Accurate predictions of breach characteristics are necessary to reliably estimate the outflow hydrograph and the resulting inundation close to fluvial dikes. Laboratory experiments on the breaching of fluvial sand dikes were performed, considering a flow parallel to the dike axis. The breach was triggered by overtopping the dike crest. A detailed monitoring of the transient evolution of the breach geometry was conducted, providing key insights into the gradual and complex processes involved in fluvial dike failure. The breach develops in two phases: (1) the breach becomes gradually wider and deeper eroding on the downstream side along the main channel and (2) breach widening controlled by side slope failures, continuing in the downstream direction only. Increasing the inflow discharge in the main channel, the breach formation time decreases significantly and the erosion occurs preferentially on the downstream side. The downstream boundary condition has a strong influence on the breach geometry and the resulting outflow hydrograph.
Successfully modelling flows over a spillway and on strongly vertically curved bottoms is a challenge for any depth-integrated model. This type of computation requires the use of axes properly inclined along the mean flow direction in the vertical plane and a modelling of curvature effects. The proposed generalized model performs such computations by means of suitable curvilinear coordinates in the vertical plane, leading to a fully integrated approach. This means that the flows in the upstream reservoir, on the spillway, in the stilling basin and in the downstream river reach are all handled in a single simulation. The velocity profile is generalized in comparison with the uniform one usually assumed in the classical shallow water equations. The pressure distribution is modified as a function of the bottom curvature and is thus not purely hydrostatic. Representative test cases, as well as the application of the extended model to the design of a large hydraulic structure in Belgium, lead to satisfactory validation results
RÉSUMÉModéliser avec succès les écoulements au-dessus d'un déversoir et sur des fonds fortement incurvés verticalement est un défi pour n'importe quel modèle intégré en profondeur. Ce type de calcul exige l'utilisation d'axes correctement inclinés le long du sens d'écoulement moyen dans le plan vertical et de modéliser les effets de la courbure. Le modèle généralisé proposé exécute de tels calculs au moyen de coordonnées curvilignes appropriées dans le plan vertical, menant à une approche entièrement intégrée. Ceci signifie que les écoulements dans le réservoir amont, sur le déversoir, dans le bassin d'amortissement et dans tout le fleuve à l'aval sont traités dans une même simulation. Le profil de vitesse est généralisé par comparaison avec le profil uniforme habituellement considéré dans les équations classiques en eau peu profonde. La distribution de pression est modifiée en fonction de la courbure du fond et n'est donc pas purement hydrostatique. Les cas tests représentatifs, aussi bien que l'application du modèle général à la conception d'une grande structure hydraulique en Belgique, donnent des résultats de validation satisfaisants.
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