Porter is the correct term. The works are until June 2023, although the river (ie the centre arch) is only closed to powered boats for the month of February. More detail just published here: https://www.camconservancy.org/public-announcement
In most parts of the river the depth is normally 3 feet, I would say. I reckon we are about 24 inches at the stern. The shoal that was causing the problem is marked on this chart (from the excellent guide by @FadeToScarlet) just to the right of bridge 10. It gives access to a wide and deep pool (with piling on the south shore) just before the weir and punt rollers, which is a very easy place to turn. I think I could probably have battled my way over the shoal, but it didn't seem a very good idea. So we backed down to the marked turning point (at which point one of the competing punt firms said "Oi mate, you can't park there"). It was fine the following day when the water was back to normal (ie 9" higher).
There are half a dozen residential moorings on the right bank above the lock, they use the lock all year round to access the water point and the pumpout (when it is working...). Maybe they used to be visitor moorings too?