Douk Gill Scar, long thought to be the main overflow rising for flood waters from the Brans Gill Head system, was finally proved to play this rôle in 1954. Ten lbs of fluorescein introduced into Hull Pot finally emerged 10 days later at both Brans Gill Head and Douk Gill Scar, the weather during the latter part of the test being rather wet. In dry or average weather, Brans Gill Head flows steadily, draining the Hull Pot group of pots, Hunt and Penyghent Pots, the Churn Milk Hole area, Silverdale Gill Pot and finally the whole of the southwest side of Fountains Fell as far over as Out Fell, while Douk Gill remains dry. In wet weather, Brans Gill increases in volume somewhat, but after a while, Douk Gill starts to flow, frequently very heavily. In severe conditions of flooding, the flow at Douk Gill Scar may be several times that of Brans Gill at the same time. Consequently, between the junction of the two passages and the outflow of Brans Gill Head, there must be an appreciable constriction which limits the flow.

If we assume that in dry weather the flow through to Brans Gill does not back up much inside the cave, then there should be a passage with an airspace leading from the entrance to Douk Gill to the hidden stream between Hull Pot and Brans Gill. This idea, of course, is an old one and has encouraged attempts to penetrate the very flat and wide bedding plane.

Further thoughts on the subject followed the partial opening up of the Fountains Fell drainage systems in the shape of Hammer Pot and Magnetometer Pot. These ideas are based on the results of six key fluorescein tests carried out by members of the Northern Pennine Club over a period of years. The results are summarised below :

Ignoring small possible variations in time due to different weather conditions, it seems apparent that these tests suggest that the main cave systems feeding Brans Gill Head can be divided into two dissimilar groups : Hull Pot and Hunt Pot systems having a long travel time in the order of 10 days for one mile, and the Fountains Fell system as a whole having an average travel time of one day per mile approximately. These facts lead one to believe :

(a) That the main water system of the Hull Pot group is of a submerged, slow-flowing type, unlikely to be directly explorable at water level, and

(b) The Out Fell - Fountains Fell - Silverdale Gill system must be predominantly vadose in character over its main length in spite of the frequency of local sumps found at the Fountains Fell end. This lends weight to the idea of penetrating Douk Gill Scar in the hope of reaching the main inlet from the Fountains Fell system which might then be explorable by means of scaling tackle.

How far back behind the outlet of Brans Gill Head may this inlet from Fountains Fell lie ? If we make a simplifying assumption, then a rough idea may be obtained. Assuming that the water system from Hull Pot to Brans Gill is submerged all the way and the speed of flow is uniform, then the velocity is 176 yards per day. Somewhere along this line the Fountains Fell inlet joins in and acquires approximately this same speed in the submerged zone, the Fountains Fell inlet being small compared with the main Hull Pot flow. Now the relationship between the times of flow for different distances on the Fountains Fell side does not allow of very much time being spent in the submerged last portion of the journey. To take a conservative view, one day might be a reasonable guess. This would imply that the junction of the two systems is not likely to be more than 176 yards behind the rising of Brans Gill Head. It might well be even nearer than this. Thus two avenues of approach are suggested :- there is a sporting chance that cave diving at Brans Gill might show results; and a better chance still of success at Douk Gill. In fact if Douk Gill is pushed with sufficient determination it will surely go.