South Galway Flooding – Tierneevin/Kilmacduagh

I recently called out to the community around Tierneevin and Kilmacduagh, Hawkhill etc. to get a snapshot of flooding issues that they had there and ‘try’ and make sense of what was happening.  In previous presentations I’ve mentioned that the area flooded but I had a lack of knowledge of finer details of the area, a fact that a certain Mr Dermot Flaherty brought to my attention on a fairly regular basis  – To thanks to Dermot for enlightening me on the dynamics and to the locals I met on the day. Thank’s as usual to Sean Brady whose fantastic drone footage has proven such a valuable asset in capturing the extend and devastation of the flooding.

[Disclaimer – I probably walked through at least 15 townlands and 2 counties in about 20 minutes so if I didn’t get the exact location of the townland … apologies and if you’re from Termon but I said you were from Beagh, then sorry too.]

Most people would be familiar with this area beyond the golf course, with the Kilmacduagh round tower dominating the skyline. In my flood maps to date, it’s the area that is shown in the circle below.

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The area of Kilmacduagh, Hawkhill and Tierneevin

Overview of drainage

From a drainage point of view this area can be seen as relatively independent of the Slieve Aughty drainage but they both have Coole lake as a common factor when it comes to severe flooding in the area.  The source of the water flow here comes from the Burren and mainly through Lough Bunny.

Lough Bunny is  a lake of about 2.5 km long and with a maximum depth of 14m.  It has no overground inflow or outflow. While most of the other lakes around Lough Bunny, have water flow that tends to flow south/west and are considered part of the River Fergus catchment, Lough Bunny has been associated in relatively recent times (1998) to the Kinvara catchment area (Also known as Galway Bay South East catchment).  Lough Bunny drains to the sea, mainly through Kinvara.

On the north shore of Lough Bunny (Closest to Boston Castle), there is a swallow-hole/sink that re-emerges into Rockvale via a series of 3-4 springs as the Rockvale river. During summer season this flow may be very faint but with high winter rains this flow can be several M3/s. This is shown in the map below:

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The following are pictures of the springs in Rockvale (March 2016)

The Rockvale river continues to flow northward and it passes under an old stone footbridge (an old mass path).

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The old mass path and footbridge upstream from Lough Skeardeen

This continues north-east and flows under a road through 2 pipes and continues  into Lough Skeardeen.

During summer months this flow may sink into the ground to re-emerge ~200 m north east and flows into Lough Avatia. In severe winters this flow can be overground.  There are other springs emerging in Kilcorkan that also flow into Lough Avatia.

The outflow from Lough Avatia then flows behind Kilmacduagh castle and continues onward to Tierneevin as the Ballyhale river and it flows under a road again through 2 small pipes close to Helebert’s house, the bridge serving at the boundary between Galway and Clare. It then flows into a seasonal Turlough called Lough Managh and then continues as the Cloonteen river under an old culvert close to Tierneevin church and on into Hawkhill Turlough.  During dry summers, this dries up completely.

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Overview of flow into Tierneevin/Cloonteen
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The bridge under the road beside Tierneevin Church

There is another small flow originating from Cloonafunshin bogs (Polliffern lough) that flows north and into Coole, passing close to the Golf club and flows into the Coole Basin (Lough Nacarriga)

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Flow from Cloonafunshin/Polliffern flowing beneath R460 (Kilmacduagh road)

In typical summers, the overall flow is very minor. In typical winters the turloughs swell and there are flows of several M3/s under the culvert at Tierneevin.

