Donegal County Council the SEED Project Ballybofey-Stranorlar, County Donegal Flood Risk Assessment
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Donegal County Council The SEED Project Ballybofey-Stranorlar, County Donegal Flood Risk Assessment www.tobin.ie The SEED Project Ballybofey-Stranorlar, County Donegal Flood Risk Assessment Document Control Sheet Document Reference 10973 – FRA for The SEED Project Ballybofey-Stranorlar – Rev A Report Status For Issue Report Date September 2020 Current Revision A Client: Donegal County Council Client Address: Lifford, County Donegal, Ireland Project Number 10973 Galway Office Dublin Office Castlebar Office Fairgreen House, Block 10-4, Market Square, Fairgreen Road, Blanchardstown Corporate Park, Castlebar, Galway, Dublin 15, Mayo, H91 AXK8, D15 X98N, F23 Y427, Ireland Ireland Ireland Tel: +353 (0)91 565 211 Tel: +353 (0)1 803 0406 Tel: +353 (0)94 902 1401 Reviewed Authorised Revision Description Author: Date Date Date By: by: A First Issue DH/CK 10/09/2020 BD 11/09/2020 BD 11/09/2020 TOBIN Consulting Engineers Disclaimer This Document is Copyright of TOBIN Consulting Engineers Limited. This document and its contents have been prepared for the sole use of our Client. No liability is accepted by TOBIN Consulting Engineers Limited for the use of this report, or its contents for any other use than for which it was prepared. Table of Contents 1.0 Introduction ......................................................................................................... 1 2.0 Appraisal of Current Planning Policies and available information on Flood Risk Management ............................................................................................. 2 2.1 The Planning System and Flood Risk Management Guidelines .................. 2 2.2 The Flood Risk Management Climate Change Adaptation Plan ................. 4 2.3 Donegal County Development Plan 2018-2024 ......................................... 5 2.4 Seven Strategic Towns Local Area Plan 2018-2024 ................................... 6 2.5 Historical Flood Events................................................................................ 8 2.6 Catchment Flood Risk Assessment and Management Study ...................... 9 2.7 Ballybofey - Stranorlar Flood Relief Scheme ............................................. 10 2.8 Geological Survey Ireland Mapping .......................................................... 10 3.0 DETAILED FLOOD RISK ASESSMENT ..................................................... 11 3.1 Fluvial Flooding.......................................................................................... 11 3.2 Pluvial Flooding ......................................................................................... 11 3.3 Groundwater Flooding .............................................................................. 11 3.4 Coastal Flooding ........................................................................................ 11 3.5 Assessment of ‘minor proposal’ in areas of flood risk ............................... 12 4.0 CONCLUSIONS ................................................................................................ 14 Table of Figures Figure 1-1 Location of the Proposed Development Sites ................................ 1 Figure 2-1 Ballybofey-Stranorlar Flood and Land Use Zoning (extract from LAP) 6 Figure 2-2 Ballybofey-Stranorlar Flood Indicator Map (extract from SFRA) 7 Figure 2-3 OPW Past Flood Event Mapping ........................................................ 8 Figure 2-4 CFRAM Fluvial Flood Mapping (current scenario, excluding climate change) .............................................................................................................. 9 Figure 2-5 CFRAM Fluvial Flood Mapping ......................................................... 10 - i - Table of Tables Table 2-1 Decision Matrix for Determining the Appropriateness of a Development .................................................................................................................. 2 Table 2-2 Climate Change Adaptation Allowances for Future Flood Risk Scenarios ......................................................................................................................... 4 Appendices Appendix 1 - Drawings - ii - 1.0 INTRODUCTION TOBIN Consulting Engineers were appointed by Donegal County Council to carry out a Flood Risk Assessment (FRA) to support the Part VIII planning application that will be submitted for the proposed Ballybofey-Stranorlar town centre regeneration project, i.e., The SEED Project. This FRA is specific to the proposed development sites in Ballybofey, shown in Figure 1-1, which comprise the currently vacant ‘RITZ’ building, a portion of the existing car park on Main Street and a brownfield site on Chestnut Road. The proposed public realm scheme involves the following: 1. Construction of a contemporary extension on the footprint of the currently vacant ‘RITZ’ building while retaining its architecturally significant façade. 