Why do settling and yield stress of mud differ in european ports?

Abstract

In some ports and waterways, hindered (delayed) settling of mud suspended in the water phase can be detected. Hindered settling phenomena are typically linked to a combination of sediment properties, suspended sediment concentration or density, hydrodynamic conditions, presence or absence of organic bridging between mud particles and the properties of the water phase such as salinity. Hindered settling may be desired or undesired for maintenance of the nautical depth - it might be beneficial if the properties meet the nautical bottom criteria for safe navigation and maneuvering; however, in case fast settlement and consolidation is necessary for efficient dredging, hindered settling is disadvantageous. Yield stress of mud has been extensively studied for the nautical bottom and port maintenance purposes over the last years. New rheological protocols have been developed for measuring rheological characteristics of mud deposits and analysing the structural recovery of mud. Additional knowledge has been gained from studying the role of density and organic matter and further comparison to the yield stresses measured in the laboratory and in the field. This work connects the knowledge of settling phenomena and rheology. Settling and rheological behaviour of mud from different European ports has been extensively studied. Variation of yield stress values in different ports has been studies by correlating rheological properties and settling of mud to other key sediment properties like density, mud composition, clay content and clay type, total organic carbon (TOC) and organic matter degradation.