Which of the following factors affects flow velocity?

Flow velocity in a river or stream is primarily influenced by the channel slope or gradient. When the slope of the channel is steep, water flows downhill under the influence of gravity, leading to a higher flow velocity. Conversely, a gentle slope reduces the potential energy that propels water forward, resulting in slower flow. This relationship between slope and velocity is a fundamental concept in hydrology, as it reflects how gravitational forces can enhance or diminish water movement through a channel.

While other factors may have an effect on overall water movement, none directly influence flow velocity with the same immediacy as channel gradient. For instance, the height of the banks determines the capacity of a river to hold water but doesn't directly impact how quickly that water flows. Temperature may affect water density and viscosity, which can influence flow characteristics, but does not have the same direct correlation with velocity as slope does. Weather conditions can impact flow indirectly by affecting water levels or precipitation but are not a primary factor in determining the velocity of water in a given channel at any specific moment.