Journal of Hydraulic Engineering

The hydrodynamic force on sediment particles is decomposed into two components, hydrodynamic drag and lift, whose estimations are made semiempirically by the introduction of drag and lift coefficients. A remarkable agreement on the estimation of drag coefficient has been attained in the literature. However, a generic consensus on the determination of lift coefficient so far remains unachievable. This article presents a state-of-the-art review of the hydrodynamic lift on sediment particles at an entrainment, highlighting the present status of lift coefficient in light of experimental observations and the theoretical foundation. The uncertainty in the estimation of hydrodynamic lift and different components of hydrodynamic lift in modeling the entrainment threshold of sediments are discussed. This article shows, for the first time, that there remains a prospect to obtain a generic consensus on the lift coefficient. Compiling and analyzing the lift coefficient data obtained from theoretical predictions, experimental observations, and numerical simulations, it is revealed that the lift coefficient data are somewhat collapsed to a thick band. This band, although subject to inevitable uncertainties, is found to provide a general consensus on the lift coefficient over a wide range of the particle Reynolds number. Finally, the article offers an insight into open questions and sheds light on how these challenges could be resolved.

Pumping systems are a topic of great relevance in the teaching of civil and environmental engineering courses related to urban water infrastructure. One key component of this teaching is the diameter selection of transmission mains in drinking water systems. This selection process includes a number of considerations which should lead the engineering student to select a technically feasible option that minimizes anticipated construction costs of the transmission main as well the energy-related expenditures. This work presented two different teaching approaches to help students acccelerate the selection process of transmission main diameters in the context of drinking water systems. These approaches include an analytical approach and a direct cost calculation approach, and consider time-varying water demand evolution based on the operation of the pumping system. An application involving a relatively simple diameter-selection problem using these two approaches was presented, along with ideas on how the method can be improved.

Early in their career, engineering students sometimes have difficulty linking academic concepts between courses and the interests that led to their enrollment. We present a design “interlude” event that is intended to improve experiential inductive learning and the vertical and horizontal integration of engineering courses. In this exercise, second year engineering students design, build, and test a scaled model of an earthen dam. The method integrates content from technical courses in which they are currently enrolled, such as statistics and fluid mechanics, and previews future courses in their curriculum, such as soil mechanics, hydrology, and hydraulics. Students consult with a range of experts, mock stakeholders, and mock protestors. Projects are evaluated for social/environmental impacts, technical design, cost, and performance, including stability, power generation, and spillway overflow. Student feedback was positive and highlights the intended benefits for the students, including interaction with industry partners, team building for the students, hands-on learning, and a better understanding of the impact of engineering projects.

The Shields diagram is a classic method for quantifying sand incipient motion in sediment transport. It is often expressed by empirical or semiempirical equations. This research applies the Padé approximant to the data in the extended Shields diagram and presents a simple generalized empirical model for the critical shear stress. The resulting dimensionless critical Shields parameter is a fractional function of the critical grain Reynolds number, which reproduces the extended Shields diagram by tending to two constants for lower and higher critical grain Reynolds numbers, respectively, and having a minimum value in the transitional regime. The proposed function results in an explicit Shields diagram in terms of grain Reynolds number and has an analytical solution for critical sediment diameter given a bed shear stress.

In this work, a large-eddy simulation of bubble plumes in linearly stratified environments is presented. The gas bubbles are treated as Lagrangian particles. The intrusion and peeling are clearly manifested in the computed flow fields. The results of about 50 simulations with different parameters reveal the importance of bubble source area for plumes on the laboratory scale. A new type of bubble plume with rapid and distinct peelings is observed which is favored by large source areas. With a proper normalization, the present data points collapse onto a single straight line after applying a virtual-source correction which reflects the source-area effect. These results provide a plausible explanation for the scatter of the previous experimental and computational data in literature. A simple relation between the trap height and the peel height is observed and its mechanism is discussed.

This study investigates the flow in an evolving scour hole downstream of a sluice gate with an apron using particle image velocimetry (PIV). The results clearly depict the sequential appearance of four rollers (large vortices) and the evolving connections between the 1st-order moment (velocity) and the 2nd-order moments (turbulent kinetic energy and Reynolds shear stress), during the three-stage (early, intermediate and equilibrium) scour process. At any scour stage, the velocity profiles on cross-jet sections exhibit global self-similarity, whereas those along the jet centerlines preserve self-similarity local to regions with significant average kinetic energy (AKE). Both the profile of the scour hole and the flow fields share self-similarity in terms of spatial distribution, when normalized with proper length and velocity scales. A substantial portion of energy is transferred from the fluid phase to the sediment phase as one of the primary factors for scour upon the incoming jet impinging on the bed, whereas turbulence is merely a secondary factor.

