SITE SPECIFIC FLOOD RISK ASSESSMENT NEW STUDENT ACCOMMODATION, FASSAUGH AVENUE, CABRA, DUBLIN / F5.1 3 RD JANUARY 2018

Transcription

1 SITE SPECIFIC FLOOD RISK ASSESSMENT NEW STUDENT ACCOMMODATION, FASSAUGH AVENUE, CABRA, DUBLIN / F5.1 3 RD JANUARY 2018 Issued For Distribution Revision Final Architect B

2 1 INTRODUCTION 1.1 It is intended to apply for Planning Permission to construct student accommodation on a circa ha site located on Fassaugh Avenue, Dublin 7. The proposed development will also include construction for an internal vehicle access road and some car parking. 1.2 This document should be read in conjunction with the following drawings: /CD/003 EXISTING SITE PLAN /CD/004 PROPOSED SITE DRAINAGE LAYOUT PLAN /CD/005 PROPOSED SITE DRAINAGE LONGITUDINAL SECTIONS /CD/006 DRAINAGE DETAILS SHEET /CD/007 DRAINAGE DETAILS SHEET /CD/010 DETAILS OF PROPOSED DRAINAGE OUTFALLS TO SEWERS 1.3 The flood Risk Assessment for this site has been carried out in accordance with the process set out in The Planning System and Flood Risk Management Guidelines for Planning Authorities published by the Office of Public Works 2 DESCRIPTION OF THE EXISTING SITE 2.1 The site is bounded by Fassaugh Avenue to the south, the railway cutting to the west and residential housing to the east and north. 2.2 Access to the site is from Fassaugh Avenue 2.3 There is an existing derelict public house and associated structures with a paved carpark located at the southern Fassaugh Avenue end of the site. The carpark is level with the public road. The building and carpark occupy approximately 25% of the site area. The rest of the site consists of undeveloped greenfield land. R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Flood Risk Assessment EB AK docx 2

3 2.4 Immediately north of the derelict public house the existing ground profile rises steeply to approximately 3.5m above the road level. The existing site elevation is highest at the north end of the site. It is understood that the current ground profile resulted from excavated material from the railway construction being stockpiled on the site. 3 DESCRIPTION OF THE PROPOSED DEVELOPMENT 3.1 It is proposed to demolish the derelict public house and associated structures at the south end of the site. 3.2 The existing excavated material stockpiled on the site during the construction of the railway will be excavated and removed. This will facilitate access from Fassaugh Avenue to all parts of the site including the new buildings. 3.3 The proposed student accommodation is divided into three multi-storey blocks. The largest blocks, A and B, will be located near the west boundary of the site. Blocks A and B will be designed as cellular structures with internal load bearing walls. Block C will be designed as a framed structure with concrete shear walls. The buildings will be supported on bored pile foundations. A common single level basement will be provided under Blocks A and B. 3.4 Access into the development will be via a new paved road from Fassaugh Avenue. 4 HISTORICAL FLOODING 4.1 The Office of Public Works website floodmaps.ie provides information on historical flooding. The Map Report reproduced in Appendix 1 is taken from this website and shows all flood events within 2.5km of the site. It is noted that there is no record of flooding on or adjacent to the site. 5 DEVELOPMENT VULNERABILITY CLASS 5.1 The proposed development involves construction of student halls of residence. As such the appropriate development vulnerability class is highly vulnerable development in accordance of table 3.1 of the guidelines R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Flood Risk Assessment EB AK docx 3

