The interaction between riparian vegetation, turbulent flow past it and the bed surface, involves highly complex and interdependent processes that can lead to the destabilization of the riverbed [1]. Past research has focused on assessing the riverbed destabilization potential downstream a vegetation patch phenomenologically using bulk flow parameters. Herein, the application of instrumented particles in assessing the risk of riverbed destabilization is pursued. Specifically, a 30mm instrumented particle [2] is used here to record the entrainment rate at distinct distances downstream a vegetation patch. The patch used to physically model the emergent vegetation has fixed diameter but distinct porosities (void volume ranging from 1.25% to 17.25%). The turbulent flow field downstream the vegetation patch is also recorded using acoustic Doppler velocimetry (ADV) allowing for the extraction of the mean and turbulent flow field and energetic flow events [3, 4]. The preliminary results suggest that the mean flow velocity deficit increases with vegetation patch density. Mean flow velocity profiles are restored to the ambient flow conditions at a faster rate compared to the turbulent intensity profiles. Strong and frequent particle entrainments can be achieved for a range of combinations of mean flow velocity and intensity resulting in the occurrence of a high rate of sufficiently energetic flow events.
References
[1] Kitsikoudis, V.; Yagci, O.; Kirca, V.S.O. Experimental analysis of flow and turbulence in the wake of neighboring emergent vegetation patches with different densities, Environ Fluid Mech 2020. https://doi.org/10.1007/s10652-020-09746-6
[2] Al-Obaidi, K.; Xu, Y.; Valyrakis, M. The Design and Calibration of Instrumented Particles for Assessing Water Infrastructure Hazards, J. Sens. Actuator Netw. 2020, 9, 3, 1-18, https://doi.org/10.3390/jsan814323.
[3] Valyrakis, M.; Diplas, P.; Dancey, C.L. Entrainment of coarse particles in turbulent flows: An energy approach. J. Geophys. Res. Earth Surf. 2013, 118, 42–53, doi:10.1029/2012JF00235.
[4] Pähtz, T. ; Clark, A. H.; Valyrakis, M.; Duran, O. The Physics of Sediment Transport Initiation, Cessation, and Entrainment Across Aeolian and Fluvial Environments. Rev. Geophys. 2020, 58, 1, 1-58, doi: 10.1029/2019RG000679.
