Observations regarding a flood event at Fisherstreet Pot, Doolin River Cave, on the 11th & 12th September 2015

The following are a number of personal observations regarding the hydrology of the broad, shallow valley through which the Aille River and Doolin River Cave meander. They also illustrate the potential for other subterranean water courses within the area.

On the 11th September 2015 rain had fallen steadily in the Doolin area throughout the day, not so much as heavy showers, but constant. The results further along the west coast were of extensive flooding, in particular around Miltown Malbay. In response to a request for assistance members of the Doolin Unit, Irish Coast Guard, were tasked. Crossing Knocknalarabana, the mountain between Doolin and Lahinch the two I.R.C.G. Toyota Hilux vehicles towing one D class inflatable boat and an equipment trailer followed a huge stream downhill some eighteen inches deep filling the entire width of the single track road. Further south along the coast road, approaching Miltown Malbay, the runoff from the fields presented significant hazards as deep broad streams swept through the field gates onto and across the main road at depths measured up to eight inches. Near the memorial, close to Freagh Point, north of Whitestrand Bay, a section of the roadside was declared unsafe, collapsing several days later.

At 21:00, 11th Sept, the rain increased becoming torrential, best likened to a pulse, which lasted eleven minutes. Following the team’s stand down we returned to Doolin base. Rainfall had all but ceased along the coast by 22:00, as indeed had the torrent cascading down the mountain road. At 00:30 on the 12th September I had the singular experience of witnessing the road actively flooding between Fitz’s Bar and Fisherstreet, Doolin; directly opposite Fisherstreet Pot. At its peak the water flooded the field, submerging the dry stone wall on the south side of the road and all but covering the wall on the north side of the road, through which it sped toward the river flooding the nearby B&B and adjacent fields. In the pitch darkness the principle direction of the current was identified and source revealed. This enormous volume of water was emerging from the fifteen metre deep Fisherstreet Pot, a downstream, alternative entrance of Doolin River Cave. To illuminate the spectacle the vehicle flood light was directed onto the pothole and a mushroom of water almost a metre in height was seen gushing through the foliage and careening down the slope. In an attempt to reduce the flood assailing the adjacent B&B, working in waist deep water, Andrew Grindrod, (I.R.C.G.), and I broke down several sections of dry stone wall on the north side to reduce the flood level in the road; this had no immediate effect. We eventually left the area as the flood level subsided below the wall summits; about an hour later.

The dashed lines present an image of the volume of resurging water able to maintain such a depth across the immediate field, passing through and over the drystone wall, flooding the road, passing over the opposite roadside wall and into the fields beyond to amalgamate with the swollen waters of the River Aille.

Meanwhile other properties in the Doolin area were flooded to around one foot in depth. The Aille River had backed up significantly at the Aille Bridge adjacent the Aille Hostel, to the point where it found its way back up the road drains to flood the housing development some hundred metres to the north. River water entered up through the normal rainwater drains in the bridge wall to submerge the roadway to a depth of two inches. Flood debris continued to amass on the upstream side of the low bridge causing the current to force its way through the tangled matrix damming the small arches. The subsequent vibration transmitted itself alarmingly through the entire bridge structure. Unfortunately onlookers could not, would not, be convinced that begging them to evacuate the bridge was genuinely urgent. The substantial wall between the river and the hostel did not prevent the adjacent hostel building experiencing significant flooding.

The upstream side of the Roadford Bridge also became a huge tangle of trees and assorted flood debris causing the river to back up, though alleviating, to some extent, the volume passing further down river to assail the Aille River Bridge. Even so the river finally overwhelmed the riverbank defences behind McGann’s to flow across the car park into the Bar, flooding it to a depth of twelve inches; musicians stopped when the power supply to the speakers fused. The following week locals were interviewed, none had previously experienced a flood issuing from the pot onto the surrounding land.

In the 1970s relevant river flow observations were obtained from, Jamie Woods, (deceased), who related how the nature of the river had altered significantly following mining operations conducted in the 1940s, confirmed by Gus O’Connor, Jack Garaghy, Paddy Sharry, Taddy Tierney and Pat O’Brien, (all deceased). In normal flow conditions the river would sink amongst the many sluggahs in the porous limestone river bed. Such grykes were exposed as mining operations gradually removed the impervious overlying Phosphatic bed. Therefore the river today will only reach Fisherstreet Bridge following heavy rainfall.

Following periods of sustained rainfall water may be seen issuing from the grassy surface of the sloping field located to the west of McGann’s Bar, on the north side of the river. The day after the Fisherstreet flood event, (12th Sept), a significant volume was seen emerging; continuing unabated for almost two days. The course of the River Aille effectively delineates the margin between the shale overburden to the south and the limestone with its overburden of sand to the north. The limestone bedrock on the northern side of the river has a depth of sand deposits between 0 and fifteen metres. There occur, irregularly, among this deposit, subsidence where cavities can reach up to ten metres in depth within this unstable stratigraphy. One such area of subsidence regularly occurs; this is monitored.

During his archaeological survey around Doolin, (1890s), TJ Westropp recorded the route of a dry river bed meandering from north of Doolin Church to gradually fade among the area of pasture at Roadford.

Following prolonged periods of rainfall a small surface stream flows along part of the route of Westropp’s dry river bed. This is rumoured to be the same stream that was utilized to water the walled garden of the demolished Doolin House, owned by the McNamara’s.

Midday, the 12th September, a visit to Clooncoose Cave found the floor of the small alcove to be flooded to a depth of 73mm, 100mm above the previous noted level.

Cheg Chester, (P.C.N.), recorded rainfall during the twenty four hour period, (11th and 12th), at Kilshanny as 120mm; that’s 4.7 inches in old money.

Dr. Les Brown, S.U.I. has conducted research between the relationship of the hydrological behaviour of Doolin River Cave and the tidal cycles of Galway Bay, further to the inconvenient overnight stay of cavers encountering the flooded exit to Fisherstreet Pot.

The tidal sequence for the 11th and 12th of September was approaching springs.
11th Sept HW   04:51 4.49m LW   10:45   1.23m
11th Sept.   HW   17:05    4.68m LW   23:12   0.86m
12th Sept HW   05:27 4.66m LW   11:21   0.70m

Following this unique flood event residents of Doolin were interviewed all affirmed they had never witnessed such a flood.

October 2017; reports were received of several areas of subsidence in the area north of O’Connor’s Bar, Fisherstreet, among the sand deposits. Noted during the construction of a house; such events are common place in this area.

Finally.
During the 1970s a Pegasus trip had to be abandoned to Doolin River Cave when on rigging Fisherstreet Pot it was found to be flooded to within three metres of the field surface. Another Pegasus trip found, on emerging into the base of the pot, an empty space where the ladder had been hung earlier in the day. On this occasion Team members also experienced a flood. As the water reached chest height they were encouraged to scale the pot as high as practicable. As time passed thoughts of those already in the Bar, turned to missing chums. A visit to the pot discovered their plight.

Pat Cronin.
Acting Officer in Charge
Doolin Unit
Irish Coast Guard
Doolin: Oct 2017

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