Avon - Tides
The Bristol Channel and Avon estuary have a very high tidal range of 15 metres (49 ft), second only to Bay of Fundy in Eastern Canada; and the gorge is relatively narrow and meandering, making it notoriously difficult to navigate. Several vessels have grounded in the gorge in the 1800's including the SS Demerara soon after her launch, the schooner Gipsy, the steam tug Black Eagle and the Llandaff City. The phrase "ship shape and Bristol fashion" arises from when the main harbour in Bristol was tidal, the bottom of which was rocky. If ships were not of stout construction then they would simply break up as the tide receded, hence the phrase.
You can read more about the Avon at the Wiki
The Geocache
This is not a Park and Grab - use the suggested parking if you are driving do not stop on the A4 Portway
The hide is a nice little spot where you can see the effects of the tide on the banks of the River Avon.
Be sure to grab the bonus information in the cache
Enjoy!