In a fluvial environment, deposition of bed load is primarily controlled by:

In a fluvial environment, deposition of bed load is primarily controlled by:

• A. Temperature and salinity
• B. The velocity of the water and size of the grains
• C. Bedrock type
• D. Channel width

Answer: (B)

Bed load deposition in rivers is controlled by how hard the flow can push grains and how big those grains are. The flow generates shear stress at the bed; when this stress is high enough to move a grain, it can be set in motion. Each grain size has a threshold of motion, so the larger the grain, the stronger the flow must be to move it. As the flow velocity decreases or encounters conditions that lower transport capacity, grains that were just barely mobile settle out and form bed-load deposits. That direct link between flow velocity (which sets the energy for transport) and grain size (which sets the resistance to motion) makes them the primary controls on where bed-load deposition occurs. Temperature and salinity don’t directly control bed-load deposition in a fluvial system, bedrock type mainly affects sediment supply rather than the immediate deposition process, and channel width influences flow patterns but not the fundamental threshold for deposition.

Bed load deposition in rivers is controlled by how hard the flow can push grains and how big those grains are. The flow generates shear stress at the bed; when this stress is high enough to move a grain, it can be set in motion. Each grain size has a threshold of motion, so the larger the grain, the stronger the flow must be to move it. As the flow velocity decreases or encounters conditions that lower transport capacity, grains that were just barely mobile settle out and form bed-load deposits. That direct link between flow velocity (which sets the energy for transport) and grain size (which sets the resistance to motion) makes them the primary controls on where bed-load deposition occurs. Temperature and salinity don’t directly control bed-load deposition in a fluvial system, bedrock type mainly affects sediment supply rather than the immediate deposition process, and channel width influences flow patterns but not the fundamental threshold for deposition.