AndyRJ
Player Valuation: £5m
That's the isolation structure, each pipe is fitted with a gate valve/ penstock to allow them to be shut off if necessary. That's why there are a row of manhole covers above at surface level.So looks like the latest video from answered my query, the bridge section looks to have flow pipes build in (and currently capped off)
View attachment 270632
It's unlikely anyone will ever want to close these very often, if at all, moving forward once the basin is full of water.