How does laminar flow behave in a river?

Laminar flow in a river is characterized by water moving smoothly and in roughly parallel layers with minimal mixing between them. This behavior ensures that the water travels in a streamlined fashion, often following straight-line paths, especially in areas where the flow velocity is low and the riverbed is smooth. As a result, the flow is stable and predictable, which is the hallmark of laminar flow.

The scenario described in the answer choice reflects the conditions that create laminar flow, such as gentle gradients and lower velocities. In contrast, turbulent flow, which often occurs in rivers with steeper gradients and higher velocities, produces chaotic and irregular movements of water, leading to swirling patterns, eddies, and mixing. This distinction underscores the importance of flow conditions in determining whether flow is laminar or turbulent.