Swallow holes

There are several swallow holes in the area.  There is one, noted in GSI surveys as the Cloonteen river sink (close to Helebert’s house)  which has been analysed and shows a lot of connectivity (17 links) to the Coole system and Kinvara. According the tracer dyes it has the following connectivity

  • Corranroo West Spring (minor flows)
  • Caherglassaun (Extremely rapid flow rates)
  • Coole North rising (Extremely rapid flow rates)
  • Gort/Kiltartan River (via Cannahowen?) (Rapid rates)
  • Pollbeaghy (Extremely rapid flow rates)
  • Loughcurra (moderate)
  • Moran’s cave (Rapid rates)
  • Pollaloughabo Cave (Rapid rates)
  • Coole South Rising (Extremely rapid flow rates)
  • Kinvara West and Central (Moderate flows)
  • Quinn’s Cave (Extremely rapid flow rates)

Overall, this swallow hole is of major significance to the area as it has substantial connectivity. There was/is another swallow hole to the north beside Carr’s house, but this may currently be blocked.

There is also another swallow hole is located at Cloonafunshin/Polliffern lough .

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Cloonafunshin/Polliffern Lough

Severe Winter flooding

In severe winter flooding (as in Winter 2015) the area got very badly flooded. The waters of Lough Bunny rose and gave more substantial flows into Rockvale and this wasjoined by other springs in Lough Atalia which prove too much for the culvert at Tierneevin.  The picture below shows Lough Managh turlough in the foreground with Tierneevin church on the very left.  Far off in the distance on the top-left you can see the outline of Lough Bunny.

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Severe flooding around Tierneevin

This can be represented by the picture below where you can see substantial flooding.

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The following superb drone video by Sean Brady shows the devestation of the floods

In particular around Tierneevin, Cloonteen many houses were under threat with the flooding and required sandbags and pumps to keep the water at bay.   Pumps were also used to pump water across the road at the culvert in Tierneevin.  The pumped water can be seen in the middle of the picture here with Tierneevin church in the lower centre left.

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Water Dynamics

The problem seems simple – the Tierneevin culvert (follow the tree line across the road)  could not handle the flow of water coming into it but there was another factor that affected this – the level of Coole Lake.

In this diagram the level of Coole lake can be seen on the left of the photo.  The levels had risen so much that Coole lake was backing up into Tierneevin (Similar to many other places). This had 2 major effects.

  1. It reduced the flow rate across the culvert
  2. It reduced swallow hole flow rates into the Coole basin

The levels of Coole lake effectively pushed back on the flow rates (overground and underground) coming out of Tierneevin. It was also Coole Lake level that flooded Flaherty’s farm in Tierneevin/Tawnagh West.

Solutions to flooding

There are a several things to consider here but the #1 is the level of Coole lake. Coole Lake at the 2015 levels cause flows to back-up in Tierneevin. We’ve seen the same for Kiltartan also.

The #1 solution to solve Tierneevin flooding is to reduce Coole Lake peak levels.

Reducing Coole Lake peak levels will allow better flow through the culvert and will allow the swallow holes to function.

There are other items that need to be addressed.

  1. As there was still an overflow at the Culvert in Tierneevin, an additional culvert would be required beside the current one (or a new more substantial culvert)
  2. Swallow holes in the area should be cleaned to ensure they have maximum capacity during flood events. There are concerns that a swallow hole has been filled in, in recent times so this would need more investigation.

Other considerations

  1. There are currently OPW proposals to solve Termon flooding by giving it a path to Lough Bunny but as we have seen we need solutions for Tierneevin in place to enable this.
  2. The road in Tierneevin has been raised substantially and therefore limit any alternative flow over the road – Better culverts are needed to ensure that they match the more substantial winter flows from Lough Bunny.

 

While the flows are not as substantial as the flows coming from the Slieve Aughty’s there is still a significant flooding problem in this area that causes a lot of distress and the solutions are within reach –  Keep Coole lake peak levels down and increase flows out of Tierneevin through swallow hole clearing and also better culverts.

-David Murray

 

Managing the mountain – ‘Slow the flow’

The Slieve Aughty mountains are one of the critical factors of the overall flooding situation in South Galway.   Our management of these mountains is completely regardless of, and more often than not, contributory toward flooding issues and this is something that needs a fundamental change if we are really serious about alleviating the flooding situation in South Galway.

