Journal of Hydraulic Engineering

A brief discussion is presented of the lasting effects of some of thefluid mechanics contributions of Dr. Hunter Rouse on the design of hydraulic structures including an early study at the Massachusetts Institute of Technology on theshape of overfall spillway crests. A description is given of the solution to a designproblem with two hydraulic‐jump type energy dissipaters as well as the design ofa three‐conduit service spillway in Indonesia. The design of a 6.8‐km‐long powercanal for the same project is discussed including the effects of 10 yr of aging onthe absolute roughness of the concrete lining. Roll waves are described that occurred in the transport of slurry with a 43% concentration in steep flumes. Lastly, the investigation of a resonant condition in a high‐pressure conduit is described;the source of the pressure fluctuation that resulted in damaging vibrations was amotor‐driven flow‐control valve having a labyrinth‐type plug.

Nonlinear multiple‐regression analysis is used to derive relations among the velocity, sediment discharge, bed‐form geometry, and friction factor of alluvial rivers. A data base comprising 339 river flows and 608 flume flows is used in the analysis. A hierarchy of formulations involving progressively more interdependencies among velocity, depth, sediment discharge, and bed‐form geometry is developed. Procedures for computing velocity‐ and sediment‐rating curves are presented. A simplified procedure for preparing depth‐discharge relations for streams with strongly, discontinuous rating curves is also presented. Rating curves for four rivers, and computed depths and velocities for two others, are presented. The accuracies of the different methods are evaluated in terms of the mean normalized errors of predicted friction factors, depths, velocities, and sediment discharges. It is concluded that these formulations yield velocity‐ and sediment‐rating curves that are as reliable as is permitted by the accuracy of the available data, which is limited by, among other things, the inherent short‐term temporal variability of stream‐flow properties.

The St. Venant equations form the basis of many one‐dimensional river models. The Preissmann box scheme is often used to generate approximate solutions, chiefly because the modeler has considerable flexibility in the choice of space and time steps. This paper contains a comprehensive Fourier stability analysis of the Preissmann scheme applied to the St. Venant equations, including the general form of the friction term. Previous analyses have either neglected or simplified the form of the flow resistance. No such approximations are made in this paper. It shows analytically that the linearized, numerical equations are stable when weighted towards the new time level and when the magnitude of the Vedernikov number is less than one. This second condition is the limit of hydrodynamic stability at which roll waves form and the numerical scheme mirrors this physical stability limit. Difficulties that occur in practical applications of this computational method must have their origin in factors omitted from the Fourier analysis, such as the treatment of boundary conditions and the nonlinear terms in the flow equations.

MacCormack and Gabutti explicit finite‐difference schemes are introduced to integrate the equations describing two‐dimensional, unsteady gradually varied flows. Both schemes are second‐order accurate in space and time, allow sharp discontinuous initial conditions, and do not require isolation of the bores. Both sub‐ and supercritical flows may be present simultaneously in different parts of the channel or in a sequence in time. The inclusion of boundaries and stability conditions and the addition of artificial viscosity to smooth high‐frequency oscillations are discussed. To illustrate application of the schemes in hydraulic engineering, two typical problems are solved and the results of different schemes are compared.

Inclusion of historical information in flood‐frequency analysis increases the accuracy of flood estimates; however, some of the major factors affecting this accuracy are the a‐priori specification of a particular probability distribution function and the method of estimating its parameters. In this study, a new nonparametric procedure is proposed that altogether eliminates the specification of a distribution and greatly simplifies parameter‐estimation problems. The nonparametric method, however, is not particularly efficient in extrapolating distribution function beyond an available record length. Thus, to overcome such a problem, a new kernal is introduced in the form of an extreme‐value distribution. Also, the smoothing parameter is estimated by a cross‐validation procedure, and a new mixture‐distribution model is proposed for inclusion of historical data into analysis. A simulation study employing a two‐parameter log‐normal distribution shows that the accuracy of flood estimates does not greatly increase with the addition of data length beyond 10 years. The present paper shows that inclusion of historical information into nonparametric analysis improves extrapolation.

The inlet of vortex drops for supercritical approaching flow is discussed. Based on detailed experimental observations collected at various inlet geometries, the shape of vortex inlet was optimized. The geometry recommended is of spiral shape, and depends mainly on the shaft radius and on the width of the approaching channel. Particular features of the inlet are its wide domain of application regarding the Froude number and bottom slope of the approaching channel, and zero transverse inlet slope. The discharge capacities of vortex drops are shown to be of the same order for both sub‐ and supercritical approach flows. Further, the surface profile along the outer guiding wall is analyzed. It is found that both the Froude number of the approach flow and the radius of outer inlet wall influence significantly the maximum height of standing wave. A nondimensional surface profile along the outer wall is given, and prominent flow features in drop inlet structures are discussed.