Volume Three. Pluvial Flood Risk Management

Transcription

1 EU Interreg IVB FloodResilienCity Project Final Report Dublin Volume Three Pluvial Flood Risk Management

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3 Document control sheet BPP 04 F8 Client: Project: Document Title: Dublin City Council Job No: Final Report - Dublin Volume Three: Pluvial Flood Risk Management Originator Checked by Reviewed by Approved by NAME NAME NAME NAME Ronnie Falconer & Kelly Kasperczyk Kelly Kasperczyk & Ronnie Falconer Kelly Kasperczyk & Ronnie Falconer DATE SIGNATURE SIGNATURE SIGNATURE SIGNATURE Kelly Kasperczyk October 2012 Document Status: Issue to Dublin City Council Copyright Copyright Dublin City Council. All rights reserved. No part of this report may be copied or reproduced by any means without prior written permission from Dublin City Council. If you have received this report in error, please destroy all copies in your possession or control and notify Dublin City Council. Legal Disclaimer This report has been prepared for the exclusive use of the commissioning party (Dublin City Council) and unless otherwise agreed in writing by Jacobs Engineering Ireland Limited, no other party may use, make use of or rely on the contents of this report. Neither this report nor the services provided by Jacobs Engineering Ireland Limited are intended for the express or implied benefit of any third party. The commissioning party shall indemnify and hold Jacobs Engineering Ireland Limited harmless from any third party claims arising out of any use or reliance on the contents of this report. No liability is accepted by Jacobs Engineering Ireland Limited for any use of this report, other than for the purposes for which it was originally prepared and provided. Opinions and information provided in the report are on the basis of Jacobs Engineering Ireland Limited using due skill, care and diligence in the preparation of the same and no warranty is provided as to their accuracy. It should be noted and it is expressly stated that no independent verification of any of the documents or information supplied to Jacobs Engineering Ireland Limited has been made. Final Report Dublin

4 CONTENTS Volume Three Pluvial Flood Risk Management PREFACE GLOSSARY ABBREVIATIONS i iv x SECTION 1 SPATIAL PLANNING AND BUILDING REGULATIONS Introduction Review of Existing Policy Documents for Relevance to Pluvial Flooding European and International Practice Proposed Policy Elements 19 SECTION 2 FLOOD RESILIENCE AND ADAPTATION MEASURES Introduction Review of Relevant Guidance Scope and Application of Code of Practice 2: Flood Resilience and Adaptation Measures 31 Appendices V3-A Code of Practice 1: Spatial Planning and Building Regulations V3-B Code of Practice 2: Flood Resilience and Adaptation Measures Final Report Dublin

5 PREFACE Dublin FloodResilienCity (FRC) Technical Report Volume Structure This technical report, Volume Three: Pluvial Flood Risk Management is one of five Volumes which accompany the Dublin FRC Project Non Technical Summary. The Non Technical Summary provides the background to the Dublin FRC Project and a summary of each of the technical report Volumes. These Volumes comprise: Volume One Volume Two Volume Three Volume Four Volume Five Rainfall and Forecasting City-Wide Pluvial Flood Risk Assessment Pluvial Flood Risk Management Detailed Pluvial Flood Risk Assessment of Pilot Areas Pluvial Flood Alerting and Warning System Integration Each Volume should be read in conjunction with the other Volumes as sections within each may be cross-referenced to other Volumes. Figure P1 illustrates both the one-way and twoway relationships between the report Volumes, with arrow size indicating relationship scale. The extent of the Dublin FRC Project study area is shown in Figure P2 which also indicates the five administrative areas within Dublin City. Figure P1: Dublin FRC Technical Report Volume Relationships Figure P2: Dublin FloodResilienCity Project Study Area Final Report Dublin i