The Situation

The situation is not good. In South Galway we have a highly karstified landscape that includes 10s of kilometers of underground rivers responsible for bringing water from mountains to the sea.  This has been explained previously in Presentation #1 : Slieve Aughty Drainage.

Because of the underground rivers, there is a finite limit to the flow that can be handled by the system.

If the underground river channels can’t handle the flow they rise and move overground and this causes overground flooding.

One of the critical factors that determines flooding is not just the volume of water but the rate of which water enters the system.  It’s like using a funnel when adding fuel to your lawnmower – you’ve got a particular volume of fuel that will end up in the tank but if you try and fill all the fuel at once it will spill over. If you slow the flow down through the funnel can take in you get a good flow but no spills!

The Slieve Aughty’s are the opening funnel of South Galway, the main catchment area of the 500 km.sq or so of the total catchment.  Slieve Aughty mountains are the main highland within this and rise to over 300m.

The undisputed fact is that water is coming off the Slieve Aughty mountains quicker than ever before.  I’m a native of the South Galway area and a these days rivers rise in Kiltartan 5-6 hours after heavy rain where as in my youth, it would take over 24 hours for a flood to fully rise.  I’ve heard plenty of other locals saying that ‘back-in-the-day’,  it would have taken days.  I’ve also looked at some of the dynamics between rain-fall and river levels ( Rain vs. Rivers in South Galway) that shows that certain rivers can rise over 1 metre just 3-4 hours after heavy rainfall.

The Slieve Aughty mountains rather than acting like a sponge seem to behaving like an irrigation channel with water is flowing off the slopes unnaturally quickly

What do you mean unnaturally quickly?

The Slieve Aughty mountains are mainly a wetland comprising of a large bog area. This type of area has an ability to soak and hold huge quantities of water.  Over the past 50 years there has been a lot of human interaction with the Slieve Aughty mountains and this interaction seems to have upset the natural drainage patterns of the mountains.  The main types of interaction are :

  1. More intensive farming + turf cutting in the area
  2. Windmill construction
  3. Forestry plantation

Along with this increase in activity there is also new infrastructure such as forestry access roads that will affect drainage patterns.

The effects of these can be seen on river level height after rainfall .  What we can see in South Galway is that water comes off the mountain very quickly leading to increases of over 1 m in some rivers in a few hours – e.g. Storm Gertrude (Feb 2016) below:

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  • Killafeen is the input to Lough Cutra on the Derrybrien river
  • Ballycahalan is the Bollyneendorish river
  • Gortmacken is on the Ownshree river at Kilchreest

Getting a grip on ‘grips’!

What is a grip?  A grip is a man-made channel that is cut into wetland area that runs in straight lines and occur in regular patterns. They can be readily seen on aerial photographs. The main purpose of grips is to drain wetlands (which, when your catchment area is prone to severe flooding may not be the best thing to do!)  and seem to have an added benefit for forestry to provide better bedding material for new plantations.

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A grip running into the bog and heading downhill – Nice and dry on Jan 14th 2016, while the lowlands are in flood.

The following is an aerial photograph of the area just south of the windfarm close to Derrybrien.  This was take on 14th Jan 2016 where South Galway floods had fully peaked. A light snowfall the night before provide us a good contrast to see the grips.

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An example of grips on Slieve Aughty north of Derrybrien (Courtesy of Sean Brady)

The following video [Courtesy of Sean Brady] shows some of the grips and how the connect and go downhill.

 

Impacts of Grips

It is intuitively obvious that combing the top of a mountain with 3-4ft rains every 12 yards aiming downhill –  will have an massing impact on the drainage dynamics. That’s why they are put there in the first place. According to the Forestry Commission of England, when establishing new forests trees need to be planted on dry ground where their roots are not constantly waterlogged. – to the Slieve Aughty bogs are being drained.

