> As already said, I can bring in people who confirm this is not a tunnel.
There's no need to "bring in people" - just discuss it with people who are familiar with OSM tagging of similar structures at https://community.openstreetmap.org/c/communities/at/59 or https://community.openstreetmap.org/c/help-and-support/tagging/71 .  By all means ask people with real-world experience of water management (or whatever) to contribute there, but it has to be a discussion with other people who tag things in OSM to achieve anything.

> It seems the only reason why you are so obsessed with the tunnel tag is to make it render it dashed in Carto
I don't see the evidence for that - you are the only person here who has mentioned OSM Carto's rendering.
