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Survey Of Wookey Hole

Reproduced by kind permission of C.D.G.

Radio Location Of Wookey 24

A general article for the uninitiated!

The published surveys of the far reaches have been put to the test by 'Prews' transmitting equipment and found, in some instances to be up to 30 degrees in error.  After the valuable work in the cave by Bob Cork and Dany Bradshaw the story can now be told………..

by Bob Cork and Alan Thomas

The radio-location of Wookey Twenty Four was part of a continuous programme to fix a survey point in each dry section of the cave necessary because of the inaccuracy of underwater surveying.

In order to radio-locate an underground point the transmitter, with its coil or aerial and its batteries, must first be taken to that point.  The coil must be laid out in an approximate circle as horizontally as possible.  The point located will be the centre of the circle.  The surface apparatus consists of the receiver and a box aerial used in the vertical plane.  Once the signal is received this aerial is rotated until minimum strength is achieved. Two stakes mark its direction. The aerial is moved to another position, usually at 90 degrees, and another direction obtained.  Where they converge is an approximate fix.  The process is repeated.  This time a silent point is obtained which is the exact fix. This point is marked with a stake and the aerial carried, and slowly rotated in the vertical plane, until a second silent point is found; the distance between these two points is the depth of the location underground.

Our practical problem was the physical effort of two divers transporting the transmitting apparatus and sufficient air to get them to Wookey 24 and back safely.  There was no lack of willing helpers as far as Wookey 9!

Accordingly, Bob Cork and Dany Bradshaw took in the coil and set it up in Wookey 24 on 27th September 1979. This proved to be an all-day trip which they found very tiring and they were somewhat pleased to find that Alan Thomas, who had no knowledge of the time they had dived or how long they would be, arrived in Wookey 9 at the same time as they returned to help them out with their gear.  The advantage of setting the coil up in advance was that the surface workers knew where it was located and had a clue where to await the signal.  To further lighten their burden for Saturday they took two 50 cu.ft. air cylinders to Wookey 22 on Friday night.  This was only a forty minute trip, what you might call resting up for Saturday.

The next morning the intrepid divers met at Wookey Hole car park with the surface party which comprised such distinguished figures as Brian Prewer, Oliver Lloyd, Dan Hasell and Alan Thomas (?Ed) together with others no less distinguished but too numerous to mention. After much discussion, muttering, eating bacon butties, drinking coffee etc., the divers were persuaded to don their soggy wetsuits and sort out their equipment.

The usual rig for diving at Wookey seems to consist of individually valved, side mounted, twin air cylinders (usually 40, 45 or 50 cu.ft. capacity) a wetsuit and a helmet such as children wear skate boarding to which is attached a pair of aquaflash underwater torches and the business end of a NiFe cell.  No additional lead is needed by most people.  For this dive they had a total of 140 cu.ft. of air each including the bottles already in the cave, sufficient for the return journey and allowing the 100% safety margin demanded by good cave diving practice.

Bob and Dany enjoyed the walk to the cave for once someone else was carrying their gear.

Watches were synchronised in Wookey 9 and the two divers submerged at 10.45am, the arranged transmitting time was to be 12.30pm.  The dive from Wookey 9 to Wookey 20 is in a large submersed passage in the conglomerate for the first 250ft after which they are in limestone.  The total dive to Wookey 20 is about 500ft and going to depth of 75ft.  There are few constrictions, even a tight section of bedding about two-thirds of the way, known as the Slot, presenting little problem even with luggage if the bottles are held horizontally.  The passage continues uphill after The Slot to the Wookey 20 sump pool.  Here it is possible to transfer to the Wookey 22 line without surfacing, though on this occasion the divers surfaced under the Spiders Web, as the multiplicity of lines in Wookey 20 is affectionately known. They had felt under some pressure from the surface party and wanted a breather to sort themselves out.

From Wookey 20 to Wookey 22 the dive is about 600ft and goes to a depth of 70ft.  Leaving the Spiders Web they went down through boulders to a depth of 15ft, turning north into an open passage twenty to thirty feet wide. The divers line was followed along the right hand wall to a depth of about 60ft where the passage levels out and after some distance enters a large chamber where even in the conditions of perfect visibility that day, the side walls could not be seen.  At the far end of that chamber the passage ascends rapidly to the Wookey 22 sump pool.  Here the fun began because it is necessary to leave the water and start caving.

The sump pool is at the bottom of a conglomerate rift some sixty to eighty feet high; the way on is up a steep slippery slope and a traverse to the right where the floor levels out, where it is littered with very sharp debris and large boulders.  At the far end of this section a twenty-five foot descent through boulders leads to a muddy squeeze into a large chamber. A further difficult climb down over sharp boulders leads to the Wookey 22 sump pool which is static.  Here, there is a permanent iron ladder in the pool to facilitate the return journey; how the ladder was got there is a story in itself and perhaps in the distant future when the 'fixed aids' debate is again in full swing someone might bring it out through Cuthbert’s.  The Static Pool is smooth-sided and the water can be twenty feet down.  The divers, of course, were still carrying their equipment.  Before continuing from Wookey 22 they had changed their partly used 45’ for the dumped 50's.  At the Static Pool they kitted up again removing boots and replacing fins etc.

