| In this study、 a hydraulic experiment of mobile bed was conducted with focus on the process of dune fading and[*]bed resistance fluctuation during a transition state under unsteady flow. The process was observed under two discharge[*]hydrographs of three hundred minutes and sixty minutes. The experiment results revealed that the bed resistance began[*]to decrease in the discharge increasing period. The height of dune decreased as the time of unsteady flow hydrograph.[*]The bed resistance decreased in accordance with the height of dune. Dune completely disappeared in the three hundred[*]minutes hydrograph、 however、 did not disappear completely in the sixty minutes hydrograph. The dune was reformed[*]again in the discharge recession period in sixty minutes case. A bivalency of water depth to the discharge was observed[*]in three hundred minutes case. Flow velocity coefficient in three hundred minutes case much increased than in sixty[*]minutes case. Comparison of the two hydrographs suggested that there was a delay of the riverbed and resistance[*]response in following the discharge curve during the transition process. |
