Sediment yield from seismically-disturbed mountainous watersheds revealed by multi-temporal aerial LiDAR surveys

摘要

The Mid Niigata Prefecture Earthquake (M = 6.8) that occurred on 23 October 2004 caused numerous landslides and landslide dams in the Imo River basin (A = 38 km~2) of Niigata Prefecture, Japan, altering sediment yield and discharge processes. Snowmelt and rain events produced more landslides in the basin in following years. We conducted multi-temporal aerial LiDAR surveys to clarify the post-seismic sediment dynamics in this seismically-disturbed mountainous watershed. The surveys revealed the following: in the 19 months after the earthquake, snowmelt and heavy rainfall events yielded 1.4 Mm of sediment (about 19% of that by seismic origin based on fieldwork and aerial photographic interpretation); landslides of seismic origin and those of rainfall or snowmelt origin had very similar distributions; as of May 2006, 70% of the sediment yielded by landslides had not been transported downstream, but remained under the scarps or beside the streams and throughout the periods after the earthquake, river bed deformation in the stream part is larger than the sediment runoff to river course in slope part; and the total amount of post-seismic sediment discharge obtained by the multi-temporal bathymetric surveys coincided fairly well with that of the post-seismic sediment runoff, as revealed by the multi-temporal aerial LiDAR surveys.