Physical models of tsunami deposition : an investigation of morphodynamic controls

A key goal of tsunami research is to quantitatively reconstruct flow parameters from paleotsunami deposits in order to better understand the geohazards of coastal areas. These reconstructions rely on grain-size and thickness measurements of tsunami deposits, combined with simple models that allow an inversion from deposit characteristics to wave characteristics. I conducted flume experiments to produce a data set that can be used to evaluate inversion models for tsunami deposition under controlled boundary conditions. Key variables in the flume experiments are sediment grain-size distribution, flow velocity and depth, and depth of water ponded in the flume before the tsunami bore was released. Physical experiments were run in a 32 m-long outdoor flume at The University of Texas at Austin. The flume has a head box with a specialized mechanical lift gate that allows instantaneous release of water to create a bore. Various sediment mixtures (silt to very coarse sand) are introduced to the upstream end of the channel as a low dune positioned just below the lift gate. The bore entrained the sediment mixture, producing an unambiguous suspension-dominated deposit in the downstream half of the channel. Deposits were sampled for grain-size and thickness trends. The experimental results capture characteristics of many recent and paleotsunami deposits, including consistent fining in the transport direction. In addition to overall fining, trends in deposit sorting and coarse (D95) and fine (D10) fractions reveal the importance of sediment-source grain-size distribution on tsunami deposit attributes.