Journal of Hydraulic Engineering

This paper, written to mark ASCE’s 150th anniversary, traces the role of hydraulic engineering from early or mid-twentieth-century to the beginning of the twenty-first century. A half-century ago hydraulic engineering was central in building the economies of the United States and many other countries by designing small and large water works. That process entailed a concentrated effort in research that ranged from the minute details of fluid flow to a general study of economics and ecology. Gradually over the last half-century, hydraulic engineering has evolved from a focus on large construction projects to now include the role of conservation and preservation. Although the hydraulic engineer has traditionally had to interface with other disciplines, that aspect of the profession has taken on a new urgency and, fortunately, is supported by exciting new technological developments. He/she must acquire new skills, in addition to retaining and improving the traditional skills, and form close partnerships with such fields as ecology, economics, social science, and humanities.

In 1965, Rouse critically reviewed hydraulic resistance in open channels on the basis of fluid mechanics. He pointed out the effects of cross-sectional shape, boundary nonuniformity, and flow unsteadiness, in addition to viscosity and wall roughness that are commonly considered. This paper extends that study by discussing the differences between momentum and energy resistances, between point, cross-sectional and reach resistance coefficients, as well as compound/composite channel resistance. Certain resistance phenomena can be explained with the inner and outer laws of boundary layer theory. The issue of linear-separation approach versus nonlinear approach to alluvial channel resistances also is discussed. This review indicates the need for extensive further research on the subject.

Grass is a cost-effective form of erosion control. Since grass prevents erosion, the relationship between grass properties and erosion rate in grassed open channels is highlighted and analyzed within the context of channel stability. The deformation of grass caused by the flow’s momentum has been taken into consideration. Results are in good agreement with the available experimental erosion rate data for grassed channels. The purpose of this paper is to show that the amount of deformation of a grass channel lining due to flow can be used to estimate the erosion rate, and, as a result, lining deformation can be used as an indicator of channel stability. The method is simple enough to be useful for design.

A new approach to estimate flood discharges in complex river geometries is presented. Discharges are determined through the combination of nonintrusive measurements of surface velocities and water levels with a Navier–Stokes solver and an inverse optimization algorithm. The numerical model is based on a finite-element solution of the two-dimensional Reynolds-averaged Navier–Stokes equations with a $k-\epsilon$ turbulence model, allowing for computation of the free water surface on adaptive, unstructured grids. The inverse modeling technique uses the Levenberg–Marquardt minimizing algorithm. In order to rule out uncertainties from the numerical model and to strictly quantify the effect of measuring errors, measurements are generated synthetically through forward computations. The methodology is illustrated for the gaging station of the Saltina River at Brig, Switzerland, which involves a complex bed geometry and where laboratory measurements for transcritical flows were available. For perfect measurements the discharge can in principle be estimated to an accuracy of ≈2%, independently of the number of measurements. Measurement errors in the water level have a small influence on the estimated discharge, whereas errors in velocity lead to a major discharge error. This error can be minimized by increasing the number of measurement points and choosing appropriate measurement positions.

Dense underflows developing two dimensionally on a slope are simulated numerically. The $k-\epsilon$ model is used for the turbulence closure. The boundary-layer approximation renders the governing equations in the form of parabolic partial differential equations, which are easier to solve numerically than elliptic equations. Evolution of vertical structures of dense underflows is computed along the streamwise direction. Excellent similarity collapses of the computed vertical structures are obtained. The computed profiles of velocity and concentration are compared with measured data, resulting in good agreement. The impact of a parameter representing the stratification level in the $k-\epsilon$ model is investigated. Appropriate values of this parameter, yielding results that are nearly identical to the integral model, are proposed. Water entrainment coefficients are estimated from computed solutions, and are observed to fall within the range of previous measurements. Finally, by using the collapsed vertical structures, profile constants defined in the integral model are calculated, which assures that the top-hat assumption necessary for deriving the integral model is valid.

The diversion of fresh water from estuaries for agricultural and municipal uses leads to an upstream shift in the brackish water zone that can disrupt ecosystems and deteriorate water quality at downstream points. Models are routinely used to predict hydrodynamic and water quality conditions in estuaries, and presented here is a modeling approach that ultimately could prove helpful in designing strategies to divert fresh water while mitigating changes in salinity further downstream. An optimization problem is formulated whereby a least-squares function of the salinity distribution predicted by the model is minimized by optimizing a parameter vector describing the diversion rate as a function of time. The optimization method is shown to rapidly identify diversion schedules in a range of test systems. Optimization is performed by a quasi-Newton method that utilizes a Broyden–Fletcher–Goldfarb–Shanno update, and an adjoint sensitivity method is formulated and applied to evaluate the gradient of the objective function with respect to the parameter vector. The sensitivity of salinity levels to diversion rates is predicted to have both intratidal and intertidal variability, giving insight into the potential for diversions at any given time and any location along an estuary to have either a rapid or longer-term effect on the salinity distribution. The controllability of salinity levels by fresh-water diversions is directly related to these sensitivities.

