Longwood Valley - sink location

[Peter Burgess]

I have been looking at my lovely geological map, and I have noticed that of the active swallet caves shown on it (Manor Farm, Longwood/August, GB, Tynings Barrow) three are located very close to the point where the streams run off the  Lower Limestone Shale, and onto the Black Rock Limestone. Longwood is the exception. This sink is some three hundred metres south of the boundary, i.e. the stream flows over a significant amount of the Black Rock Limestone before sinking. This led me to thinking along these lines:

The active sink for Longwood used to be located similarly to the others, ie somewhere close to the Bristol Waterworks compound at Lower Farm, or within the farm compound. In order to provide a useful water supply for the farm, at some time in the past, the swallet was deliberately blocked, and the water was artifically diverted and channelled to run on the surface through the farm settlement. It found a new place to sink down the valley, which is where it now sinks, and was probably an active swallet at some earlier time in the cave's development.

It may also be significant that the Charterhouse lead works ran a leat from the top of Longwood Valley round the shoulder of the hill into Velvet Bottom, so the  interference with the water flow in Longwood Valley might date from the middle of the nineteenth century when this leat was built (according to Stanton and Clarke in the UBSS 1984 paper "Cornish Miners at Charterhouse-on-Mendip").

Consider also that of the four caves I mentioned, only Longwood has a significant 'upstream' series, running back up the valley.

Has anyone considered this before, and is there evidence underground that in the not too distant past, the upstream series once carried the whole stream from an active swallet, now blocked?

 

[Andy Sparrow]

Sounds perfectly logical.  The upstream 'August' passages are the largest in the cave, while the active stream inlet in Longwood is hardly fully mature, what with the wet chimney and the Sewer.  Also, the active swallet downstream from the blockhouse used to be quite a deep open hole but has now filled with sediment to the extent that it blocks and overflows in wet weather.  This suggests to me that at some time in recent history it may have been excavated to encourage it to take the stream but has now, like Flange Swallet in West Twin, refilled itself.

 

[graham]

It's a tad simplistic to assume that streams will always run off the impermeable rocks onto the limestone and then sink immediately and continue to go underground at that one point forever more.

For instance, you have to remember that the process of valley formation above the geological boundary will affect the precise point at which the stream reaches the limestone. Then there is the fact that underlying bedrock may be buried under superficial deposits that mask the bedrock boundary. Further, the stream will bring with it sediments that may, as Andy notes, fill existing sinks causing new ones to be formed at different points.

To give a couple of other examples of how this works:

Little Neath has developed in tandem with the river valley as the latter cuts into the limestone and has exposed more and more of it in the valley floor.

Something like fourteen different (fossil and active) stream sinks have been identified at G.B.and Charterhouse of which two are currently active, neither of which is an entrance used by cavers.

At the Doolin Road Sink (Doolin, Co. Clare) the site of engulfment has altered so frequently as sinks are blocked with the high sediment load in the water that none of them have eroded a passable passage, despite there being a large stream passage a short distance underground where the various inlets have joined together.

 

[Peter Burgess]

Is there an obvious location underground where a possible old swallet inlet actively took water into the upstream series? I haven't been there for so long, I really can't remember much about it. Now someone is going to suggest I go and look for myself.

 

[Peter Burgess]

Thanks for the insight, Graham. It's why I asked the questions, because, yes, we cannot assume that because three of four caves have sinks on the boundary, that all caves should do so. If there is evidence underground of an active streamway that has not flowed for, say, 150 years, then it adds a bit more weight to the argument, even if it doesn't provide conclusive proof.

 

[graham]

Is there an obvious location underground where a possible old swallet inlet actively took water into the upstream series? I haven't been there for so long, I really can't remember much about it. Now someone is going to suggest I go and look for myself.

The valley bottom has been modified by the "hand of man" over the years and so the fossil sinks are not particularly obvious. IIRC the uppermost part of the upstream passage comes close to the surface near to the edge of the farm wall that cuts down into the valley from the east.

 

[bill chadwick]

Peter, is your lovely old Geological map sol old that it might be out of copyright?