The dive from the Static Pool is 360ft long and 60ft deep descending rapidly from the surface to a silted-up passage which narrows to a slot which is passed on the left.  The passage then gradually rises to surface in a muddy pool in Wookey 23.  Like this one the following sumps are static under normal conditions but ripple marks in the mud suggest that it is an overflow in time of spate.  These static sumps hold silt in suspension for a long time so the return journey is like diving in cocoa and not very pleasant even if you like cocoa.

The divers clambered out of the mud-walled sump pool by kicking their toes into the soft mud and inching their way up the slope, pausing only occasionally to fall back in. Once out of the water in Wookey 23 they were in a wide muddy floored passage along which they stumbled and made their way to the 30ft diameter lake at the far end, where a duck led them into a small pool from which it was difficult to get out.  A lower passage brought them to Sump 23 which was only 15ft long and roomy.  Thus they surfaced in the large passage which is Wookey 24.

They de-kitted, emptied the water that had seeped into the transmitter box, fortunately doing no harm, and continued to the two connected chambers where they had laid out the coil on the previous Thursday.  It was now 12.25pm.  The apparatus was quickly assembled and the transmission began only a few minutes late. The arrangement was that they would transmit for one hour.  However, watching a small needle flip up and down can be very boring and as they had noted on a previous trip potential side passages they decided to go exploring. At the northern end of the second chamber the roar of water can be heard.  A 25ft climb over large boulders and a traverse along a narrow rift-like passage leads to a point above the foaming torrent of the River Axe which here disappears into a boulder choke.  Upstream the active streamway passage enlarges; traversing above the water becomes difficult and it becomes necessary to swim.  A line assists the caver from here to Sting Corner, the right-angle bend in the streamway, just beyond which it becomes possible to walk again. Their first attempt at climbing the wall opposite Sting Corner where a void could be seen at a height of about 30ft ended in double splash as a Bob and a Dany both plummeted back into the streamway.  They did not like this place!  And moved on.

Beyond Sting Corner the water is twelve to fifteen feet deep and about ten feet wide.  With a strong current, a hauling line is very useful. The whole passage is in conglomerate, with thick slippery manganese deposits on the walls.  Further on the passage becomes shallower and the water faster flowing, continuing eastwards to Sump 24.  The going now, becomes harder.  At one point along the streamway it is possible to climb up about 50ft on the left hand side and enter an oxbow, the other end of which is only a few hundred feet from Sump 24.

Here the two divers made their second attempt at finding new passage.  They entered a hole at the western end of the oxbow and followed a three foot wide fifteen foot high rift which became blocked with debris after 150ft. They managed to remove a boulder from the top of the blockage and thus get by.  The way on was no wider but increased in height.  After 200ft a climb over two large boulders brought them to the head of a rift about 50ft deep for which they would have needed tackle. Having none they then traversed along the rift for about another 50ft to where it became impassable.  The only way on would be below.  Stones dropped down the rift could be heard bouncing beyond the visible bottom.  As they returned it seemed obvious that the passage floor along which they had come was formed by boulders jammed in the rift.  They then carried a rough line and compass survey.

They returned to their radio location station without incident.  The transmitter had been transmitting for one and quarter hours and the meter was reading a low output.  It was nearly two o'clock so they turned off the transmitter and packed up.

The journey out was uneventful except for occasional problems such as Dany playing with the coil halfway through the static sump 22 in nil visibility on the pretext that it had come undone.  And Bob, having descended and entered the last twenty feet of the Wookey 22 dry slope faster than he intended and entered the water in a most inelegant manner midst a clatter of cylinders, was not amused to hear "that’s one way to do it youth" followed by a loud guffaw.

From Wookey 22 they could have had a relatively easy trip out carrying only the radio-location gear and leaving the spare (now empty) cylinders to be recovered later.  But with characteristic whole heartedness they decided to carry the lot and have done with it.  They had little trouble in the good visibility and the desire to get out overcame the drag caused by the extra gear.

They were relieved when they surfaced to find a fair number of the surface party waiting in Wookey 9, not only to carry the gear but to tell them of the success of the operation.

The story of the surface party is soon told.  Leaving the cave as soon as Dob and Dany had dived they returned to the car park to fetch the receiver equipment.  They assembled in a field to the west of Green Lane where the residents, mainly horses and cattle seemed to think that radio-location was the most interesting thing that had happened for a long time.  Naturally everyone confidently predicted where Wookey 24 would prove to be. Naturally all were wrong.  The signal was soon received very clearly and Brian Prewer, designer and builder of the apparatus led them eastwards towards Green Lane.  The point was finally found to be in a field belonging to Madame Tussauds on the other side of the lane.  The whole operation had taken place in very pleasant sunshine and when completed they adjourned to the Hunters before returning to the cave to meet the divers.