Significance of boulder shape, shoreline configuration and pre‐transport setting for the transport of boulders by tsunamis

Abstract

Research on tsunami‐induced coarse‐clast transport is a field of rising interest since such deposits have been identified as useful proxies for extreme‐wave events (tsunamis, storm waves) that provide crucial information for coastal hazard assessment. Physical experiments are, beside in‐situ observations, the foundation of our understanding of how boulders are transported by tsunamis and provide clues to the development of empirical equations and numerical models describing the processes and fundamental mechanics. Nevertheless, investigating tsunami‐induced boulder transport is a comparatively young discipline and only a few experimental studies focusing on this topic have been published so far. To improve the knowledge on nearshore tsunami hydrodynamics, physical experiments utilizing real‐world boulder shapes have been carried out simulating three different shore types in a wave flume. Crucial insights were gained into boulder transport hydrodynamics and data resulting from the experiments were analysed in an empirical, statistical, quantitative and qualitative manner. The regular cuboid boulder – one of the specific shapes used in the experiments – showed the longest transport distances compared to a complex, natural boulder and a flat cuboid boulder, but also significant fluctuations regarding the total transport distance. The experiments indicate a strong influence of the shore shape on boulder transport behaviour. Experimental setups of increased mean transport distances also led to a higher spreading of results. This spreading was further amplified between the idealized‐shaped cuboid and the complex‐shaped boulder, which is associated with a lower drag coefficient. Due to the highly sensitive boulder reaction to divergent experimental setups, the need to recognize boundary conditions overcoming commonly considered parameters (e.g. roughness or Flatness Index) in field studies and numerical models is underlined. Beside the strong influence of initial boulder submergence and alignment, both the boulder shape and shore type influence the boulder transport pattern, increasing the total transport distance by more than 350% in some cases. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Hydrodynamic Model Tests for Seaweed as a Source of Energy Reduction during Extreme Events

“…To generate the wet bed bore, an initial still water depth 'd s ' was ensured in the laboratory by adjusting the height of the barriers in the front end and rear end of the flume (Table 1). The generated bore in the wet bed case had an initial aerated bore front, followed by a quasi-steady flow phase; the characteristics were almost similar to the traditional tsunami bore [28][29][30]. The generated bore details are provided in Table 1.…”

A Numerical Modeling Approach for Better Differentiation of Boulders Transported by a Tsunami, Storm, and Storm‐Induced Energetic Infragravity Waves

“…This effect can be considered using the model of . The boulder shape controls the boulder transport distance (Oetjen et al, 2020(Oetjen et al, , 2021, and the flatness Index of the boulder is considered a crucial parameter for boulder transport (Oetjen et al, 2021). The model of also includes these effects.…”

Dynamics of Stone Habitats in Coastal Waters of the Southwestern Baltic Sea (Hohwacht Bay)

“…In this case, we do not expect that cobbles are more rounded by the transport into SA1 since the distance to the next seaward lying lag deposit is rather short (60-100 m). We assume that they were transported because of their already high degree of roundness since, along with the pretransport environment, the shape and size influence the transport distance [81,82]. Schrottke et al (2006) show the mobility of small cobbles originating from lag deposits in water depth from 3.4 m up to 5.6 m with a mainly landward transport direction [30].…”