What do you call a deep basin formed at the bottom of a waterfall by erosion?

A deep basin formed at the bottom of a waterfall as a result of erosion is known as a plunge pool. This geological feature is created when the force of the water falling over the edge of the waterfall erodes the rock beneath it. Over time, the continuous impact of the water can deepen this basin, leading to a characteristic shape often associated with powerful waterfalls.

In contrast, a catchment area refers to the region where all the water drains into a particular river or stream, and a hydrograph basin is related to the graphical representation of river discharge over time. Velocity pool is not a standard term used in fluvial geomorphology and does not accurately describe a feature associated with waterfalls. Understanding plunge pools is essential in the study of river morphology and the processes of erosion and sediment transport.