There was something else that caught my attention. To the right of the location in this first video, there was a change in slope, where two concrete slabs came together at an angle. At the same location, water was flowing from two directions, the stream lines joining at almost 90deg angle.
This caused the flow to have its top surface split in two. Are these standing waves? What else are they called and what causes their formation? The change in slope? Flow directions joining at 90deg angle? A combination of both? Watch the video and let me know.