Flooding on the M18 in South Galway- What’s the story?

The construction of the M18 Gort-Tuam has some been in the news recently as there are concerns over the impact the motorway will have on local winter water flows and consequential flooding and threat to homes and livelihoods.

In South Galway, over the past few weeks, the motorway has had a definite impact on flooding and consequently, the flooding had an impact on the motorway construction.

In this article,  I will be looking at the area of Gort-Raheen. The area around Kilternan also has some issues and I welcome any input on the issues here.

M18 Gort-Tuam at Corker/Raheen

The M18, Gort-Tuam section,  which is currently under construction, travels north from Gort, close to Coole Park and then onto Corker and Raheen. There will be an overpass at Corker close to Nolans house.

gort0.JPG

The main cause of concern is that Kiltartan area is a convergence point (and bottleneck) in the South Galway river flow as it is sinks underground rivers from Ownshree, Ballylee and Gort/Beagh rivers. With high levels of rains in the Slieve Aughty,  these flows swell and overflow the swallow-hole at Tommy Murray’s in Kiltartan. The levels build up and flow through a new culvert (3.5m x 1.5m)  from Kiltartan into Corker.

This Kiltartan-Corker overflow normally flows down into Raheen through an old culvert there but now the new motorway is obstructing it

Note, there is also a nominal winter flow from Coolfin turlough that needs to get across Raheen.

Trouble from the start

A few days after the heavy rains in mid Dec, as the waters rose in the first wave of flooding, the Kiltartan-Corker culvert (Beside Eugene Nolan’s house)  started to flow and gradually increase. This would have normally flowed through Corker and into the Corker-Raheen culvert to flow into Raheen which then flows into the Coole basin.  A day or so later the levels in the Corker side were rising much more than they should so I investigated this (along with John Nolan) one fine winters day – The situation was not good. The first thing we noticed is that the levels on the Corker side were very high at the motorway construction and we found some machinery that was close to flooding.

IMG_1127
A machine becoming caught in the build up in Corker hampered by the new motorway embankment

The reason became apparent very quickly. The motorway construction embankment was acting like a dam and was not letting water through and this was the cause for the water build up in Corker and consequently the back-up into Kiltartan.  The only water flowing into Raheen was seepage through the rock – nothing in comparison of what was flowing building up on the opposite side of the motorway.

IMG_1130
The flow seeping through the motorway construction from Corker to Raheen

We contacted Tony Collins from the NRA the next morning and explained the situation.  The motorway has culverts planned but during the early stages the embankment was just a means of moving machinery around – it’s not the finished design.

In fairness, the NRA acted immediately and they came out straight away and dug a channel across the motorway.  Here is the result of the digging a channel through the embankment:

The water immediately rushed through into Raheen but was already challenging the old culvert there and overflow was hampered by ditches.  This was only the start of the water flows and as more water came down from Ballylee and Gort. The following diagram shows the two channels crossing through the motorway construction.

gort4

Increasing flood levels

The levels of water flowing into Kiltartan increased significantly and the Kiltartan-Corker culvert was completely overrun and this tried to get across the Motorway.

 

The area of Corker  was very vulnerable as you had significant flows going into it and a motorway construction hampering it reaching Raheen (which was merging with Coole Lake).  This also backed up in Kiltartan and caused flooding of the church. As a rule of thumb, if the water is flowing across the road at the culvert in Corker (above), water is in Kiltartan church.

As the levels of Coole lake rose it started to merge with the levels of Raheen. In less than a week, the levels had risen so much they submerged the motorway construction.

motorway3
The new M18 motorway is going from Gort (right) to Tuam (left) of this picture . You can see several 100 metres of the motorway construction under water. There is also a significant flow across this.

(Courtesy of Sean Brady Aerial Photography)

Key Issues

The M18 motorway construction has the following key impacts on the local area.

  • The M18 must be capable of allowing an unimpeded flow from Kiltartan, through Corker into Raheen where it can join the Coole basin. It must take into consideration the ever increasing flows from the Slieve Aughty basin because they mostly all travel through Kiltartan.  If the NRA don’t put in the right culvert/bridge sizings, several homes, farms and Kiltartan church will be flooded.  Also the levels of Kiltartan will determine the flow capacity of the underground rivers and will a have a big influence on Ballylee and Castletown(Gort) levels.
  • The M18 at Corker must also consider flows from the Coolfin turlough overflow whose route has been changed by the motorway construction
  • The M18 construction must consider emergency access to Kiltartan and Corker families (18 people) as they can potentially become landlocked between flood waters and the motorway. This access should include the transportation of farm animals and haulage vehicles.
  • The M18 construction must ensure it does not damage or block any underground channels especially the Kiltartan->Coole underground channel.  This channel carries most of the Sieve Aughty  drainage from as far away as Kilchreest to Derrybrien.  The motorway construction is passing directly over it, however exact route is unknown and care should be avoid damaging the channel in the general area.

Obviously a flooded motorway is something that should be avoided and is a very serious issue for all concerned.

The Solution

One of the key solution to local impacts is to ensure that the Kiltartan-Corker overflow can flow efficiently into Raheen and Coole basin.This would be the construction of properly sized culverts from Kiltartan into Corker, under the new M18 and then into Raheen.  From experience of culvert design to date in the region, my recommendation for ‘properly szied’ to take take the maximum estimated flow rates from all the analysis and then triple the number.  Don’t take half measures as has been done in the past.

In addition to the culverts the overriding solution to many of the M18 flooding issues would be to keep the Coole lake to a safe level during flooding events. This would mean lowering the lip of the Coole basin where it flows into Caherglassaun and providing a managed flow into the sea at Kinvara.

The motorway design should be revisited to include local access routes for the homes in the vicinity of Corker, Coole and Kiltartan e.g. via relief road.

I’ve heard local people say that even though the flooding is causing a lot of distress, its a saving grace because we now have an idea of what we are dealing with. I understand this position but wouldn’t be as optimistic – Who knows what dynamics are going to happen over the next 20-30 years – Plan for 2x-3x what we know now.

-David Murray

 

 

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4 thoughts on “Flooding on the M18 in South Galway- What’s the story?”

  1. It’s sad that you had to write this article. The ‘impact study’ or whatever the technical term is for it that should have been carried out by the road planners / designers was obviously not adequate. And this route should also probably been decided on, so close to Coole Park. There were a lot more routes that could have been chosen, It beggars belief that a major motorway is being built almost through a national treasure like Coole Park.

    Liked by 1 person

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