Influence of Erodible Beds on Shallow Water Hydrodynamics during Flood Events

David Santillán,Luis Cueto-Felgueroso,Luis Garrote,Alvaro Sordo-Ward

doi:10.3390/w12123340

Abstract

Flooding has become the most common environmental hazard, causing casualties and severe economic losses. Mathematical models are a useful tool for flood control, and current computational resources let us simulate flood events with two-dimensional (2D) approaches. An open question is whether bed erosion must be accounted for when it comes to simulating flood events. In this paper we answer this question through numerical simulations using the 2D depth-averaged shallow-water equations. We analyze the effect of mobile beds on the flow patterns during flood events. We focus on channel confluences where water flow and sediment mobilization have a marked 2D behavior. We validate our numerical simulations with laboratory experiments of erodible beds with satisfactory results. Moreover, our sensitivity analysis indicates that the bed roughness model has a great influence on the simulated erosion and deposition patterns. We simulate the sediment transport and its influence on the water flow in a real river confluence during flood events. Our simulations show that the erosion and deposition processes play an important role on the water depth and flow velocity patterns. Accounting for the mobile bed leads to smoother water depth and velocity fields, as abrupt fields for the non-erodible model emerge from the irregular bed topography. Our study highlights the importance of accounting for erosion in the simulation of flood events, and the impact on the water depth and velocity fields.

Highlights

The numerical simulation of flood events to model fluvial hydraulics and flood inundation areas has become a key tool to assess flood risks, effectively manage and control flood events, and evaluate practices on flood prevention, protection and mitigation—the so-called flood control
To test the implications of sediment erosion and transport for river hydraulics during flash floods, we simulate the erosion on a real river confluence during a flood event
The simulations allow us to study the interplay between bed erosion and water flow patterns and to discern whether erosion has to be taken into account in eroded beds during flood events

Summary

Introduction

The numerical simulation of flood events to model fluvial hydraulics and flood inundation areas has become a key tool to assess flood risks, effectively manage and control flood events, and evaluate practices on flood prevention, protection and mitigation—the so-called flood control. One of the most widely used approaches to model fluvial hydraulics at a river scale is based on the numerical solution of the one-dimensional (1D) Saint Venant equations [4]. This approach requires low computational resources, allowing us to simulate long river length. Despite the simplifying assumptions of these approaches, in-channel flows are satisfactorily simulated by 1D models

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Conclusion