抄録
To reconstruct the history of high-magnitude floods in a mountain gorge channel, botanical evidence from two vertically isolated strath terraces assumed to be affected only by large, infrequent floods was investigated. The maximum water level was estimated from peak and bankfull discharges during major storm events of the past 20 years. Injury of shrubs significantly indicated that overflow on the downstream terrace occurred in 1993 storm event, but no flood event overflowed both terrace surfaces according to the estimation of peak and bankfull discharges. We also found field evidences that a landslide on the slope opposite the downstream terrace generated a landslide dam in 1993 storm event. Formation of the landslide dam probably caused local overflow onto the downstream terrace during the 1993 event. Therefore, it is essential to investigate not only the hydrologic characteristics, magnitude, and frequency of discharge, but also the spatial and temporal patterns of lateral sediment input to the channel to understand flood behavior in mountain gorge river systems.
