Sedimentation processes in silt-rich sediment systems

Sediment found in China’s Yangtze and Yellow River systems is characterized by large silt fractions. In contrast to sand and clay, sedimentation and erosion behaviour of silt and silt–clay–sand mixtures is relatively unknown. Therefore, settling and consolidation behaviour of silt-rich sediment from these river systems is analysed under laboratory conditions in specially designed settling columns. Results show that a transition in consolidation behaviour occurs around clay contents of about 10 %, which is in analogy with the transition from non-cohesive to cohesive erosion behaviour. Above this threshold, sediment mixtures consolidate in a cohesive way, whereas for smaller clay percentages only weak cohesive behaviour occurs. The settling behaviour of silt-rich sediment is found to be in analogy with granular material at concentration below 150 g/l. Above 150–200 g/l, the material settles in a hindered settling regime where segregation is limited or even prevented. The results indicate that for modelling purposes, multiple sediment fractions need to be assessed in order to produce accurate modelling results.