What process involves moving sediments downstream in a river?

The correct answer is transportation. This process refers specifically to the movement of sediment and materials downstream by the flow of the river. In a river system, sediment can be moved in various forms: as dissolved matter (solution), as small particles that are suspended in the water (suspension), or as larger fragments being rolled or slid along the riverbed (traction or saltation).

Transportation is a crucial part of the river's dynamics, as it shapes the river's morphology, influences erosion and deposition patterns, and affects the ecosystem along the riverbanks and floodplains. Understanding how sediments are transported helps explain how rivers carry nutrients and play a pivotal role in forming new landforms downstream, contributing to the overall landscape evolution.

Erosion involves the wearing away of the riverbanks and riverbed, while deposition is the process of sediment being laid down as the river loses energy, typically at bends or where the river meets standing water. Flooding refers to the overflow of water onto land that is normally dry, which is related to excess water rather than the movement of sediment. Hence, transportation distinctly focuses on the movement aspect within the river system.