4 6 PLUVIAL FLOODING 6.1 The flood risk map for Dublin City (map 2019 / Map / 238A), reproduced in Appendix 2 is taken from The Draft Preliminary Flood Risk Assessment (August 2011) published by the Office of Public Works. This map indicates that the site is not at risk from pluvial flooding. 6.2 The Office of Public Works flood mapping data is also available on the MyPlan.ie website managed by the Department of Environment, Community and Local Government. An extract from this website is presented in Appendix 3. This map also indicates that the site is not at risk from pluvial flooding. 6.3 A pluvial flood map for the site is contained in Appendix 4. This is an extract from the Flood ResilienCity Final Report Volume 2, Appendix B produced for Dublin City Council by Jacobs Consulting. This map indicates that the railway cutting west of the site is at risk from pluvial flooding. It is noted that the site of the proposed development is substantially higher than the existing railway cutting. 6.4 The proposed development will maintain the existing direction of overland flow towards the south of the site and away from the proposed buildings. Furthermore it is noted that the proposed stormwater attenuation system is designed for a 1% AEP flood event allowing for 20% increase due to climate change. The site is at minimal risk from Pluvial Flooding. 7 FLUVIAL FLOODING 7.1 The flood risk map for Dublin City (map 2019 / Map / 238A) reproduced in Appendix 2, is taken from The Draft Preliminary Floor Risk Assessment (August 2011) published by the Office of Public Works. This map indicates that the site is not at risk from fluvial flooding. 7.2 The River Tolka is approximately 1.2km north of the site and the River Liffey is approximately 2.0km to the south. Therefore, the site is not at risk from fluvial flooding from these rivers. 7.3 In the case of fluvial flooding the site location meets the criteria for Flood Zone C as set out in Clause 2.23 of the Guidelines. As such, it is concluded that there is no risk of fluvial damage. R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Flood Risk Assessment EB AK docx 4

5 8 ROYAL CANAL 8.1 The Royal Canal is located approximately 250mm north of the site. If the canal was to overflow the resulting flood water would flow into the railway cutting and away from the proposed development. 9 TIDAL FLOODING 9.1 The Tidal Flood Extent Map for Dublin City (map NE / RA / EXT / HEFS / 19 / 0) reproduced in Appendix 5, is taken from The Irish Coastal Protection Strategy Study Phase III (August 2013). This map shows the tidal flood zone for the 10% AEP, 0.5% AEP and 0.1% AEP events. 9.2 It is stated on map NE / RA / EXT / HEFS / 19 / 0 that the estimated flood levels would be 3.67m AOD, 4.07m AOD and 4.28 AOD for the 10%, 0.5% and 0.1% AEP events respectively. The lowest proposed ground floor level for the new buildings will be m AOD. 9.3 In the case of tidal flooding the site location meets the criteria for Flood Zone C as set out in the Clause 2.23 of the Guidelines. As such it is concluded that there is no risk of tidal flooding. 10 GROUND WATER FLOODING 10.1 The flood risk map for Dublin City (map 2019 / Map / 238A), reproduced in Appendix 1 is taken from The Draft Preliminary Flood Risk Assessment (August 2011) published by the Office of Public Works. This map indicates that the site is not at risk from flooding due to ground water It is noted that there is no record of flooding on this site due to ground water It is considered extremely unlikely that ground water levels on site will rise above ground level. However if this was to occur the water would follow the overland flood routes and away from the buildings. 11 PROPOSED DRAINAGE AND WATER SUPPLY SYSTEMS 11.1 The surface water drainage from the building roofs and paved areas will collect in a below ground drainage network of 225mm diameter pipes which will drain by gravity to the surface water pumping station near the southern site boundary. R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Flood Risk Assessment EB AK docx 5

6 11.2 A flow control device in conjunction with an attenuation tank will limit the maximum rate of discharge of surface water from the site to 2l/s as agreed with Dublin City Council Drainage Department The pumping station will incorporate a pump with sufficient capacity to convey the design flow. A second pump will also be provided as back-up. The two pumps will operate in duty-standby rotation. The attenuation tank will insure that the surface water drainage system can provide 24- hour emergency storage in the unlikely event of failure of both pumps The proposed site drainage system is designed to achieve self-cleaning velocity. This will prevent the build-up of silt deposits in the system which could cause blockage and possibly result in flooding All elements of the proposed site drainage systems (pipelines and manholes) will be tested to ensure that they are watertight Water supply mains will be pressure tested to ensure that they can perform satisfactorily without bursting or leakage With the incorporation of the mitigation measures described above the risk of flooding associated with the proposed drainage and water supply systems is negligible. R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Flood Risk Assessment EB AK docx 6

