Irish Coastal Protection Strategy Study

The Irish Coastal Protection Strategy Study (ICPSS) is a national study that was commissioned in 2003 with the objective of providing information to support decision making about how best to manage risks associated with coastal flooding and coastal erosion. The Study was completed in 2013 and provides strategic current scenario and future scenario (up to 2100) coastal flood hazard maps and strategic coastal erosion maps for the national coastline. This major study provides invaluable and essential information required to inform policy in this area, particularly for local authorities in relation to the proper planning and development of coastal areas.

Phase 2 (South East Coast), PHASE 3 (North East & South Coast), PHASE 4 (SOUTH WEST & WEst Coast) and PHASE 5 (NORTH WEST COAST) Work Packages 2, 3 & 4A – Technical Reports and Work Package 9a report appendices

The reports published here present the work undertaken and the findings of Phases 2, 3, 4 and 5 of the ICPSS Work Packages 2, 3, 4A and 9A for the coastline of Ireland. It follows on from an earlier Phase 1 study involving a general overview of coastal protection in Ireland which was concluded in October 2004.

Work Packages 2 and 3 essentially comprise the assessment of extreme coastal water levels and flood hazard at a strategic level, whilst Work Package 4A comprises a strategic level assessment of the coastal erosion hazard. Work Package 9A comprises future scenario strategic level assessments of extreme coastal water levels and flood hazard associated with projected future changes in climate and glacial isostatic adjustment (GIA).

The prediction of extreme water levels and the assessment of both coastal flood and erosion hazard is a key element in the development of any coastal protection strategy. Typically this information is derived from the analysis of long-term historical tidal records, mapping and/or ortho-photography. Unfortunately this kind of data is not widely available in Ireland and alternative methodologies involving analytical and numerical modeling techniques had to be developed as part of this strategic study.

The objective of Work Package 2 was to establish extreme coastal flood extent maps for the coastline of Ireland associated with a water level having a 0.1% annual exceedance probability (AEP). Thus, the present likelihood of flooding from coastal waters is less than 0.1% each year for areas outside the extreme coastal flood extent.

In Work Package 3, coastal flood extent and flood depth maps were derived for the coastline of Ireland primarily for a water level having a 0.5% AEP. Predicted coastal flood extent maps were also derived however for a range of additional exceedance probabilities ranging between 50% and 1.0% AEP.

A Digital Terrain Model (DTM) of the coastline of Ireland was derived. For the east and south coast the DTM was derived primarily from airborne Light Detection and Ranging (LiDAR) data whereas for the south west, west and north west coast it was derived primarily from airborne Interferometric Synthetic Aperture Radar (IfSAR) data.  Each report presents where the different airborne survey data was  used in the study to define the extent of the predicted coastal floodplain. This is shown on the 0.5% AEP flood depth maps which identify the extent of the LiDAR DTM (in other locations the IfSAR data was used). The predicted flood extents were calculated by combining the results of tidal and surge modelling, statistical analysis, and the DTM using GIS technology. The resulting predicted coastal flood extent and flood depth maps for the coastline of Ireland are presented in these reports (Refer to Appendices). All of these coastal flood extent and depth maps are broadly classified as flood hazard maps for the purposes of this study.

In Work Package 4A, the hazard and potential risk posed by coastal erosion was assessed and quantified by estimating the potential future position of the coastline in the years 2030 and 2050.

Aerial photographic records of the coastline from 1973-75, 2000 and 2006 were used as the primary basis for the erosion assessment. The coastlines, as depicted by the seaward limit of vegetation etc, were digitised from each photographic series and a GIS system used to compare these and establish the extent of coastal change over the intervening time period. From this information, an annualised rate of erosion was derived and used to project where the coastline could potentially retreat to by 2030 and 2050 assuming the rate of retreat remained constant.

The resulting erosion maps are presented in these reports (Refer to Appendices). All of these coastal erosion extent maps are broadly classified as erosion hazard maps for the purposes of this study.

It is important to note that the flood hazard mapping undertaken in this ICPSS study is for strategic purposes. Furthermore, any defence works potentially protecting the coastal floodplain are not taken into account. This means that areas may be shown to flood, even though at present a flood defence is protecting them. In addition the flood extent mapping only takes into account coastal flooding; any significant impact from fluvial or other sources (sewers etc.) is not accounted for and needs to be considered separately.

Similarly the erosion mapping undertaken in this study is also for strategic purposes. In contrast to the flood extent mapping, it was not possible to eliminate the effect of existing coastal defence structures from the erosion assessment. Consequently there will be areas where no erosion line is shown that would be vulnerable should the present defences fail or not be maintained in the future. Equally there may be potential erosion shown in areas that are now adequately defended by coastal protection structures that were introduced during the assessment period (1973 - 2006).

These reports outline how the extreme water levels for a range of locations over the study area (the coastline of Ireland) were derived, how the coastal flood extent maps and flood depth maps, for this area, were derived and also how the coastal erosion hazard and potential risk was assessed.

The Work Packages 2, 3 and 4A  reports do not include consideration of any impacts or effects due to climate change or other long-term changes, as the primary purpose was to establish the current level of hazard.

In Work Package 9A projected future scenarios for the year 2100 were considered including allowances for projected future changes in climate and glacial isostatic adjustment (GIA). Two future scenarios were considered representing a Mid Range Future Scenario (MRFS) and High End Future Scenario (HEFS).

The allowances for mean sea level rise are + 500 mm and + 1000 mm (up to 2100) for MRFS and HEFS respectively. Land Movement (GIA) allowances vary around the coastline and are presented in each report.

Predicted coastal flood extent maps for the year 2100 for both future scenarios (MRFS and HEFS) were derived for 0.5 % and 0.1% AEPs.  These MRFS coastal flood extent maps are shown in Work Package 9A - Appendix 1 and the HEFS coastal flood extent maps are shown in Work Package 9A - Appendix 2.

The strategic coastal flood and erosion hazard maps produced in this study will be of particular interest to local authority planners in considering such potential coastal flood and erosion hazard associated with future proposed development (both strategic and non-strategic) at the planning stage. These maps will also be of assistance to local authorities and emergency services generally in respect of the management of such hazards and their likely social, economic and environmental impacts.

Whilst every effort has been taken throughout this study to optimize the accuracy of the flood and erosion hazard maps produced, there are unavoidable inaccuracies and uncertainties associated with these maps. These uncertainties are discussed and highlighted throughout the reports and in the disclaimer and guidance notes appended to these reports. All mapping presented in these reports should be read in conjunction with these appended disclaimers and guidance notes.

 NOTE: The main technical reports for ICPSS WP2,3 & 4A Phase 4 West Coast and Phase 5 North West Coast will be published in the coming weeks.