Abstract
The Fukui heavy rainfall on July 18, 2004, caused severe damage along the valley plain of the Asuwa River characterized by an incised meander. Dike breaks along the river resulted in the deposition of a large amount of sediment, so-called crevasse-splay deposits, on the plain. This study reports the characteristics of the deposits based on a field survey and aerial photograph interpretation in the township of Takada, Fukui city. Boulders probably supplied from the dike body and riverbed spread at the front of break points. The boulders are lobate or lingulate in planar view. Sand deposits covering paddy fields occurred on the western side of the boulders. The deposits extended toward the west-northwest by more than 200 m and were approximately 80 cm thick at maximum. However, the decrease in thickness downstream was not marked. To the south of the sand deposits, sun-cracked muddy facies were pronounced on the surface, although sandy deposits had covered the original surface before the flood. This is probably because the floodwater drained slowly in these areas during the recession phase and mud accumulated. Alignment of the farmland before land consolidation suggests that the plain had probably received repeated floods similar to this event.
