River surge flow is waves that naturally occur. From the NPS website, "This is one of the few places in the world where one can experience surge flow, a stream flowing in rhythmic waves on sand. Three elements are needed to produce the phenomenon: a relatively steep gradient to give the stream a high velocity; a smooth, mobile creekbed with little resistance; and sufficient water to create surges".
It's such a unique thing to see that I probably stood and watch it for an hour.
It's such a unique thing to see that I probably stood and watch it for an hour.