Journal of Hydraulic Engineering

The predictions from a numerical sediment transport model inevitably include uncertainty because of assumptions in the model’s mathematical structure, the values of parameters, and various other sources. In this paper, the writers aim to develop a method that quantifies the degree to which parameter values are constrained by calibration data and the impacts of the remaining parameter uncertainty on model forecasts. The method uses a new multiobjective version of generalized likelihood uncertainty estimation. The likelihoods of parameter values are assessed using a function that weights different output variables on the basis of their first-order global sensitivities, which are obtained from the Fourier amplitude sensitivity test. The method is applied to Sedimentation and River Hydraulics—One Dimension (SRH-1D) models of two flume experiments: an erosional case and a depositional case. Overall, the results suggest that the sensitivities of the model outputs to the parameters can be rather different for erosional and depositional cases and that the outputs in the depositional case can be sensitive to more parameters. The results also suggest that the form of the likelihood function can have a significant impact on the assessment of parameter uncertainty and its implications for the uncertainty of model forecasts.

The standard circular-crested weir is often found in engineering applications and is used as a discharge measurement device or as an overflow structure. This research determines the discharge coefficients for ten circular-crested weir configurations with various combinations of up- and downstream angles. Two different weir heights and four different overflow depths are considered for each weir shape. For free overflow, the discharge coefficient is determined experimentally by using the total head of the approach flow. The results indicate that the upstream weir face angle has only a small effect on the discharge coefficient. In contrast, increasing the downstream weir face angle increases the discharge coefficient notably. A new formula for the discharge coefficient is presented, including both the up- and downstream weir face angles. Further, the hydraulic performance of the circular-crested weir, the resulting discharge reduction from tailwater submergence, and transition flow are discussed.

Emergencies resulting in uncontrolled flow through spillway gates often lead to millions of dollars lost to repairs, lack of dam productivity, property damages, and risks to public health and safety. A considerable need exists for reliable emergency dewatering systems to prevent these consequences. Stop logs are the most commonly used dewatering system for spillway gates but are typically designed for maintenance purposes only. They have been found in most cases to be unreliable for emergency closure under flowing conditions. Considering the economic advantages a dewatering system would provide were it functional for the dual purposes of maintenance as well as emergency closure, a new stop log design was developed. This study assesses the design that enables deployment under no-flow conditions as well as flowing, or emergency conditions. The information found in this study provides dam owners, operators, and engineers with options to reduce damages resulting from uncontrolled releases owing to partial or complete failure of spillway gates, including the failure of gates to close after having been raised.

A B-jump is defined as the jump having the toe section located on a positively sloping upstream channel and the roller end on a downstream horizontal channel. This jump often occurs in the stilling basins with a horizontal bottom and located downstream of a steep channel. For a B-jump, a completely theoretical approach is not sufficient to solve the momentum equation and to establish the sequent depth ratio. In this paper, by using the laboratory measurements carried out in this investigation, some available empirical relationships useful for estimating the sequent depth ratio are tested. Then, by using the $\Pi$ theorem of the dimensional analysis and the incomplete self-similarity theory, a generalized functional relationship for estimating the sequent depth ratio for different types of jumps is deduced. The estimate of the coefficient appearing in this relationship is dependent on the particular type of jump. In conclusion, the analysis established that the sequent depth ratio for a B-jump depends on a parameter $E$ accounting for the toe section position, the upstream Froude number ${\mathsf{F}}_1$, and the channel slope.

Thermal stratification is a common phenomenon in deep lakes and reservoirs, which often results in water-quality deterioration, including such problems as hypolimnetic anoxia, the release of pollutants from sediments, and algal blooms. Hypolimnetic oxygenation and destratification are the two commonly used methods for resolving these water-quality problems. A new water-quality improvement device, the water-circulating aerator, was designed to destratify lakes and reservoirs, by circulation and oxygenation of upper and lower layers of water. The design of the structure of the water-circulating aerator is detailed. Three mathematical models were built to optimize this structure, estimate the rate of water flow in the aerator, and calculate the rate of oxygen transfer from air bubbles to water in the aerator. These models were verified by experiments. The water-circulating aerator system has been successfully applied in a stratified reservoir to increase dissolved oxygen to reduce the releasing of ammonia-nitrogen from sediments under anoxic conditions.

