How was water
velocity created

The water velocity was created due to the increasing inclinations of the slopes that the water flowed over.

Explanation:

As the water flowed over different surfaces, its velocity kept on exhibiting different values throughout. The surfaces that were more inclined naturally increase the velocity of the water as it flowed over them. With the incidence of flat surfaces, the velocity of the water decreased as the gravitational pull began acting perpendicular to the flow of water.