Monitoring channel responses to flood events of low to moderate magnitudes in a bedrock-dominated river using morphological budgeting by terrestrial laser scanning

Abstract Changes to channel morphology reflect geomorphic work by flood events of differing magnitude and frequency. Advances in remote sensing and digital terrain processing now allow for sophisticated analysis of spatial and temporal changes in erosion and deposition. Although the morphological budgeting approach using digital elevation models of difference has been widely applied to track volume estimation of changes to erosion and deposition over time, appraisals of geomorphic effectiveness in high-energy confined and partly confined channels are still lacking. This study applied terrestrial laser scanning to monitor three reaches of the Liwu River, a bedrock-dominated river in eastern Taiwan, from 2009 to 2012, to investigate channel responses to flood events of low to moderate magnitude and appraise their geomorphic effectiveness. Variability in geomorphic effectiveness reflected valley confinement and the composition/configuration of geomorphic units on the channel bed. Annual low magnitude flood events reworked gravel and sand deposits, creating local scour and fill ( 3 (~ 1 m in depth) and were able to modify channel configuration in partly confined and unconfined reaches. Frequent changes of scour/fill position on the channel bed indicate that the Liwu River is highly sensitive to flood events of low to moderate magnitude. This reflects an active orogenic river system that is characterized by a steep channel and narrow valley floors with limited accommodation space but abundant sediment.