Geography of senior high school: What does the flow mean in the picture?

This traffic is not our mobile phone "data traffic", it is real traffic.

The size of "flow" in the question represents the amount of water. A large flow means a large amount of water per unit time and a small amount of water per unit time.

Rainfall is a common weather, and its flow direction goes without saying. Even if it is moderate rain, its water volume is very large. If it rains cats and dogs for a long time, it will cause floods.

Glacier melt water, you think about it, is that ice turns into water and flows down the mountain. How big can it be? At most, it is the amount of mountain springs. Do you think the traffic will be large? But the output time is long, the output is relatively stable and the price is expensive, so it is also the main supplementary water source of the river.

Geography is a very interesting subject. Work hard! !