Poulbruíon, Sliabb Eilbbe

Alternate name :-

Townland :-

Civil Parish :-

County :-

I.T.M. :-

Lat / Long :-

Elevation :-

Length :-

Depth :-

Faunarooska

Killonaghan

Clare

514461 x 705150

53.090082° N 009.276962° W

250 metres

0 metres

6 metres

Historical – introduction

Since the early 1980s northwestern Sliabh Eilbhe received intermittent attention from “The L.A.D.S.” (Mark Lumley, Steve Milner, Mike McDonald and author); their partially successful efforts somewhat limited by annual visits.

As Covid-19 constraints eased, the Sliabh Eilbhe Project was intensely resumed. December 2020 saw a solitary survey conducted across the windswept slopes. Initial findings were somewhat confusing, requiring cross checking of published records to accurately identify recorded cave entrance positions. To increase entrance precision two G.P.S.R’s were deployed, each entrance recorded as an I.T.M. map reference, (Irish Traverse Mercator). By end of January 2021, over seventy new sites had been recorded. More to the point, almost each of these sites - sinks, collapses and depressions were noted as taking, at the very least, a tiny trickle of a stream. Many sites are invisible among the dense ground cover until, suddenly, encountered. From early on negotiating the landscape with a stout staff became the norm. Gradually, the shale boundary, and adjacent landscape, was examined south to the area of the most northerly sinks feeding Faunarooska; F5 and F6. Sink F5 is believed successfully identified, requiring confirmation; to be absolutely sure. An outstanding task is to precisely locate, record and eliminate F6.

Theory

A large network should exist beneath the extensive western flank of Sliabh Eilbhe. Past efforts hampered by available time and seeming scarcity of streams draining the shale capped summit. Recent discovery of numerous sinks, along the shale boundary, suggests a rainfall catchment to potentially rival Poulnagollum. Though lessor in catchment, development and number, The L.A.D.S. explored similar sites and features along the western flank of Knockaunsmountain, (1980s), most drain into Poulnagrai.

Potential catchment

Attempting to quantify rainfall for the western flank of Sliabh Eilbhe, the Drover’s Road was used as a western limit. Similar constraints were applied confining the study area between the summit ridge of Sliabh Eilbhe, Pollantobar and just above the northern limit of Faunarooska, (F5). The study area is a catchment of 0.6 square kilometre.

One millimetre of rain over 0.6 Sq. Km equates to 600,000 litres. Such rainfall volume goes a long way toward explaining why these well drained, steep, sloping limestone pastures, with their shallow soil depth, remain fertile and lush throughout the year.

If rainfall on the 0.6 Sq./Km study area equaled the 20mm recorded at Carnaun, 3rd August 2024. This single event would equate to 12,000 cubic metres/tonnes = 12,000,000 litres. Over the previous two decades Cheg Chester has recorded an average, annual rainfall of three metres. If cautiously applied to the study area this figure becomes 1.800,000,000 litres = 1.8 Billion litres.

Potential resurgence/s

Minor springs exist. Though small, in an area where no surface streams exist, for any distance, each water source is highly valued. Utilized to supply cattle troughs scattered throughout the landscape: under no circumstance whatsoever disturb, impede or otherwise interfere with them or their outflow.

Between the 2nd and the 9th of August, Carnaun recorded 65mm of rain. Following this, a significant volume of brown water was seen discharging from a previously unnoticed submarine resurgence; precisely what direction the rain blew in from requires research. The resurging water seen flowing north: an obvious dark brown presence, perhaps sixty to seventy metres wide. The north-westerly wave direction pressed the resurging stream up against the coast, along which it was seen to flow for at least a kilometre. On checking data, the published ITM for Poulgorm was found to be incorrect. This site was later confirmed as indeed Poulgorm.

Image shows Study Area III, Discharge, potential resurgence and drainage corridor

Site description

Poulbruíon is a shallow, narrow rift, aligned northeast-southwest. Twelve metres back from the edge of the limestone terrace, overlooking pastures; sweeping two and a half kilometres down to the Atlantic Ocean coastline. Discovered conducting the long term Sliabh Eilbhe Project. Poulbruíon is northwest of a main drain channel, also aligned northeast-southwest, at the end of a shallow associated channel, slightly elevated above the adjacent main drainage channel. This main channel continues on, passing a developing collapse, several minor sinks, Pluais Gabhar, A1e, Poulballyelly and Pollapooka II.

