Journal of Hydraulic Engineering

The continuous discharge of coalbed natural gas-produced (CBNG-produced) water within ephemeral, cohesive channels in the Powder River Basin (PRB) of Wyoming can result in significant erosion. A study was completed to investigate channel stability in an attempt to correlate cohesive soil properties to critical shear stress. An in situ jet device was used to determine critical shear stress $\left({\tau }_c\right)$ and erodibility $\left(k_d\right)$ ; cohesive soil properties were determined following ASTM procedures for 25 reaches. The study sites were comprised of erodible to moderately resistant clays with ${\tau }_c$ ranging from $0.11\text{to}15.35\mathrm{Pa}$ and $k_d$ ranging from $0.27\text{to}2.38{\mathrm{cm}}^3∕\mathrm{N}\cdot \mathrm{s}$ . A relationship between five cohesive soil characteristics and ${\tau }_c$ was developed and presented for use in deriving ${\tau }_c$ for similar sites. Allowable discharges for CBNG-produced water were also derived using ${\tau }_c$ and the tractive force method. An increase in the allowable discharge was found for channels in which vegetation was maintained. The information from this case study is critical to the development of a conservative methodology to establish allowable discharges while minimizing flow-induced instability.

This paper proposes a dam-breach model which predicts, in a simple but physically based manner, not only the peak discharge but the whole outflow hydrograph and breach development. The following aspects are taken into account: the geometry of the embankment, the shape of the reservoir, the hydraulic characteristics of the flow through the breach and its erosive capacity, and the shape of the breach. The model needs only one calibration parameter and can be easily applied to real cases. The application of the model with a single value of the calibration parameter produced excellent results in the simulation of 12 historic earthfill dam failures, with a discharge range covering three orders of magnitude.

A sensitivity analysis of the model presented in the companion paper is made and, on the basis of the results a criterion is proposed for the choice of values to assign to the side slopes of the breach, in order to use the model for prediction. Moreover, the sensitivity analysis shows that the outflow hydrograph and its peak value depend not only on the dam height and the stored volume, but also on the vertical distribution of the water mass in the reservoir. The model is compared with some previously published methods and the disadvantages, limitations, and errors that can be made using parametric models and predictive equations are pointed out. Finally, easy to use equations interpolating the numerical results of the model are provided that predict not only the peak discharge but the whole outflow hydrograph for overtopping failures.

Potential flood hazards that would be created by breached embankment dams need to be evaluated to select spillway design floods and to prepare emergency action plans. The breaches are often modeled simply, usually in the shape of a trapezoid that is defined by its final height, base width or average width, and side slopes, along with the time needed for the opening to form completely. Data collected from 74 embankment dam failures were used to develop mathematical expressions for the expected values of the final width and side slope of a trapezoidal breach along with its formation time. Information is provided that allows variances of the predicted quantities to be calculated as well. The findings of the statistical analysis were then applied in a Monte Carlo simulation to estimate the degree of uncertainty of predicted peak flows and water levels downstream from breached embankment dams.

Experiments were carried out to investigate the behavior of horizontal gas–liquid injection in a water tank. Measurements of bubble properties and mean liquid flow structure were obtained. The turbulence in the liquid phase appears to help generating bubbles with relatively uniform diameters of $1–4\mathrm{mm}$ . Both bubble properties and mean liquid flow structure depended on the gas volume fraction and the densimetric Froude number at the nozzle exit. It was found that the bubbles strongly affected the trajectory of the water jet, which behaved similarly to single-phase buoyant jets. However, at gas volume fractions smaller than about 0.15, the water jet completely separated from the bubble core. Bubble slip velocity was also found to be higher than the terminal velocity for isolated bubbles reported in the literature. Dimensionless correlations were proposed to describe bubble characteristics and the trajectory of the bubble plumes and water jets as a function of the gas volume fraction and the densimetric Froude number. Finally, applications of the results for aeration/mixing purposes are presented.

