Solving South Galway Flooding – Good start but complexity slowing feasibility study

There has been a lot going on over the past 6 months with substantial level of data gathering from extensive home/farm flooding surveys, public consultation, LIDAR and satellite data collection.  This information is crucial in developing an accurate and complex hydrology model of South Galway that will allow

  1. A more accurate prediction of flooding dynamic  that will feed the Cost-benefit analysis
  2. The impact of proposed solutions (attenuation, bunding, channels)

There is a lot of data required to develop an accurate model and the models itself is very complex to develop. This we are told is leading to a delay in the final feasibility study being pushed out from Jan 2019 to May 2019, and could mean a delay in overall project by the same timeframe.

Other concerns are that the NPWS has put more or less a moratorium on Swallow holes reinstatement/maintenance (anticipated light maintenance – removal of wraps and tress won’t be a major issue).

Abbreviations :

  • RH: Ryan Hanley, Engineering Design Consultants
  • MMD : Mott McDonald,, Environmental consultants
  • GCC : Galway County Council
  • OPW: Office of Public Works
  • SGFRC : South Galway Flood Relief Committee

Information Compilation

A lot of the feasibility study stage is about compiling a lot of information relevant to flooding to assess flood extents and feed cost-benefit analysis which will determine the justification and budget for flooding solutions.

Land Surveys

RH have (almost) completed the most extensive survey of land, homes, farms in South Galway  to date in relation to flood levels.   The survey team collected finished floor levels, path levels, historic flood levels, flooded road levels, bridge and structures data including :

  • 174 houses, Farm buildings, septic tanks, fuel storage
  • 24 additional farm buildings
  • 10 commercial properties,
  • 47 bridges and culverts and several kilometres of roads.

This information is currently being compiled by RH into a GSI database to be used in the cost-benefit analysis.

Note : There are several areas that have not been completed yet, as they are waiting on additional LIDAR result before surveys are commissioned – if you are concerned, please contact Galway County Council.

LIDAR

LIDAR gives an extremely accurate land topography (heights of land to a few CM) .  There was some historical LIDAR Data around South Galway but several key pieces were missing.  This year additional LIDAR flights were commissioned to fill in some missing pieces (Around Caherglassaun-Cahermore, Caherawooneen, Turloughmore/Tulla, Kilmacduagh, Gortnaculla, Liseen, Tarmon).  There is still more to be commissioned around Kilchreest, Ardrahan, Killinney, Lough Cutra and the M18 towards Tubber

Salinity Monitoring

MMD is looking to get salinity monitoring (Kinvara Bay)  data from EPA and NUIG and this will be added to the Hydrology model

Public consultation Day

Public Consultation Day took place on 3 May 2018 in O’Sullivan’s Hotel, Gort, and was attended by representatives from GCC, OPW, RH & MMD. 55 people signed the attendance sheet but many more attended.  The themes :

  • Concerns that the scheme would affect salinity in Kinvara Bay
  • Assurances that the proposed scheme would include measures to reduce rapid run-off the Slieve Aughty Mountains

Hydrology Modelling

The hydraulic Modelling has been significantly complex and initial (3d) models were too slow for running the number of scenarios that needed to be run for forecasting, solution iteration etc. These models were replaced by simpler models (1d) that would fit initial feasibility study assessment.  The more accurate models that will still be used for signoff but there is more work in creating these models leading to delays.

hydrology model

Turlough Levels Monitoring

There has been a significant increase in the number of Turlough Monitors in South Galway and many people will have seen GSI people installing monitors (mainly temporary) .  The following GSI monitors were installed in Autumn 2016:

  • Caranvoodaun
  • Caherglassaun
  • Coole
  • Blackrock
  • Garryland
  • Newtown
  • Hawkhill
  • Managh
  • Termon North & South
  • Ballinduff
  • Roo
  • Coy
  • Cahermore
  • Labane
  • Kiltartan
  • Tulla

These monitors were installed in Summer 2017.

  • Cockstown
  • Ballyboy
  • Ballylee Sinks (north and south)
  • Castletown sink

There are also several permanent monitors being installed. Here is a shapshot image of the monitors.

Gort_stations_GSI
South Galway Turlough Monitors – Courtsey of Geological Survey Ireland (2018)

Turlough Levels (Satellite)

As several of the monitors are new, GSI/TCD are also using new techniques to analysing satellite imagery to determine real-time Turlough levels over the past 3 years.  This imagery is produced by the ESA Sentinel-1 satellites using SAR (synthetic aperture radar) and works through cloud or at nighttime  and is particularly good at highlighting waterbodies. It has captured hi-resolution imagery of Ireland every 2-3 days since 2015 and therefore has captured flooding events/water levels so it can be used to determine Turlough/flooding levels where there was no monitors – (The good news is that this applies to all of Ireland, and not just South Galway).

Gort_SAR.png
SAR Imagery of South Galway – Christmas Day 2015 :   Geological Survey Ireland (2018), ©Copernicus data (2018)

Weather Prediction/Climate change models

There is significant work on developing more realistic Weather prediction/climate change models for the 1:100 year, 1:1000 year rainfall.   TCD/GSI are working on updating their models to have more accurate weather forecasting. This are collaborating with the Irish Centre for High-End computing to do weather, climate and rainfall prediction  to provide long term ‘synthetic rainfall simulations‘ that will be used by the hydrological model to provide the 1:100 flood limit estimations.

Uplands Attenuation

From being highlighted as Public Consultation day and also from the SGFRC There has been some additional work on looking at potential uplands attenuation.  What happens if you slow-the-flow and flatten the peaks?  Some attenuation scenarios show limited impact on upland and lowland Turlough while other attenuation scenarios show possible lowering of low-land Turloughs by 1.5m and consequently lowering upland Turloughs by 0.5m. This is the kind of early analysis being done with the model currently.

