It is generally known as a plunge pool.
The body of water at the bottom of a waterfall is called a plunge pool. It is formed by the force of the falling water eroding the rock below, creating a deep pool. Plunge pools can vary in size and depth depending on the characteristics of the waterfall.
a plunge pool is a deep pool,lake or pond that often sits under a waterfall. It erodes with the waterfall and becomes deeper as the waterfall erodes more. It erodes stones and rocks in the plunge pool
The sound made by a waterfall is often described as "roar," "rumble," or "cascade." It is created by the rush of water falling and crashing into rocks or the pool below.
A waterfall.
Waterfalls create a washed out, deeper, area below them due to the principles of erosion. As the water falls in the area, the mass and velocity of the water digs into the soil below and washes it away. This effect creates deeper pools below the falling water.
The gravitational potential energy of the water at the top of the waterfall is converted into kinetic energy as it falls. This energy is then transferred to the water and surrounding environment as thermal energy and sound upon impact with the pool below.
It is at Multnomah Falls located in the Columbia River gorge outside of Portland OR
Call a plumber
If it is a rather large waterfall, the water is filling up the bowls in the waterfall till it spills over back into the pool. If you have to keep adding water after using the waterfall it could be a leak in the waterfall itself. If you don't have to add water when the waterfall is not in use and you do when you use it, well, guess what? Probably a leak in the waterfall. If it is a natural rock waterfall look for cracks in the grout between rocks. If artificial rock, look for cracks everywhere.
The Deep End or diving zone
how tall is the waterfall? What's the flow rate? What's the temp of the water and the ambient temp of the surrounding air?
It moves backwards as the continuous flow of water erodes away the rock, causing the waterfall to move