Modelling tsunami induced coarse clast transport , combination of physical experiments, advanced numerical modelling and field observations

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While coastal areas are highly attractive for population and industry, they are also highly exposed to extreme-wave events (tsunamis, storm surges). Considering the expected continuing population and industrial growth, there is an urgent need to assess frequency-magnitude relationships and damage potentials with high accuracy. Based on such assessments, it is possible to develop hazard management plans and hazard-mitigation strategies. Even though high-magnitude tsunamis may cause disastrous impacts, their recurrence intervals are in the range of hundreds to thousand years. Thus, at particular coasts with short historical records, no observations or even measurements of such worst-case scenarios might be available. In this case marine sediments deposited onshore provide, evidence for an extreme-flooding event. By associating specific sediment characteristics with the necessary wave-energy for particle movements, distinct characteristics of the hydrodynamic process inducing the sediment transport (tsunami or storm surge/wave setup-up) can be derived. Since subaerial blocks and boulders are more resistant towards erosion and human impact as fine sediments, they are more suitable for such investigations. However, distinguishing between storm and tsunamis is in most cases a tough task. Numerical models can support such interpretations, but still suffer from several simplifications as negligence of sedimentary load, interactions between multiple boulders or complex boulder shapes. Furthermore, these factors are also neglected in state-of-the-art physical laboratory experiments. Likewise, only experiments utilizing idealised shaped body-models on uniform shaped bathymetries and coastal topographies are known.The proposed project aims at bridging four substantial gaps in the state-of-the-art. Firstly, the behaviour of (i) complex and idealised model boulders and (ii) interactions between them during the tsunami runup will be analysed and compared by laboratory experiments. Investigations of the influences on boulder transport mode, path, and distance due to (iii) non-uniform bathymetric settings and (iv) sedimentary load follow afterwards. The next step comprises the development, calibration, and validation of a numerical two-phase model by using results of the physical experiments. Based on photo-technically recorded and numerically implemented data for topography and block deposits, the model shall be able to simulate tsunami-induced transport events with an unprecedented accuracy by project close-out. For the post-project future, the model application is intended for the island of Bonaire (Netherlands Antilles), where the coastal boulder sedimentology is already documented in high detail.