There are some studies that argue that the grips don’t make the water flow more, but they help to bring the water flow earlier – Sounds like they are describing that overflowing funnel to me.

Changes to the hydrological management of upland habitats can be detrimental to the characteristic vegetation and species of the uplands, as well as increasing the risk of soil erosion and flash flooding. [RSPB/DEFRA]

 

Rather than a square kilometer of land soaking water slowly you could have 100s of these narrow channels that transport the water instantly off the mountain. T

Who is responsible for the grips?

One body – Coillte Coillte manages about 7% of land cover in Ireland.  Its core purpose is “to enrich lives locally, nationally and globally through the innovative and sustainable management of natural resources – but it’s not a charity –  It’s is a commercial company operating in forestry, land based businesses, renewable energy and panel products. So what about the Slieve Aughty Mountains?  you can see the main highland catchment area for the Slieve Aughty mountains highlighted below:

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Coillte  Properties highlighted in Green – Catchment area for South Galway circled in Yellow

Its tagline is  :

Coillte manages its forests to deliver social, economic and environmental benefits.

I think it’s fair to say that from its tagline,  Coillte should be in the position to deliver positive environmental benefits from managing the land of the Slieve Aughty’s.  Are Coillte actually engaging in practices that dramatically affect the hydrological dynamics of the mountain that will then affect flooding probability in South Galway?

Also, come to think of it,  where is our National Parks and Wildlife Service (NPWS) again? Forestry works require an Environmental Impact Assessment (EIA)  before commencing disturbing operations including harvesting, establishment , engineering and other development works prior to commencement.  Why has the NPWS not anticipated the downstream impacts and devastation that rapid run-off will cause?

Forestry Access Roads

Many forestry access roads in the Slieve Aughty’s are constructed below bog level and have drains for carrying run-off water and can become the main conduits to the system. It is a common occurrence to see the floor of the a bog with planted forest 3-4 ft above road level.  This again improves drainage but leads to rapid run-off during severe weather.

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An access road with open drain in Mountains above Kilchreest (Windmill in background)

Impacts of Windfarms

I haven’t found any detailed studies  (yet) on the impact of windfarms on drainage and flooding.  Recently Dr Professor Johnston highlighted the likely hydrological impacts of a windfarm development in the Finn valley in Donegal and was concerned that, if the development was to go ahead, flooding events of past week would be tenfold in their extremity.  It makes sense that if you strip the top of a mountain of 500,000 cubic meters of peat and soil, it will have an impact on the drainage dynamics. We’ve already seen a landslide caused by the construction of the windmills close to Derrybrien.

Running off the mountain

Other studies have shown that in heavy rain fall, water will cascade overland on grasses and contribute as much as drains.   A project called the Pontbren project prompted the formation of a government-funded  Flood Risk Management Research Consortium’ to do more in-depth analysis on water flows and came up with proven metrics on the effects of tree belts across the mountain.

Slowing the flow!

One of the best very recent examples of really effective flood management is what happened in the town of Pickering, in the UK.  This town was flooded four times between 1999 and 2007 – and being refused a conventional flood defense as too expensive – the local people took matters into their own hands, “working with nature, not against it”. They formed a committee and ran a project called ‘Slow the flow at Pickering’ and used a range of land management measures to help slow the rush of water. These included:

  • Constructing low-level bunds (reservoirs or catchment pools)
  • Planting more trees, especially along streamsides and in the floodplain
  • Restoring woody debris dams in small streams
  • Targeted blocking of moorland drains
  • Restoring wetlands

Bund strorage/Resevoirs

Bunds create additional flood storage capacity and can be designed to only operate during flood events by storing overflow water.  After flooding events, the water slowly dissipates back into the system.  Surely there are areas within the Slieve Aughty mountains where it would be possible to create these bunds/resevoirs to store 100s of 1000s of cubic metres of water?

