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The water waves resulting from the collapse of a dam are important unsteady free surface flows in civil and environmental engineering. Considering the basic case of ideal dam break waves in a horizontal and rectangular channel the wave patterns observed experimentally depends on the initial depths downstream (hd) and upstream (ho) of the dam. For r = hd/ho above the transition domain 0.4–0.55, the surge travelling downstream is undular, a feature described by the dispersive Serre–Green–Naghdi (SGN) equations. In contrast, for r below this transition domain, the surge is broken and it is well described by the weak solution of the Saint–Venant equations, called Shallow Water Equations (SWE). Hybrid models combining SGN–SWE equations are thus used in practice, typically implementing wave breaking modules resorting to several criteria to define the onset of breaking, frequently involving case-dependent calibration of parameters. In this work, a new set of higher-order depth-averaged non-hydrostatic equations is presented. The equations consist in the SGN equations plus additional higher-order contributions originating from the variation with elevation of the velocity profile, modeled here with a Picard iteration of the potential flow equations. It is demonstrated that the higher-order terms confer wave breaking ability to the model without using any empirical parameter, such while, for r > 0.4–0.55, the model results are essentially identical to the SGN equations but, for r < 0.4–0.55, wave breaking is automatically accounted for, thereby producing broken waves as part of the solution. The transition from undular to broken surges predicted by the high-order equations is gradual and in good agreement with experimental observations. Using the solution of the new higher-order equations it was further developed a new wave breaking index based on the acceleration at the free surface to its use in hybrid SGN–SWE models.

A culvert is a covered channel designed to pass water through an embankment. The recognition of the adverse ecological impacts of culverts on upstream fish passage is driving the development of new culvert design guidelines, with a focus on small-bodied fish species seeking low velocity zones to minimise energy expenditure. Herein a hybrid modelling technique was applied, combining physical modelling, one-dimensional theoretical calculation and three-dimensional computational fluid dynamics modelling. The results reveal fundamental turbulent processes that may affect small-body-mass fish navigability and provide new insights for the development of standard box culvert design guidelines. Systematic validations were performed to a wide range of initial conditions and smooth barrel geometries. A physical relationship was derived from numerical and experimental data of past and present studies, correlating the dimensionless flow area with a normalised local velocity V/Vmean.

The flooding of urbanized areas constitutes a major hazard to populations and infrastructure. Flood flows during urban inundations have been studied only recently and the real-life impact of fluid flows on individuals is not well understood. The stability of individuals in floodwaters is re-assessed based upon the re-analysis of detailed field measurements during a major flood event. The results emphasized that hydrodynamic instabilities, linked to local topographic effects and debris, constitute major real-world hazards. A comparison between a number of flow conditions deemed unsafe for individuals, along with guidelines, suggests that many recommendations are over-optimistic and unsafe in real floodwaters and natural disasters. A series of more conservative guidelines is proposed, particularity relevant to flood events.

In open channel, canals and rivers, a rapid increase in flow depth will induce a positive surge, also called bore or compression wave. The positive surge is a translating hydraulic jump. Herein new experiments were conducted in a large-size rectangular channel to characterise the unsteady turbulent properties, including the coupling between free-surface and velocity fluctuations. Experiments were repeated 25 times and the data analyses yielded the instantaneous median and instantaneous fluctuations of free-surface elevation, velocities and turbulent Reynolds stresses. The passage of the surge front was associated with large free-surface fluctuations, comparable to those observed in stationary hydraulic jumps, coupled with large instantaneous velocity fluctuations. The bore propagation was associated with large turbulent Reynolds stresses and instantaneous shear stress fluctuations, during the passage of the surge. A broad range of shear stress levels was observed underneath the bore front, with the probability density of the tangential stresses distributed normally and the normal stresses distributed in a skewed single-mode fashion. Maxima in normal and tangential stresses were observed shortly after the passage of a breaking bore roller toe. The maximum Reynolds stresses occurred after the occurrence of the maximum free-surface fluctuations, and this time lag implied some interaction between the free-surface fluctuations and shear stress fluctuations beneath the surge front, and possibly some causal effect.

In plunging jets and at hydraulic jumps, large amounts of air bubbles are entrained at the impingement of the liquid jet into the receiving body. Air is entrapped and advected into a turbulent shear layer with strong interactions between the air bubble advection process and momentum shear flow. In this new physical study, air–water flow measurements were systematically repeated with identical inflow length, inflow depth and inflow velocity in a vertical supported jet (PJ) and a horizontal hydraulic jump (HJ). Detailed measurements were conducted with the same instrumentation. Both similarities and differences were observed between the two multiphase gas–liquid shear flows. Visual observations showed a key difference in the outer region, with a buoyancy-driven flow in the plunging jet with negligible void fraction, versus a strong recirculation motion with uncontrolled interfacial aeration in the hydraulic jump. Differences were also observed at the impingement perimeter, in terms of fluctuation frequencies and amplitudes, for identical inflow conditions. Both flow conditions yielded intense local singular air entrainment and close results were observed in terms of void fraction, bubble count rate, bubble chord sizes and interfacial area in the shear layer, in both the plunging jet and hydraulic jump. The transfer of momentum between impinging jet and receiving water, as well as the effect of buoyancy, were however affected by the flow geometry.

