Irish Coastal Protection Strategy Study Phase 3 - North East Coast Work Packages 2, 3 & 4A - Technical Report IBE0071/June 2010 rpsgroup.com/ireland rpsgroup.com/ireland Office of Public Works Irish Coastal Protection Strategy Study - Phase III Work Packages 2, 3 & 4A Strategic Assessment of Coastal Flooding and Erosion Extents North East Coast - Dalkey Island to Omeath Final Technical Report - June 2010 Track of Low Pressure from 10/01/62 - 12/01/62 65 o N 956.2 6 o 963.3 0 N hPa hPa 953.9 hPa 953.8 12 hPa 5 o 5 3N6 o W 950.6hPa 949.9 hPa Latitude 951.4 hPa 961.3 50o N 10/1/62 hPa 06:00 972.8 hPa 45 o N o o o 24 W 12 W 0 Longitude Office of Public Works Irish Coastal Protection Strategy Study - Phase IIIa Work Packages 2, 3 & 4A Strategic Assessment of Coastal Flooding and Erosion Extents North East Coast - Dalkey Island to Omeath Final Technical Report - June 2010 DOCUMENT CONTROL SHEET Client Office of Public Works Project Title Irish Coastal Protection Strategy Study, Phase IIIa, Work Package 2, 3, & 4A Document Title Strategic Assessment of Coastal Flooding and Erosion Extents Document No. IBE0071/EFORev03 No. of DCS TOC Text List of Tables List of Figures This Document Appendices Comprises 1 3 103 1 2 10 Rev. Status Author(s) Reviewed By Approved By Office of Origin Issue Date 01 Draft CR/MB BE AKB Belfast Dec 07 02 Draft Final CR/MB MB AKB Belfast Aug 08 03 Final CR/MB MB AKB Belfast June 10 Irish Coastal Protection Strategy Study Strategic Assessment of Coastal Phase 3 – North East Coast Flooding and Erosion Extents Irish Coastal Protection Strategy Study - Phase IIIa Work Packages 2, 3 & 4A Strategic Assessment of Coastal Flooding and Erosion Extents North East Coast - Dalkey Island to Omeath Draft Final Technical Report Table of Contents 1.0 Executive Summary ...............................................................................1 2.0 Introduction ............................................................................................4 3.0 Storm Surge Modelling and Analysis ...................................................6 3.1 Numerical Modelling.................................................................................6 3.1.1 Model Extension and Calibration..............................................................6 3.1.2 Historic Storm Surge Selection.................................................................8 3.2 Boundary Conditions ..............................................................................13 3.2.1 Tidal Boundary .......................................................................................13 3.2.2 Meteorological Boundary........................................................................13 3.2.3 Other Boundary Conditions and Adjustments.........................................15 3.3 Storm Surge Simulations........................................................................15 3.3.1 Calibration of Storm Surge Model ..........................................................15 3.3.2 Storm Surge Modelling – Validation .......................................................18 3.3.3 Effects from Seiching/Local Wind Set-up and Gusts in Dublin Bay and North East Coast ............................................................................19 3.4 Detailed model of Carlingford Lough ......................................................22 3.5 Output from the Storm Surge Simulations..............................................23 4.0 Wave Climate Modelling ......................................................................25 4.1 Introduction.............................................................................................25 4.2 Joint Probability of Waves and Water Levels .........................................32 4.3 Extreme Wave and Water Level Conditions at Selected Points .............35 5.0 Extreme Value Analysis of Water Levels............................................36 IBE0071/BE/EFOR04ICPS III i Irish Coastal Protection Strategy Study Strategic Assessment of Coastal Phase 3 – North East Coast Flooding and Erosion Extents 5.1 Introduction.............................................................................................36 5.2 EVA for Areas with Low Current-Surge Interaction: Points P1-3, 7- 16 and 18-26 ..........................................................................................38 5.3 Joint Probability of Tidal & Storm Surge Water Levels: Points P1-3, 7-16 & P18-26 ........................................................................................40 5.4 Dundalk Bay and Portmarnock...............................................................42 5.5 Carlingford Lough...................................................................................43 6.0 Floodplain Mapping .............................................................................45 6.1 Creating Flood Heights for the Floodplain Mapping ...............................45 6.2 Accuracy of Predicted Combined Tide and Surge Levels ......................50 6.3 Flood Mapping Methodology ..................................................................50 6.4 Accuracy of the Digital Terrain Model.....................................................51 6.5 Accuracy of the Digital Terrain Model and Flood Extents.......................53 6.6 Uncertainty and Limitations of Flood Extent Maps .................................54 6.7 Presentation of Floodplain Maps – Extreme Flood Extent, Indicative Flood Extent and Flood Depths..............................................55 7.0 Erosion Risk Assessment ...................................................................70 7.1 Introduction.............................................................................................70 7.2 Data Collection & Processing.................................................................70 7.3 Identification of Coastal Change.............................................................71 7.4 Discussion of Results .............................................................................71 7.5 Uncertainty and Limitations of Erosion Maps .........................................72 7.6 Presentation of Erosion Maps ................................................................73 8.0 Conclusions and Recommendations .................................................93 8.1 Conclusions............................................................................................93 8.2 Recommendations .................................................................................95 Glossary of terms..................................................................................................96 References...........................................................................................................103 Appendices..........................................................................................................104 Appendix 1: Storm Track Figures......................................................................105 Appendix 2: Validation Figures of Storm Surge Simulation............................110 Appendix 3: Extreme Value Analysis of surge residual: Points 1 – 3, 7-16, 18-26 ....................................................................................................117 IBE0071/BE/EFOR04ICPS III ii Irish Coastal Protection Strategy Study Strategic Assessment of Coastal Phase 3 – North East Coast Flooding and Erosion Extents Appendix 4: Wave Modelling Tables showing Inshore Wave Climate at 8 Locations ............................................................................................162 Appendix 5: Correlation Plots for Points 4, 5, 6 and 17 ...................................168 Appendix 6: Quality Control Survey Report .....................................................173 Appendix 7: Floodplain maps including flood extent maps for 0.1% and 0.5% AEP events, and flood depth maps for 0.5% AEP event (issued under separate cover) ..........................................................231 Appendix 8: Erosion Maps for 2030 and 2050 (issued under separate cover) ..................................................................................................232 Appendix 9: Confidence in Flood Extents and Erosion Lines ........................233 Appendix 9a: Confidence in Flood Extents ......................................................234 Appendix 9b: Confidence in Erosion Lines ......................................................255 Appendix 10: Digital Data IBE0071/BE/EFOR04ICPS III iii Irish Coastal Protection Strategy Study Strategic Assessment of Coastal Phase 3 – North East Coast Flooding and Erosion Extents List of Figures Figure 1: Extent of Irish Sea Tidal Surge Model (ISTSM)........................................... 7 Figure 2: Tide gauge record from Dublin North Wall .................................................. 9 Figure 3: Digital recorded surface elevation at Dublin with predicted water level and surge residual (different scale) ................................................................................. 10 Figure 4: Friction coefficient used in the surge model .............................................. 15 Figure 5: Correlation between wind velocities from the UK Met Office wave data set and ECMWF operational atmospheric analysis model for a location in the Irish Sea ................................................................................................................................. 16 Figure 6: Mean wind speeds from operational surface analysis, wind speeds in m/s ................................................................................................................................