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1

Scour downstream of J-Hook vanes in straight horizontal channels

Pagliara S., Kurdistani S., Santucci I.

Acta Geophysica

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2013

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Vol. 61, no. 5

1211--1228

EN

J-Hook vanes are grade control structures used to stabilize the riverbed. This paper aims to investigate the behaviour of J-Hook vanes as a grade-control structure in straight rivers. Scour downstream of J-Hook vane structures like other grade-control structures depends on the shape of the structure and the river hydraulic conditions. The purpose of this study is classifying the scour geometry and predicting the main scour parameters such as the scour depth, length, width, and the ridge height and length downstream of the J-Hook vanes in straight rivers. Experiments were carried out in a horizontal channel. For each length of the structure, three heights in different hydraulic conditions, including densimetric Froude numbers, water drops, and opening ratios, were tested. Results show that the densimetric Froude number, the drop height, and the height of the structure are the key parameters to form and classify the scour. Equations have been derived using dimensional analysis and experimental data to predict the maximum scour depth, the maximum length of the scour, the maximum scour width, and the maximum height and length of the dune. All the experiments were conducted in clear water conditions.

2

Rock grade control structures and stepped gabion weirs: Scour analysis and flow features

Pagliara S., Palermo M.

Acta Geophysica

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2013

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Vol. 61, no. 1

126--150

EN

Rock and stepped gabion weirs are peculiar hydraulic structures that received relatively little attenti on in technical literature. Neverthe- less, they can be successfully used for river restoration instead of tradi- tional hydraulic structures. They have the advantage of being elastic structures and to preserve the natura l environment. They can easily adapt to the in situ conditions and can be effortle ssly modified according to the different hydraulic or geometric cond itions which can occur in a natural river. The present study aims to anal yze the effects of their presence on flow pattern and on the scour hole occurring downstream. The analysis involved scour processes, hydraulic jump types, stilling basin morphol- ogy and flow patterns. Two different hydraulic jump types were distin- guished and classified. It was show n that the flow regime deeply influences the scour process, which evolves much more rapidly when a Skimming Flow regime takes place. Empirical relationships are pro- posed to evaluate maximum scour depth, maximum axial length, and non dimensional axial profiles.

3

Expanding pools morphology in live-bed conditions

Pagliara S., Palermo M., Carnacina I.

Acta Geophysica

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2011

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Vol. 59, no. 2

296-316

EN

Sediment load plays a fundamental role in natural river morphology evolution. Therefore, the correct assessment of the role of the sediment load on natural or anthropic pools morphology downstream of river grade control structures, such as rock chute or block ramps, is of fundamental interest for preserving the fish habitat and the river morphology. This work presents an experimental study on the sediment load influence on rectangular expanding pools downstream of block ramps in live-bed conditions. Several longitudinal and transversal expanding ratios have been tested. Ramp slopes were varied between 0.083 and 0.25. The effect of the pool geometry and the sediment load on hydraulic jump downstream of block ramp as well as scour morphologies and flow patterns have been analyzed. Equations were derived to evaluate the maximum scour hole depth, the longitudinal distance of the section in which it occurs, and the maximum water elevations both in the pool and in the downstream contraction.