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

If you're interested in wave physics, the Severn Bore is related to solitons.

A soliton is a wave that is sort-of self-sustaining. Normal waves spread out and sink as they propagate through a medium (because some bits of the wave travel faster than others).

But in a soliton, the front and back parts of the wave are 'attracted' to the middle, so the wave tends to stay together.

The best analogy I've heard is this: imagine a bunch of similar fitness people running on a very long mattress in single file. They'll make a big dent in the mattress, so the fast people at the front are always running 'uphill', and the slow people at the back are always running 'downhill'. So they tend to stay together.

Light-Solitons can be used down long optical fibres to avoid the need for lots of repeaters.

Actually it's more related to fluid mechanics - something called a hydraulic jump - a very common phenomenon. The Severn bore is just really really dramatic.