7 APPENDIX 1: MAP REPORT FROM OPW WEBSITE FLOODMAPS.ie R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Flood Risk Assessment EB AK docx 7

8 Summary Local Area Report This Flood Report summarises all flood events within 2.5 kilometres of the map centre. The map centre is in: County: Dublin NGR: O This Flood Report has been downloaded from the Web site The users should take account of the restrictions and limitations relating to the content and use of this Web site that are explained in the Disclaimer box when entering the site. It is a condition of use of the Web site that you accept the User Declaration and the Disclaimer. Map Legend Flood Points Multiple / Recurring Flood Points Areas Flooded Hydrometric Stations Rivers Lakes River Catchment Areas Land Commission * Drainage Districts * Benefiting Lands * 25 Results Map Scale 1:8,183 * Important: These maps do not indicate flood hazard or flood extent. Thier purpose and scope is explained in the Glossary. 1. Flooding at Glendhu Park, Cabra, Dublin 7 on 24th Oct 2011 Start Date: 24/Oct/2011 County: Dublin Flood Quality Code: 3 Additional Information: Reports (1) More Mapped Information 2. Tolka December 1954 Start Date: 08/Dec/1954 County: Dublin Flood Quality Code: 1 Additional Information: Photos (2) Reports (13) Press Archive (9) More Mapped Information 3. Tolka November 2002 Start Date: 13/Nov/2002 County: Meath, Dublin Flood Quality Code: 1 Additional Information: Photos (126) Reports (9) Videos (3) Press Archive (13) More Mapped Information 4. Dublin City Tidal Feb 2002 Start Date: 01/Feb/2002 County: Dublin Flood Quality Code: 1 Additional Information: Photos (32) Reports (10) Press Archive (27) More Mapped Information 5. Tolka River 24th Oct 2011 Botanic Gardens Start Date: 24/Oct/2011 County: Dublin Flood Quality Code: 2 Report Produced: 11-Jul :53

9 APPENDIX 2: FLOOD RISK MAP FOR DUBLIN CITY (MAP 2019 / MAP / 238A) R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Floor Risk Assessment EB AK docx 8

10 jfinglas, GLASNEVIN k Government of Ireland Osi permit number EN Location Plan : j k CLONTARF j k Legend: j k Flood Extents DUBLIN CITY Fluvial - Indicative 1% AEP (100-yr) Event Fluvial - Extreme Event Coastal - Indicative 0.5% AEP (200-yr) Event No Fluvial Data Available For Area Coastal - Extreme Event Pluvial - Indicative 1% AEP (100-yr) Event Pluvial - Extreme Event Groundwater Flood Extents Lakes / Turloughs PFRA Outcomes k j j k Probable Area for Further Assesment Possible Area for Further Assesment Important User Note: The flood extents shown on these maps are based on broadscale simple analysis and may not be accurate for a specific location. Information on the purpose, development and limitations of these maps is available in the relevant reports (see Users should seek professional advice if they intend to rely on the maps in any way. If you believe that the maps are inaccurate in some way please forward full details by contacting the OPW (refer to PFRA Information leaflets or Have Your Say on No Fluvial Data Available For Area No Fluvial Data Available For Area Office of Public Works Jonathon Swift Street Trim Co Meath Ireland Project : PRELIMINARY FLOOD RISK ASSESMENT (PFRA) No Fluvial Data Available For Area No Fluvial Data Available For Area Map : PFRA Indicative extents and outcomes - Draft for Consultation No Fluvial Data Available For Area Figure By : PJW Checked By : MA Figure No. : No Fluvial Data Available For Area 2019 / MAP / 238 / A Drawing Scale : 1:50, Kilometers Date : July2011 Date : July 2011 Revision 0 Plot Scale : A3