6 Volume Three Structure Section 1. This Section provides an introduction to Spatial Planning and Building Regulations relevant to Pluvial Flood Risk Management. It reviews a wide range of existing local and national policy and guidance documents, as well as other studies and plans relevant to pluvial flood risk management in Dublin. It also considers wider European guidance and practice to inform the development of an appropriate Code of Practice covering Spatial Planning and Building Regulations, which is included as Appendix V3-A. Section 2. This Section provides an introduction to Flood Resilience and Adaptation Measures suitable for managing surface and overland flows, and creating resilience in existing buildings. It identifies a wide range of national, European and international guidance documents to inform the development of a Code of Practice covering Flood Resilience and Adaptation Measures, which is included as Appendix V3-B. Recommended measures are grouped under three categories: Generic and Early Win Measures; Community Flood Resilience Measures; and Site Specific Measures. Appendix V3-A: Code of Practice 1 Spatial Planning and Building Regulations outlines how pluvial flood hazard definition in addition to pluvial flood risk assessment and management can be integrated into the application of sustainable planning and building control activities in Dublin City for both new and modified/extended developments. Appendix V3-B: Code of Practice 2 Flood Resilience and Adaptation Measures outlines measures suitable for managing surface and overland flows and creating resilience in existing buildings. The Code of Practice outlines how responsibility for these measures is shared between Government agencies / Municipality, developers and the community. In evaluating appropriate measures, opportunities for benefits additional to flood risk mitigation are sought including amenity enhancement, biodiversity enhancement and carbon reduction/sequestration. Recommendations for providing information to at risk properties to enable effective resilience and resistance measures to be retro-fitted or included in a new property are also made. Volume Three informs the following Dublin FRC technical report Volumes: Volume One - Rainfall and Forecasting: Some of the flood control mechanisms summarised in Volume Three, Code of Practice 2 Flood Resilience and Adaptation Measures (Appendix V3-B) can support the flood forecasting and warning systems discussed in Volume One. Volume Four - Detailed Pluvial Flood Risk Assessment of Pilot Risk Areas: Code of Practice 1 Spatial Planning and Building Regulations (Appendix V3-A) outlines the processes through which the Dublin FRC modelling and mapping outputs can be used to facilitate spatial planning and pluvial flood risk assessment. Code of Practice 2 Flood Resilience and Adaptation Measures (Appendix V3-B) provides a manual of pluvial flood risk management measures ('corrective measures') which was used to inform the modelling appraisal of corrective measures in the Pilot Areas as outlined in Volume Four. Final Report Dublin ii

7 Volume Five - Pluvial Flood Alerting and Warning System Integration: Some of the flood control mechanisms summarised in Volume Three Code of Practice 2 Flood Resilience and Adaptation Measures (Appendix V3-B) can support the recommended technologies for pluvial flood alerting and warning system integration as outlined in Volume Five. Sustainable Pluvial Flood Risk Management Both Codes of Practice presented in this Volume support Dublin City Council s established approach to sustainable flood risk management through adoption of the 4As Model Awareness; Alleviation; Avoidance; and Assistance. This model represents an integrated approach to sustainable flood risk management which has been developed and tested by the Scottish Government. Specifically, the strengthening of spatial planning and building regulations through Code of Practice 1 seeks to Avoid inappropriate development in areas likely to be vulnerable to pluvial flooding. Where this is not possible, and particularly for retrofitting measures in areas which are already developed, Code of Practice 2 provides guidance on ways to increase resistance and resilience to pluvial flooding the Alleviation component of the 4As model. Awareness raising is an essential precursor for both elements and Assistance is appropriate should flooding occur. Through a more recent initiative Beyond the 4As, Dublin City Council considers other specific elements in the overall sustainable flood risk management process the 7As : Awareness raising (politicians and policy makers, professionals, and the public) at strategic level; and at process level: Assessment of existing and emerging hazards; Analysis of the resulting risks; Avoidance of the known risks where possible; Alleviation of the unavoidable risk where practical; Action in response to the residual risk: and Assistance in recovery from the impacts. Final Report Dublin iii

