Journal of Hydraulic Engineering

Climate and land-use/land-cover changes are amplifying hydrological uncertainties, which are increasing the probability of flood magnitudes exceeding their design values. Consequently, bridges are more likely to get submerged. The vertical contraction of flow during a submergence event causes the flow beneath the bridge to accelerate and transit from atmospheric flow to pressure flow. The pressure flow increases the velocity gradient and bed-shear stresses, thereby increasing the scouring potential of the flow and the risk of bridge failure. Laboratory and numerical experiments have been performed to relate the magnitude of pressure-flow scour to the flow geometry and flow, bed, and fluid properties. These developed prediction equations have found a place in design manuals. Nevertheless, many aspects of the pressure-flow scouring are confounding and are still unknown after 3 decades of research. In this article, an overview of the pressure-flow scour phenomenon is presented. The focus is on the important but special case of pressure flow with no pier that has received maximum attention in the literature. The experimental studies on pressure-flow scour are summarized, and inconsistencies and gaps in the reported results are highlighted. A compendium of data compiled from all existing data sets is used for evaluating the design equations and investigating their relative strengths and shortcomings. Based on the anomalies identified in the literature, the article questions the applicability of empirical and semitheoretical models for the pressure-flow scour phenomenon and suggests directions for future research.

Manholes in combined sewers may become surcharged during storm events, resulting in complex mixing conditions. Although manhole hydrodynamics are reasonably well understood, predicting mixing across a surcharged manhole remains a challenge. An analytical compartmental mixing model for manholes, based on jet theory, has been further developed and applied to generate cumulative residence time distributions (CRTDs), which describe mixing. The modeled CRTDs were compared with the experimentally derived CRTDs of over 850 manhole configurations to evaluate how well the new compartmental model represents physical processes. The model underpredicts short-circuiting in manholes with manhole diameter to pipe diameter ratios greater than 4.4 and consequently overestimates mixing. Otherwise, the modeled CRTDs show good agreement with the experimental CRTDs. The new compartmental model represents key manhole hydrodynamics that are not represented in current software modeling packages, which assume manholes are instantaneously well-mixed. The compartmental model provides good predictions of the experimental downstream concentration profiles, although with reduced peak concentrations in those manhole configurations where short-circuiting is not well-predicted. Despite this, the compartmental model still predicts concentrations downstream of a manhole in closer agreement with the recorded data than the complete instantaneously well-mixed assumption. As an analytical model requiring no inputs other than manhole geometry, the new compartmental model applies to a wide range of manhole configurations, is robust, and is useful for predicting manhole mixing in practical applications.

Flash flood events threaten the safety of people either because of the direct impact of the flow on people and car stability or because of structural damages to buildings. Traditionally, buildings stability is assessed with ex post analyses by vulnerability models applied to the results of hydraulic models where buildings are permanently present on the flooded domain. However, in the case of building collapse, the geometry of the computational domain should be adapted during the simulation and, accordingly, a more realistic approach would require the coupling of hydraulic modeling and structural analysis. This paper provides an example of a simple methodology implementing this procedure in HEC-RAS 2D using the results from a physically-based structural vulnerability model for masonry buildings. After positively testing the capabilities of the solver to model the flow field around isolated obstacles as well as the flow field in urban districts on complex bathymetries, the proposed procedure is applied to the reconstruction of the flood event in the Corna di Darfo village (Northern Italy) after the collapse of the Gleno dam in 1923.

In this study, a new sediment removal system, namely the vortex hydrosuction (VHS) method, is introduced as an alternative hydrosuction technique with higher efficiency. Unlike the conventional hydrosuction systems, VHS benefits from a generated vortex flow for suspending the settled particles. The ability of 27 different VHS systems to remove noncohesive sediment is assessed. The results indicate that the efficiency of the best VHS is about 24 times higher than conventional hydrosuction. On average, the VHS increase the volume and depth of scour holes by around 13 and 2 times more than conventional hydrosuction, respectively. Sensitivity analysis of significant parameters indicates that by increasing 100% and 300% of the nozzles’ Froude numbers ($F{r}_n$), the performance of VHS would increase 43% and 110%, respectively. Moreover, the generated vortices in the cylinders with smaller diameters are stronger compared with cylinders with greater diameters; thus, by increasing 20% and 47% of the cylinder diameter dimensional parameter (i.e., $D/d$), the performance of VHS would decrease about 16% and 59%, respectively.

The results of experimental studies into the behavior of nonbuoyant discharges impacting a solid boundary are presented. The discharges were released perpendicular to the boundary at nondimensional heights ($H/d$) ranging from to 36 to 173, where $H/d$ is the ratio of the jet discharge height above the boundary to the jet diameter. Although the primary focus was on concentration field measurements using a laser-induced fluorescence system, additional velocity field data are presented from a recent study that used a similar discharge configuration and a particle tracking velocimetry system. Integral models provided a relatively simplistic framework for quantifying and interpreting the flow behavior in the vicinity of the boundary. The new data sets enabled defining the scale of the impact region based on the ability of integral techniques to model the flow entering and leaving this region. These data sets also offered insights into the flow behavior in the impact region and provided the basis for determining the influence of the impact region on the flow behavior.

Storage tanks are essential components of water supply systems to store water to face normal and emergency conditions and to level off required pressures. However, tanks can also be the source of water quality deterioration due to poor mixing and long residence times. In this paper, the effect of the tank configuration and of the operating mode on water mixing and renewal in cylindrical small-scale tanks of typical configurations is assessed. Results show that nearly complete mixing conditions can be attained in the tanks with inlet and outlet pipes located at opposite walls. Short-circuiting and the formation of dead zones is demonstrated in tanks with inlet and outlet pipes located close together. In fill-and-draw mode, water mixing is enhanced by a wide water-level variation, but renewal takes longer than in steady-state conditions. In addition, an empirical formula is proposed for estimating the turnover time in cylindrical tanks operated at a constant level. By identifying the configurations and operating conditions that promote mixing, this paper contributes to better water quality management in existing and new storage tanks in distribution systems.

Freshwater flocculation in the Usumacinta River delta during the high flow season was confirmed and supported by field data and the results from experiments conducted in a rotating annular flume and in a settling column device. Although the stream intensity and a bottom macroform generated and disturbed the 3D turbulence components in the cross section, the flow patterns followed the logarithmic law and the Nezu and Nakagawa models. The Rouse model can be applied to predict suspended sediment flux; however, flocculation led to diffusivity ratios less than 0.63 and effective settling velocities close to $1\mathrm{mm}/\mathrm{s}$ that were consistent with the mass conservation equation. When comparing the suspended load patterns of several lowland rivers, flocculation stages are related to shear rate; furthermore, in contrast to saline environments, the representative aggregate size in freshwater systems is presumably higher than the Kolmogorov microscale.

The principle of maximum entropy (PME) relies on information theory, Shannon entropy, and four constraints, namely the total probability and conservation laws of mass, momentum, and energy. This paper applies PME theory to an exactly accurate data set available in the literature to develop a model that relates the friction factor ($f$) to the entropy parameter ($M$). The proposed model exhibits fair adherence to the experimental data, and it was validated by multiphase flow pumping tests with concentrated iron ore slurry. Extending the use of the proposed model for multiphase flow, particularly mineral slurries, allows for the determination of apparent viscosity and Reynolds number without resorting to rheological measurement. The deviations between the $M$ parameter obtained from the proposed model and that reported in the literature were smaller than 5% for the iron ore slurry. It has been demonstrated that the PME is a particularly important tool for hydraulic systems, especially in multiphase flow such as that of mineral slurries containing a high content of solids.