11 APPENDIX 3: AN EXTRACT FROM THE OFFICE OF PUBLIC WORKS FLOOD MAPPING DATA FROM THE MYPLAN.IE WEBSITE R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Floor Risk Assessment EB AK docx 9

12 SITE LOCATION An extract from the Office of Public Works flood mapping data from the MyPlan.ie website managed by the Department of Environment, Community and Local Government. R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Floor Risk Assessment EB AK docx 1

13 APPENDIX 4: PLUVIAL FLOOD MAP EXTRACT FROM THE FLOOD RESILIENCITY FINAL REPORT VOLUME 2, APPENDIX B PRODUCED FOR DUBLIN CITY COUNCIL BY JACOBS CONSULTING. R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Floor Risk Assessment EB AK docx 1

14 Ponding Areas Dublin North West/Central ± Sheet 1 of 5 1. Dublin North West 2. Dublin North Central Dublin Central 5. Dublin South Central Dublin South East Dublin City Council Administrative Boundaries Note: Please refer to report for information on Type 1 model limitations Client Project Dublin Flood Resilien City Project Type 1 Model Title Ponding Areas Sheet 1 of 5 Drawing Status Job No. Figure No. Scale FINAL v Km Copyright Ordinance Survey Ireland. Licence number 2010/22/CCMA/ Dublin City Council. Nov 29, 2010 NTS Drawn 0 Revision /001 Review Checked LM PS Copyright reserved Jacobs UK Ltd 28 Adelaide Street,Rochester Building, Belfast, BT2 8GD Approved JC RF

15 APPENDIX 5: TIDAL FLOOD EXTENT MAP FOR DUBLIN CITY (MAP NE / RA / EX / 19 / 1) TAKEN FROM THE DRAFT PRELIMINARY FLOOD RISK ASSESSMENT (AUGUST 2011). R:\Docs\PROJECTS\26 000\26 098\F5.1\ Final Planning Pack\Flood Risk Assessment\Site Specific Floor Risk Assessment EB AK docx 1

16 Location Plan : Government of Ireland Osi permit number EN ± NOTE: MORE DETAILED MAPS SHOWING COMBINED TIDAL AND FLUVIAL FLOOD HAZARD FOR PART OF THIS AREA (DODDER CATCHMENT ONLY) HAVE BEEN PREPARED UNDER THE RIVER DODDER CATCHMENT FRAM STUDY. PLEASE REFER TO FOR MORE INFORMATION EXTENT MAP Legend: 0.5% AEP FLOOD EXTENT (1 in 200 chance in any given year) 0.1% AEP FLOOD EXTENT (1 in 1000 chance in any given year) High Water Mark (HWM) Node Point Point 34 Node Label (refer to table) Point 22! USER NOTE : USERS OF THESE MAPS SHOULD REFER TO THE DETAILED DESCRIPTION OF THEIR DERIVATION, LIMITATIONS IN ACCURACY AND GUIDANCE AND CONDITIONS OF USE PROVIDED AT THE FRONT OF THIS BOUND VOLUME. IF THIS MAP DOES NOT FORM PART OF A BOUND VOLUME, IT SHOULD NOT BE USED FOR ANY PURPOSE. Elmwood House 74 Boucher Road Belfast BT 12 6RZ Northern Ireland Office of Public Works Lower Hatch Street Dublin 2 Ireland Project : IRISH COASTAL PROTECTION STRATEGY STUDY - PHASE III Map : NORTH EAST COAST FLOOD EXTENT MAP Water Level (mod Malin) per AEP Node Label WL 10% WL 0.5% WL 0.1% Point Map Type : FLOOD EXTENT Source : TIDAL FLOODING Map area : RURAL AREA Scenario : HIGH END FUTURE SCENARIO Figure By : PJW Date : Sept 2012 Date : Sept 2012 Checked By : JMC & JR Revision Figure No. : NE / RA / EXT / HEFS / 19 Drawing Scale : 1:25, Kilometers 0 Plot Scale : A3