Journal of Hydraulic Engineering

A method, based on a rigid water column model, for analyzing slow transients in pipe networks is graph‐theoretically formulated using incidence matrices. The formulation is made to facilitate its implementation on digital computers, thus leading to a more refined analysis of slowly changing transient conditions occurring in complicated pipelines. This approach is more advantageous than the loop method for slow transients, particularly with respect to analyzing problems occurring when valves are shut off. The paper presents a derivation of appropriate ordinary differential equations (ODEs) of the first order, numerical methods of integrating stiff ODEs, and a technique for correcting discharges in pipes to conserve mass continuity. Numerical results obtained using rigid versus elastic water column models are compared.

Experimental results are presented which show that the onset of interfacial instability can be described by an empirical stability equation derived from interfacial mixing experiments. Also, new theoretical stability equations are derived using standard velocity distribution equations applied to the interfacial zone. These theoretical equations compare favorably with stability conditions predicted by the empirical equation, especially at high Reynolds numbers.

An analysis of numerical stability of a two‐dimensional depth‐averaged hydrodynamic model is made by examining the linearized finite difference governing equations based on Fourier analysis. The eigenvalues of the amplification matrix are solved by an iteration technique. They are used to check the derived theoretical stability criterion that has an exponential form. Two case studies are considered, one dealing with a small channel with a sidepool and the other dealing with the large shallow Songkhla Lagoon. The results obtained by the stability analysis and by running the hydrodynamic model are found to agree closely for the case of the small channel. From these results, an equivalent empirical stability criterion similar to the Courant condition is established for practical purposes.

The hydrodynamic characteristics of viscous flow through periodic arrays of cylinders are studied by different methods: (1) Nonintrusive laser Doppler anemometry (LDA) to measure local velocity distributions; and (2) numerical solutions of the Navier‐Stokes equations using both finite differences (FD) and finite elements (FE). The Reynolds number based on average distance between the cylinders and average fluid velocity ranges between 1 and 300. Streamlines, velocity, and pressure distributions are presented for various Reynolds numbers. The simulated velocity profiles obtained by the two numerical methods are compared and found to be in agreement with the LDA measurements. Applicability of the results to flow through porous media is discussed.

A revision is proposed in the formulation of the rational method and in the procedure of its application. Two misleading concepts are eliminated: that a watershed has a unique time of concentration equal to the time of flow along the watershed; and that a rainfall event of a given occurrence probability results in a runoff event of the same probability. Based upon laboratory results and field data, a method is proposed that links the peak discharge to the intensity and duration of the causative rainfall, with no explicit reference to a time of concentration. The relationship uses an envelope curve for variables derived from measurable data. Upon application of the relationship to a complete series of rainfalls, subtracting abstractions, a complete series of runoff peaks would be generated. This series is readily suitable for a statistical analysis, similar to that applied to a measured series, from which the design discharge is determined.

Excessive production of frazil ice in rivers may lead to the occurrence of ice jams and attendant flooding during winter. An often‐discussed means of minimizing frazil‐ice production, and thereby for mitigating frazil jams, is regulation of river flow in order to facilitate rapid ice‐cover formation. A numerical model of ice‐cover formation by frazil‐ice accumulation over stage‐regulated pools is exercised to assess the durations of flow‐discharge regulation that would be required for ice covers to form over river pools of diverse length, regulated downstream depth, and channel slope. The numerical model indicates that for a given navigation pool, there exists an optimum river discharge that corresponds to a minimum time required for an ice cover to form. Optimal discharge is a function of pool length, channel slope, and downstream flow depth, but is invariant with air temperature.

The paper describes a simplified method of designing an efficient side‐channel spillway, with particular reference to an L‐shaped weir. The method can be used with minor modifications for a straight weir or one U‐shaped in plan. The invert of the collecting trough slopes down from the crest of the end weir to the chute. The invert is designed to be as high as practicable so as to reduce construction costs. An additional benefit from this design method is that the spillway operates with little wave action. The usual momentum equation has been extended to include the downstream component of velocity of approach of lateral inflow. The spillway trough profile is designed directly by an iterative process which has been computerized. The design shape should be checked by hydraulic modeling, but, in the example given, was found to require very little alteration.

Debris flows cause the destruction of engineering facilities including buildings, roads, and culverts. A slit dam may be used to control small volumes of debris that can damage or destroy small watershed infrastructure, such as culverts. The height and spacing of the dam posts and the location of the dam are the primary design factors. The posts may be arranged in single or double rows with the spacing of the slits a function of the culvert diameter being protected. The height of the dam is a function of the slope on which it is placed. The advantages of slit dams include the simplicity of design and installation and the relatively low cost. They are also stronger than other baffle systems and debris fences.