Breaching Flow Slides and the Associated Turbidity Current

Abstract

This paper starts with surveying the state-of-the-art knowledge of breaching flow slides, with an emphasis on the relevant fluid mechanics. The governing physical processes of breaching flow slides are explained. The paper highlights the important roles of the associated turbidity current and the frequent surficial slides in increasing the erosion rate of sediment. It also identifies the weaknesses of the current breaching erosion models. Then, the three-equation model of Parker et al. is utilised to describe the coupled processes of breaching and turbidity currents. For comparison’s sake, the existing breaching erosion models are considered: Breusers, Mastbergen and Van Den Berg, and Van Rhee. The sand erosion rate and hydrodynamics of the current vary substantially between the erosion models. Crucially, these erosion models do not account for the surficial slides, nor have they been validated due to the scarcity of data on the associated turbidity current. This paper motivates further experimental studies, including detailed flow measurements, to develop an advanced erosion model. This will improve the fidelity of numerical simulations.

Large‐Scale Experiments on Breaching Flow Slides and the Associated Turbidity Current

“…The experimental setup consists of several components: a breaching tank, removable confining wall, false floor, damping tank, and sedimentation tank. As triggering mechanisms of breaching flow slides are still poorly understood (Alhaddad et al, 2020), the experiments were performed for oversteepened, unstable slopes that initially fail due to the gravitational force. To this end, the slope of the confining wall can be adjusted in order to investigate a range of initial slope angles between 50° and 80°.…”

Modeling of Breaching-Generated Turbidity Currents Using Large Eddy Simulation

“…Turbidity currents are vital agents of sediment transport that deliver sediment from the river mouths to deeper waters [2]. Moreover, they pose a serious threat to flood defense structures, such as dikes and embankments [3], and submarine structures placed at the seafloor, such as oil pipelines, and communication cables [4].…”

“…Many numerical models for density or gravity currents have been proposed in the literature (e.g., [19][20][21][22][23]). To date, however, there are very few numerical investigations dealing with breaching-generated turbidity currents [3,11,24]. Moreover, these numerical efforts were mostly restricted to layer-averaged, one-dimensional models.…”

“…These depth-averaged models require several empirical closure relations (e.g., the near-bed concentration, bed shear stress, and water entrainment at the upper boundary), which reduces the accuracy of the simulation results [25]. Alhaddad et al [3] applied the one-dimensional model of [26] to a typical case of a breaching slope, demonstrating that the results are highly sensitive to the type of breaching closure relation used.…”

“…The triggering mechanism of turbidity currents in this work is different from the standard lock-exchange configuration mostly used in the numerical models; sediment particles are released from the bed surface, generating the flow. An adequate prediction of this process has been always difficult, as it involves both geotechnical and hydraulic features [3]. To date, furthermore, no validation of existing breaching erosion models has been presented.…”