Journal of Hydraulic Engineering

The collector network of a coastal sewage system is normally combined and evacuates domestic and industrial runoff wastewaters in rainy weather. This means that overflows can arise at certain points in the network in rainy weather. The volume and duration of these overflow points and, consequently, the capacity of the coastal interceptor-collectors, are conditioned by the environmental regulations governing receptor waters, and more specifically, in most cases, by those governing bathing waters. The most widely accepted criteria on the quality of these waters are those established by the corresponding directive in terms of exceedance time of fecal coliform concentration limits [nonfulfillment time (NFT)]. This random variable is itself conditioned by a series of factors, and can be studied by means of complex models with high computing costs. This paper briefly presents a method with a probabilistic focus for studying coastal sewage systems, in which the use of neural networks is proposed as a means of reducing computing costs. More specifically, neural networks with optimum functional link are used, in which optimization is carried out genetically.

Field measurements were undertaken to determine the spread of a nonbuoyant surface plume in homogeneous and stratified coastal waters with strong tidal currents. In the homogeneous current the concentration profiles of marked fluid, released near the free surface, were Gaussian in both the lateral and vertical directions; the lateral spread was much larger than the vertical spread. In the stratified current the lateral concentration profiles were Gaussian. The marked fluid spread quickly in the vertical direction, reaching the pycnocline a short distance downstream from the point of release. The lateral spread was less than that in the homogeneous current. In both the homogeneous and stratified currents the spreads were nonlinear. The maximum concentration of marked fluid, occurring long the plume axis, decreased nonlinearly with the diffusion time.

This paper presents the results of an experimental study on the dilution of circular nonbuoyant turbulent surface jets of diameter d, discharged perpendicularly into relatively deep cross-flows with depth D in the mixing region. The jet velocity was varied from 2.1 to 12.3 times the velocity of the cross-flow. Concentration measurements were carried out as far as x/d= 630, where x is the distance downstream from the nozzle along the cross-flow. Minimum dilutions of about 100 were attained in this mixing region. A general correlation has been developed to predict the minimum dilution in terms of the transformed distance αx/d, where α is the ratio of the jet to cross-flow velocity. The concentration profiles in the vertical and the transverse directions were found to be similar. Expressions were developed to describe the growth of the width and thickness of the deflected jets. The effect of submergence of the jet nozzle on the minimum dilution was also investigated.

A new solution to the stable-channel paradox has been derived based on the contribution of secondary flow to the redistribution of boundary shear stress. This new solution was then combined with the entropy-based bank profile equations, the flow-continuity condition, an appropriate frictional resistance relation, and a sediment transport relation to develop a new geometric model for straight stable alluvial channels. Furthermore, the effect of nonuniform boundary particle sizes was introduced to make the new geometric model applicable to a wide range of both laboratory experiments and natural alluvial rivers. A FORTRAN program was developed to compute the design procedure. The comparisons between the cross-sectional shapes, depths, and widths calculated by the new geometric model and field and laboratory data show that the proposed geometric model is in reasonable agreement with the data both for well-graded and for nonuniform bed materials.

By introducing the concept of “SDS (subdepth scale) turbulence” to model three-dimensional (3D) turbulence with length scales less than the water depth and treating it explicitly with a proper separate modeling, an SDS-2DH model has been developed to simulate the evolution of horizontal large-scale eddies in shallow water. Applying this model to river flows with transverse shear due to vegetation drag, the horizontal large-scale (HLS) eddies were found to dominate horizontal momentum mixing. The bottom friction and vegetation drag, acting as sinks of vorticity, play the key roles in the development of the horizontal large-scale eddies and in Reynolds stress generation. The SDS-2DH model can directly describe effects of flow geometry, such as vegetation layer width, on the large-scale eddy development and, hence, predicts turbulence-mixing better than the k-ε model.

A new numerical technique by Chang is described and used to solve the one-dimensional (1D) and two-dimensional (2D) Saint Venant equations. This new technique differs from traditional numerical methods (i.e., finite-difference, finite-element, finite-volume, spectral methods, etc.). Chang's method treats space and time on the same footing, so that space and time are unified—a key characteristic that distinguishes the new method from other techniques. This method is explicit, uses a staggered grid, enforces flux conservation in space and time, and does not require upwinding, flux-splitting, flux limiters, evaluation of eigenvalues, or the addition of artificial viscosity. Furthermore, the scheme is simple, easy to implement (see Appendix I), and can be extended to higher dimensions. First, the new technique, as developed by Chang, is introduced, explained, and applied to the 1D Saint Venant equations. To illustrate its effectiveness, an idealized dam-break and a hydraulic jump in a straight rectangular channel are simulated. The numerical results obtained using the new method are compared with results from other, more conventional techniques of similar complexity, experimental data, and an analytical solution. Next, Chang's scheme is extended for solution of the 2D Saint Venant (i.e., shallow water or depth-averaged) equations. The writers do not follow Chang's 2D development but instead employ Strang's method of fractional steps, which transforms the 2D problem into two 1D problems. The new 2D scheme is applied to an oblique hydraulic jump, and the results are compared with an analytical solution.

To simulate slow transients in wide rectangular open channels of finite length, the St. Venant equations are approximated by a single Burgers' equation for flow depth. Flow velocity is expressed as a function of flow depth and its gradient to satisfy the continuity of flow. The Burgers' equation model has three constants uniquely determined with the Froude number of initial uniform flow to satisfy approximately the conservation of momentum for small perturbations of flow depth about an initial constant. For a given set of fixed boundary depths, depth profile and channel storage of final steady nonuniform flow are readily obtained in analytical form. This is a useful feature of the Burgers' equation model. Comparison of the Burgers' equation model with the St. Venant equations is made based on numerical results.

