[H-QR06] Innovative applications of luminescence and ESR dating to geosciences

[HQR06-P05] Understanding sediment transport from residual luminescence signals

*Toru Tamura¹ (1.Institute of Geology and Geoinformation Geological Survey of Japan, AIST)

Keywords:luminescence, sediment transport, river, coast

Residual luminescence signals retained in modern sediments in fluvial and coastal environments are known to provide a tracer of sediment transport. Residual luminescence signals are generally lost by exposures to the sunlight during sediment transport from upstream to downstream in rivers or from updrift to downdrift in coasts. Thus, spatial variations in residual luminescence retained in sediments on paths of sediment transport provide quantitative information, such as transport direction. In recent years, some studies attempted at utilizing residual signals for quantifying transport rate in rivers. Existing attempts rely on two different models. The first model expresses the downstream gradient of residual signal as a sum of sediment exchange rate between the river channel and flood plains, and bleaching rate of sediment grains that are transported in the channel, and then estimates the transport rate and exchange rate based on the best fit of the model for the observation. The second model assumes different values of the average transport distance (D), transport interval (R), and bleaching probability of single grains, simulates bleaching histories of an individual grain, and then obtains a combination of D and R or transport rate (D/R) that give the best fit for the observation. Both models so far are hampered by limited understanding of bleaching processes. In the second model, the bleaching processes are represented by a variable, P. While the first model considers the bleaching rate, it only relies on simplified bleaching experiments and assumptions. For coastal sediment transport, a similar model to the first model, coupled with the beach and surf zone processes, was considered but is potentially improved by thorough understanding of bleaching processes especially in shallow water. Thorough observation in modern fluvial and coastal environments and bleaching experiments in flumes are essential for improving bleaching processes and making residual luminescence signals a reliable and quantitative tracer of sediment transport.