Fine sediment deposition and erosion are significant management and engineering issues in the water environment. High soil erosion rates and a legacy of pollution have resulted in the formation of thick, often contaminated, deposits of fine sediment in lakes, lowland rivers, and reservoirs that reduce capacities and impact water quality, especially when sediment erosion mobilises previously bound contaminants.
Fine sediment is also the foundation on which many hydraulic structures are built, especially in lowland and coastal settings, but erosion of the soft substrate is a primary cause of failure. However, despite decades of research on fine sediment, we still do not have a universal, physics-based model to predict the susceptibility to erosion (i.e. erodibility) of fine, cohesive sediment, as is the case for granular sediment, like sand and gravel.
Researchers at Cranfield University are using UKCRIC research infrastructure to support the development of new mechanistic models of erodibility in the EPSRC funded project ‘Improved prediction of cohesive sediment erosion based on inter-particle forces’. Experiments are currently ongoing in the UKCRIC Sediment Erosion Flume to determine how clay mineralogy and water chemistry interact to affect erodibility.
The flume, based in Cranfield’s National Research Facility for Water and Wastewater Treatment, is a unique facility in the UK. It was custom-designed to quantify erosion threshold and rates with depth in sediment cores with state-of-the art control systems that generate, monitor and control water flow, suspended sediment concentrations and bed sediment levels.
These precise empirical measurements of erodibility from the UKRIC flume are helping to validate new computation dynamics models of cohesive sediment erodibility. In the first phase of modelling, Cranfield researchers developed new molecular dynamics models of clay cohesion to determine how counterions in the clay mineral and cations in the water affect attractive forces between clay particles, which we ran on the UK’s Archer2 supercomputer. In the second phase of modelling, the team is scaling up the simulations using coupled CFD-DEM models to determine how sediment composition and water chemistry affects erosion thresholds and rates.
This combination of materials dynamics modelling and precise empirical measurements is laying new groundwork for a universal model of cohesive-sediment erodibility for application to engineering and water quality problems.