1. Lab. of Erosion Control, Dep. of Forest Science; Graduate School of Agriculture, Kyoto Univ.; Kitashirakawa Oiwake-cho, Sakyo-ku Kyoto 606-8502 Japan
2. CREST, JST; K's Gobancho, 7, Gobancho, Chiyoda-ku Tokyo 102-0076 Japan
3. Hodaka Sedimentation Observatory, Research Center for Fluvial and Coastal Disasters; Disaster Prevention Research Inst., Kyoto Univ.; 436-13 Nakao, Okuhidaonsengo, Takayama-shi Gifu 506-1422 Japan