8 GLOSSARY Aggregated Micro-Storage Annual Exceedance Probability (AEP) Attenuate Blue Roof Breakline Catchment Climate Change Climate Fluctuation Coastal Flooding Contour Polygon Screening (CPS) Convective Available Potential Energy (CAPE) Convective Rainfall Conveyance Flow Critical Infrastructure A corrective/mitigation measure used for storing surface water in hard standing areas in built up areas (car parks, roof areas, sports facilities). This measure has the potential to maximize benefit from many relatively small storage areas and optimize the control of this storage in real time. This is the technical term used to express the likelihood, or chance, of a particular event (e.g. flood or rainfall) being equaled or exceeded in any one year. It is usually expressed as a percentage or a ratio i.e. the 10% AEP event or 1 in 10 AEP. In technical terms the rarity of an event is sometimes also referred to as a return period i.e. the 10% AEP event is equivalent to an event having a 10-year return period, but the use of return periods can be confusing to the wider public. Providing temporary storage or other measures designed to reduce the volume of surface runoff which could cause flooding. A particular focus of attenuation is on reducing peak flows through an area. A form of roof which is designed to capture water, most typically rainfall. Two dimensional geographical features (railway lines, rivers, roads and canals) which are represented in the modeling software as lines that may have a significant impact on the propagation of the rainfall runoff. A catchment area or drainage basin is an extent or an area of land where surface water or fluvial flow converges to a single point; usually the exit of the basin, where the waters join another water body, such as a river, lake, reservoir, estuary, wetland, sea, or open sea. Long term variations in global temperature and weather patterns caused by natural and human actions. Variations in global temperature and weather patterns. Coastal flooding that results from a combination of high tides and stormy conditions. If low atmospheric pressure coincides with a high tide, a tidal surge may happen which can cause serious flooding. A GIS based technique for assessing topographical data and identifying hazardous depressions with regard to potential flooding. A measure of the amount of energy available for convection (which can lead to intense rainfall). Convective rainfall originates from convective clouds and falls with rapidly changing intensity over a small area for a relatively short period of time. This is essentially the carrying capacity of a surface or culverted watercourse or a below-ground sewer or drainage system. It is significantly influenced by the roughness of the river or stream bed, or the piped system. Debris carried along in the flow and/or obstructions can reduce conveyance flow. In relation to sewer design capacity the conveyance capacity of urban drainage networks is usually such that they will flow full in a 1 in 5 AEP (20%) rainfall event. In a more extreme event they will usually surcharge up to road level and no more flow will enter through road gullies. In a 1 in 10 AEP (10%) rainfall event and events greater than this severe road flooding and property flooding may result. Infrastructure (assets) essential for the functioning of society and the economy related to electrical generation, telecommunication and public health (i.e. hospitals, power stations, treatment works). Final Report Dublin iv

9 Culvert Dam extreme operation / failure flooding Debris Factor Department for Environment, Food and Rural Affairs (DEFRA) Depth Duration Frequency (DDF) Depth Gauge Digital Elevation Model (DEM) Digital Terrain Model (DTM) Direct Rainfall approach Drainage Infiltration and Exfiltration Dry Mapping Exceedance Flow External Resistance Measures External Stakeholder Extreme Rainfall Federated Emergency Response Plan (FERP) Flood A channel or pipe that carries a watercourse below the level of the ground. Some reservoirs hold large volumes of water above ground level. Although the safety record for reservoirs is excellent, it is not impossible that a dam could fail. This would result in a large volume of water being released very quickly. A variable used to quantify hazard which represents the fact that deep, fast flowing flood waters might mobilize loose objects and move them along flow paths thus increasing flood hazard. DEFRA is the UK government department responsible for policy and regulations on the environment, food and rural affairs Rainfall depth-duration-frequency (DDF) curves describe rainfall depth as a function of duration for given rainfall probabilities. A gauge used to measure the depth of accumulated rainfall. A digital elevation model which shows topographic information including buildings and vegetation. A digital terrain model which show topographic information excluding buildings and vegetation. A hydraulic modeling approach which involves the application of rainfall hyetographs representative of storm events to active model cells within a two dimensional domain. In relation to sewer and drainage systems these terms are often used to describe seepage into or out of a drainage system through joints and cracks in the pipework. However for the purposes of this Pluvial Flood Study they are used to describe that portion of surface water flow that is carried into the below-ground system (infiltration) mainly via the roadside gullies, and the portion of flow which floods out from the belowground system when capacity is exceeded (exfiltration). Digital mapping of potential pluvial hotspots using the Rolling Ball and Contour Polygon Screening Techniques. This mapping is based on topography (LiDAR) and does not include any hydraulic or hydrological assessments. It is usually applied for preliminary assessments. This is normally used to describe the flow which exceeds the capacity of the below-ground sewerage or drainage system to carry stormwater flows. The Exceedance Flow is the portion that surcharges and floods at the ground surface and flows along the surface, often together with direct runoff from pluvial flooding. Measures designed to keep flood water out of properties and businesses (i.e. flood guards). Resistance measures can be fitted to prevent surface water entering buildings. Measures can be fitted to new properties or retrofitted to existing properties Stakeholders considered to be involved or affected but not as directly integrated into existing arrangements for flood risk management and risk identification. Defined within this study as rainfall that leads to (or is likely to lead to) pluvial flooding. Whilst all rainfall is, by definition, pluvial, it is only intense rainfall events that give rise to pluvial flooding A FERP is designed to harmonize federal emergency response efforts with those of the provinces/territorial governments, non-governmental organizations, and the private sector. The temporary covering by water of land not normally covered with water Final Report Dublin v

