Spatial variability in heavy rainfall induced sediment discharge volume from mountain catchments with similar topography, geology and rainfall conditions

Abstract

Predicting sediment discharge volumes from mountain catchments is one of key issues to assess damage induced by sediment laden flood. We evaluated sediment discharge volumes from mountain watersheds due to the sediment disaster July 2017 in Northern Kyushu using LiDAR data and rainfall data having a high in time and space resolution. Specific sediment discharge volumes from first-order catchments were highly varied by two order of magnitude despite no obvious differences in rainfall condition and relief of catchment. Fifteen to twenty five percent of first order catchments discharged larger than 500% or smaller than 20% of median specific sediment discharge volumes. Averaged specific sediment discharge volumes from second or third order catchments were almost the same as first order catchment.

However, spatial variability of specific discharge was dramatically decreased with increase of stream order. These patterns were probably due to mixing of randomly distributed sediment discharge in first-order catchment.