These ripples are waves travelling through the water. Like ocean waves ... so the peaks of the resulting wave are higher and the troughs are lower. If two waves meet each other out of phase ...

A few months ago the North German Lloyd liner Brandenburg came into New York harbor with her crows nest, 50 feet aboye the water ... from trough to crest of 40 to 50 feet. Much higher waves ...

The stream being shallow and its surface in waves, the crest of the water-wave was pushed up-stream as the up-stream flank of the sand-wave received additions of material. The scour of the water ...