I'm confused. If you follow the main channel, you don't go over the wall.
I've no experience of what depths are encountered around or inside the wall, and frankly, I have no intention of finding out. I follow the channel that's indicated by leading lines on the chart and by the leading marks on the shore. From Beachley, up Slime Road to Pillhouse Rocks (leading marks behind you, on the Beachley shore). Then cross the estuary, again following the leading marks astern and keeping the Cardinal and the lattice tower to starboard. From there on it's really just a matter of keeping all the marks to starboard (just) until you get to Sharpness or make the crossing to Lydney.
Not sure what the OP was about as it is now deleted, but the reservoir is strictly out of bounds (although the odd boat does go through it. I remember rescuing a YW Dayboat which had capsized during a windy race at TSC, and recall hearing the mast scraping over the wall as it drifted across upside down on the tide. Amazingly, the mast survived!)
I wish I hadn't posted the original thread . Background, I had a strange feeling that last time we took the trip up the Navionics took us over the reservoir. I must have bl**dy dreamt it - checked the charts and route in the plotter last weekend and it was no where near. I used the new 'autoroute' funtion on the iPad Navionics and transferred it to the Raymarine and checked that too and the rest I must have dreamt (my poor little brain never shuts off).
However, like you've said Snifter I've seen folk blatting over it too and taking a straight line through the bridges and not following the channel - this proves I'm paranoid but in that area I think its OK to be just that little bit paranoid .