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What is a Stationary or Standing Wave?

Stationary Waves

A stationary or standing wave forms when water is pulled back against the flow by gravity.

When water flows over an underwater ledge and then drops suddenly, it speeds up and falls down to a point that is now lower than the surrounding water, which effectively creates a temporary ‘hole’ in the water. Holes are both dangerous and interesting because of what happens next.

The water tries to return to level and so water from around the hole will pour back in to try to fill it, and the slightly odd thing is that it will even flow upstream to fill it. Since the water is still pouring down over the ledge, the result is a curious and precarious balance where the water flowing down keeps creating the hole and the water flowing back up to fill it creates a continuous flow of water upstream, which in turn often results in a stationary wave or standing wave that appears to be going the wrong way. The wave doesn’t move upstream, but it appears to surge upstream without moving.

Hole and Stationary Wave to right of hole. Illustration by Neil Gower.

The above is an excerpt from the book, How to Read Water by Tristan Gooley.

Stationary Waves