Fwd: Forest of Dean (FOD) Wet Sink (Slaughter Stream Cave) Project - Advice wanted please

[MARK TRINGHAM]

Dear All,
In 2018 I realised that some re-survey work was needed in Wet Sink 
(Slaughter Stream Cave), hereafter termed 'SSC'  in support of of a 
Gloucester Speleological Society water tracing study. Also I have 
started a speleogenesis and geological study into this cave, which at 
13km long and ~ 110m deep and largely formed in dolomite is a curious 
and impressive beast! It's 3 times longer than the next longest FOD 
Cave, Miss Graces Lane, and although entirely natural it contains 
interesting iron and manganese (?) deposits, fossil layers and 
archeological remains such as 'Norman' the dog skeleton. The cave has 
even featured in an episode of 'Extreme Archeology'.

The cave was well surveyed mostly around 1991 to 1993 with a lot of hard 
work put in by GSS and RFDCC, using best techniques available at that 
time (Suunto compass/clino and tape) under the leadership of Paul 
Taylor. This resulted in a comprehensive Compass software database and a 
1995 2D plan view drawn in ink at 1:500 scale on transparent paper and 
photo-reduced scale versions of same. A further ~1.9 km was later 
discovered and surveyed during the period 1997 to 2000 in the 'Remelt 
Plant' and 'Heat Exchanger' series and this was added to the Compass 
database and shown as a line drawing on issued maps, but the passages 
still not yet drawn up. A redrawing of the cave plan was also made by 
Paul around 2017 in A3 pdf digital format as part of a FOD wide survey 
dataset compilation including over 110km of caves, mines and tunnels and 
lodged with the UK survey database. The survey drawings were all great 
for finding the way around and relating passages to the numerous sinks 
and other shorter caves in the same catchment area, such as Seymours 
Swallet and Redhouse Lane Swallet. However elevation plots were not made 
and not many passage cross-sections recorded. Also the inclination data 
gave unrealistically deep values (>20m too deep) for the deepest point 
in the cave relative to the Slaughter resurgence at the River Wye near 
Symonds Yat. Also some sections of streamway did not have realistic 
slopes resulting, in a few extreme cases even sloping partly the wrong 
way.  The cave plan was drawn up by Paul using the Compass survey line 
plots, coordinates and cave survey sketches. Around 60% of survey 
stations had LR recordings, but only about 20% had UDs and therefore 
elevation views and relationship between sinks, springs in the cave and 
sumps and geological layers could not be precisely established.

Advice request: 1) Compass has an easy to use magnetic declination 
database built in, where you feed in the date,  lat/long and elevation 
and it gives you magnetic declination for anywhere in the world. I have 
used this and incorporated the values into the data acquisition spanning 
1991 to 2020. Does anyone know of an alternative source of historical 
magnetic declination data for UK against which i can check this ? Its 
especially important in SSC because many cumulative passage lengths 
exceed 2km and any systematic error of say >0.3 degrees will move cave 
points ~10m horizontally. Declination from true north was apparently 
-5.4 deg in 1991 and is -0.74 today.
Advice request 2) Should I apply declination corrections to match True 
North or to match NGR? End plan is to draw up new entire survey in 
Therion. NGR Convergence is about -0.48 degrees from True North here.

The summary work flow so far has been:
a) Check/clean up Compass database using original survey notes and 
drawings, adding in whatever LRUD data is available. Paul Taylor is 
still involved with this project and has done a sterling job finding 
original survey sketches, data and cave drawings after 27 years for me 
to use and he has worked on several of the re-survey trips. Paul is 
leading the present water tracing study too.
b) Untie all loop closures so that original and new data acquisition can 
be compared like for like.
c) Compare new pocket topo data (~4km recorded so far)  along key routes 
in the cave, in particular the streamways, to the old data and focus 
further attention where its needed most. This has been achieved both by 
adding pocket topo data into Compass for a while on home PC. But then 
later getting all the Compass data successfully into pocket topo using 
Footlegs converter. This means that in the cave I can now see old vs new 
data in 'real time' in pocket topo and look out for particular survey 
needs and see roughly what is coming next along the survey route. Also I 
have been able to add any little bits which were missing before (this 
has added cumulative ~300m to the surveyed cave length so far). The new 
data recorded has elevation plots and plenty of passage x-sections to 
help with speleogenesis and water tracing work. DistoX2 calibration has 
been checked before starting work on every trip and recalibration needed 
twice so far. The comparison in plan view so far between old and new 
surveys is pretty good, albeit with some progressive offsets up to 
around 20m in spatial position, but all passage segments match well, 
showing no significant errors before, such as missed stations or 
reversed azimuths. The one major loop in the cave down 'Coal Seam 
Passage' that rejoins the streamway had a 1993 mistie ~ 12m 
horizontally, again pretty good, but now achieved in pocket topo to <2m 
horizontally and 0.2m vertically.
d) Side branches that 'stand-alone' and seem fine in the old data such 
as Pirate Passage (1063m) and Echo Passage (770m) and which have fairly 
complete LRUD data have been tied into the new pocket topo dataset and 
will not require further attention until drawing up is done digitally in 
Therion.

Biggest differences old/vs new datasets seen so far are where steep or 
complex passages occur, such as the Entrance Series which has a double 
spiral going down to -55m below entrance and then gradual depth 'drift' 
going up or down streamways due to old inclinometry being slightly off, 
but which over long distances does accumulate significantly.

Advice request 3): If we find original suunto clinometer used and see 
any calibration error, is there any reason not to apply a correction 
retrospectively to the old data? This would improve accuracy of the old 
data retained in the new database and reduce the new acquisition 
required. Has anyone had suunto clinometer issues before that they 
overcame?

Foward plan on surveying is to complete whatever new acquisition is 
needed in pocket topo, probably a further ~2.5 km. Then after all survey 
data is cleaned up, start work in Therion and in the end produce and 
publish a digital survey drawing fit for such a fine and interesting 
cave. BTW I have almost zero previous knowledge of Therion at present. 
This can then form a reliable 3D framework in which to fit the water 
tracing and speleogenesis observations.

Some rock sampling (~50 samples) have already been collected and are 
already at Univ Manchester geology department for future petrographic 
analysis to quantify/understand dolomite vs limestone, but covid has 
held this up for at least 1 year already.

There is probably a fascinating story to unravel on Iron and Manganese 
mineralisation in SSC which we will only start to work on in the coming 
months. BTW furthest parts of the cave take ~ 5 hours fairly strenuous 
one way travel time to reach, so some underground bivi's will be used 
and 10 to 15 hour trips can be split between 2 or 3 days.

Advice Request 4): Can anyone suggest improvement to the work flow in 
progress or suggest other things we didn't think of? Is there anything 
special about Therion I need to know at this stage that would affect 
present work flow?

After ~11 survey trips so far I am finding it difficult to find enough 
survey helpers from GSS/RFDCC on a regular basis to complete reaminder 
of the acquisition within a reasonable time. Is anyone on this list keen 
to help in say November/December 2020? All help will be properly 
acknowledged and i want the end survey result to be issued under GSS 
club name but  'open access' after completion.

Please see attached plan summary jpeg.
Regards,
Mark Tringham


Mark


Mark
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