STUDY ON HYSTERESIS EFFECTS OF FLOODS ON BEDLOAD TRANSPORT WITH A PIPE HYDROPHONE IN UPSTREAM OF NUNOME-DAM

Abstract

We installed a pipe hydrophone and monitored bedload transport for 3 years at an upstream site of the Nunome Dam in Nara Prefecture. A few dozen times of flood events were observed each year including large-scale floods, such as the typhoon No.18 last year. The hysteresis curve between discharge and bedload was examined by comparing bedload transport between rising and receding phases in each flood event. The curve of each event changed according to the previous occurrence of large flood. Bedload at given discharge was almost equal between rising and receding phases for small floods, while that of receding phases increased for a large flood, and that of rising phases increased for a few subsequent smaller floods. Bedload is likely to increase temporally after a sediment supply from banks and tributaries occurring during large floods.