Excessive supersaturation of dissolved gases, primarily nitrogen and oxygen, can cause gas bubble disease, and eventual mortality, in fish. This potential threat is currently a concern in efforts to aid anadromous fish survival in the northwestern United States. In an effort to better understand dissolved gas supersaturation and assist in its mitigation, physically based relationships have been expanded and developed to predict dissolved gas supersaturation below spillways. This paper discusses the predictive technique as applied to the dissolved gas supersaturation that occurs because of the stilling basin and the river reaches immediately downstream of the structure. Gas transfer across both the water surface and the bubble interface are considered. Extensive field data from three spillways on the Columbia and Snake Rivers is used to fit coefficients that the predictive relationships require. The inclusion of more physically based parameters will allow for the evaluation of the operation and design of the structures and may provide insight for efforts to mitigate high dissolved gas concentrations downstream of such structures.

The equations that define Newtonian pipe flow are well established and used routinely by engineers and scientists throughout the world. The same cannot be said for non-Newtonian flows, which have a higher degree of complexity. This paper presents a coherent set of equations for the laminar and turbulent flow of Herschel-Bulkley fluids. These equations are consistent with those used for Newtonian fluids and previous work on the behavior of generalized non-Newtonian fluids. A numerical model for non-Newtonian flows is discussed and has been compared with experimental measurements from different sources. This model has been used to run a series of simulations to find the coefficients required for a new turbulent friction factor correlation. A new Reynolds number has been defined that represents the conditions in turbulent flows more realistically than the existing Metzner-Reed Reynolds number.

Presently available formulas for estimating the maximum depth of scour near bridge piers often lead to unreliable results. A fully three-dimensional hydrodynamic model is therefore used in this study to simulate the flow occurring at the base of a cylindrical bridge pier within a scour hole. The results of the numerical simulation are compared with laboratory observations by Melville and Raudkivi (1977). Quantitative and qualitative agreement between the studies is quite good. Discrepancies between the results of the two studies are of an order that may be attributed to choices in numerical model parameters. The simulations may be supplemented by Lagrangian particle-tracking to estimate the depth of the equilibrium scour condition.

In this paper the physics of the flow past a submerged vane at high angles of attack is presented. The data presented were collected during an experimental study of flow past vanes at various angles of attacks in a deformable-bed straight rectangular channel. The first few experimental runs were undertaken to establish the optimal angle of attack required to generate the strongest secondary circulation in the flow. At this optimal angle of attack, the flow features responsible for the transverse movement of bed sediment are clearly identified. The differences between the flow features observed near the vanes at both low and high angles of attack, are also outlined. These include, among others, two counterrotating vortices for vanes at high angles of attack as opposed to the widely acclaimed hypothesis of a single vortex for low angles of attack.

The U.S. Federal Highway Administration (FHA) method for computing bridge backwater was modified on the basis of significantly large prototype data (Neely 1966; Bradley 1978). Both the water surface profile and the backwater amount given by the original FHA method, which was developed after extensive laboratory model studies, differed appreciably from those recorded on natural reaches around highway bridges. Although a satisfactory explanation for this discrepancy was not given, most of the design charts of the FHA method were modified according to the prototype data (Bradley 1978). Here, a clear-cut explanation is given, and a modification for the bridge subroutine of the commonly used package program HEC-2 is suggested.

An experiment was conducted to examine the maximum penetration of a dense jet issuing vertically from a round source. This flow simulates the discharge of brine solution from desalination plants and other industrial discharges into the ocean. The experiment was designed to reveal the effect of the source mass flux. The behavior of a turbulent buoyant jet from an ideal point source in a calm and homogeneous environment is controlled by two source parameters, namely the momentum flux, M_o, and the buoyancy flux, B_o. For this limiting case, the maximum vertical penetration of a dense jet, Z_m, normalized by a length scale, L_m, which is proportional to ${\mathit{M}}_{\mathit{o}}^{3/4}{\mathit{B}}_{\mathit{o}}^{-1/2}\text{,}$ must be constant. In agreement with previous investigations, the results of this experiment showed that Z_m/L_m is constant for large densimetric Froude number jets (F> 7.0), confirming that in this regime the source mass flux has a negligible effect on maximum jet penetration. The experiment also showed that Z_m/L_m was always less than the asymptotic point source solution for small densimetric Froude number jets (F< 7.0) due to the effect of source mass flux.

On the basis of traditional particle-in-cell methods, a particle model has been developed to simulate flow over large areas. Under the assumption that the fluid medium is an assembly of many small, independent fluid particles, the momentum equation for a particle is derived for shallow-flow conditions. In the formulation used, only two forces are involved. One is the hydrostatic force arising from the accumulation of different numbers of particles at different locations. The other is a friction force that varies inversely with flow depth and quadratically with particle velocity and bed roughness. The velocity and spatial positions of all particles are averaged at fixed grid points to obtain the overall flow behavior. The particle model is demonstrated through an application to a documented 1954 flood in the Jingjiang River flood diversion area in Hubei, China. The flood lasted 300 h, with the total discharge volume being 4 billion m³. Good agreement between computed and observed water levels was obtained. Convergence of the method is demonstrated by repeatedly doubling the number of particles employed in the computation until there is little change between simulations.