Fully coupled free‐surface flow and sediment transport modelling of flash floods in a desert stream in the Mojave Desert, California

Abstract

For most of the year, a dry‐bed desert wash is void of water flow. Intensive rain events, however, could trigger significant flash floods that bring about highly complicated hydrodynamics and morphodynamics processes within a desert stream. We present a fully coupled three‐phase flow model of air, water, and sediment to simulate numerically the propagation of a flash flood in a field‐scale fluvial desert stream, the so‐called Tex Wash located in the Mojave Desert, California, United States. The turbulent flow of the flash flood is computed using the three‐dimensional unsteady Reynolds‐averaged Navier–Stokes equations closed with the shear stress transport k − ω model. The free surface of the flash flood at the interface of air and water phases is computed with the level‐set method, which enables instantaneous tracking of the water surface as the flash flood propagates over the dry bed of the desert stream. The evolution of the desert fluvial stream's morphology, due to the action of the propagating flash flood on the mobile bed, is calculated using a Eulerian morphodynamics model based on the curvilinear immersed boundary method. The capabilities of the proposed numerical framework are demonstrated by applying it to simulate a flash flood event in a 0.65‐km‐long reach of the Tex Wash, the intricate channel morphology of which is obtained using light imaging detection and ranging technology. The simulated region of the stream includes a number of bridge foundations. The simulation results of the model for the flash flood event revealed the formation of a highly complex flow field and scour patterns within the stream. Moreover, our simulation results showed that most scour processes take place during the steady phase of the flash flood, that is, after the flash flood fills the stream. The transient phase of the flash flood is rather short and contributes to a very limited amount of erosion within the desert stream.

Data‐Driven Prediction of Turbulent Flow Statistics Past Bridge Piers in Large‐Scale Rivers Using Convolutional Neural Networks

“…Also, RANS modeling of the validation testbed requires roughly 1450 CPU hr. The CPU time required for successful LES of natural rivers in this study is consistent with those of others (see, e.g., Constantinescu et al., 2011; Fischer‐Antze et al., 2008; Kang et al., 2011; Khosronejad et al., 2016; Khosronejad, Kang, et al., 2019; Khosronejad, Diplas, et al., 2020; Le et al., 2019; Stoesser et al., 2003). For instance, Constantinescu et al.…”

“…High-fidelity numerical simulations are a crucial tool for studying flood-flow dynamics and sediment transport in natural waterways [1][2][3][4][5][6][7][8][9][10][11]. However, high-fidelity simulations of natural rivers require extensive computational resources, owing to the high Reynolds numbers of the flow, wide range of scales of vortical flow structures, and large size of natural rivers.…”

“…High‐fidelity numerical simulations provide a crucial tool to study flood flow dynamics and sediment transport of natural waterways (Ercan & Younis, 2009; Khosronejad et al., 2016, 2017, 2018, 2019; Khosronejad, Diplas, et al., 2020; Khosronejad, Flora, & Kang, 2020; Khosronejad, Flora, Zhang, et al., 2020; Khosronejad, Kang, et al., 2019; Le et al., 2019; Liu et al., 2010). However, high‐fidelity simulations of natural rivers require extensive computational resources, owing to the high Reynolds numbers of the flow, the wide range of scales of vortical flow structures, and the large size of the natural rivers.…”

“…(2008) used a RANS‐based model to study sediment transport and vegetation‐structure interaction in the Danube River under flood conditions. More recently, high‐fidelity numerical simulations have been used to capture the instantaneous characteristics of the flow in natural waterways using more advanced turbulence closures, such as detached eddy simulation (DES) (Constantinescu et al., 2011) and large‐eddy simulation (LES) (Khosronejad, Flora, & Kang, 2020; Khosronejad, Flora, Zhang, et al., 2020; Khosronejad, Kang, et al., 2019). Such studies have proven highly valuable for a greater understanding of flow dynamics and sediment transport processes in natural waterways; however, their high computational cost has limited their practical adoption in the engineering community.…”

Essentially non-oscillatory and weighted essentially non-oscillatory schemes

“…Efficient wave modelling using non-hydrostatic pressure distribution and free surface tracking was investigated in Bihs, Kamath, Aggarwal and Pakozdi (2019a). Fully coupled free-surface flow and sediment transport modelling of flash floods in a desert stream were studied in Khosronejad, Kang and Flora (2019). Numerical modelling of breaking wave kinematics and wave impact pressures on a vertical slender cylinder were investigated in Chella, Bihs, Myrhaug and Arntsen (2019b).…”