Author(s): V. Pennisi; A. Cancelliere; R. E. Musumeci; E. Foti; S. J. McLelland

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Keywords: Biota; Earth levee stability; Eco-hydraulic approach; Burrowing animals; CFD modelling

Abstract: Studying the impact of biota on failure mechanisms is necessary for accurate predictions of levee stability. This is critical to flood prevention and requires an eco-hydraulic approach to investigate earth levee stability. The failure of levees is one of the main causes of flooding, generating costly damage every year. Failure mechanisms arise due to different phenomena, with seepage and piping induced by the changing river water level during floods playing a significant role, particularly when combined with internal erosion and deteriorated structures. Burrowing animals and plant roots may compromise the hydraulic performance and the structural integrity of earth levees. Earth levees are subject to a wide range of wildlife intrusion patterns that lead to mass removal and subsequent deformation as well as enhanced seepage pathways that can accelerate piping mechanisms. Thus, the evaluation of the vulnerability of earth structures must be carried out taking into account also the presence of biota. This paper presents the preliminary results of the MIUR industrial project “Dottorato Innovativo a Caratterizzazione Industriale,” the purpose of which is to investigate the performance of a deteriorated earth structure, considering the simultaneous combination of two factors: dynamic change of the river stage during floods and bio-induced modification of the levee structure, focusing on the effects of burrowing animals. The goal of the research is to assess the influence of biota on the structural integrity of earth levees using an eco-hydraulic and eco-hydrological approach to account for the presence of animal burrows. To achieve this aim, two analyses have been carried out: numerical modelling using a 3D computational fluid dynamics model to consider a more complex burrow geometry, and experimental activities to take into account the fluid dynamics and the erosion phenomena. Numerical modelling and experimental activities were conducted on a homogeneous scaled-down levee model. A CFD model (Flow3D ©) has been used for numerical comparison of the failure mechanism for undisturbed levees with that of levees weakened by the presence of burrows. Different porosities and permeabilities have been investigated. In this way, it is possible to define the evolution of the phreatic surface and the critical time before levee failure. Simulations of disturbed levees will consider the effect of different burrow lengths. This will then be developed further to consider more complex den geometries, like those produced by crayfish. Experimental modelling is currently being undertaken in a physically based analogue model to study the failure mechanism of modified bio-levees at the University of Hull (UK). The test levees are constructed from mixed sand and clay. Experiments will investigate levee erosion with different water levels. Preliminary experiments investigated an undisturbed levee with the erosion patterns being quantified using time-lapse GoPro images. Further experiments will investigate the effects of burrow density, length, and angle relative to the flow direction. These experiments will elucidate the key parameters for further investigation.

DOI: https://doi.org/10.3850/978-981-11-2731-1_310-cd

Year: 2018