10 Flood Alert Flood Defence Flood Depth Estimation System (FDES) Flood Forecast Flood Hazard Flood Information and Warning System (FLIWAS) Flood Risk Flood Studies Report (FSR) Flood Warning Flow Paths Fluvial Flooding Food and Agriculture Organization of the United Nations (FAO) GeoDirectory Geographic Information Systems (GIS) Dissemination to interested parties of an early indication that a flood event exceeding a critical threshold is possible and a warning may be given. Infrastructure used to protect an area against floods such as floodwalls and embankments; they are usually designed to a specific standard of protection (design standard). The Flood Depth Estimation System (FDES) is a GIS based tool (which Jacobs has developed) which allows for the calculation of flood damages based on the depth outputs from the TUFLOW modeling software. The prediction of a flood event through the application of measured and/or modeled scenarios. The potential for a flood to cause damage or harm usually shown as the extent of flooding for a flood with a specific probability or likelihood. A flood hazard does not necessarily lead to harm unless there is a receptor such as people or property that could be harmed or damaged. The Flood Information and Warning System is a web based GIS orientated application for the monitoring of forecasts and aiding the implementation of Emergency Plans and evacuation plans. Flood Risk in flood risk management is defined as a product of the probability or likelihood of a flood occurring and the consequence of the flood, for example damage to property or harm to people. The Flood Studies Report, published in 1975, is used in relation to rainfall events in the United Kingdom. It has since been replaced by the Flood Estimation Handbook. The resultant dissemination of a forecast to a body of interested parties in order that they may prepare for the flood event with the aim of reducing its impact. Usually given once a critical threshold has been reached and involves taking action. Surface water flow paths with supporting gradient and accumulation information. Flooding resulting from water levels exceeding the bank level of a river. Also known as river flooding, this occurs when a watercourse cannot accommodate the volume of water draining into it from the surrounding land. It is generally infrequent, but flooding can occur rapidly or over a long duration depending on the nature of the upstream catchment. Watercourses are more likely to be overwhelmed when rainwater cannot be absorbed into the land onto which it falls. It might be very steep, water logged, or built over. Rapid melting of snow also leads to river flooding in some cases. Also, obstructions such as collapsed buildings/walls can exacerbate flooding. Flooding from small urban watercourses can be a particular problem in urban areas even though the catchment area may be small. Impermeable sealed surfaces in built up areas can result in increased and more rapid runoff to these small watercourses such that flows in the watercourse can build up rapidly and result in flash flooding (an extreme form of fluvial flooding). Urban watercourses are often culverted over long sections and the entrances to these culverts can often be flooding hotspots. These watercourses are also often constricted in places resulting in bottlenecks which can make flooding worse. Debris, both natural and man-made also often accumulates in urban watercourses which not only constricts the watercourse but can accumulate at culvert screens and even block these screens in extreme cases. The Food and Agriculture Organization of the United Nations (FAO) is a specialized agency of the United Nations that leads international efforts to defeat hunger, serving both developed and developing countries. A property database showing locations of properties in Ireland. Attribute information includes data such as property number, street name and coordinate information. A geographic information system integrates hardware, software, and data for capturing, managing, analyzing, and displaying all forms of geographically referenced information. Final Report Dublin vi

