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

Linked Author(s): Cristina Fael, Cátia Taborda

Keywords: Suspended ashes; Partially vegetated channel; Rigid emergent vegetation; Experimental tests

Abstract: Wildfires are responsible for feeding ash to watercourses that are downstream of the burned area. The presence of riparian vegetation promotes the retention of ash from wildfires during the first rainfalls. Thus, the study of the transport of wildfire ash suspended in flows in rivers with vegetation is relevant for the management of watersheds and the conservation of biodiversity. In this scope, the present study focuses on the vertical profiles and turbulence intensities in the free region of a flow with suspended ashes in a partially vegetated channel. An experimental campaign was carried out in the Laboratory of Fluvial Hydraulics and Structures of Universidade da Beira Interior. The emergent vegetation stems were inserted on the right side of the channel in an extension of 6.00 m long and 0.30 m wide. The matrix was made with rigid cylinder tubes with two areal number densities, 500 stems/m2 and 1034 stems/m2, in a staggered array. The ashes adopted has a specific gravity of both the whole ash (Gs=2.64) and its fine fraction (Gs=2.54). The present work allows to conclude that: the streamwise velocities are higher at the interface for the sparser matrix and, moving away from the vegetation, the differences between the two vegetation areal number densities becomes increasingly smaller, existing an intermediate region where both areal number densities’ velocities overlap, and, in the outermost region of the channel, velocities are higher for the denser matrix; the spanwise velocities present similar behavior for both matrices; the turbulent intensity is not affected by matrix areal number density.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221119

Year: 2022