Settling velocities of coarse organic solids

Area of Science:

• Environmental science
• Hydrology
• Fluid dynamics

Background:

• Settling velocity is key for stormwater modeling, predicting particle fate and nutrient loading.
• Inorganic particle settling is well-understood, but organic particles lack standardized estimation methods.
• Organic particles, like leaves and seeds, exhibit variable properties affecting their settling.

Purpose of the Study:

• To investigate the settling velocity of organic particles, specifically tree leaves and seeds.
• To evaluate the applicability of existing settling velocity equations, such as the Ferguson and Church Equation, for organic matter.
• To improve the representation of organic particles in stormwater models.

Main Methods:

• Conducted settling velocity experiments using various tree leaves and seeds.
• Analyzed particle settling data in the context of the Ferguson and Church Equation.
• Investigated the sensitivity of the drag coefficient (C2) to particle type and shape.

Main Results:

• The drag coefficient (C2) in the Ferguson and Church Equation was found to be sensitive to organic particle type and shape.
• Averaging C2 by particle type and species yielded a strong correlation (R² = 0.83) between observed and predicted settling velocities.
• The study provides a refined approach for estimating organic particle settling.

Conclusions:

• The Ferguson and Church Equation, with adjustments for organic particle characteristics, can effectively predict settling velocities.
• Stormwater modelers can better represent organic particles using these findings.
• Further research on diverse organic particle types is recommended to expand the dataset.