11 Greater Dublin Strategic Drainage Study (GDSDS) Groundwater Flooding Gulley Gulley Monitor Hydraulic Modelling Hydraulic Roughness Hydro-meteorological Monitoring InfoWorks CS The GDSDS was a study commissioned in June 2001 to carry out a strategic analysis of the existing foul and surface water systems in the local authority areas of Dublin City, Fingal, South Dublin, Dun Laoghaire- Rathdown and the adjacent catchments in Counties Meath, Kildare and Wicklow Groundwater flooding occurs when water levels in the ground rise above the ground surface. It is most likely to occur in areas underlain by permeable rocks, or alluvial/coastal deposits. These can be extensive, regional aquifers, such as chalk or sandstone, or may be locally confined deposits such as sand or river gravels in valley bottoms underlain by less permeable rocks. An artificial hole, cavity or pit in a gutter which is covered with a grating and normally conveys surface water to a drainage system. A monitor used for measuring water levels within gullies. Computer software based method of modeling the flow of water in rivers and drainage systems. A means of accounting for the effect on the resistance to flow of surface materials, irregularities, obstructions and vegetation. A method for monitoring/forecasting conditions associated with flooding. InfoWorks CS is a modeling software package which is used to undertake hydrological modeling of the urban water cycle. Other applications include urban flooding and pollution prediction and the modeling of water quality and sediment transport throughout a network. Internal Resilience Measures Internal Stakeholder Interreg (IVB) Isohyets Light detection and Ranging (LiDAR) Mass-balance Equation Natural Infiltration No Flow Condition Measures designed to reduce the impact of water that enters property and businesses. This can involve ensuring that the walls, floors, and fixtures are less damaged by water (or not at all), and also re-organising the house so that valuable and costly items (including service meters and the boiler) are above the level of the flood. Stakeholders currently participating in the risk management and risk identification processes. Community initiative that aims to stimulate interregional cooperation in the European Union. It is a financial instrument of the European Union's Cohesion Policy. It funds projects which support transnational cooperation. The aim is to find innovative ways to make the most of territorial assets and tackle shared problems of Member States, regions and other authorities. A line joining points of equal precipitation on a map. A high Resolution digital terrain model showing elevation/topographic information. Can be supplied in either "filtered" (buildings and vegetation filtered out) or "unfiltered" (buildings and vegetation have not been stripped out). In analysing stormwater events it is convenient to consider the mass balance relationship which can be expressed in the form: Total Rain = Exceedance Flow (surface as defined above) + Conveyance Flow (below-ground as defined above) + Ground Infiltration (rainfall infiltration into sub-soils, gravels and bedrock) + Detained Infiltration (rainfall infiltration detained in storage systems) Precipitation that soaks into subsurface soil and strata naturally. A parameter used in hydraulic models to stop flow from passing through an area or node. For example where flood defenses are present, a "No Flow condition can be applied to a model. Final Report Dublin vii

12 NOAH Numerical Weather Prediction Office of Public Works (OPW) Ordnance Survey Ireland (OSI) Pluvial flooding Ponding Preliminary Flood Risk Assessment (PFRA) Principal Stakeholder Radio Detection and Ranging (RADAR) Raingauge Rainfall Duration Rainfall Hyetographs Rainfall infiltration Rainfall Intensity Rainfall Pattern Rapid Flood Spreading Model (RFSM) Receptor An Interreg IIIB organization for research in to the rapid transfer of data with respect to flood prevention. The NOAH partnership aims to strengthen the transfer of information between relevant EU funded projects, experts and public institutions, improve the knowledge base and transfer between water management authorities in order to strengthen transnational cooperation on these issues. A form of weather prediction which utilises mathematical models of the ocean and atmosphere. The OPW is a service organization. Its clients include Government, other Departments, Offices and Agencies and the public. Core services provided by the OPW are property maintenance, property management, architectural and engineering services, heritage services, project management and procurement services, and flood risk management. Ordnance Survey Ireland is the national mapping agency of the Republic of Ireland. It provides digital/hardcopy products and mapping services. It provides a range of urban, rural, tourist and leisure maps at a variety of scales. They also provide other products such as aerial photography and digital terrain models. Pluvial flooding is defined as flooding which results from rainfall-generated overland flow and ponding before runoff enters a watercourse or sewer or when it cannot enter because the drainage system is already full to capacity. It is also known as surface water flooding. The capacity of local drainage (both natural and man-made) is overwhelmed and surface ponding occurs sometimes to a significant depth. Such ponding, often in low spots in the ground surface topography can occur rapidly and be a particular risk to basements other below-ground facilities. Where slopes are steep, resulting high flood velocities along roads and streets can also be a hazard to pedestrians and traffic. An area where runoff collects in a depression and cannot drain. The Preliminary Flood Risk Assessment (PFRA) is a requirement of the EU Floods Directive. The objective of the PFRA is to identify areas where the risks associated with flooding might be significant. These areas (referred to as Areas for Further Assessment or AFAs ) are where more detailed assessment is required to more accurately assess the extent and degree of flood risk. The more detailed assessment that will focus on the AFAs are being undertaken through Catchment-based Flood Risk Assessment and Management ( CFRAM ) Studies. Person, group, or organization that has direct (key) stake in an organisation (or project) because it can affect or be affected by the organisation's projects, actions, objectives, and policies. Radio Detection and Ranging (RADAR) is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. A gauge used to measure the depth of accumulated rainfall. The length of time a rainfall event lasts. A graphical representation of rainfall distribution over time. Precipitation that enters drainage systems or below-ground strata. A measure of the amount of precipitation over time. Variations in precipitation frequency, duration and intensity averaged over time for particular areas. The Rapid Flood Spreading Model (RFSM) is a modeling approach which is used in pluvial studies and surface water management plans to represent overland flow at a high level (large scale). It is topography based and provides and an indication of ponding areas and the potential depths of flooding within these areas. It is usually applicable for national or regional studies. Different sensitive receptors, that could possibly be affected by flood events (i.e. human health, critical infrastructure, environmental and cultural heritage and economy). Final Report Dublin viii

