Journal of Hydraulic Engineering

Bridge pier scour poses major concerns for public safety and riverine communities because of its ability to undermine pier foundations. A new collar design is introduced as an improvement on the existing Flat Plate Collar (FPC). Uniquely, the three-dimensional collar is specifically designed to contain the horseshoe vortex and guide it safely downstream, while protecting the riverbed around the pier base from the passing accelerated flow. Large shear stresses are thereby prevented from contacting the riverbed, and thus scour is considerably reduced. The collar design was achieved in an iterative hybrid manner through the use of OpenFOAM (CFD) software and by employing experimental tests. Collar designs were tested numerically and adjusted until an improved shape was reached. Then, a physical model of the new collar and an FPC were constructed and tested experimentally. The collar is demonstrated to reduce scour, more than that of an FPC; however further revisions are required for it to be an effective scour solution.

Presented are insights from three-dimensional numerical models used to identify optimal performance configurations of rock vanes and bendway weirs placed in midsize rivers, such as the Middle Reach of the Rio Grande. These transverse instream rock structures are used to control channel thalweg alignment and reduce flow velocity near the outer bank of river bends. The numerical models (validated and verified using a hydraulic model) showed rock vanes to be considerably more effective at reducing near-bank velocity than bendway weirs. Optimal-performance configurations of rock vanes were found be (1) planform angle (relative to adjacent upstream bank) of 45° to 85°; (2) structure spacing of $3/4$th of channel top width (bank full); and (3) structure projected length of $1/5$th to $1/3$rd of channel top width (bank full). Additionally, velocity at the tip of both rock vanes and bendway weirs more than doubled compared with the baseline velocity along the outer bank. The insights lead to a layout guideline, based on hydraulics considerations, for series of rock vanes and bendway weirs.

Effective modeling of pipe network anomalies can supplement fluid transient diagnostic techniques. This study focuses on comparing modeling approaches for predicting the transient response due to air pockets entrapped outside the main flow path (offline), in particular testing the assumption that the flow inside the cavity can be predicted based on a lumped element. This assumption has been consistently made in previous modeling investigations in the time and frequency domains. The results are compared to a system frequency response model without the lumped inertia assumption by quantifying timing and signal frequency distribution errors. It is found that removing the lumped inertia assumption improved the prediction of the reflected and transmitted pulse frequency distributions by averages of 50% and 30%–35%, respectively.

We developed an integral plume model to simulate the behavior of bubble plumes generated from line-source geometry in stratified ambient reservoirs by adapting the double-plume integral model developed for point-sources to a line plume. The model, based on top-hat velocity and buoyancy profiles, uses an Eulerian integral modeling approach and predicts the hydrodynamic, chemical, and thermodynamic behavior of the bubbles using a discrete bubble model. Existing integral models for line-source bubble plumes consider only the upward motion of bubbles and entrained water. To accurately predict intrusion formation, mixing patterns, and efficiency of bubble plumes in stratified environments, the downward flow of plume fluid from the maximum extent of plume rise to the trap height should also be included. To solve this problem, we presented a derivation of a continuously peeling double-plume model for line plumes and calibrated the model peeling factor to data for trap height in two stratified reservoirs. We applied the calibrated model to predict the gas transfer and vertical fluxes of oxygen from an oxygenation system in Carvins Cove reservoir and compared the predictions of the double-plume model to that using a standard single-plume model. We showed that the amount and the vertical distribution of entrainment into the plume differs in the double-plume model compared to the single-plume; hence, the type of model (double-plume or single-plume) would affect the results of simulations in coupled reservoir circulation models.

Rigorously derived shallow water equations (SWEs) are applied to results of large eddy simulation (LES) of a continuously fed gravity current in order to assess (1) sensitivity of current depth results to its definition; (2) coefficients in depth-averaged continuity and momentum equation due to the nonuniformity of density and velocity profiles; and (3) sensitivity of entrainment coefficient to definition of current depth. It is shown that using different definitions of the current depth may produce significantly different numerical results. The coefficients due to nonuniformity in the continuity equation are very close to unity, whereas the coefficients in the momentum flux and the pressure term in the momentum equation are different from unity by a margin that is very sensitive to the definition of current depth. The entrainment coefficient is more sensitive to the selected parameterization than to the definition of the current depth.

Free-surface flows play an important role in many environmental hydraulic problems. Owing to their characteristic large spatial and temporal scales, reduced complexity models, such as depth-integrated shallow water (DI-SW) models, have so far been largely preferred to three-dimensional (3D) approaches. Even if they can reproduce water levels satisfactorily, DI-SW models do not natively provide flow velocity at the bed, which is pivotal for estimating scour effects induced by impulsive flows, such as those resulting from dam breaks. However, resort to fully 3D modeling is often impractical due to the high computational demand required; nonetheless, recent works have shown impressive performance of the lattice Boltzmann method (LBM) compared to classical numerical methods while proving to be as accurate in many fields, suggesting LBM makes such computations affordable on desktop computers. So far, a comprehensive assessment of a LBM-based, fully 3D, free-surface model is still lacking. In this work, a LBM model is compared to data from a large series of dam-break-flow experiments, in terms of water levels and, where available, flow velocities. Comparisons with available DI-SW models are also carried out. Results show that the LBM model can correctly simulate both water levels and velocity distributions, the latter often being inaccurately reproduced by DI-SW models. To provide guidelines for the correct modeling of such flows, considerations are also given to opportunities to use either no-slip or free-slip boundary conditions, the latter being preferable if underresolved boundary layers are present.

Data and insights are presented on air entrainment in a hydraulic model of the stepped spillway for Gross Dam, Colorado, soon to be the tallest stepped spillway in the United States. The spillway’s chute was steep (2.0V:1.0H) and curved, and converged about 20% from its top to its base width. Data show that streamwise values of air concentration and flow depth were practically constant near the chute’s end for the spillway’s design discharge. The chute’s planform curvature resulted in nonuniform flow depth across the chute; flow depth along the chute’s centerline was greater than flow depth at the sidewall but contained slightly less entrained air. At the end of the chute, the average air concentration (volumetric proportion of bulked flow) varied from about 0.55–0.61. The depth-averaged concentration of entrained air near the end of the chute decreased with increasing water discharge, and was less than the equilibrium value suggested by the literature. The chute’s converging sidewalls caused slight increases in flow depth and reductions in flow velocity near the sidewalls.