Why does the Zambezi River have rapids and narrow channels upstream of Victoria Falls?

The Zambezi River’s flow characteristics upstream of Victoria Falls are defined by the river's varying topography as it moves toward the falls. In the stretch between the Cuando River confluence and the falls, the river’s width fluctuates significantly.1

The presence of rapids and narrow channels in this section is primarily due to the river encountering numerous rock islands that break up the flow. While the river also features open reaches containing sand islands, these rocky obstructions force the water into the narrow channels that characterize this part of the upper course.1