An efficient hybrid finite-difference scheme capable of solving the dispersion equation with general Peclet conditions is proposed. In other words, the scheme can simultaneously deal with pure advection, pure diffusion, and/or dispersion. The proposed scheme linearly combines the Crank–Nicholson second-order central difference scheme and the Crank–Nicholson Galerkin finite-element method with linear basis functions. Using the method of fractional steps, the proposed scheme can be extended straightforwardly from one-dimensional to multidimensional problems without much difficulty. It is found that the proposed scheme produces the best results, in terms of numerical damping and oscillation, among several non-split-operator schemes. In addition, the accuracy of the proposed scheme is comparable with a well-known and accurate split-operator approach in which the Holly–Preissmann scheme is used to solve the pure advection process while the Crank–Nicholson second-order central difference scheme is applied to the pure diffusion process. Since the proposed scheme is a non-split-operator approach, it does not compute the two processes separately. Therefore, it is simpler and more efficient than the split-operator approach.

Significant mass balance “errors” have been reported with finite-element techniques, leading to sweeping statements that “Finite elements do not conserve mass locally.” These reports of mass balance “error” emerge when mass flux estimates are based upon post-processing of the approximated solution variables. Fluxes computed in this way appear to be nonphysical. For example, even under steady-state conditions, the flux entering and leaving a closed region may appear unequal. This has serious consequences for a typical model application that might require the estimation of flow division in a branching stream, or details about the effects of sources or sinks. In this paper, we show that by remaining consistent with the discrete approximation given by the finite-element statement, the resulting flux estimates will preserve mass balance. As a consequence, it can be shown that general finite-element approaches for hydraulic engineering do, indeed, conserve mass locally, as well as globally. These locally conservative, “consistent” flux estimates are computed for time-dependent mass conservation in one and three dimensions.

An analysis of the hydraulic behavior of pipe networks often involves imprecise or uncertain quantities. Typical examples of these quantities are the roughness coefficient of old pipes, which becomes increasingly difficult to determine as the network ages, and the demands of the network, which can vary significantly according to the number of users connected to the network. These are quantities for which there is often only semiquantitative information which generally implies a degree of subjectiveness and that cannot therefore be expressed either with precise values or through statistical distributions. In this article we show how the fuzzy set theory provides conceptual tools for one to deal with this kind of information and to calculate how the uncertainties of the available information can spread to the unknowns of the problem, that is, to the discharges and piezometric heads. After a brief review of the fuzzy set theory, the way the hydraulic problem can be described within a fuzzy approach framework is given. Following this review, a suitable method, based on interval algebra and optimization theory, is introduced to solve the corresponding fuzzy equations and it is illustrated through examples.

An accurate, simple, and efficient approximation to the Vardy–Brown unsteady friction equation is derived and shown to be easily implemented within a one-dimensional characteristics solution for unsteady pipe flow. For comparison, the exact Vardy–Brown unsteady friction equation is used to model shear stresses in transient turbulent pipe flows and the resulting waterhammer equations are solved by the method of characteristics. The approximate Vardy–Brown model is more computationally efficient (i.e., requires one-sixth the execution time and much less memory storage) than the exact Vardy–Brown model. Both models are compared with measured data from different research groups and with numerical data produced by a two-dimensional turbulence waterhammer model. The results show that the exact Vardy–Brown model and the approximate Vardy–Brown model are in good agreement with both laboratory and numerical experiments over a wide range of Reynolds number and wave frequencies. The proposed approximate model only requires the storage of flow variables from a single time step while the exact Vardy–Brown model requires the storage of flow variables at all previous time steps and the two-dimensional model requires the storage of flow variables at all radial nodes.

This paper presents a simple graphical technique for studying the hydraulics of two-layer inviscid flows with a hydrostatic pressure distribution. A control curve, which relates the internal energy with the flow rate, is developed for each internal hydraulic control. A plot of control curves is used to study two-layer exchange flows. The control curve approach provides a direct and graphical solution to the flow. In particular the approach provides insight into how a two-layer flow is controlled by its channel geometry.

A new method for detecting spikes in acoustic Doppler velocimeter data sequences is suggested. The method combines three concepts: (1) that differentiation enhances the high frequency portion of a signal, (2) that the expected maximum of a random series is given by the Universal threshold, and (3) that good data cluster in a dense cloud in phase space or Poincaré maps. These concepts are used to construct an ellipsoid in three-dimensional phase space, then points lying outside the ellipsoid are designated as spikes. The new method is shown to have superior performance to various other methods and it has the added advantage that it requires no parameters. Several methods for replacing sequences of spurious data are presented. A polynomial fitted to good data on either side of the spike event, then interpolated across the event, is preferred by the authors.

The writers would like to thank the discussers who, with their very precise and pertinent observations, will enable the writers to better define certain aspects of the methodology proposed in their paper.