In this work, we investigate the temporal evolution of the jet-driven scour depth in a pothole lying on a cohesionless granular bed, by using diverse approaches. First, we present new experiments which encompass cases with jet angles ranging from 45 to 90° from the horizontal, several initial water depths, and different particle sizes, supplementing experiments developed recently by the last two authors. In particular, we address relatively-large angles, mostly absent in previous analyses. Our results first confirm the existence of two very different stages in the scour process, essentially overlooked in datasets used to obtain the traditional formulas-developing and developed phases; they then provide unprecedented evidence of the very distinct behavior at 90°, characterized by a step-wise behavior. Second, after revisiting the rationale of a theory our new, and other datasets. Finally, we provide interesting interpretations of the scour process by using the results of the theory.

Plunge pool scour involves a significant risk with trajectory spillways because of structural undermining at a dam foot or destabilization of adjacent valley slopes. An experimental program towards the understanding of plane plunge pool scour of a completely disintegrated rock surface was conducted, in which the following items received attention: jet shape, jet velocity, jet air content, tailwater elevation, granulometry, upstream flow to the scour hole, and the end scour profile in terms of the basic scour features. These effects were experimentally investigated based on a systematic variation of the governing scour parameters. The results of this paper allow answering questions that have so far not been addressed. Design equations were proposed to sketch the main tendency of the data sets. The significant effect of the densimetric particle Froude number was substantiated. This research may be used to estimate the prominent scour features for nearly two-dimensional jet arrangements involving a pre-aerated high-speed flow.

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Large wood debris transported by floods affects the scour morphology at bridge piers, thus increasing the bridge failure potential. The characteristic size and shape of the riparian vegetation includes various roughness and permeability conditions of the debris surface. The interaction between two-dimensional flow and rough debris accumulations increases the shear stress, the turbulence and consequently affects the scour evolution process at bridge piers. An experimental study on the bridge pier clear-water scour evolution in the presence of wood debris was conducted at the PITLAB research centre, University of Pisa, Italy. A debris accumulation is characterized by roughness, shape and porosity. Flow intensities range from 65 to 100% of the threshold velocity and included up to 18% of the total flow area. Flow depths were varied from 2.67 to 5.67 times the pier diameter. The effects of wood debris roughness and porosity were analysed in terms of scour temporal evolution and scour morphology

The temporal development of plunge pool scour was investigated using a novel experimental approach. Longitudinal profiles along the scour hole were recorded with an optical method to allow its definition at any time, from the initiation of scour to nearly the end-scour condition. The characteristics of the scour hole geometry were investigated, namely the maximum scour hole depth, the maximum ridge height, and their locations relative to the scour hole origin. It is demonstrated that the evolution is logarithmic, similar to that found for bridge pier and abutment scour. A distinction is further made between the developing and the developed scour hole phases. The main issue of the present research was to define the developed scour hole characteristics because the developing scour phase is influenced by turbulence features that may be difficult to assess. This work therefore allows for an appreciation of the temporal evolution of a scour process of engineering interest.

This note deals with the influence of debris accumulation on scour around bridge piers. Clear-water experiments in different hydraulic conditions have been carried out with three wood debris shapes: rectangular, triangular, and cylindrical. A wide range of debris thickness and width were studied in order to determine their influence on the maximum scour hole depth temporal evolution. The ratio of the pier diameter to the channel width was varied between 0.05 and 0.12 with total bridge contractions up to 20%. A proposed relation presents a simple design procedure to predict the increase in scour depth, which mainly depends on the flow contraction due to the debris accumulation

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Hydraulic jumps, which frequently occur in hydraulic structures, have been extensively studied over the last century. However, only a few studies have evaluated hydraulic jumps in flows over rough beds and there are no studies that consider the air entrainment effect on conjugate depths. The current paper reports the results of an experimental investigation of hydraulic jump properties in flows over adverse-sloped rough beds, including the effect of air entrainment. Furthermore, a semi-theoretical predictive relationship is proposed to estimate jump characteristics for a wide range of hydraulic and geometric conditions covering both rough and smooth beds