Characteristics of Past Flood Behavior Reconstructed from Botanical Evidence in a Mountain Gorge River System

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.

[1]  S. George,et al.  Signatures of high-magnitude 19th-century floods in Quercus macrocarpa tree rings along the Red River, Manitoba, Canada , 2000 .

[2]  Oliver Korup,et al.  Recent research on landslide dams - a literature review with special attention to New Zealand , 2002 .

[3]  R. Gill.  A Review of Damage by Mammals in North Temperate Forests: 1. Deer , 1992 .

[4]  J. Alestalo.  Dendrochronological interpretation of geomorphic processes , 1971 .

[5]  I. Hashimoto,et al.  Geology of the Sambodake District in the Miyazaki Instruction Forest of Kyushu University , 1957 .

[6]  R. D. Jarrett.  Hydraulics of High-Gradient Streams , 1984 .

[7]  D. Yamaguchi.  A simple method for cross-dating increment cores from living trees , 1991 .

[8]  T. Marutani,et al.  Construction of changes in the density and distribution of Sika deer (Cervus nippon) through time based on dendrochronological method. , 1999 .

[9]  R. D. Jarrett.  Errors in slope-area computations of peak discharges in mountain streams , 1987 .

[10]  G. Brierley,et al.  Channel bed adjustments following major aggradation in a steep headwater setting: findings from Oyabu Creek, Kyushu, Japan , 2004 .

[11]  J. Phillips.  Geomorphic impacts of flash flooding in a forested headwater basin , 2002 .

[12]  R. S. Sigafoos.  Botanical evidence of floods and flood-plain deposition , 1964 .

[13]  A. Gottesfeld.  British Columbia flood scars: maximum flood-stage indicators , 1996 .

[14]  A. Harvey.  Effective timescales of coupling within fluvial systems , 2002 .