Viscosity of Cohesive Sediment‐Laden Flows: Experimental and Empirical Methods

Abstract The rheological behaviors of suspended sediments are crucial for investigating near‐bed particle dynamics; for these investigations, the viscosity of a highly concentrated suspension is primarily focused on quantifying its resistance to deformation. By using a rotational viscometer, the relationships between relative viscosities ( η r ) for different sediment types and their volumetric concentrations ( ϕ ) are studied for low‐to high‐concentration slurries. The results show that the conventional Einstein formula for diluted sand severely underestimates η r . In the case of pure silts and non‐cohesive quartz, η r demonstrates a gradual linear increase, reaching values around order of 10 1 as ϕ increases within the range of 0.2–0.4. Meanwhile, the η r values of clays exhibit an exponential rise before leveling off at a plateau. Specifically, the η r values of kaolinite, montmorillonite, and bentonite rise with ϕ lower than 0.3 and reach to plateau of values of thousands, which rise more rapidly than chlorite and illite. The modified viscosity model based on Costa (2005, https://doi.org/10.1029/2005GL024303 ) agrees reasonably well with observations and produces similar η r ∼ ϕ relationships. In addition, the model is coupled with a hydrodynamic model to simulate the deposition of a thickened tailings slurry and a one‐dimensional dam break. The proposed model performs well in predicting the quasi‐equilibrium profiles of the non‐Newtonian fluid, which are validated by available analytical solutions. The results suggest that future models should be focused on the effects of flow properties, especially for non‐Newtonian fluids, and on large‐scale modeling applications, which can increase the accuracy of predictions of the transport characteristics of sediments and pollutants in rivers, lakes, and coastal areas.