Cheers.. that's quite a lot of water...
What do you mean when you say "the main part" however?
Ps: doesn't deep level lead to a junction in which in situated: "The Bonsor east shaft"? This is presumably flooded below here, allowing you to see a dogey hole in the tunnel floor flooded up to an excessive depth....
Cheers
Kein geneis kanaf - Cain gnais canaf
Byt vndyd mwyhaf - byth onddyth moyav
Lliaws a bwyllaf - Líows o boylav
Ac a bryderaf - ac o boryddarav
Kyfarchaf y veird byt - covarcav yr vairth
Pryt nam dyweid - poryth na'm dowaith
Py gynheil y byt - Pa gonail y byth
Na syrch yn eissywyt - na soroc yn eishoyth
Neur byt bei syrchei - nour byth bai sorochai