It would be good to add it as a custom layer on my interactive map of mendip caves.

 

[Les W]

A substantial amount of water sinks just upstream of the rickety foot bridge, in an alcove on the east side of the stream. This water is presumabaly the water that pours from the roof of one of the upstream galleries. This is quite near the known upstream end of the main cave.

 

[graham]

Peter, is your lovely old Geological map so old that it might be out of copyright?

It would be good to add it as a custom layer on my interactive map of mendip caves.

Not a chance. The map was published by the BGS and is therefore crown copyright. That means forever, effectively.

 

[Peter Burgess]

Peter, is your lovely old Geological map sol old that it might be out of copyright?

It would be good to add it as a custom layer on my interactive map of mendip caves.

There is surely no problem with using the information to create your own plan, with permission from HMSO (?), and adding that to your cave map? Plenty of papers have been published with geological plans in them, all information derived from the BGS surely? Anyway, the map only covers ST45, which is only a small part of Mendip as a whole. I don't know whether other squares of Mendip have been published to the same detail.

Actually, why not just add the boundaries between the principal strata? This info is available from the lower scaled BGS maps, widely available.

 

[Peter Burgess]

A substantial amount of water sinks just upstream of the rickety foot bridge, in an alcove on the east side of the stream.

I know exactly where you mean. I have previously thought that the alcove looked man-made. Could be this was the place the farm once chose to allow the stream to sink, after it had served its purpose on the farm. The stream above this point appears to be contained behind an artificial bank, and does not seem to flow along the lowest part of the valley here.

 

[Les W]

Peter, is your lovely old Geological map so old that it might be out of copyright?

It would be good to add it as a custom layer on my interactive map of mendip caves.

Not a chance. The map was published by the BGS and is therefore crown copyright. That means forever, effectively.

So why do OS maps come out of copyright after 50 years (or some such time limit)
Are they not crown copyright?

 

[graham]

So why do OS maps come out of copyright after 50 years (or some such time limit)
Are they not crown copyright?

Are you sure that they do?

 

[Les W]

So why do OS maps come out of copyright after 50 years (or some such time limit)
Are they not crown copyright?

Are you sure that they do?

Yes

http://www.ordnancesurvey.co.uk/oswebsite/aboutus/yourinforights/copyright/index.html

 

[Brains]

http://www.bgs.ac.uk/about/copyright/arrangement.html

Had a quick glance at this and there appears no mention of a 50 year rule, but dont suppose that means it does or does not exist! It does however state:

"(f ) Please note that a BGS licence does not authorise the reproduction of Ordnance Survey maps. Likewise, an Ordnance Survey licence does not authorise the reproduction of BGS material. Most BGS maps make use of Ordnance Survey topography, reproduction of which may be permitted by the licences issued independently by the Ordnance Survey. Users who do not have an Ordnance Survey licence to reproduce the topography must make their own arrangements with the Ordnance Survey. "

I reckon a specific enquiry to BGS would be needed to clarify the issue, unless you want to get out there and do some primary original mapping, and be able to prove it...

 

[Les W]

From the BGS website you so kindly linked to Brains

http://www.bgs.ac.uk/about/copyright/IPR_definitions.html

The section on Crown Copyright reproduced below says that ALL crown copyright expires 50 years after the end of the year that a work is published.
The bit about 125 years from when something is "made" is superceded by thye act of publishing.

Crown copyright

Copyright protected material, which is produced by employees of the Crown in the course of their duties. HMSO manages all Crown copyright protected material, and delegates some responsibilities to its agencies e.g. Ordnance Survey.

Most material originated by ministers and civil servants is protected by Crown copyright. As are publications resulting from Government Department commissioned works. Works produced by Royal Commissions are Crown Copyright, unless joint authorship by non Crown personnel is involved.

Crown copyright subsists in material for 125 years from the end of the year in which they were made, or, (if they were published within 75 years of that “made in” date), for 50 years from the end of the year of publication.

The status of Crown Copyright is not affected by EC legislation; i.e. OS topography will be subject to 50 years copyright protection, not the revised 70 years.