The Bristol Channel and River Severn are lethal if you don't have a reliable craft that is fully marinised and that will remain afloat indefinitely with engines off and a flooded plenum. In particular the Severn is very, very dangerous - looks lovely at high water on a calm day - don't be deceived - it changes in a moment and kills people.
This club used to do training and experience days from Sharpness but there haven't been any in recent years. They used to be good fun !
Before going on the water, find a flat field with short grass and get the hang of land operations - also if the craft breaks down you can recover it without the risk of drowning. Beach operations risk upsetting the locals and authorities and will wear out skirts alarmingly quickly.
Making the craft work is only the very first part of becoming a safe operator. They are huge fun - we were out last week on exercise with the emergency services - but can seriously bite you. Usually if you ditch the only thing that can reach you in the Bristol Channel is another hovercraft - or a helicopter ! It is also a very high maintenance area due to the mud, sand and suspended grit in the water.
There is a huge amount of information on the club site - well worth a few hours reading it. Some very experienced operators and a wealth of knowledge in the club.
Remember the first rule of hovercraft - no matter the size of the operating area, all hovercraft have a magnetic attraction to the largest single immovable object in the vicinity that they will, at some point, attempt to move by the transfer of kinetic energy.
PM me if you want more information about the Somerset side.