Muddy sediments are abundant across aquatic ecosystems, consisting of mineral grains and biological material. Erosional characteristics of these cohesive sediments are impacted by micro-organisms providing bio-stabilisation. Deposition may be impacted by chemical and biological composition, along with turbulence properties, which in turn influence flocculation of suspended particulate matter. Flocculation processes affect settling velocity, porosity and density characteristics. Cohesive sediments absorb contaminants, as well as influencing interactive processes between sedimentary dynamics and hydrodynamics, through their bio-physical attributes. It is therefore beneficial to predict muddy sediment transport processes via numerical modelling. Accurate modelling relies on quantitative erosional and depositional data for calibration. Through collation and analysis of field- and laboratory-derived data sets, this study examined aspects of erodibility and deposition across several aquatic environments (including estuarine, intertidal and lake sediments). A range of case studies examined floc properties, sediment composition, erosion thresholds, turbulent shear stress and suspended particulate matter concentration. Investigation of floc dynamics in estuarine sediments revealed larger, faster settling flocs in muddy sediment (mean settling velocity, Wsmean = 4.1-5.2 mm.s⁻¹; mean floc effective density, ρe,mean = 317-352 kg.m⁻³). In mixed sediment, flocs were smaller and settled more slowly (Wsmean = 3.8-4.0 mm.s⁻¹; ρe,mean = 288-508 kg.m⁻³). Comparison of oil-contaminated sediments revealed the importance of floc size class and mineral type. On the addition of oil, larger, faster settling flocs were produced in pure bentonite cases, while smaller, slower settling flocs were observed in kaolinite cases. In highly organic lake sediments (organic content = 62%), settling velocity varied over increasing suspended sediment concentration and between floc size classes (macroflocs faster than microflocs by 0.95 mm.s⁻¹). Such findings may be utilised to increase the understanding of complex sedimentary and hydrodynamic interactions within aquatic environments. This study provides quantitative data, applicable to the improvement of predictive numerical model reliability.

Many aquatic environments are dominated by muddy sediments. These cohesive sediments, however, often contain a mixture of sand, mud and organic material, giving rise to complex interactional behaviour, the nature of which is often controlled by bio-physical attributes. An understanding of these complex interactions is paramount in the accurate prediction of sediment transport processes in numerical models, facilitating monitoring and management of marine environments. Calibration of such models relies on quantitative erodibility and depositional data. Muddy sediments flocculate; a process impacted by complex sedimentary and hydrodynamic interactions. The degree of sediment stability describes the degree of flocculation and depends on interactive forces (including bonding cohesion) between suspended particulate matter and turbulent shear stress, as well as mineralogy and biological composition. Erodibility and deposition properties rely greatly on the formation and break-up of these flocs, in turn impacting processes of sediment transport. This study examines, through the use and comparison of various data sets, aspects of both erodibility and deposition for several different sedimentary conditions. Collation of a range of quantitative field and laboratory-derived sedimentary and hydrodynamical data sets (e.g. sediment composition, floc properties, bed density, mass erosion rates, erosion thresholds, suspended particular matter concentration, turbulent shear stress) from a range of aquatic scenarios (including estuaries, intertidal areas, shelf seas, and lakes) are utilised to investigate the impacts of related controlling and influencing parameters on sediment transport, in particular to assess coastal erosion and sustainability. Case studies include: water quality monitoring, contaminated sediments, and dredging applications; these will be used to demonstrate / illustrate various applications of this sedimentary-hydrodynamic investigation. This research augments our understanding of the interactive processes within different cohesive sediments, providing quantitative analysis to inform and ultimately improve our mathematical representation of bio-physical sedimentary processes for implementation within predictive numerical modelling.