Coastal boulder deposits hold the potential to aid in the reconstruction of past extreme wave events. However, commonly used hydrodynamic equations for calculating wave heights from transported boulders can be inaccurate. New and alternative methods need to be explored in an interdisciplinary way to ensure a more complete picture of the phenomenon of boulder transport is achieved. Through the use of a physical experiment, this study aims to investigate the influence of different tsunami wave types, wave parameters and boulder shapes on boulder transport distance. The experimental results also allow for a novel application of dimensional analysis to enable comparisons with other experiments as well as a field case study. In the experiment an elongate irregularly shaped boulder showed transport distances up to 1 m farther than a cuboid shaped boulder under the influence of the same waves. The irregularly shaped boulder had a predominant transport mode of rolling, whereas the cuboid shaped boulder predominantly underwent sliding transport. Tsunami wave type also influenced boulder transport distances, with N-waves frequently showing greater transport than E-waves of a comparable wave steepness. Key offshore wave and boulder parameters were then compared through dimensional analysis using Buckingham's Pi Theorem, enabling comparisons to other datasets to be made. Data from another published experimental study and a field study in Settai, Japan, showed reasonable agreement, particularly for the shorter period field data. These findings emphasize the importance of incorporating boulder shape, wave type, and dimensional analysis into future studies, providing a foundation for more accurate reconstructions of past tsunami events.

Tsunami events are traditionally represented in the geological record by a sequence of fine-grained sediments, but increasingly coastal boulder deposits are being used as indicators of past tsunami events. The emplacement mechanism of many boulder deposits, however, is heavily debated and determining whether the inundation event was a tsunami or storm remains an unresolved challenge (Cox et al., 2020). Using physical experiments, we aim to achieve a better understanding of how tsunamis move coastal boulders. This knowledge will aid field geomorphologists in the identification of the emplacement mechanism for coastal boulder deposits and allow for the determination of wave parameters. In January 2023, physical experiments using the HR Wallingford Tsunami Simulator were completed as part of the MAKEWAVES collaboration. These experiments investigated the movement of a cuboid and irregular shaped boulder model when impacted by different tsunami waveforms on a plane beach. We propose new empirical formulae to describe relationships between transport distance and different tsunami waves.

Most established laboratories that perform physical modelling have particular methods for hydraulic model studies. Physical modelling procedures in different laboratories vary in e.g. wave generation techniques; typical storm sequences; wave calibration techniques; scaling of short duration (impulsive) loadings; scaling of permeable materials; monitoring of damage and quantifying small armour movements; overtopping analysis; analysis and verification procedures; factors of safety etc. The potential differences in modelling results are difficult to judge, but may be significant in some cases. Reliable comparison of model test results will only be possible if the test set-up, measurement techniques and modelling approach are verifiably (i.e. geometrically, dynamically and kinematically) similar. This is often not the case, so comparisons between model results from different laboratories and data transfer between laboratories are complicated. This paper presents new guidelines (available for download at http://www.hydralab.eu/) to form a basis for a more unified physical modelling approach, which simplifies data transfer and the interpretation of modelling results gathered by varying laboratories and modelling approaches. To achieve this more unified modelling approach, guidelines for good laboratory practice in physical (experimental) model testing of coastal structures exposed to wave action have been developed.