Page - 453 - in Book of Full Papers - Symposium Hydro Engineering

COMMISSION INTERNATIONALE DES GRANDS BARRAGES ------- VINGT-SIXIÈME CONGRÈS DES GRANDS BARRAGES Autriche, juillet 2018 ------- EXPERIMENTAL STUDY ON BED EROSION DOWNSTREAM FROM A DAM* Zhijing LI, Jun WANG CHANGJIANG RIVER SCIENTIFIC RESEARCH INSTITUTE CHINA ABSTRACT The nature of flow, sediment transport and bed erosion were studied in a laboratory flume using mixed-size sediment under clear water conditions. During each experiment, water depth, bed and water surface elevation, bedload transport and bed state were continuously monitored. Steady inflows were established with an unit discharge of about 0.01 m(2) s(-1) to 0.03 m(2) s(-1). Well sorted gravel and sand were employed to compose four kinds of sediment beds with different gravel/sand contents, i.e., uniform 100% gravel bed, uniform 100% sand bed, and two graded sediment beds respectively with 53% gravel and 47% sand as well as 22% gravel and 78% sand. For different sediment beds, the experiments were conducted under the same discharges, thereby allowing for the role of sediment composition in dictating the bed erosion to be identified. The measured bed elevation for all the twenty runs show that significant degradation is spotted, yet the scour is mainly confined to the upstream part. For a specific sediment sample, the degradation enhanced with the increase of the inlet flow discharge. Under a specific unit-width flow discharge, the degradation for the four sediment samples generally follows the rule that the scour process increases with the increase of sand content in the sediment bed. However, it also exhibits an interesting phenomenon that the maximum scour depth with pure sand is not the largest, instead the case with 78% sand content features the deepest scour. In line with this observation, the scour with pure sand extended considerably farther *titre de l'articlecomplet 453