Estimate of adjacent surface drainage areas

Permission was sought from the landowner, further to him previously granting PCN permission to dig Poulfantaiseach, and to examine the landscape to the vicinity of F5 and F6; feeding Faunarooska Cave.

It is a ‘busy’ area: Poulfantaiseach is one hundred, twenty metres southeast, adjacent to Halliday’s Hole, (named for Pegasus member Simon Halliday, lost pushing Lancaster Hole, terminal sump). Pluais Gabhar, (aka Goat Hole), is located near the top of a rugged valley, suggestive of a significant geological fault. Around the upper, southern end, of this fault is a cluster of sites, in addition to those mentioned above. Further to these sites, some recorded as lost, between late 2020 and early 2021, seventy plus other sites were recorded, consisting of sinks depressions and collapses. The Project covers a large area owned by multiple landowners; permission must be sought prior to any visit.

Image showing sites immediately adjacent the south end of the apparent fault.

Digging

Poulbruíon was recorded 21st August 2023 using two GPSR’s: digging began 28th October. Reviewing the site, the deepest part of the rift chosen to sink a shaft appears a good choice. Increasing depth continues to expose a clear North/South boundary. South Side comprising differing coloured silt and clay stratigraphy, with occasional boulders; large and small. North Side, compacted boulders are the norm, tight against each other. Differing compacted coloured clays fill gaps. Numerous flat boulders all slope down toward this boundary; almost centre of the shaft.

Of note, the south face is susceptible to collapse after heavy rain; a broad, shallow area, to the south offers drainage directly toward the shaft. Evidence of an adjacent sink overflowing shown by a surface water flow flattening vegetation. A stream is clearly audible: its varying volume fueling imagination. A one metre deep by a half diameter cavity formed against the eastern cleft, at ≈-3m, is evidence of an obstructed stream below. Backing up, issuing from the cleft. It may also explain oft encountered gaps, found among the boulders. A crevice, similar that of the eastern, was thought to be developing on the western side of the shaft. As of September 2024 this does not seem to be the case.

Fitting support stemples to the north face

View north with collapse at east side

Excavating is problematic. Procedures similar to digging out Considine’s Cave yet evolve. Differing strata, north and south, present shoring challenges. Commonly, scaffold tube, (50mm), is installed horizontally, at reducing vertical centres to respond to increasing lateral pressures; presently 350mm.

View southeast, stream cleft & lower stemple

Tripod designed to support various lifting configurations

Dealing with two minor, recent slumps of the South face has caused the floor to become a quagmire with frustrating, concomitant results. The tripod provides a secure structure to lift normal loads and heavier boulders; using differing forms of mechanical advantage. Circumstances require hauling to now be directed through an offset pulley system to assist wear and tear issues of aging diggers. Such a system will include increasing the size, and number of kibbles to facilitate two operators. Spoil area around the shaft is no longer viable. A railway is being constructed to tram spoil out of the depression onto the moorland, to level the undulating area around the depression: there will be no spoil heap. September 2024, work continues…

Detailed information relating to the following Images can be found in 'The Logs' for the corresponding date.

September 16th 2024

Installation of the new working platform

September 20th 2024

Preliminary work on the construction of a railway to convey spoil to a higher elevation

Sliabh Eilbhe Project Update 1st October 2024

Poulbruíon is within the northwestern sector of the ongoing Sliabh Eilbhe Project. It is almost a year since digging began at this site; one of several in an area of increasing significance. Prior to the last quarter of 2023, into 2024, focused digging was delayed due to time required removing the significant amount of infrastructure and safely installing a galvanized scaffold tube grill cover over the twenty-eight metre shaft at Considine’s Cave; freely accessible via an unlocked lid. During this time several activities were underway. Digging and shoring took place at adjacent Poulfantaiseach, PC pursued the souterrain study and time spent dealing with the unexpected, though delightful, recording of a Stone Axe, found in Pluais Gabhar, (Goat Hole). Along with the adjacent sink, A1e, Pluais Gabhar, (Goat Hole), was erroneously reported in the 1970s as “bulldozed flat”. Anyone familiar with this landscape would not accept such foolish observations.

