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Dive Report - Le Grande Souci. St. Vincent Sur L'Isle. Dordogne, France.

By Clive Stell

Over the Easter holidays this year divers from the Wessex (another caving club on Mendip) and divers from the BEC joined forces to dive the deepest cave in the Department of the Dordogne in France.  Although the depth of this site is relatively modest compared with some of the extremely deep sumps in other parts of France, it is still significantly deeper than any British site.

Since the mid seventies when a French diver descended to a depth of 40m there had been no diving at the site until members of the British CDG showed an interest in the mid nineties. During the past few years, as more cave has been found, the terminal depth has slowly increased.

The Souci appears to be a small pond approximately 15m by 8m in a hollow, shaded by trees on flat farm land adjacent to the village of St, Vincent: an unlikely looking spot for a deep dive.

The cave drops vertically for the first 40m, passing through a 1.5m wide slot at a depth of 6m and then slowly widening.  At 12m depth, a large chamber is entered through the roof and the walls are lost in visibility that never exceeds 2m.  The steeply sloping, debris covered floor is reached at -40m.  During the past few years divers have continued down the slope in an attempt to find ongoing passage and moving water but due to the silt on the floor and the resulting atrocious visibility the attempts were destined to fail.

In 1998, Malcolm Foyle and Robin Brown laid a diving line from the shot line at a depth of 37m out into the unseen void. After 10m a wall of the chamber was found.  At this point the wall was undercut, so the line was continued in this direction following the junction of the steeply descending roof and the wall.

In September 1998, Jonathan Edwards and I continued MSF and RABs' exploration, reaching a depth of 70m. At this depth, divers experience nitrogen narcosis, a condition similar to being drunk, caused by the nitrogen in air becoming toxic when inhaled at depth.  Due to the narcosis, it was not possible to safely belay the diving line and it was therefore removed back to a depth of 60m.

Any further exploration at the Souci was going to be logistically more difficult as the divers could not breathe air at these depths.

As plans were made for the next trip, Tim Chapman arrived back in Britain and rejoined the team after not diving the Souci since 1996.  Unfortunately Jon was unable to get to France due to work commitments but a strong diving team was still assembled and all the necessary kit for a series of mixed gas dives was prepared.

For the deep dives this Easter the divers breathed Trimix (oxygen, helium. nitrogen) to reduce the narcosis and make the dives safer.

The first dive fell to Robin who checked the condition of the lines laid over the previous years. He reported that all was well and that the visibility was the usual 2m.

Over the following days the deep line was slowly extended with the cave continuing to descend at a steep angle.  As the dives got deeper and longer the amount of gas required for each dive increased. For the final dives, 6 cylinders with 3 different gas mixes were used.

The first two deep dives extended the cave to the same depth as reached during the summer of 1998.

The following deep dives then continued the cave horizontally in what appeared to be the roof of another chamber but due to the poor visibility nothing was clear.  At a depth of seventy metres and with no clear way on I decided that it was time to drop into whatever was below.  After descending for six metres, and without a wall or the floor in sight, the maximum dive time was reach and the line was reeled back to seventy metres.  The surface was regained after a total dive time of over two hours.

Other areas of the cave were also looked at.  Tim decided to explore a small pool adjacent to the main site. Over the years it had been thought that this would simply drop into the main chamber.  Due to the uninviting nature of this second site, until now, no one had been willing to test the hypothesis.  The first dive was spent clearing rotting tree trunks and various items that had been dumped over the years.  After the entrance was cleared sufficiently for a diver to enter the cave, slow progress was made, in near zero visibility, to a point approximately 20m from the entrance and at a depth of 12m.  With no obvious link with the main chamber, in ongoing, but very awkward passage, the site was abandoned to concentrate on the main site. Meanwhile the diving continued in the main pond.  At 35-40m depth, lines had been run out from the shot line and around the walls of the main chamber.  All the lines were then surveyed including the deep line, down to a depth of 70m. During the following evening, whilst drinking heavily, the survey was drawn up.  This gave a good impression of the size of the main chamber around the shot line and also indicated other areas which needed further examination.  The line survey confirmed the large size of the main chamber, which due to the poor visibility has yet to be seen.  The survey also indicated that the line around the chamber was now 3-4m from the deep line after going right round one side of the chamber.

During the next dives it was confirmed that the line did in fact goes right around the right side of the chamber and the line was joined to the deep line.  A further line was laid around the left side of the chamber in an attempt to circumnavigate it; this line has yet to be completed.

Plans were being made for the final attempt on the end of the system.  By now the tanks of helium brought over from England were getting low and the gas mixes that we could achieve were not ideal.  This resulted in much worse narcosis for the final dive than is ideal.  We already had the deepest site explored by British divers in Europe but the pressure was still on.  The sump had allowed us to go deeper than the previous year but we knew that the site continued downward and this was our last opportunity to get further as there was no more helium.

All of the kit required for the final dive was assembled and the various cylinders were staged at the pre-planned points in the cave.  It was time for the final dive.  As I left the surface my mind was eased by the now familiar line which led me past my two deco tanks at -9m and on down through the unseen chamber to my travel mix bottles hanging above the floor of the chamber at -35m.  Everything was going well.  I continued along the horizontal part of the line leading to the wall of the chamber then on down into a steeply descending section decorated with roof pendants.  The line then started to level out and I arrived at the final belay at -70m.  I had decided to make a vertical descent from this point and expected to reach the floor within a few metres of the depth reach on my previous dive.  I picked up the line reel and slowly sank; the minutes raced by on my dive computer and the depth gradually increased.  To my surprise, I reached both the end of the line on my line reel and the maximum depth for my decompression tables. Still the cave continued downward.  I swam forward for a metre or so and made contact with the wall.  Finding a large knob of rock I tied the line off but moments later, in the now zero visibility, I felt something hit my fin.  The belay had broken off.  My maximum time had been reached and with no time to belay the line properly.  I clipped a small block of lead to the end of the line and retreated to start the long decompression.

The maximum depth of the cave found so far is 93m from the ground level with 87m of this underwater making this both the deepest dive in the Dordogne and the deepest cave.

A return trip with more equipment is planned.

The Divers were:

Robin Brown, Tim Chapman, Malcolm Foyle & Clive Stell.  Thanks to Fish and Lizzy for surface support.

During the decompression the divers all noticed strange occurrences including; falling rocks and flying zebras, on reflection, this could be why the French named the site "the Big Scary One."

Many thanks to Andy and Christian Kay for all their support and hospitality.

In response to requests from several members, this article expands the recent BB article on the hydro-chemical studies in Wookey Hole.  In particular, it is important to note the fact that the work is going to be published as a paper jointly by the authors listed below.  They are the three divers who collected the water samples, myself, and a non-member, Alan Knights.  Alan will probably not be known to the readers.  He works at the Inorganic Chemistry department of Bristol University, and made an invaluable contribution to the analysis of the Wookey Hole samples.  To provide proof of the accuracy of the analyses, it is necessary to make a complete analysis of all ions present in the samples, and examine the balance between the total concentrations of positive and negative ions.  Two ions, sulphate and nitrate, are notoriously difficult to measure.  With his expertise in the use of an ion chromatograph, Alan has analysed samples for these two ions with great precision, and at the same time checked that no other unsuspected negative ions were present in the samples.  Since 1994 he has cooperated with me in the St. Cuthbert's stream studies by making similar analyses for the same two ions.