You ent got to run of lol this is a forum isn’t it ?
they do normally have signs you have one at the entering manhole lid , says hydro break in chamber , then at a set distance upstream saying hydro break down stream incase you get washed into it hence the chains on large tunnels ... also just to tell you the chains “ now days “ we get told only to attach on one end and leave the rest on the benching this is because debris get stuck on the cha and cause blockages . You also have a warning sign hydro break upstream and the closest manhole after it incase your working in a flood to make you aware some one could open this , it’s very rare these signs are actually put in because it’s a much more modern policy .... than the hydro break itself.
Catch pits are more old fashioned so if you have done a lot of manhole “lifting” be surprised if you haven’t seen one these usual link up from your road gullies to catch any silt shingle etc , they are a manhole ring around 6m deep depending on levels you will have around 3m of silt / water then a outlet pipe normally 8” that lets the water go to main storm drain this stops the big drains getting “dirty” and the hoover lorries love these as makes their job easy
If their is a road close to a large stream with grass in-between covered in manhole lids high chance these are catch pits which also stops the head wall silting up , all depends if your a “lifter” or the head wall type