2. Replacement of the existing car park on Main Street with civic space comprising a playground, seating area, and water feature. 3. Construction of a multi-storey car park on the brownfield site on Chestnut Road. The existing site layout and proposed public realm scheme are provided in Appendix 1. The purpose of this report is to communicate any potential flood risks, from various sources, to the proposed future developments and to the people using the space. Due to the proximity of the River Finn to the subject site, fluvial flooding was considered as a potential source of risk to the development. Ballybofey Town Centre Figure 1-1 Location of the Proposed Development Sites 1 2.0 APPRAISAL OF CURRENT PLANNING POLICIES AND AVAILABLE INFORMATION ON FLOOD RISK MANAGEMENT This Flood Risk Assessment was carried out in accordance with the following flood risk management guidance documents: • The Planning System and Flood Risk Management Guidelines • Flood Risk Management Climate Change Sectoral Adaptation Plan • Donegal County Development Plan 2018-2024 • Seven Strategic Towns Local Area Plan (Ballybofey-Stranorlar) 2018-2024 An appraisal of the following was also carried out: • Historical Flood Events • Catchment Flood Risk Assessment and Management (CFRAM Study) • Ballybofey-Stranorlar Flood Relief Scheme • Mapping by the Geological Survey of Ireland 2.1 The Planning System and Flood Risk Management Guidelines The Planning System and Flood Risk Management (PSFRM) Guidelines (OPW/DEHLG, 2009) discuss flood risk in terms of Flood Zones A, B, and C, which correspond to areas of high, medium, or low probability of flooding, respectively. The extents of each flood zone are based on the Annual Exceedance Probability (AEP) of fluvial and coastal flood events. The PSFRM Guidelines also categorise different types of development into three vulnerability classes based on their sensitivity to flooding. Table 2-1 shows a decision matrix that indicates which types of development are appropriate in each flood zone and when the Justification Test must be. The AEPs used to define each flood zone are also provided. Table 2-1 Decision Matrix for Determining the Appropriateness of a Development Flood Zone Development Appropriateness Annual Exceedance Probability (Probability of Highly Less Water (AEP) flooding) Vulnerable Vulnerable Compatible A Fluvial & Pluvial Flooding Justification Justification Appropriate (High) More frequent than 1% AEP Test Test B Fluvial & Pluvial Flooding Justification Appropriate Appropriate (Medium) 0.1% to 1% AEP Test C Fluvial & Pluvial Flooding Appropriate Appropriate Appropriate (Low) Less frequent than 0.1% AEP Note: Given that coastal flooding is not a potential source of risk to the proposed development, the probabilities for coastal flooding have been omitted from this table. With reference to table 3.1 of the PSFRM Guidelines, amenity open space and car parking facilities are classified as “water compatible”. The guidelines classify buildings used for leisure/commercial (i.e. the Ritz building) as “less vulnerable” in terms of their sensitivity to flooding. New developments of this type would typically be assessed against a 1% Annual Exceedance Probability (AEP) flood event. However, 2 Section 5.28 of the PSFRM Guidelines notes the following in relation to the assessment of “minor proposals” in areas of potential flood risk: “Applications for minor development, such as small extensions to houses, and most changes of use of existing buildings and or extensions and additions to existing commercial and industrial enterprises, are unlikely to raise significant flooding issues, unless they obstruct important flow paths, introduce a significant additional number of people into flood risk areas or entail the storage of hazardous substances. Since such applications concern existing buildings, the sequential approach cannot be used to locate them in lower-risk areas and the Justification Test will not apply. However, a commensurate assessment of the risks of flooding should accompany such applications to demonstrate that they would not have adverse impacts or impede access to a watercourse, floodplain or flood protection and management facilities. These proposals should follow best practice in the management of health and safety for users and residents of the proposal.” On this basis, the works proposed as part of the SEED project are considered a minor proposal and the Justification Test is not applicable. The proposed upgrades must therefore be assessed against the following criteria if the site is found to be in a 1% AEP flood zone: (1) Effect of the development on flood risk elsewhere: a. Impact