The propagation of pressure waves in two-component bubbly flow was analytically and experimentally investigated. An analysis is presented that accounts for the effects attributable to liquid compressibility, pipe elasticity, and temperature rise across pressure waves. Analytical results indicate that the effects of liquid compressibility and pipe wall elasticity are important at low gas content, although the effect of temperature change is generally negligible. Pressure waves were generated in the laboratory by rapid closure of a valve at the downstream end of a horizontal pipe. The experimental results indicate that there were two major pressure surges generated by valve closure; the first was attributable to stoppage of the two-phase mixture at the valve, and the second attributable to the arrest of the liquid column at the upstream end of the mixing device. The transient flow model provides a satisfactory prediction of the initial pressure rise at the valve and the average velocity of the initial pressure waves.

The goal in the field of modeling of hydraulic transients is a comprehensive model for pipe networks that is computationally fast and accurate. The fastest models are the one-dimensional (1D) models that use instantaneous acceleration–based (IAB) properties, but unfortunately these models are not as accurate as the more demanding 1D convolution-based (CB) models or quasi two-dimensional models. Focusing on a single pipe, this paper investigates the fundamental behavior of the much more accurate 1D CB model to find two coefficients for use with the two-coefficient formulation of the much-used modified IAB (MIAB) model for complete closing of a downstream valve. Two coefficients are found based on the weighting function used in the CB model, and these coefficients vary along the pipe length. Simulations are compared with two experimental results from tests performed at University of Adelaide in Australia in 1995. The experimental results are for different initial Reynolds numbers of approximately 2,000 and 5,800. The results show very good agreement between simulations and experiments. The improvement of the MIAB model is not general, and for the time being, only complete closure of a downstream valve in a single pipeline at low Reynolds numbers has been investigated.

The widely used Todini and Pilati method for solving the equations that model water distribution systems was originally developed for pipes in which the head loss is modeled by the Hazen-Williams formula. The friction factors in this formula are independent of flow. Rossman’s popular program EPANET implements elements of the Todini and Pilati algorithm, but when the Darcy-Weisbach head-loss formula is used, it does not take into account the dependence of the friction factors on the Reynolds number, and therefore flow, in computing the Jacobian. We present the correct Jacobian matrix formulas, which must be used in order to fully account for the friction factor’s dependence on flow when the Todini and Pilati method is applied with the Darcy-Weisbach head-loss formula. With the correct Jacobian matrix the Todini and Pilati implementation of Newton’s method has its normally quadratic convergence restored. The new formulas are demonstrated with an illustrative example.

Vortex formation at intakes can cause damage, clogging, reduced flow efficiency, and even loss of life. For practical prediction of vortex risk, engineers often compare expected design parameters with published data by using parameter proximity to evaluate the relative risk of vortex formation. Unfortunately, this procedure is ill-defined, and the resulting risk estimates are highly subjective. In response, a formal equivalent of the data proximity procedure was developed by implementing the nearest neighbors algorithm on available experimental and field data. This database was partitioned and the machine learning parameters adjusted to obtain a stochastic model with maximum predictive accuracy. Unlike the flow parameters and submergence, the approach geometry was not found to be a significant factor in the model, although this may be attributable to data noise and range of tested values. The final model, which excluded the channel approach geometry, fit all vertical intake vortex formation data to within 0.1% error and perfectly fit the horizontal intake data. Probability charts generated from the model show regions of vortex formation and problems more numerous and larger on average than regions of low vortex probability, thus validating consideration of potential vortex formation risk for conservative intake design.

A preliminary study on submerged jumps with baffle walls and blocks downstream of a sluice gate was conducted. Two series of experiments were carried out on baffle walls and baffle blocks. The momentum equation was utilized to derive a relation for the drag coefficient that was validated by the experimental data of the baffle wall series. The baffle block series consisted of five Froude numbers and a range of submergence factors with one configuration of baffle blocks. The inlet depth factor was found to be a function of the submergence and Froude number. It was observed that the energy dissipation efficiency was a function of submergence with the maximum efficiency being in excess of that of the corresponding free jump.