Which element of a river's behavior refers specifically to its flow rate?

The element of a river's behavior that specifically refers to its flow rate is velocity. Velocity measures how fast the water is moving at any given point in the river, typically expressed in meters per second. It is a crucial factor in understanding river dynamics, as it influences sediment transport, erosion, and the overall shape of the river channel.

Peak discharge, on the other hand, pertains to the maximum amount of water flowing through a river at a certain point, usually during periods of flooding or heavy rainfall. Lag time refers to the delay between the peak rainfall and the peak discharge in the river, reflecting the time it takes for water to flow into the river from the surrounding land. Energy relates to the river's capacity to perform work, like eroding banks or transporting materials, but it does not specifically focus on the flow rate itself. Therefore, velocity is the best term to describe the speed at which water flows in the river.