This paper presents a stochastic approach to describe input uncertainties and their propagation through the nonlinear shallow-water equations. The formulation builds on a finite-volume model with a Godunov-type scheme for its shock capturing capabilities. Orthogonal polynomials from the Askey scheme provide expansion of the variables in terms of a finite number of modes from which the mean and higher-order moments of the distribution can be derived. The orthogonal property of the polynomials allows the use of a Galerkin projection to derive separate equations for the individual modes. Implementation of the polynomial chaos expansion and its nonintrusive counterpart determines the modal contributions from the resulting system of equations. Examples of long-wave transformation over a submerged hump illustrate the stochastic approach with uncertainties represented by Gaussian distribution. Additional results demonstrate the applicability of the approach with other distributions as well. The stochastic solution agrees well with the results from the Monte Carlo method, but at a small fraction of its computing cost.

The direct numerical simulation of turbulent flows in a compound open channel is described. Mean flows and turbulence structures are provided, and are compared with numerical and measured data available in the literature. The simulated results show that twin vortices are generated near the interface of the main channel and the floodplain and that their maximum magnitude is about 5% of the bulk streamwise velocity. Near the interface, the simulated wall shear stress reaches a maximum, contrary to experimental data. A quadrant analysis shows that both sweeps and ejections become the main contributor to the production of Reynolds shear stresses near the interface. Through the conditional quadrant analysis, it is demonstrated how the directional tendency of dominant coherent structures determines the production of Reynolds shear stress and the pattern of twin vortices near the interface. In addition, the time-dependent characteristics of three-dimensional vortical structures in a compound open-channel flow were investigated using direct numerical simulation (DNS) data.

The middle reach of the Yangtze River, customarily called the Jingjiang River, together with its diversion channels and Dongting Lake, form a large complicated drainage system. In the last five decades, significant geomorphological changes have occurred in the drainage system, including the shrinkage of diversion channels, contraction of Dongting Lake, changes in the rating curve at the Luoshan station, and cutoffs of the lower Jingjiang River. These changes are believed to be the cause of the occurrence of abnormal floods in the Jingjiang River. Qualitative analyses suggest that the first three factors aggravate the flood situation in the lower Jingjiang River, while the last factor seems beneficial for flood prevention. To quantitatively evaluate these conclusions, a finite-volume numerical model was constructed. A series of numerical simulations were carried out to test the individual and combined effects of the aforementioned four factors, and these simulations showed that high flood stages in the Jingjiang River clearly are related to the geomorphological changes.

Results of two laboratory experiments on the cohesive sediment deposition behavior are presented. Data indicate that an annular flume, either with or without the channel bed and the top ring rotating in opposite directions to minimize the secondary circulation, can be used to study the deposition behavior of cohesive sediments. Direct observations on when and where the bed is formed suggest that deposition only occurs when the local bed-shear stress $\left({\tau }_b\right)$ is less than a critical value. Secondary circulation in the flume, which produced upward current near the inner corner and downward current near the outer corner, did not prevent deposition near the inner corner (because of the small ${\tau }_b$ ) nor promote deposition near the outer corner (because of the relatively large ${\tau }_b$ ).

Experiments have been performed to assess the efficiency of mechanical mixers in destratifying water bodies. The effects of Reynolds number, physical scale, and Richardson number were all considered. The results demonstrated that the variation of mixing efficiency with Richardson number was well described by two different power-law regimes. At low Richardson numbers, the efficiency increased with increasing Richardson number. Above a critical value, however, the efficiency decreased rapidly with further increases in Richardson number. The experiments further showed that, over the range of Reynolds numbers considered, the results collapsed fairly well. Finally, experiments at different physical scales showed reasonable agreement. The main conclusion of the present technical note is that the destratification efficiency of mechanical mixers can be well parameterized by an overall Richardson number. The results, however, are specific to the particular geometric configuration studied. It is hoped that the present technical note will help to guide future studies of destratification systems in small lakes and reservoirs and fluid mixing in the chemical and process industries.