Following recent public consultation and the emerging preferred scheme, it has come to light that TII (Transport Infrastructure Ireland) , also known as NRA (National Roads Authority) made some significant blunders in the motorway design and construction at Kiltartan/Raheen that may have significant impacts on flooding in the area in the future. The flooding sensitivity and unpredictability highlighted by locals and the OPW was not considered in the design of the flooding mitigation and there was a lack of future-proofing that will now pose challenges to the South Galway Flood Relief Scheme
Flooding Concerns Highlighted
Before the severe flooding in November 2009 locals David Murray and John Nolan met with the National Roads Authority (NRA but now TII) and highlighted concerns of building the M18 Motorway across a flood overflow path that happened in previous years between Kiltartan, Corker, Raheen and into Coole.
After the severe flooding in 2009, David Murray compiled a report that outlined the flooding dynamics in Kiltartan and the concerns, if the motorway was going to go ahead, to ensure properly sized and placed culverts to account for this overflow. This report include maps, videos and photos of the flooded area.
The report (referencing the New N18 (M18) outlined various concerns.
Properly sized and placed culverts would allow water to flow eliminating buildup of hazardous flooding levels. One beside Eugene Nolan’s house in Corker and an upgrade to existing culverts at Raheen. These culverts would be needed in addition to culverts on the new N18. As this route will be modified during new N18 development, it could make sense to include these modifications.
Kiltartan Flooding Report, March 2010
The report was sent to the NRA and others along with various emails and it was indicated that these would be taken into consideration by the ‘experts’ on the scheme.
The concerns have been raised in regard to building of the new N17 to ensure that this overflow can be handled with properly sized and placed flood culverts.
Kiltartan Flooding Report, March 2010
This was highlighted to the NRA in 2010 who were still designing the motorway. Additional communications also questions the flow rates used in the design but the culvert designs were deemed sufficient.
Upgrading Kiltartan-Corker Culverts
There is a history of flawed flood mitigation works in this area 1995, where the road was continuously raised to keep traffic open but which eventually became a dam that contributed to flooding of Kiltartan Church. See previous article: Flood Alleviation – What happens when our experts get it wrong?
An additional report to the OPW after the several 2009 floods, highlighted the flooding situation in Kiltartan highlighted the ongoing saga of raising roads without putting in culverts. The Kiltartan-Raheen Road was raised 3-4 times since 1995 and which subsequently created a dam that kept water back in Kiltartan and contributed to flooding of Kiltartan Church. This was as indicted below.
The OPW did the analysis and looked at levels where it became very obvious on how much the road had been raised in the past. Here the red lined ‘mound’ that holds the Kiltartan-Raheen road has been raised continuously since 1995.
The recommendations in the report was to install culverts through this ‘mound’ as follows:
The key things to note here is that
- The invert-level (or Base level) of the Culvert is 11.74m (Above Sea level)
- The cluvert installed was too small to take subsequent flows (2015)
The OPW report concludes as follows:
It is considered absolutely essential that the design of the new motorway take into account the water dynamics at Kiltartan so as to avoid any flow restrictions. The flow to be considered while designing the motorway was determined under this report and found to be approximately 100m3/s.
Kiltartan Flooding Report January 2011
The report also recommended the following :
M18 Design Flaws
It now appears that there were significant design flaws in the motorway culvert designs. From data obtained during public consultation – The levels of the culverts installed 700m downtream in the M18 Motorway were higher than the upstream culverts on the Kiltartan-Raheen road. In fact the base (invert) level of the lowest culvert under the M18 motorway at Kiltartan is over 2 ft above the base level of the upstream Kiltartan-Corker Culvert, meaning that the water would have to rise just under 2ft way up the culvert before it would work.
Here you can see the lowest Culvert Base at 12.4 M (above sea level/OD) where as the culver based in Kiltartan-Corker is 11.74m, and Corker -Coole Culvert is 10.43m.
TII/NRA may defend themselves and say that the motorway culverts were aligned with the topography of the land in question but this doesn’t really hold. Why were the culverts not aligned (or below) the level of the overflow?
- There was already a land profiling works done after 2009 flow
- In 2015, it was again obvious that the culverts and profiling weren’t working as water was backing up
- Flooding in South Galway has been deteriorating and unpredictable. There were no provisions made about future scenarios
- It was highlighted that Kiltartan was a ‘Pinch Point’ in the overall South Galway Flooding Dynamics
TII can claim that they were not making any additional changes to the hydrology of the area but what there were doing was constructing a substantial obstacle for any future works. If they were worried about unpredictable and changing hydrology, surely the topology of the land itself would have restricted flows and they could have installed culverts at a lower level to at least align with the Kiltartan-Corker culvert (which was at 11.74m) .
It is clear that the M18 Culverts at Raheen were not designed with consideration of local concern, OPW concerns and the future of the area in mind
Keeping ‘things as they were’ in an area where the flooding situation has been deteriorating for the past 4 decades with full knowledge of the longevity and immutability of a Motorway is poor reflection of road engineering and TII and will now likely incur a significant cost.
South Galway Flood Relief Scheme Recommendations
The emerging preferred South Galway Flood Relief Scheme Feasibility has indicated that the M18 Motorway will need a new large culvert to take something like 40m3 of flow. The report defines:
Augmenting the culvert capacity under the M18, e.g. installing a new 45m long 7.5m x 2.5m culvert complete with headwalls and with invert of 11.1mOD (invert designed to be lowered if necessary).
So there it is, in black and white, the base level of the culverts will be 11.1m (or lower) and will need to be 7.5m wide and 2.5m high. In the current scheme of culverts, it will look like this:
What is the impact of doing nothing:
According to the feasibility study, if the existing M18 culvert capacity is not augmented and only the flood relief channel works undertaken, the 1:100 flood levels in Kiltartan and Corker would rise over 2 ft. over the proposed targets and scenario and properties at properties at Corker and Kiltartan would be under significant flood threat. This is a scenario that must be avoided.
What is happening now?
So is this work part of the South Galway Flood Relief Scheme? According to the feasibility report, this is ‘Under Review’ but the onus and cost of adding this new culvert must come under responsibility of TII. They commissioned the design, they were notified by local people and OPW about the flooding risk and they built their culverts at a level that is too high to allow further flood mitigation. The installation of these new culverts at the right level needs to be done and paid for by TII and must not be allowed to threaten the delicate cost-benefit ratio and the viability of this scheme.
Flooding in Kiltartan has been exacerbated in the past. Roads were installed across overflow routes without proper consideration of volume and flooding levels and churches and land flooded. Once again Kiltartan is in the same situation as now a motorway has been installed without proper consideration of volume and flooding levels. TII now has a responsibility to fix this flawed design.
South Galway Floods 