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Equilibrium Scour Morphologies Downstream of Block Ramps Located in Both Straight and Curved Channels

Author(s): Stefano Pagliara, Michele Palermo

Linked Author(s): Michele Palermo

Keywords: Block ramps, curved rivers, river morphology, sediment transport

Abstract: The local scour occurring downstream of block ramps is carefully analyzed and studied in correspondence with straight river branches. But no studies are performed in order to analyze the scour mechanism in correspondence with river bends. In the present study, a dedicated model is built in order to analyze the scour process under several hydraulic conditions and ramp configurations. Namely, a succession of block ramps is tested in a laboratory flume, characterized by three different curvatures. Four ramps are located in the mentioned branches, whose slope is fixed at 0. 083. Tests are conducted adopting one uniform bed material. Block ramps are located in the flume in such a way that both the effect of the upstream and downstream curvature on the scour process could be highlighted. The resulting equilibrium morphology downstream of the block ramp mainly depends on the channel geometric configuration and hydraulic conditions. Namely, the scour morphology results to be either three-dimensional or bi-dimensional are based on the river geometric configuration. In addition, the presence of the upstream curvature further amplifies the scour three-dimensionality, as the flow velocity distribution in the channel cross-section depends on the river curvature, i. e. , its asymmetry is strictly related to the channel curvature. In the present paper, the resulting equilibrium morphologies are carefully surveyed and analyzed, highlighting both the effect of hydraulic conditions and channel bed curvatures. The analysis is conducted to identify those combinations of both hydraulic and geometric parameters which determine an increase of the scour depth with respect to the reference configuration, i. e. , that in the straight branch of the channel. The results of the present paper can be useful to optimize the stilling basin design in the perspective of a harmonization of both hydraulic functioning of the analyzed river restoration structure and reduction of their impact on the natural contest

DOI:

Year: 2017

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