天竜川における出水履歴が河床の水質機能に及ぼす影響

Abstract

Transport dynamics of sediments, POM and solutes are complex phenomena interacting each other in a river ecosystem. In order to know the effects of geomorphological changes by floods on filtering efficiency of the drifting materials, we conducted field surveys on longitudinal changes of water quality in the Tenryu River. Samples of water and suspended sediments were collected at 19 sampling stations three times in 2016-2017 and analyzed chemical parameters of major ion, concentration of suspended sediments. River bed changes were measured as eroded and deposited area of each bar structure using satellite images taken before and after the previous floods occurred just before the survey. The results showed that variability of the hydrochemistry is controlled by temporal and longitudinal factors. The attenuation coefficient of the hydrochemistry was related to the river bed changes of the bar structure. These results suggest that beneficial effects of the water purification function improved by the riverbed fluctuation by the flood.