow water are presented and compared with experimental data.

A high-resolution, unstructured grid, finite-volume algorithm is developed for unsteady, two-dimensional, shallow-water flow and scalar transport over arbitrary topography with wetting and drying. The algorithm uses a grid of triangular cells to facilitate grid generation and localized refinement when modeling natural waterways. The algorithm uses Roe’s approximate Riemann solver to compute fluxes, a multidimensional limiter for second-order spatial accuracy, and predictor–corrector time stepping for second-order temporal accuracy. The novel aspect of the algorithm is a robust and efficient procedure to consistently track fluid volume and the free surface elevation in partially submerged cells. This leads to perfect conservation of both fluid and dissolved mass, preservation of stationarity, and near elimination of artificial concentration and dilution of scalars at stationary or moving wet/dry interfaces. Multi-dimensional slope limiters, variable reconstruction, and flux evaluation schemes are optimized in the algorithm on the basis of accuracy per computational effort.

Extended-period simulation of incompressible and inertialess flow in water distribution systems is normally done using numerical integration techniques, although regression methods are also sometimes employed. A new method for extended-period simulation, called the explicit integration (EI) method, is proposed. The method is based on the premise that a complex water distribution system can be represented by a number of simple base systems. The simple base systems are selected in such a way that their dynamic equations can be solved through explicit integration. In this paper a simple base system consisting of a fixed-head reservoir feeding a tank through a single pipeline is analyzed. It is then illustrated how a complex water distribution system can be decoupled into simple base systems and its dynamic behavior simulated using a stepwise procedure. The EI method is compared to the commonly used Euler numerical integration method using two example networks. It is shown that the accuracy of the EI method is considerably better than that of the Euler method for the same computational effort.

RiverSpill is a geographic information system-based software package that calculates time-of-travel and concentration of contaminants in streams and rivers. The purpose of RiverSpill is to serve as a tool for response, planning, and training for the protection of the nation’s surface drinking water from deliberate (homeland security) threats. RiverSpill uses real-time stream flow data, a hydrologically connected stream network, and the locations and populations served by each public, surface drinking water intake. Accidental water contamination events such as spills from transportation infrastructures (highway, railroad, and pipeline), wastewater treatment plants, and hazardous materials storage sites may also be simulated. RiverSpill contains a comprehensive database of potential constituents of concern and their chemical or biological attributes. Spills may be modeled as either instantaneous or continuous events. Times-of-travel and concentration curves calculated with RiverSpill have been compared with those measured in several streams and rivers using dye. The dye measurements have been used to evaluate and calibrate RiverSpill to specific rivers.

Experiments on the near-field mixing of wastewater discharged from multiport diffusers into a stationary density-stratified environment are reported for conditions typical of ocean sewage outfalls. Dilutions were measured with a microconductivity probe in which the test tank was stratified with a nonconducting solution; geometrical characteristics such as rise height and layer thickness were measured by planar laser-induced fluorescence in which the test tank was stratified with refractive-index matched fluids. The port spacing was varied over a wide range encompassing rapidly merging to nonmerging plumes. The end of the near-field occurs at a distance of order one plume rise height from the diffuser. At this point the turbulence and mixing induced by the discharge is effectively damped by the ambient stratification, and little near-field mixing occurs beyond it. The results were analyzed in terms of line and point-source parameters to deduce the ranges of port spacings for which line and point plume solutions apply. Equations to predict the near-field characteristics are presented.

Experiments on the near-field mixing of wastewater discharged from multiport diffusers into stratified flowing waters are reported for conditions typical of actual ocean sewage outfalls. Dilutions were measured by a newly developed three-dimensional laser-induced fluorescence system combined with refractive-index matching and by a microconductivity probe. The plume dynamics are complex. Depending on port spacing, plumes discharged from the upstream diffuser side may merge first with themselves, and then with the plumes discharged from the downstream side. Or the plumes that are horizontally opposed may first merge, followed by lateral merging. In all cases, however, the wastefield eventually becomes laterally homogeneous. The results are analyzed in terms of line or point-source parameters and it is found that they can be predicted by assuming the discharge to be a line plume when $s∕l_b<1.0$ and as point plumes for $s∕l_b⩾6.0$ . Semiempirical equations to predict the near-field dilution, near-field length, and plume rise height are presented.

The behavior of flow through porous media has been the subject of study for a long time. The relationship relating friction factor and Reynolds number using the square root of intrinsic permeability as the characteristic length is examined for flow in porous media with converging boundaries. An experimental investigation of the effect of convergence of streamlines on the linear and nonlinear parameters for different radial flow lines in a converging permeameter for different ratios of radii of the test section is also studied. In the present case, crushed rocks of sizes 11.64 and 4.73 mm were used as media and water as fluid, to develop curves relating friction factor and Reynolds number for different radial flow lines with different ratios of radii of the test section of the permeameter.

The $k\text{-}\epsilon$ turbulence closure model is used to simulate obstructed round buoyant jets in a static uniform ambient, and the results compare well with available experimental data. On the basis of the axial line velocity distribution, three regions in the flow behind the disk are identified: the wake region, the transitional region, and the self-similarity region. The length of the wake region, which varies with flow and geometrical parameters, and the existence of self-similarity are also addressed.