The movement of water within the river channel

• A. Channel flow
• B. Surface runoff
• C. Evaporation
• D. Drainage basin

Answer: (A)

The movement of water within the river channel is channel flow. This describes water that is confined to the main conduit of the river, moving between its banks as it travels downstream. Channel flow is the actual transport of water through the narrow, defined path of the river, governed by gravity, the channel’s shape and roughness, and the slope, which together determine how fast and how much water passes a point (the discharge).

This is different from surface runoff, which happens when rainwater flows over the land surface before it enters the river, and from evaporation, which is the loss of water to the atmosphere from surfaces. It’s also distinct from the drainage basin, the entire geographic area where precipitation collects and drains toward the river, not the movement of water once it’s already inside the channel.