STUDY ON THE MICROTOPOGRAPHY OF VALLEY PLAIN IN THE RIVER AND ITS FLUVIAL GEOMORPHOLOGICAL MEANINGS.

Masaki WAKUI, Shoji FUKUOKA, Yutaka SATOH, Chihiro EGAWA and Keiya MIKATA

1 950-0965 10 22 Ph.D 112-8551 1-13-27

3 950-0965 10 2

The estimation of possible maximum flood discharge due to climate change is an important issue in order to examine measures for the disaster prevention and reduction in the river basin. In general,the extremal discharge is estimated by the meteorological approach. Here, the other approach is attempted to investigate geological and geomorphological traces of the past extremal floods left in valley plains. In this study, we focused on the Yosasa River of Tochigi Prefecture where various studies and analysis has been carried out since the large flooding in 1998, then we carried out the microtopography investigation left at valley bottom. Therefore, we showed that the extremal discharge is estimated by steps and soil structures in the valley bottom.

Key Words : valley plain , microtopography , step, Yosasa River, extremal discharge,

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