Modeling of sediment transport in rapidly-varying flow for coastal morphological changes caused by tsunamis

Kei Yamashita, Yoshiki Yamazaki, Yefei Bai, Tomoyuki Takahashi, Fumihiko Imamura, Kwok Fai Cheung

Research output: Contribution to journalArticlepeer-review

1 Citation (Scopus)

Abstract

Tsunamis can cause significant coastal erosion and harbor sedimentation that exacerbate the concomitant flood hazards and hamper recovery efforts. Coupling of the non-hydrostatic model NEOWAVE and the sediment transport model STM provides a tool to understand and predict these morphological changes. The non-hydrostatic model can describe flow fields associated with tsunami generation, wave dispersion as well as shock-related and separation-driven coastal processes. The sediment transport module includes non-equilibrium states under rapidly-varying flows with a variable exchange rate between bed and suspended loads. A previous flume experiment of solitary wave runup on a sandy beach provides measurements for a systematic evaluation of sediment transport driven by shock-related processes. The extensive impacts at Rikuzentakata, Iwate, Japan and Crescent City Harbor, California, USA from the 2011 Tohoku tsunami provide pertinent case studies for model benchmarking. We utilize a self-consistent fault-slip model to define the tsunami source mechanism and field survey data to determine the characteristic grain sizes and morphological changes. The near-field modeling at Rikuzentakata gives reasonable fits with observed large-scale erosion and sedimentation associated with transition of the incoming wave into a surge and formation of a hydraulic jump in the receding flow. The non-hydrostatic module becomes instrumental in resolving tsunami waves at the far-field shore of Crescent City. The results show good agreement with local tide-gauge records as well as observed scour around coastal structures and deposition in basins resulting from separation-driven processes. While the erosion patterns in the laboratory and field cases can be explained by suspended sediment transport in the receding flow, bed load transport can be a dominant mechanism in sediment laden flows and scour around coastal structures.

Original languageEnglish
Article number106823
JournalMarine Geology
Volume449
DOIs
Publication statusPublished - 2022 Jul

Keywords

  • Coastal morphology
  • Non-equilibrium state
  • Non-hydrostatic flow
  • Rapidly-varying flow
  • Sediment transport
  • Tsunami

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