MONITORING OF SEDIMENT PROCESSES AT THE TENRYU RIVER ESTUARY

Abstract

 Sediment processes at the Tenryu River estuary were analyzed using X-band radar observations, bathymetry data collected by fishing vessels, and numerical calculations using XBeach. At the estuary, we observe two sediment processes: (1) sediment transports from the river to the coastal region, or river terrace, by the floods, and (2) sediment transports from the river terrace to the adjacent coastal area by the waves. We show a synthetic monitoring method to observe these sediment processes. In 2021, several prominent floods transported sediments from the river to the coastal region. We analyze these from the results of X-band radar observations and XBeach calculations. We show the deformation of the river channel, river sandbar, and surface flow velocities during the floods. Then, the deformation processes of the river terrace are derived from the X-band radar observations and depth collected by the fishing vessels. We analyze the refraction of the waves above the river terrace and estimate the depths. From the overall results, we describe qualitatively and quantitatively the sediment processes at the estuary and show the amount of sediments provided by the floods.