Karst investigations
around the village of Casterton
Back in March I was contacted by Nick
Cotton, County Councillor for South Lakes, Kirkby Lonsdale area about the
problems of road flooding in the area between the X-roads at bottom of Bullpot
Farm lane and Langthwaite X-roads, which is the next junction to the north
along the roman road. This area in on a isolated block of Carboniferous
Limestone around the village of Casterton. We have started digging at several
sites in the area and other cavers have dug here in the past. (see Red Rose Journal
8. page 54)
The following article is a précis of
the document sent to Cumbria County Council Highways department explaining what
we intend to do in the area and asking for permission to dig next to the public
highway. We also assured them that we had public liabilty insurance via our
club and the BCA. We have since opened
up Slab Cave near the railway bridge (Bridge Sink on the attached map) and we
will be regularly digging here and at other sites over the summer months.
Investigation of the underground
(Karst) Hydrology
in the Casterton area of South
Cumbria
PRELIMINARY REPORT
by Hugh
St.Lawrence and Andy Hall, FRGS
and members of the Red Rose Cave & Pothole Club
Background
Localised
flooding and subsidence of roads to the east of Casterton village is causing
concern to both the local council and highways department of Cumbria County
Council. Even moderate rain waters overpower the installed drainage systems,
and in heavy rain conditions flood waters surge from surface holes, run down
the roadways and cause erosional damage or long-term ‘ponding’ of water on the
road surface.
Through
Nick Cotton of Cumbria County Council, the Red Rose Cave & Pothole Club has
been invited to investigate these phenomena, which may be related to and
influenced by the presence of a natural karst hydrological system in the
underlying limestone bedrock. The caving club has substantial knowledge of
karst drainage systems and includes members with considerable hydrological
experience.
The
area is well known to the caving club which, over the years, has noted the
presence of karst features (stream sinks, shakeholes and risings). No enterable
cave has ever been found, although substantial amounts of water appear to
travel underground for distances up to 1 kilometre.
On
Tuesday 13th March 2018, four members of the club re-visited the
area and made a preliminary inspection
of the main sites of concern. They also visited features farther afield in
order to try and define the extent of the hydrological system. A dye test from
the highest sink was carried out and the results show the extent of the
underground system. The trace travelled underground in less than two days to
the two risings near Casterton village.
Site Inspection
Site 1. Between Bull Pot x-roads and Langthwaite
x-roads. Ponding of
water on the road between Bull Pot x-roads and Langthwaite x-roads. In winter this water can freeze
creating particularly hazardous icy sections.
Our review:
.
A small stream at the Bull Pot X-roads is channeled
under the road and then through drainage pipes to a manhole/drain soak away
approx. 130 metres north of the x-roads.
This manhole/drain appears to be choked and no further drainage outlet
could be seen. In wet weather this drain will inevitably overflow down the road
to where it ponds in several sections lined by shallow earth verges. Although
porous limestone bedrock underlies this area, there are no bedrock exposures
and the area is almost certainly covered by thick deposits of impervious
glacial clay (till). Water will find difficulty draining into the limestone
below unless there are cracks and fissures; in this localised area there appear
to be none. Indeed, a stream to the east of the road along this section is
unable to sink into the limestone until it reaches the Langthwaite x-roads
area.
The
best action that can be taken to alleviate the ponding problems are un-blocking
of choked drains/manholes, and the installation of short relief drainage pipes
to channel water into fields adjacent to the ponding areas. There appears to be
sufficient gradient to achieve this. This would be a job for CCC.
Site 2. Langthwaite
x-roads area.
.
Ponding of water beneath the railways bridge; surging floodwater at the x-roads
in wet conditions; erosion of the road near the railway bridge; subsidence of
the road north of the x-roads.
Our review:
.
Unlike site 1, these problems may be related to a
karst hydrological system, most likely an immature cave system in the limestone
bedrock. Only 200 metres from the Casterton Risings, the Langthwaite x-roads
may be a convergence point for underground water routes from more distant sink
holes. There are numerous small collapse
features in the area, many of them very recent (see photos), suggesting an active
‘evolution’ in the underground landscape. This has potential to alter
underground water flow routes, as well as destabilising the overlying
ground. The hydrological system may
extend up to a kilometre northwest of the Langthwaite x-roads, and a full study
of sinkhole sites and testing of their water courses could be carried out. One
test mentioned above has already been carried out.
But
of immediate concern, and to help alleviate the localised problems around the x-roads
and bridge, there needs to be a thorough investigation and excavation of sites
around the x-roads.
1. To
the east of the x-roads a substantial stream sinks into a concrete blockhouse.
It is believed that this blockhouse may have been built on top of a natural
limestone drain or sink, but this has obviously become choked - the sinking stream requires little
encouragement to overflow onto the x-roads and down towards the bridge. As a matter of priority this blockhouse needs
to be un-blocked. un-blocked.
2. Between
the x-roads and the bridge is a gully by the side of the road which took a
small pipe drainage under the road and channelled it into a limestone crack,
capped with a concrete slab. This limestone sink appears to have become choked.
There are also worrying signs that much of the gully is subsiding into cavities
below, and this poses a particular threat of road collapse. Recent collapses in
the field to the south of the hen run suggest that there is a lot of
underground evolution in this area.
Investigative excavations need to be carried out along this section to
establish the extent of the problem and the potential dangers. .
3.
One hundred metres north of the x-roads the road
dips into a hollow which was the site of a recent (3 or 4 years?) road collapse
which was filled in and mended by the council. However, in wet weather a stream
flows down the side of the railway embankment and sinks beneath stone walling
adjacent to the collapse site. This is almost certainly a cave development
feature – given enough time the sinking water may well undermine the road
repair fill leading once again to subsidence or collapse of the road.
Conclusion and Next Steps
We
would like to do several things in the Langthwaite x-roads area referring to
the three items above:
- Across
the road to the east is a stream sink into a pipe and covered concrete
blockhouse at SD 62860 79899. We propose to lift the slabs, clear out the
floor of the blockhouse and hopefully more of the water will then sink
here. We would also examine the floor for any chance of entering the
underlying cave system. It would be helpful to know which farmer uses this
land so we can discuss it with him.
- There
is a capped hole at roadside just east of the old railway bridge that was
inconclusively investigated by some of our members a few years ago.
Filling them in is not really an option as this could stop the water flow
and cause further flooding under the old railway bridge. We would like to
excavate here using shoring if necessary. We would cordon off the area and
protect it with cones and tape as it is right next to the road. It would
be helpful if you could supply suitable signage for this but it would not
be necessary to close the road. We would always have someone on the road
surface to control the infrequent traffic. We would also need a trailer
parked in the space up the road to put spoil in but hopefully a local
farmer could supply this and dump the rubble in the field to the east of
the cross-roads where there is other rubble already. We would make any
holes safe at the end of the process capping with a suitable cover from
concrete slabs.
- The
sink to the North of the X-roads is also worth investigating. This is away
from the road and we spoke to the farmer when he was repairing the
roadside fence after a recent accident. Again the aim of any excavations
here would be to improve the surface and underground drainage.
There
are other sites that we are interested in opening up that might be useful to
improve the surface drainage but they are not near the public highways. The
main sinks are located near Fell Garth and Bell Gate to the North east and
drain to the risings near Casterton village at SD 62541 79863. These would be
worth excavation but this would be a longer term project and would need
landowners permission.
Andy Hall
Diagram of area North of Bullpot
X-roads Diagram of Karst area around Langthwaite
X-roads Flooding Area around Langthwaite X-roads
Adding OBA to main sink Collapse under wall Slab Pot
Main rising near village