No abstract

Breaching of earthen embankments is a complex process that often results in disastrous inundations of the hinterland. The process has been studied during the last decades by means of physical and numerical modeling with particular reference to the dam case, while for river levees only few specific studies have been conducted. Moreover, the understanding and prediction of the breach final configuration are still scarce and not yet deeply addressed, despite their importance for mitigating flood risk in the protected areas. The paper attempts to examine the existence of a final equilibrium stage in the river‐breach system under specified conditions based on a significant data set from new laboratory experiments. Using these data, together with those of previous studies, a new hypothesis for the final equilibrium of the river‐breach system is proposed which is supported by new flow formulae and field data.

Seepage through earthen levees is a mechanism often observed during floods and can lead to levee failure if combined with internal erosion. This notwithstanding, hazard maps for levee failure are often elaborated solely considering the mechanism of overtopping. In this work, the assessment of levee vulnerability relative to seepage is investigated by considering the characteristic time scales of the phenomena and the main factors upon which they depend. In particular, the persistence of hydrological load is compared with the critical time of seepage associated to the emergence of the phreatic line along the landside of levees. The results can easily be applied to long river reaches, elaborating of through seepage‐hazard maps and locating the levees that are more vulnerable to seepage failure.

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Side weirs are hydraulic structures widely used for flow control in rivers and canals. Whenever the water level rises above the side weir crest elevation, a fraction of the main flow is diverted so that the water discharge flowing downstream in the main channel is reduced. In movable bed channels, the lateral outflow may have significant interactions with the sediment transport processes affecting the side weir flow. The spilled discharge creates a reduction of the downstream sediment transport capacity with a consequent deposition in the side weir proximity. In addition, sediment in the main channel can be diverted into the lateral branch. To investigate these interactions, experimental data at the laboratory scale have been collected and analyzed. The increase of the spilled discharge induced by the local sediment deposition is described according to the classical De Marchi hypothesis. Furthermore, the sediment transport leaving the main channel through the lateral structure is modeled in terms of the stream power associated with the bed-shear stress. Results allow for prediction of the bed dynamics and for the development of new design criteria.