One of the key drainage areas in South Galway is the The Cannahowna Catchment, which flows off the southern slopes of Slieve Aughty hills close to Derrybrien and makes its way through Derrywee, Lough Cutra, the Beagh River, the Punchbowl and on through Gort. Note : This article will primarily focus on some of uplands areas as flooding in Gort itself has been well documented and analyzed.
This is an overview of the area that we are looking at.
Overview of drainage and geography
As one of three main rivers in the Slieve Aughty western slopes, the Gort river starts off as the Owendalulleegh in the peaks of the Slieve Aughty Mountains and it winds its way down the mountain and into Lough Cutra. The catchment itself is called the Cannahowna Catchment, whose name is attributed to emergence of the Gort River from an underground cavern close to Gort – literally – the ‘Head of the river’
The catchment area is 136 Km2 and the river starts from the highest peak of the Northern Slieve Aughty mountains in an area called Cashlaundrumlahan. It is at this peak where the infamous Derrybrien windfarm is located and this high peak is the source of the Owendalulleegh River passes under the Black Road (From Derrybrien to Killeenadeema) and then swings west in the valley below Derrybrien.
The following shows the flow from Cashlaundrumlahan to the sea – over 50km away and goes underground 6 times.
The peak of the mountain, Cashlaundrumlahan, is home to a massive windfarm (71 turbines) which sites on a 4 square kilometre site. This windfarm has a controversial past – and probably a controversial future also as it was the source of an environmental disaster in the form of a bogslide.
The Owendalulleegh river (also known as the Derrywee river in some places) flows past places like Knockavana, Tooravoola, Derrybrien, Inchamore, Derrywee, Derrykeel, Chevy Chase, Laherdaun, Derreen, Gortacarnaun and finally Killafeen before if flows into Lough Cutra.
Many places here related to ‘Derry’ or its Irish ‘Doire’ which means Oak tree as well as ‘Knock’ meaning ‘cnoc’ or wood. This is a reflection of the great oak forests and woods that used to cover the Slieve Aughty Mountains. Peppered along this are many lime Kilns used for making limestone.
The Owendalulleegh river twists and turns as it flows west. There are numerous fords, steppingstones and small bridges crossing the river and in summer time – the river can be very low.
The Owendalulleegh flows into Lough Cutra, a large body of water that laps the lovely Lough Cutra Castle.
The river overflows the lake at Russaun and flows out as the Beagh River.
Unlike its predecessor, which ended in a tranquil lake, the Beagh river after a further 2km, carves deeper and deeper into the limestone land and ends up disappearing in the dramatic swallow hole. The underground system reappears just 100m in a massive collapsed circular depression called the ‘Punchbowl’.
The water drama continues as the river reappears just 250m water to the west in an emergence and flows as the Blackwater river, deep inside the ground before ending just 200m later in a Swallow hole just 10m from the Ennis Road outside Gort. It then flows underground west giving rise to collapses such as the Ladle and later the Churn before re-emerging as a full river at Cannahowna (Literally meaning – the head of the river)
This river then flows in towards Gort Town, flows under the Gort Bridge and then past Lavally/Kinnicha and towards Castletown where It disappears into 2 swallow holes.
A normal winter sees this water system transition from low summer levels to high winter flows. Unlike the other catchments, this catchment doesn’t have Turloughs, but it has a substantial body of water in Lough Cutra. Lough Cutra provides a very good natural attenuator for the Gort Lowlands. The river levels rise and some low-lying land liable to flooding around Kinincha is really the only land that suffers frequent minor flooding in this catchment.
Sometimes though, the attenuation in Lough Cutra is not enough, especially if we get multiple storms one after the other. Here we see the attenuation happening in Lough Cutra during the wettest December in 130 years – December 2015 – and the peak being Storm Desmond.
The Blue line is the height of the river at Killafeen bridge going into Lough Cutra.
The Red line is the height of the river at Russaun Bridge coming out of Lough Cutra
As Storm Desmond raged, nearly 81mm fell at Malin Head in Donegal for one 24-hour period alone, marking the dampest day at Ireland’s most northerly point since 1955. The effect on Owendalulleegh caused a 6Ft rise in the river level in just 24 hours. However, if you look at the levels at Russaun, the outlet of Lough Cutra, this is much smoother and not as spikey, 2ft around 13 hours after the input peak.
Even though there is attenuation, this peak can be too much. In 2015, while we had several winter storms, Beagh had minor flooding and Gort itself did not flood. In 2009, however we had one week of very heavy rain and this caused downstream from Lough Cutra to flood. The following graph shows the differences between the 2009 and 2015 events.
The rainfall (top of the graph) shows a much more concentrated period in November 2009 and consequently the flows from the Beagh River are much more substantial and for longer duration. It also highlights the threshold of 40M3/second flow rate which is the limit the Beagh River can reach before Gort would flood. As this level, though some parts of Beagh are already flooding.
The 2015-2016 graph does show the spike of Storm Desmond but with Lough Cutra’s attenuation it didn’t cause as much damage as the week of heavy rain did in November 2009.
2009 Flooding Situation
In 2009, the prolonged period of heavy winter rains caused Lough Cutra level to rise and increase flows in the Beagh river substantially.
Flooding in Dereen
The first flooding situation seems to happen when water rose close to the bridge in Derrywee and some roads were cut off there – but not for an extended period. The metal footbridge normally 9ft above the water, was 1ft under the water.
Flooding in Russaun, Beagh
The river emerged from Lough Cutra and flowed in the back of Cahill’s sheds (and narrowly missed the home house) and rose 2ft above road level at Russaun bridge. It continued flooding downstream and spread out flooding Kilbecanty Angling Club clubhouse and isolating the local community.
