Which parameter is used to determine flow pattern, type of flow, and whether a non-cohesive particle will settle through a water column?

• A. Darcy's law
• B. Bernoulli's principle
• C. Reynolds number
• D. Froude number

Answer: (C)

Reynolds number is the parameter that tells you how inertial forces compare to viscous forces in a fluid. That balance controls how the flow behaves around a particle and through the water column, which in turn determines both the flow pattern (laminar vs. turbulent) and whether a non-cohesive particle settles smoothly or with disturbances.

When Reynolds number is low, viscous forces dominate, the flow is smooth and orderly, and a particle settles in a predictable, nearly steady way (described by Stokes’ regime). As Reynolds number increases, inertial forces become more important, the flow around the particle can become unsteady and turbulent, the drag changes, and the settling behavior becomes more complex.

This same concept also governs flow pattern in open channels or pipes: small Reynolds numbers yield laminar flow, large Reynolds numbers yield turbulent flow. The other options describe different ideas that don’t capture this direct link between inertial vs. viscous effects and the settling behavior in a water column.