This paper analyzes the influence of the geometry of bridge piers and supplied debris on the formation and growth of wood debris jams at bridge piers. A total of 162 laboratory experiments were conducted. Experimental results showed that the maximum size of debris jams formed by the accumulation of cylindrical debris (i.e., wooden dowels) is smaller than that of jams formed by natural nonbranched wood of irregular shape. In addition, experiments with branched debris resulted in jams that were significantly smaller and less stable than those with nonbranched natural debris. Finally, comparison of experiments conducted with six different pier shapes indicated that the shape of the pier has negligible effects on the maximum size of a woody debris jam. The only exception to this observation was for square piers, which showed slightly larger debris jam sizes than the other types of piers tested.

Part of the difficulty in simulating or understanding the erosion of cohesive soils is the near impossibility of replicating field conditions, including the constantly varying pore water pressure and resulting seepage pressures in response to changing overlying flow depth and groundwater conditions. Unlike granular soils, for which pore pressures respond to imposed conditions in a relatively short time, pore pressures in cohesive soils tend to take considerable time to reach steady state under new imposed conditions. Consequently, pore pressure gradients can exist within the soil matrix. Herein, we evaluate the influence of pore pressure gradients on critical shear stress for entrainment of cohesive soils. The Erosionometer, a test device previously introduced for fast and accurate determination of the critical shear stress of cohesive soils based on physical shearing and uplifting of the soil surface, is modified to test for the critical shear stress while a hydraulic pressure gradient is applied to the sample surface. Tests on multiple cohesive soils demonstrate that the critical shear stress increases linearly with increasing drainage gradient (downward seepage pressure).

Classical models for one-dimensional (1D) flood routing calculations were tested in a synthetic benchmark and in a real dam break case, the observed flashy hydrographs on the Doce River after the collapse of the Fundão Tailings Dam in Brazil. The application of existing methods presented unsatisfactory results, with an error in prediction of the peak discharge up to $-18\%$, and differences in timing to peak up to 4 h. An improved 1D flood routing approach is proposed, solving the dynamic equation into an equivalent linear diffusive wave format. This modified method reformulates the hydraulic diffusion coefficient in terms of the Froude number and flood wave celerity, which are parameters more coherent with the linear model assumption and provide more realistic flood wave attenuation. The solution given by this approach can be carried out using the Crank Nicolson or QUICKEST schemes. The relative percent difference (RPD) in predicted peak discharge is reduced to less than $-0.1\%$.

The current capacity of many spillways may be insufficient due to the increase in flood flows as a result of climate change. In those cases, the dam may be overtopped, generating new loading scenarios downstream of the dam. To date, information regarding the behavior of air-water flows in the plunge pool of free-falling jets is scarce. This study combines experimental and numerical approaches to analyze the submerged hydraulic jump generated downstream of overflow nappe impinging jets. A back-flushing Pitot tube and an optical probe were used to measure the velocity field and air entrainment rate. The velocity field allows to validate computational fluid dynamics (CFD) simulations. The choice of the turbulence model played a key role in the wall jet resolution. To the best of our knowledge, for the first time, it was possible to estimate the Sauter mean air bubble diameter in the entire submerged hydraulic jump. The results are in agreement with recordings obtained with a high-speed camera.

In recent studies, computational fluid dynamics (CFD) simulations in OpenFOAM have been used to model the oscillation of a planar jet impinging onto a free surface and analyze methods to suppress the subsequent flow characteristics. This phenomenon occurs in several industrial processes, such as dipping, and is likely to affect the quality of products, with consequent rejection, resulting from the free surface wavering induced by the jet. Therefore, to prevent this, CFD was used to analyze alternatives, lowering the higher costs of manufacturing and on-site testing solutions. The predicted flapping frequency is benchmarked against experimental data and used to perform grid independency tests and select the most appropriate Reynolds-averaged Navier-Stokes (RANS) turbulence model. Finally, various deflector geometries, placed above the inlet jet, were tested to reduce the free surface oscillations.

Flood modeling by numerical solution of the two-dimensional (2D) shallow-water equations is ordinary practice. HEC-RAS 2D was recently released along with a suite of test cases showing the very good performance of the code in many practical situations. However, validation test cases aimed at demonstrating the capability of the software to deal with dam-break floods on very steep and irregular bathymetries are very limited. This paper tests HEC-RAS 2D against the discharge hydrographs measured in a historical physical model built in Froude similitude to analyze the consequences of the hypothetical collapse of the Cancano I dam (northern Italy) and the propagation of the resulting dam-break wave along the 15-km reach of the downstream alpine valley. The experimental hydrographs and the measured extent of the flooded areas are well reproduced by the numerical simulations. Moreover, the results obtained with HEC-RAS 2D are in very good agreement with those obtained using TELEMAC 2D, which confirms the suitability of the HEC-RAS 2D software for dam-break flood studies in steep alpine valleys. The data of the test case are made available to the scientific community for validation purposes.