Channels

In order to progress the solution RH have drawn in conceptual channels (link – 20m each side, depth unfixed) between the different areas and are working with MMD to do an initial Environmental Investigation – looking at habitats, impacts etc of proposed work.

Initial Environmental Assessment

Initial findings highlight some bat populations, woodlands and limestone shelfs as part of Coole Park and Caherglassaun.  While it might be ok to take away some woodland within the channel., digging into limestone shelves may be more problematic.  The salinity of Galway Bay will also need to be addressed.  The channel definition have allowed the advancement of seasonal ecological surveys so the 2018 season isn’t lost.

Advanced Works

The SFGRC highlighted several areas could be problematic for the South Galway Communities that would need to be resolved in the short term.  GCC outlined in the project brief the possibility of doing some Advanced works and RH created an overall list of some areas for potential advanced works.

 

Advanced Works Description Status
Reinstatement of Swallow Holes There was potential to re-instate some significant swallow holes that have become filled in over the years. This has hit a proverbial black hole – NPWS have indicated that Swallow hole clearance is not likely to form part of the scheme, as the effects of clearance are difficult to predict and it would be extremely difficult to demonstrate that work around swallow holes would not have a significant effect on Natura 2000 Sites.  It was accepted that clearance of large artificial deposits (bale rap, and timber debris etc.) could potentially be removed.

SGFRC highlighted that this could be seen as maintenance of an SAC which doesn’t require appropriate assessment.

Overall – SGFRC are not happy with this position.

Culverts between Caherglassaun and Cahermore (Leeches) SGFRC highlighted concerns of the GCC-made dam between Caherglassaun and Cahermore. The concerns here is that the new height of the road with a few 12 inch pipes  will hold back water into Caherglassaun/Coole/Tierneevin, Gort, Crannagh, Kiltartan, Corker etc.  And add flood risk to these communities before flood scheme gets under way. Stalemate here –  GCC raised the road without any proper analysis (threw a few 12inch pipes down) but raised the road 6ft so as long as this remains – they may be responsible for uplands flooding.   If GCC install bigger culverts, again without proper analysis, then again they could be responsible for downstream flooding.

 

With the lack of detailed flow analysis – it is difficult to ascertain what to do here as an interim measure.  Work will probably not proceed.

 

Cahermore to Kinvara Overland Flowpath Reinstatement Measures SGFRC highlighted concerns that the Cahermore pipe outlet is 18 inches below the surrounding land and that it needs be fixed.  They also highlighted that the link between Cahermore and the pipe could benefit from a culvert Will form part of the permanent solution rather than Advance Works
Rinrush Access SGFRC/RH discussed several options a Rinrush Emergency Access Road to help avoid the complete isolation of the community there for 6+ weeks during flooding Early stages but this looks promising for the Rinrush community but with details to be worked out (Needs environment assessment, landowner agreements) etc.
Roxborough Demesne: This is the 1st house that floods – flash flood for several hours backs into Paddy McGlynn’s place. Early stages but looks favourable for advanced works – probably done in phases. Volume of water being dealt with won’t have any impact on Grannagh/Blackrock. (Needs environment assessment etc)

 

Timeline

Unfortunately, with its complexity and refactoring, it is looking like the hydrology modelling completion aspect will delay feasibility study by 5 months. (the initial model was supposed to be delivered in Jan)  – there seems to be a correlation of several factors:

  • Model has been previously used in Academia and not as a core technology for analysis and simulations – it was too slow to produce results.
  • The updates to the model are quite complex and difficult to converge
  • More aspects to the model – salinity and uplands rapid-run-off analysis

GSI have indicated that they don’t foresee any more delays in the model and that it’s now in good shape – it will be continuously refined as more data comes in.

Conclusion

The success of this project relies heavily on science as this is an incredible complex and sensitive project.  One the positive sides- Galway County Council, the consultants and GSI are so far extremely thorough.

  • Full land Surveys – to understand homes being threatened
  • Turlough monitors/Satellite SAR analysis
  • LIDAR data for accurate hydrology modelling
  • Full hydrology modelling of the Turlough network
  • Latest Weather prediction techniques.

Also the consultants have been creative in working out ways to continue to progress -developing channel concepts to allow environmental feasibility to progress.  The steering committee seem to be adaptive and supportive where change is needed.   There is additional work being undertaken which will have a positive impacts on the accuracy of results.

While this complexity and widening scope of work is pushing the feasibility study out by 4-5 months – It is not clear on the impacts on the overall project and if this 5 months will be added to the complete project or if something can be done to bring the timeline in? – This is question we will ask GCC.

Another concern is the NPWS position on ‘untouchable’  Swallow-holes, limestone shelves, etc  that may end up blocking some aspects of a solution. We all want to avoid a situation where a solution is not possible because of an environmental snag even if we can prove overall that this is a significant environmental benefit to this scheme.  This has become one of the big risks for this project and I will be addressing the Swallow-hole situation in an upcoming blog

Overall, the SGFRC is complementary of the thoroughness of the work being done by Ryan Hanley, Mott MacDonald, GCC, GSI/TCD and is supportive of getting the right level of accuracy to ensure we get a long-lasting flood solution.  We don’t want to have to be revisiting this again in 10 years time – However, we can’t afford more slips that introduce another winter cycle into the flood relief program.

-David Murray,

Chair South Galway Flood Relief Committee

 

 

 

 

 

 

 

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2 thoughts on “Solving South Galway Flooding – Good start but complexity slowing feasibility study”

  1. David, thank you once again for a concise description of a very complex project. You manage to make clear the various concerns that need to be addressed in a way even I could understand!

    Liked by 1 person

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