h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I don't know if you saw the programme on BBC2 'Local Heroes', which had a piece on solitons, which are waves that travel amazing distances without decaying, and pass through other waves without losing their form, but...... *pause for breath*... I think the Severn Bore is one. It starts near me, at Bristol, and goes upstream to you, Gloucester. This is quite amazing when you compare it with yer average wave-on-a-beach. Similar things happen on canals with the wash of narrow boats. The interesting thing about solitons is that higher waves travel faster and pass through slower waves as if they weren't there, and so go on for miles. I suspect the sudden depth change in the Bristol Channel gives the necessary shock to the water in order to form a soliton and the volume of the water at spring high tide is sufficient to produce a large enough wave to travel up the Severn. Just a thought.

I didn't see the programme but I know that there is the width tapering and also a deep shelf which alters the depth. The water is forced into such a small space it creates a large powerful wave!