In hydraulic engineering numerous devices like stilling basins, baffled aprons, and vortex shafts are known under the collective term of energy dissipators. Their purpose is to dissipate hydraulic energy, i.e. to convert this energy mainly into heat. Dissipators are used in places where the excess hydraulic energy could cause damage such as erosion of tailwater channels, abrasion of hydraulic structures, generation of tailwater waves or scouring. Energy dissipators are an important element of hydraulic structures as transition between the highly explosive high velocity flow and the sensitive tailwater. This volume examines energy dissipators mainly in connection with dam structures and provides a review of design methods. It includes topics such as hydraulic jump, stilling basins, ski jumps and plunge pools. It also introduces a general account of various methods of dissipation, as well as the governing flow mechanisms. The book will be of interest to Civil and Environmental Engineers, Hydraulic and Mechanical Engineers working in academic and professional environments.

Environmental Hydraulics is a new text for students and professionals studying advanced topics in river and estuarine systems. The book contains the full range of subjects on open channel flows, including mixing and dispersion, Saint-Venant equations method of characteristics and interactions between flowing water and its surrondings (air entrainment, sediment transport).Following the approach of Hubert Chanson's highly successful undergraduate textbook Hydraulics of Open Channel Flow, the reader is guided step-by-step from the basic principles to more advanced practical applications. Each section of the book contains many revision exercises, problems and assignments to help the reader test their learning in practical situations. ·Complete text on river and estuarine systems in a single volume·Step-by-step guide to practical applications·Many worked examples and exercises

The simulation of shallow flows over obstacles is an important problem in environmental fluid dynamics, including exchange flows over seabed sills, atmospheric flows past steep mountains and water flows over river bedforms. A common mathematical treatment consists in using vertically-averaged models instead of vertically-resolved ones by introducing a suitable shallow water approximation. The dispersionless Saint Venant equations are a useful tool, albeit accuracy is not enough in many circumstances. The next approach consists in resorting to the Serre–Green–Naghdi theory, which is well known to produce good solutions for long non-breaking waves. However, a common feature of flows over obstacles is the generation of breaking waves at its lee side, which are important to model, given their role in the mixing and transport of passive scalars downstream of the terrain barrier. The Serre–Green–Naghdi theory fails to model these flows, producing unrealistic trains of undular waves. A widely used practice consist in resorting to a patching approach in a numerical setting where the solutions of Serre–Green–Naghdi and Saint Venant equations are assembled once wave breaking is detected by case-dependent empirical parameters. In this work an alternative method to dealt with wave breaking over obstacles within the Boussinesq-type approximation is proposed. The exact depth-averaged equations for flows over uneven beds are developed and presented as function of the vertical acceleration and non-uniformity of velocity with elevation. By introducing a suitable kinematic field, a new high-order phase resolving system of non-hydrostatic equations is presented, containing the usual dispersive corrections of Serre–Green–Naghdi theory plus high-order corrections for velocity profile modeling. It is found that the new theory allows the simulation of both breaking and non-breaking waves in shallow flows over obstacles without introducing any case-dependent calibration parameter. The new shallow water approximation is thus an alternative method to deal with wave breaking in Boussinesq type models.

A compression wave is an unsteady rapidly-varied open channel flow motion, characterised by an increase in water depth. A detailed investigation was conducted in a prismatic asymmetrical channel, to better understand the physical processes observed in tidal/tsunami-bore affected estuaries with irregular topography. The prismatic channel was equipped with a 1 V:5H transverse slope across the full channel width. The free-surface data presented three-dimensional unsteady flow features, and the velocity measurements showed a drastic impact of the surge on the flow field, with strong three-dimensional features. With the arrival of the surge front, the transverse velocity component became large in the shallow-water section, indicating some unsteady secondary motion and recirculation during and shortly after the passage of the surge. The Reynolds shear stress data were associated with large turbulent stresses and shear stress fluctuations. For d1/D < 1, both velocity and shear stress data showed a transient longitudinal x–z shear plane, about y/W 0.5–0.6, with conjugate transverse flow reversal for 0.5–0.6 < y/W < 1. In the transient shear plane, high Reynolds stress magnitudes and shear stress fluctuations were observed behind the surge front, up to one to two orders of magnitude larger than boundary shear stress levels observed in steady flows in compound channels.