Gus
The hydrology of Brants Gill/ Douk Gill ??? – an interesting question.
A good few years ago (late 80's) the underwater boulder choke in Brants Gill was examined in earnest by Biffo & I, and the water was found to flow up through gaps in the boulders. Such was the flow that pebbles dropped down fluttered in the current, hovered, then got blown back up & spat at the diver!
We theorised that the boulder choke restriction was sufficient to cause backing up behind it in high flow (flood) conditions. This would explain why, chronologically, Douk Gill starts to resurge next (being up dip) then finally Dub Cote (which is even further up dip) when even Douk Gill can't get rid of the volume of water either.
As Pitlamp prudently points out - access to Douk Gill is strictly forbidden (and anything else on the land nearby), which was a problem. Also the back end of Douk Gill was known to consist of an extremely low bedding plane which would require consdierable enlargement, and the cave floods suddenly and absolutely epically!!!
The next thing I considered was Dub Cote. The passages in the back end are long & generally small in cross section. However, I had been impressed by the size of the passages between sump one and sump five. There was one bedding spotted by Geoff Crossley years before which he had not been examined thoroughly at the time due to large amounts of silt. I persuaded Geoff that we should go & have a look at this, as I believed it could bring the flood water, when the fabled Master Cave (at least the Fountains Fell arm) backed up, into these large sections before flowing to its normal weather resurgence at Brackenbottom Risings, or Dub Cote entrance itself as the flood resurgence. The large quantities of silt could be expected. As the flood receded, water flow would slow and sediment get dropped. After our first dive to the bedding, Brian Judd took over the exploration. He subsequently found a significant length of bedding passage heading towards Larch Tree Hole – though sadly it was very low and silty all the way, until it got too silly even for Juddy! I still believe that this is/ was a hydrological link to the Master Cave.
I can only suggest that you have many happy hours' armchair caving in front of you. Of particular use/ inmterest will be the CDG Northern Sump Index, the Bradford Pothole Club Bulletins (re: Brants Gill, Diuk Gill & Dub Cote), and the ULSA review with its riveting descriptions of the bottom end of Penyghent Pot, the surveys and excellent OS map with cave survey overlay.
Hope this helps...
Scoff
BPC/ CDG