Not until the end of February, (2024), did digging really begin at Poulbruíon, with installation of horizontal stemple supports for shoring required to sink a shaft. The removed fill being a mixture of silts and boulders. Delivering materials to this remote location is somewhat problematic, perhaps time consuming, but not insurmountable. As with Considine’s Cave, (North End), safe shoring plays a large part and is of significant cost. Operations realized, September 2024, that manhandling kibbles from the now, three metre deep shaft was unsustainable. Actual digging stopped, and work on suitable, minimal infrastructure began. A stock proof cover to the open shaft became a level, stable working platform. Thinking ahead to winter weather, an inclined rail system, to convey spoil up and out of the depression nears completion, having taken advantage of a period of kind weather. As of 1st Oct 2024, the rail system only requires the rails to be set to the gauge of the dram. Once complete, the rail system will only convey material to an adjacent hollow, once the Poulbruíon depression reaches capacity. All materials for the working platform and the rail system are parts of the infrastructure built to cope with digging Considine’s Cave.

Details of these digs, sites and photographs are recorded within the Pegasus Club Logs and also on the M.C.R.A website; https://www.mcra.org.uk/logbooks/index.php?/category/Pat_Cronin

September 30th 2024

First stage of the railway nearing completion

14th October 2024

Showing Safety Lid Open

Showing Safety Lid Closed

28th December 2024

Suspension of operations

Commitments conspired to prevent several Team members regularly attending digging trips. Hauling, and shoring the regularly exposed unstable sections, time consuming primary issues. At the present depth of five metres, west and east walls continue vertically as solid bedrock. The south end is predominantly silts, with small pockets of sand, and clays, within this matrix differing sized stones and larger boulders often appear. The north end is of heavier silts, which become less, absent, below three metres. At this depth loosely compacted boulders, with large gaps inbetween, become the norm – barely resting/balancing upon each other: exposed it’s like handling unevenly shaped marbles. Reasonable stability has been achieved by insertion of 12mm steel rebar between 0.8m and one metre long, their ends rest upon the horizontally set, 50mm galvanized steel tube stemples, each secured by 16mm galvanized steel bolts, these stemples are vertically spaced at an average of 0.5m centres.

From the start significant surface runoff compelled insertion of pvc panels behind the 200mm square steel mesh, to prevent destabilization, and slumping of the upper southern face area. As depth increased sections of the south end became faced with coursed stonework, built upon inserted 12mm rebar. During insertion these lengths of rebar often encountered stones within the silts. On at least two occasions, following heavy rain, the rebar lengths prevented large face collapse, confining the slump, to a metre of height and 0.4m depth of face. Exposed boulders where often found resting upon the rebar lengths, providing limited support to adjacent clays. This evolved method improved confidence, and overall stability.

Reflecting on progress the digger chose to moth ball the site until such time the team were available to resume the project. Believing solitary effort best spent on a more practicable project. Dismantling the hauling tripod frame, its associated infrastructure – removal of the dramway, and general site clearance, was reasonability swift. The working platform remains as a safe cover, with a scaffold tube frame to prevent harm to curious cattle, and dull humans.
A chance meeting with Farmer allowed the plan to be explained. Touchingly, he offered his assistance, even though, he’d recently had steel inserts to support his spine: a very nice man.

Removing the infrastructure the frustrated digger reviewed the situation, weighing time and effort consumed with, and shoring, the two faces, suddenly realizing that simply removing the entire spoil behind the northern shoring, removed the problem, halving travel to Liscannor to purchase, convey and install half the shoring material. In short replicating, in part, the South End excavation of the south end of Considine’s Cave.

At surface the rift tapers to a tiny joint; over a distance of some three metres beyond the northern shoring. The western wall is quite straight, the eastern wall slowly curves to meet the west. Best guess is this formation continues down vertically - the spoil, after three metres, becoming loose rocks and easily handled form of spoil. To reach the present 5 metre depth, a conservative estimate of spoil to remove is some 15m³, without any allowance for gaps between boulders, the weight approaching 15 tonnes. The upper area of silt spoil could be landscaped around the southern depression perimeter, the stone used to build a dry stone wall.

Pat Cronin 25th January 2026

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