In reply to teflonpete:
I have surfed it on 3* and that was quite hairy. If you fall off the back of the wave, there is an amazing amount of chop behind it, which I wasn't prepared for.
We put in at Newnham and surfed it for a bit there - it's nice and wide there and good for the novice. Getting out was tricky, due to the chop, but there are a couple of storm drains that make a nice, sheltered eddy on the Western bank. The Eastern bank is grassy and a mud flat at low tide, but you're a bit stranded if you get out that side.
Got out and legged it up to the Severn Bore Inn, but were too late to catch it there. Roadside parking will be busy, both with surfers and sight-seers. Rocky put-in, wouldn't like to have to get out there in a hurry.
After the Bore pub, the river gets pretty narrow and there are rocks and trees at the edges, which makes it quite dangerous.
Further attempt to catch it under the A40 bridge, I think - sat there waiting in the water, but it had died out by then. There's a carpark on the Western side. The put-in under the bridge is very muddy and slippery - fortunately, someone else had tied a throwline as a handrail, or getting out would have been a nightmare.