Abstract
Field observation of topographic changes of ebb tidal flat caused by the large flood associated with Typhoon 9719 was conducted at the Yasaka River mouth in Morie Bay in Oita Prefecture. Large amount of sediment deposited on the ebb tidal flat due to the flood of maximum discharge of around 1, 500m3/s. Topographic changes were measured with an accuracy of 1 cm along four survey lines across the ebb tidal flat as well as aerial photographing of tidal flat right after the flood. Flood ran aground of the tidal flat from the meandering main stream of the Yasaka River to form many sand dunes. Numerical simulation of two dimensional flood flows was carried out and observed results were well reproduced by this numerical simulation.
