How does water reach the top of the waterfall?

Typically,a river flows over a large step in the rocks that may have been formed by a fault line.As it increases its velocity at the edge of the waterfall,it plucks material from the riverbed.This causes the waterfall to carve deeper into the bed and to recede upstream.Often over time,the waterfall will recede back to form a canyon or gorge downstream as it recedes upstream,and it will carve deeper into the ridge above it.