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Influence of Ashes on Lateral Momentum Transfers: Experiments on Partially Vegetated Channel

Author(s): Catia Taborda; Cristina Fael; Cesar Santos; Hugo Canilho; Ana M. Ricardo; Rui M. Ferreira

Linked Author(s): Cátia Taborda, Cristina Fael, Ana M. Ricardo

Keywords: Suspended ashes; Partially vegetated channel; Rigid emergent vegetation; Lateral transfers

Abstract: Forest fires, in addition to the substantial economic losses and the negative impact on terrestrial ecosystems, are responsible for several problems in aquatic environments. Ashes which are mobilized by rainfall from slopes to river systems, besides polluting watercourses, their transport in suspension can directly affect the hydrodynamic processes, such as the transport capacity of other sediments and/or nutrients, the mass and momentum transfers between the vegetation and the open central channel and in the sediments deposition. In order to investigate the influence that ashes have on the vegetation interaction with the central open channel, essential hydrodynamic parameters were studied to have a comprehensive understanding of lateral mass and momentum transfers. In that regard, experiments were carried out in the partially vegetated channel located in the Laboratory of Fluvial Hydraulics and Structures of Universidade da Beira Interior. The channel with 12.60 m long, 0.80 m wide and 1.00 m deep has on the right side of the channel an extension of 6.00 m long and 0.30 m wide of emergent vegetation stems, occupying 35% of the channel cross-section. Vegetation was simulated with rigid cylindrical wooden stems in a staggered array, with 1 cm diameter and 0.15 m high, through two different densities that are representative of the natural vegetation. To ensure a constant ash concentration throughout the entire experimental investigation, an ash feeding system was placed in the upstream stabilization tank. The present study suggests that suspended ash maintains the flow susceptible to large-scale structures akin to KH instabilities, aspects that play a significant role in mass and momentum transfers.


Year: 2022

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