Modelling Spatiotemporal Dynamics of Large Wood Recruitment, Transport, and Deposition at the River Reach Scale during Extreme Floods

Andreas Zischg,Silvana Deplazes,Bruno Mazzorana,Niccolo Galatioto,Rolf Weingartner

doi:10.3390/w10091134

Andreas Zischg, Silvana Deplazes + Show 3 more

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https://doi.org/10.3390/w10091134

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Abstract

Large wood (LW) can lead to clogging at bridges and thus cause obstruction, followed by floodplain inundation. Moreover, colliding logs can cause severe damage to bridges, defense structures, and other infrastructure elements. The factors influencing spatiotemporal LW dynamics (LWD) during extreme floods vary remarkably across river basins and flood scenarios. However, there is a lack of methods to estimate the amount of LW in rivers during extreme floods. Modelling approaches allow for a reliable assessment of LW dynamics during extreme flood events by determining LW recruitment, transport, and deposition patterns. Here, we present a method for simulating LWD on a river reach scale implemented in R (LWDsimR). We extended a previously developed LW transport model with a tree recognition model on the basis of Light Detection and Ranging (LiDAR) data for LW recruitment simulation. In addition, we coupled the LWD simulation model with the hydrodynamic simulation model Basic Simulation Environment for Computation of Environmental Flow and Natural Hazard Simulation (BASEMENT-ETH) by adapting the existing LW transport model to be used on irregular meshes. The model has been applied in the Aare River basin (Switzerland) to quantify mobilized LW volumes and the associated flow paths in a probable maximum flood scenario.

Highlights

Riverine floods in many parts of the world are a threat to people, settlements, and infrastructure and a major cause of significant losses [1]
The simulated volume represents the volume of large wood (LW) that passed the lower system boundary (LSB)
The results of simulated LW volume must be above the observed value

Summary

Introduction

Riverine floods in many parts of the world are a threat to people, settlements, and infrastructure and a major cause of significant losses [1]. In mountainous areas, the impacts of floods can be accentuated by sediment transport or large wood (LW) transport. Both sediment and LW transport can lead to bridge clogging with subsequent channel outbursts [5]. This is especially valid for the recruitment areas of LW that reach Bern (Figure 6). Important locations for deposition of LW within the floodplain are the Aare River bridge near Rubigen (see Figure 5), the heightened highway between Rubigen and Münsingen, the railway bridge near Uttigen, and several spots mostly along the banks or edges of the wetted area. Major depositions are simulated mainly on 2 spots along the highway north and south of the bridge with different deposition patterns. Other specific deposition spots can be found on the left- and right-hand sides of the bridge in the upstream direction

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