Author Topic: Grove Cliff Caves Survey  (Read 338 times)

Offline tim.rose2

  • Tim R
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Grove Cliff Caves Survey
« on: June 07, 2019, 11:34:39 pm »
Following our success at connecting up Grove Cliff Caves, Grove Cliff Fissure and Rumble Chasm as reported on other threads, it seemed like a good idea to produce a new survey.  Myself, Sas and Richard took on the task!  First job was to learn how to survey a cave as none of us had done such a thing before.  A bit of research on the net and a little time remembering how basic trigonometry works and all seemed clear what we needed to achieve.  Now I don't doubt the job would have been quicker if I'd sought help from an expert, however there is a certain amount of fun and a lot of satisfaction in working these things out for yourself.

Next was to buy some appropriate kit.  With no intention of becoming a cave surveyor, I intended to go cheap so hundreds of pounds on a modified Disto was out of the question.  Instead I settled on the combination of a Hersch LEM40 for £40 and a Silva sighting compass for £20.  Sas and I decided to calibrate ourselves with the compass and with a little practice we could reproducibly get the same bearing for a couple of points out our living room window.  Data would be recorded on paper (I'd made up some charts) and we had a suitable hard back folder to carry it in.  This became known as 'the desk'. 

Then we started playing underground.  Sas and Richard worked out a good system, which I wrecked when I joined the fun!  By god surveying like this is slow and boring.  I've developed a new found respect for anyone who's surveyed a big cave.  Anyway, once we'd gotten past a few teething issues, the job was simple, just tedious.  In total we took 181 survey stations over approx. 16 hours underground spread across 5 trips.  Turns out the data collection was the easy bit.

Once back at home after each trip I started to work out how to process the data.  My first attempts involved manually typing the data into Pocket Topo and then importing into Therion.  This is probably not the best way to go about it, but was the best I could work out from the help files / tutorials available.  Now I don't doubt Therion is a brilliant piece of software, but to a technophobe like myself it's far from intuitive.  Many hours were spent swearing at the computer screen.  As the saying goes, if at first you don't succeed, give up and find an alternative...

At this point I was contemplating buying some large chart paper and doing it by hand as I've no problem producing a scale drawing when along comes a dicky bird who suggests trying Compass instead.  Personally I found it much easier to use (i.e. I could).  This gave the centre line data which I then exported to Inkscape to draw up.  My final task was an accuracy check - having 6 entrances and knowing exactly where they are on google earth allowed a simple overlay of a screen shot.  I was pleased to see it all matched nicely so we have confidence in our data.  Unfortunately we were unable to obtain GPS coordinates; Sas's phone couldn't get a descent signal at the entrances - I'm guessing that's because they're at the base of a cliff?  Similarly, the accuracy by taking coordinates from Google Earth was insufficient resulting in distortion and hence the overlay not matching so I gave up on that idea.

So the results...
The total cave length is now 583 m, of which all but 9 m (Allotment Dig) is mass movement rift.  I therefore believe this is the longest cave of it's type in the UK.  Happy to stand corrected on that though.  Below is an image of the centre line survey with the colours representing depth.  I thought I'd post that here with the above story of the trials and tribulations of producing it and save publishing the drawn up survey and story of exploration for Descent. 



So what next?  Well with any luck we won't find anymore cave and then there's no need!