Planting more trees

A hydrology department (Centre for Ecology and Hydrology) initially took measurements comparing the speed at which the soils under the pasture and those in the fenced
off woodland could absorb water.

The results were striking, showing that the infiltration rates inside the woodland were 60 times those on the pasture ten metres away, and that the beneficial effect extended beyond the edge of the woodlands.

 

This prompted the formation of a government ‘Flood Risk Management Research Consortium (FRMRC) , to do more indepth analysis. The FRMRC setup various studies:

  • They measured infiltration and flow rates and build up a picture of how water moved from fields to streams.
  • They examined the way rainwater flowed through small channels in the soil (using simulated rain, coloured blue with food dye)
  • They investigated the influence of tree shelterbelts (thin strip of woodland across pasture/grassland) on the amounts and patterns of rainfall reaching the ground both directly underneath, and on the leeward side of the plantings.

Tree Drainage : Research found that water flowed along the pathways provided by living tree roots, rather than through earthworm channels and other cracks in the soil.  This overturned existing theories that suggested water flowed only along channels left by dead tree roots. The experiment with dyed water showed that the pathways tree roots provided for water were strongly influenced by tree species. Birch trees have a spherical root structure and this caused the water to be channelled into a bulblike area at the top of the soil; ash trees have horizontal surface roots from which vertical roots extend down into the soil. Water here was channelled along these vertical roots in finger-shaped patterns to a greater depth.

Tree Shelterbelts :  It was shown that in winter, high wind speeds blow small
raindrops in an almost horizontal direction across the shelterbelt. This sheltering effect led to less rainfall both directly underneath the tree canopy and over a width
equal to the average tree height from the leeward edge. In contrast, low wind speeds and large raindrops in summer fall almost vertically, directly onto the canopy causing little or no rainfall depletion on the leeward side:

The Pontbren results have shown conclusively that strategically planted narrow, fenced shelterbelts of trees across slopes capture surface run-off from the pasture land above and allow it to soak more rapidly into the soil.

Restoring woody debris dams in small streams

Woody debris dams are accumulations of trees, branches, root boles, twigs etc that are seen as a vital component of our mountain watercourses. Their function as ‘leaky’ dams can reduce peak flow rates and increases floodwater storage

Woody debris helps regulate the energy of running water by decreasing the velocity.
Thus the ‘travel time’ of water across the catchment is increased.

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A Large Woody Debris (LWD) dam in Pickering
Large woody debris (LWD) dams are a common feature in natural woodland streams and they have the  ability to increase flood storage by raising water levels and reconnecting streams with their floodplain. In pickering, a total of 129 LWD dams were installed within the Pickering Beck catchment and a further 38 in the River Seven catchment.
This is something that Coillte could support in the Slieve Aughty region.

 

Grip/Gully Blocking

There a lot of articles on Grip/Gully blocking that outline the positive effects that they have on the

Grip blocking can help to restore natural drainage patterns, encourage re-vegetation, reduce erosion, and minimise the knock-on effect of hydrological change downstream. [DEFRA, UK]

One paper was looking at the hydrological affects of blocking drains and they were able to reduce peak flows substantially.

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There are assessment guidelines, implementation guides lines but the best guideline would be not to have downward facing drains in the first place.

Conclusion

The following are they key facts:

  1. The key catchment area for the South Galway is the Slieve Aughty mountains
  2. Coillte,  who aim to deliver social, economic and environmental benefits, are the owners of much of this land.
  3. The water is coming off the mountains very fast, leading to rapid rise in river levels in hours.
  4. There are many proven solutions (resevoirs, drain blocking, planting native trees) to restoring natural hydrological flows and these solutions are within our reach
  5. NPWS should be enabling these solutions

 

The good news is that there are solutions within reach that mean that we technically don’t have to ‘move mountains’. The only mountain in our way is that of bureaucracy which will need quite a few grips to streamline!

We need to ‘Slow the Flow‘ in South Galway

-David Murray