[1] As flowing water splashes over and around the rocks, air bubbles become mixed in with it and portions of the surface acquire a white color, forming what is called "whitewater".
[2] For a rapid to form, a necessary condition is the presence of a gradient, which refers to the river or stream's downward slope.
[4] This impacts the river's flow or discharge, which is measured as a volume of water per unit of time.
Constriction refers to when rivers flow through narrower channels, thus increasing the velocity of the water.
Obstacles may occur by human activity, natural landslides and earthquakes, or accumulation of sediment or debris.