Journal of Hydraulic Engineering

A mathematical model for the numerical simulation of a submerged buoyant round jet in a stably stratified flowing water body was developed in the present study. The model solved, in a local reference frame, the equations of conservation of mass flux, momentum flux, heat flux, and salinity flux. The model was validated by comparing numerical and experimental results available in the scientific literature. The mathematical model was then used to analyze the behavior of submerged buoyant jets in various flow conditions under stable or neutral stratification. The combined effects of the ambient velocity and of the ambient stratification on the jet behavior are analyzed and discussed. The present approach may offer a useful tool for the engineering solution of a wide class of environmental and industrial problems.

Based upon the results of a series of 47 bed‐development experiments, the evolution of bed features subsequent to their initial generation from flat bed conditions is examined. For each such experiment, bed profiles were measured at frequent time intervals as sand‐wave configurations developed under the action of open‐channel water flow. The two sediments used for these experiments were of geometric mean size 0.20 mm and 0.82 mm, respectively. In line with the bed‐form unification model of bed development postulated by Saudkivi and Witte in 1990, the principle of bed‐form propagation speed decreasing with increasing bed‐form height and the mechanisms of bed‐form coalescence and bed‐form throughpassing are all found to be central to bed evolution processes. A quantitative relation between bed‐form speed and bed‐form height is presented. Bed‐development predictions based upon bed‐form unification models can be seen to clearly parallel the present experimental results. Stability analyses based upon potential flow theory, while not adequately describing the mechanics of bed‐form development, nevertheless correctly predict the periods of accelerated growth recorded for the present experiments.

A model has been developed to simulate the suspended transport of fine‐grained sediment, both cohesive and noncohesive, in the Pawtuxet River, Rhode Island. The model utilizes the results of extensive laboratory and field studies to specify the parameters governing deposition and resuspension processes. The SEDZL modeling framework, which accurately and realistically simulates cohesive resuspension and deposition, including the effects of flocculation, has been modified to include the simulation of noncohesive suspended transport. Several field studies were conducted during the spring of 1992 to collect bathymetric, stage‐height, suspended‐solids, and sediment‐bed data. The hydrodynamic and sediment transport models were calibrated and validated during a 33‐day period, which included two high‐flow events, each of which approximately correspond to the annual flood. The successful calibration exercise indicates that the model can be confidently used as a predictive tool.

The effect on turbulence of adding coarse sand, carried as bed load, in flows of water and clay suspensions was studied. The results showed that the mean velocity of the flows carrying bed load was smaller and the turbulence intensity was greater than those in the flows without bed load. The presence of bed load resulted in higher Reynolds stress and larger velocity gradient, and thus greatly enhanced the energy transmitted from the mean motion to turbulence. In flows of clay suspension, turbulence developed in the lower flow with quite high turbulence intensity, while laminar flow occurred in the upper flow. However, with bed load the entire flow became turbulent. The position of maximum turbulence intensity was more distant from the bed. The average turbulence intensity increased with rate of bed‐load transport. The spectrum of turbulent energy shifted to higher frequencies in bed‐load‐carrying flows.

A calculation procedure for the analysis of flow near a change in a slope from mild to steep in a wide rectangular channel is presented and evaluated. It is assumed that the viscous effects are negligible and that flow is irrotational. The potential‐flow solution used here is of the inverse type, in which the real $x‐y$ plane is mapped on a rectangular strip in an auxiliary plane where the governing potential‐flow equations are solved numerically and the unknown free‐surface location is determined by an iterative procedure. This method is applied to two especially demanding cases of very steep transitions beyond the range of previous Boussinesq equation methods. The predictions are compared with laboratory measurements and the agreement is found to be good.

An analytical solution of the nonlinear storage routing equation is presented. The solution is applicable for the particular case of a constant‐area reservoir and a culvert outlet. It allows for arbitrary inflow hydrographs, which can be approximated by a series of linear segments. The resulting solution is an implicit expression relating the outflow or storage with time. Explicit algebraic equations for the maximum storage and outflow in terms of the reservoir and inflow parameters have also been obtained. The analytical results have been applied to a specific inflow hydrograph to formulate simple design equations for a circular culvert outlet and a constant‐area reservoir which compared well with similar published equations.

The hydraulic jump occuring close to a gate‐type structure is analyzed both by theoretical and experimental means. The transition phenomenon between a classical‐hydraulic jump and the supercritical sluice gate underflow may be modeled with the jump‐position parameter. This ratio $\lambda$ is equal to the distance between the toe of jump and the gate, and the roller length of a classical jump. For $\lambda >2$, the hydraulic jump is almost classical, whereas blowout of the jump occurs for $\lambda >1$. Typical‐impact jumps are found for $\lambda =1.2$. For impact jumps, the average tailwater depth is always smaller than the sequent depth. However, significant tailwater oscillations, eventually under resonance conditions, are set up, which increase as $\lambda$ decreases. The mechanisms of both resonance and blowout are explained, and frequency is also correlated to $\lambda$ and found to decrease with increasing $\lambda$. Finally, a relation between the relative‐gate opening and the approach Froude number is introduced for which incipient blowout was noted.

A simple surface wave develops, for example, after a dam break in a reservoir, or when water is suddenly withdrawn from one end of a long open channel. The present contribution is on simple internal waves, which can develop at the thermocline of a stratified reservoir when a sudden change of the inflow rate occurs due to man‐made or natural causes. Use is made of the fact that the interface along a simple wave advances with the local long‐wave speed, and of flow continuity. General analytical solutions for the velocity difference between the upper and lower layers along simple waves, and for their shape, are derived for Boussinesq flows. Also, the conditions are outlined under which a simple wave becomes unstable, and an internal bore develops. An example is provided for the shape and extent of a simple wave, which is due to a sudden dense inflow into a stratified reservoir. Such a wave is stable.

A method for selecting a sediment‐transport formula for mathematical modeling of a specific gravel stream is described and illustrated with an example. This method is based on the measured changes in stream morphology instead of site‐specific gravel transport data. In the approach, several transport formulas are tested based on their applicabilities in simulating stream‐channel changes. It is the working hypothesis that a sediment formula suitable for mathematical application should generate stream‐channel changes that can be substantiated by measurements. For Stony Creek in California, the Meyer‐Peter Muller, Yang, Parker, and Engelund‐Hanson formulas were tested separately. Sediment deliveries obtained using the Yang and Parker formulas are more or less similar. Simulated erosional and depositional changes are also similar and compare favorably with the measurements. The Meyer‐Peter Müller formula predicted lower transport rates while the Engelund‐Hanson formula produced higher transport rates. On the basis of the tests, the Yang formula and Parker formula were selected for Stony Creek applications.

Streambed and water‐surface configurations depend on flow characteristics, fluid characteristics, and sediment characteristics. These streambed and water‐surface configurations are called classes (regimes) of flow. The classes of flow have significant influence on velocity distribution, resistance to flow, rate of sediment transport, and stage discharge relationship. At present several categories of flow classes have been introduced. The most general categorization of flow classes is that of Vanoni, who in 1975 identified eight flow classes. In all the studies done so far it has been observed that there is a significant overlap between the adjoining flow classes. The demarcations between the various flow classes have been drawn by judgment; thus the separation of the various flow classes is subjective. In the present study, flow classes have been demarcated by using dimensionless parameters similar to those used with the Shields criterion of incipient motion. In so doing, a demarcation parameter was developed to demarcate various flow classes for sand‐bed alluvial channels.