As it hit the next bridge, (Beagh), it immersed the bridge and flooded the area in the vicinity. The water rose quickly on November 26th the water rose swiftly into the home of Hugh O’ Donnell (close to the bridge) and eventually, he with his 87-year old mother, had to be air-lifted by Shannon Rescue helicopter to safety. It continued and flooded some sheds downstream and cut off access to the area.
Flooding in Gort
In 2009, as the Cannahowna river swelled Gort found itself in trouble – the water backed up around Kinincha and Ballynamantan, the Kinincha road and Crowe St. started to flood.
There was severe flooding in Crowe Street where many homes and businesses were flooded and access to the town was severely restricted.
In Beagh, one home and one business flooded, many farms and several sheds were flooded and several families were isolated for several weeks. In Gort in 2009, the town had to be bypassed to get around the flooding. Combined with general paralysis of South Galway, the businesses in the towns suffered dramatically. For the Beagh community this was like a flash-flood that never happened previously and that threatened the community and that threat is still felt by come locals to this day. There is a lot of anger and speculation on how mountain mismanagement has brought this situation.
In living memory and from previous generations, there were never any accounts of flooding to this level experienced before. While there can be potential increases due to climate change and global warming many in the local communities indicated that water is coming down from the mountain much quicker than it did in previous decades – irrespective of the weather. People have been highlighting potential links between rapid-runoff and more recent mountain development such as the Derrybrien windfarm and Coillte Forestry.
In 2003, The Derrybrien windfarm developers (ESB) without doing a proper Environment Impact Analysis for the development proceeded with development and inadvertently caused a massive landslide. The original EIA indicated that there would be no additional drainage on the 4 SQ KM site on the main Slieve Aughty Peak. After the landslide happened the developers put in place a ‘Robust-Drainage’ Scheme, which involved digging 6ft x 8ft drains from each of the 70 turbine bases to keep the mountain dry. This ‘robust-drainage’ scheme proposed ‘drainage for each access road, all turbine bases and each repository site . . . continuously for the life of the windfarm project and thereafter’. It is estimated that over 30km of drains were dug in a 4km2 site on the very top of the mountain.
It should be noted that this scheme was put in place without doing any further Environmental Impact Assessment which stated that “construction of turbine bases does not result in long-term drainage of the surrounding peat”.’
Did this have an impact on the hydrology? – sure it did, but they never did this required analysis as part of their EIA. In fact, there is a compelling argument that a ‘robust-drainage’ scheme employed after the Derrybrien Windfarm Landslide in 2003-2004 altered the hydrology of the catchment.
Similarly, 263 Hectares of forestry were clear-felled in one sweep and there were other sites undergoing afforestation.
Trinity College as part of a study involving looking at forestry practices noted that clear-felling (and subsequent planting) can increase run-off by over 18%. It can also take several years before there is a balance and trees that are matured (>15 years) help to attenuate runoff from the site.
A positive number here means that the operation increases run-off by that amount. A negative number means that run-off is decreased. Historically as part of the Slieve Aughty mountain management – there was no proper impact analysis done on the increase of run-off into the Cannahowna catchment, which was (and is) contrary to planning regulations and environmental impact assessments. Within a few years of this ‘robust drainage scheme’ and clear-felling – communities downstream about 20km from the Windfarm flooded for the first time recorded – Coincidence?
I doubt it!
The main solution to flooding in Beagh and Gort is to manage the mountain properly and ensure that the right mitigations are put in place to alleviate any flooding risk. Several newer windfarm developments now include attenuation measures to dampen and mitigate their impacts but this hasn’t been part of the Derrybrien (or Kilchreest) Windfarm development. This could yet be part of the retrospective mitigation measures that need to be addressed as part of the ongoing European Court Order (The one where we are fined €15,000 a day until this problem is addressed)
Mature forestry can decrease run-off times and could be used to good effect to mitigate flood relief.
There needs to be an overall Slieve Aughty catchment management strategy that has a plan for each of the sub-catchments. From a forestry perspective, this is something that the South Galway Flood Relief Committee has recommended to the Irish Forest Service and Coillte and there has already been some policy change for forestry operations in the Slieve Aughty. This needs to be broader and more sustainable over the next 30-40 years to ensure that the right level of forestry canopy is maintained to ensure a positive flood relief impact.
The solution here is that on a per-catchment basis (Owenshree, Boleyneendorrish and Cannahowna) there has to be a balanced approach across the life-cycle of the forestry. By ensuring there is a significant canopy of mature trees to counter any felling and reforestation operations this is the only real sustainable solution going forward.
Changing the hydrology of the upper Slieve Aughty Catchments will have a definite impact on the downstream catchment and there are communities at risk here. There has been no hydrology analysis of these impacts and by ignoring planning regulations and European law – these operations are essentially illegal.
The Derrybrien Windfarm European Court order is compelling our Government (through heavy fines) to right the wrongs that have been done here in the past and put some mitigations in place now that should have been part of the original Windfarm Development.
Mountain operations (not only Forestry practices) and must now be analyzed and crafted such that there is positive flood relief benefit for the overall South Galway catchments.
Anything less will leave our communities exposed and will allow leave our Government and various departments exposed to yet another European fines. The Derrybrien Windfarm debacle has send a very clear and sharp message to our Government bodies, windfarm and forestry developers that the real impacts on the community must be taken into consideration or there will be severe financial consequences. We now need to shine the light on current operations and ensure that they adopt a more sustainable approach to the Slieve Aughty Mountains.