13 Return Period Risk Rolling Ball Technique Sewer flooding Stakeholder Street as Streams/Roads as Rivers (SaS/RaR) Surface Water Sustainability Sustainable Urban Drainage System (SuDs) Tidal Flooding Tipping Bucket Raingauge TUFLOW Wet Mapping A return period, also known as a recurrence interval, is an estimate of the interval of time between flood events or river discharge flow of a certain intensity or size. It is a statistical measurement denoting the average recurrence interval over an extended period of time, and is often used for risk analysis (i.e. whether a project should be allowed to go forward in a zone of a certain risk) and also to dimension structures so that they are capable of withstanding a flood event of a certain return period. In flood risk management, risk is defined as a product of the probability or likelihood of a flood occurring, and the consequence of the flood. A GIS based form of analysis used to predict pathways of preferential flow direction based on terrain slope. Flooding caused by a blockage or overflowing due to heavy rainfall in a sewer or urban drainage system. Sewer flooding can occur when combined sewers (which carry both foul sewage and stormwater) are overwhelmed by heavy rainfall or when they become blocked, or can be attributed to infrastructure failure (e.g. pumping station failure). The likelihood of flooding depends on the capacity of the local sewerage system. Land and property can be flooded with water contaminated with raw sewage as a result. Rivers can also become polluted by sewer overflows. In urban areas, pluvial flooding and sewer flooding often combine, polluting the floodwater. It should be noted that in some newer developments foul sewage and stormwater is conveyed in separate systems. In such cases flooding due to heavy rainfall is usually associated with the stormwater system. A person or organization affected by the problem or solution, or interested in the problem or solution. They can be individuals or organisations, and include the public and communities. This specific type of measure is used to manage surface and overland flow. It involves the identification of designated surface and overland flow pathways along streets and roads through the urban environment most likely to designated storage areas. Rainwater (including snow and other precipitation) which is on the surface of the ground (whether or not it is moving), and has not entered is not being conveyed by a watercourse, drainage system or public sewer. Surface Water Flooding is the term often used to describe the combined surface flooding from multiple sources and can include pluvial flooding, sewer flooding, groundwater flooding at the surface and flooding from small urban watercourses. Sustainability is the long-term maintenance of responsibility, which has environmental, economic, and social dimensions. It is a term used to define an approach (relating to the implementation of measures or a plan) which does not compromise the interconnected needs of the economy, society and environment in the future. Methods of management practices and control structures that are designed to drain surface water in a more sustainable manner than some conventional techniques. Flooding resulting from sea levels exceeding high tide levels, or coastal flood defences. This type of flooding occurs in coastal areas and places where tidal influence may affect water levels (i.e. estuaries, coastal inlets) A tipping bucket raingauge is a meteorological device that can measure rainfall intensity as well as the total amount of precipitation that has fallen. Modeling software that simulates pluvial flooding for a range of rainfall events of various severities (in duration and intensity) Pluvial flood maps which have been produced as an outputs from the TUFLOW model, which demonstrate the possible flood depth, velocities and hazard. Final Report Dublin ix

14 ABBREVIATIONS 1D/2D AEP ARF CAPE CFRAM CoP CPS DCC DDF DEFRA DEM DTM EPA EWA FAO FDES FEH FERP FLIWAS FRC FRM FSR FSU GDSDS GIS GPRS GSM IZ LiDAR MEM NOAH NRA OPW OSi PFRA PRA PSTN Radar RBD RDBMS RFSM SAFER SaS/RaR SuDs TBR WMO WPG One dimensional/two dimensional Annual Exceedance Probability Areal reduction factor Convective Available Potential Energy Catchment Flood Risk Assessment and Management Study Code of Practice Contour Polygon Screening Dublin City Council Depth-duration frequency Department for Environment, Food and Rural Affairs, UK Digital Elevation Model Digital Terrain Model Environmental Protection Agency European Water Association Food and Agriculture Organization Flood Depth Estimation System (software developed by Jacobs) Flood Estimation Handbook (UK) Federated Emergency Response Plan Flood Information and Warning System FloodResilienCity Flood Risk Management Flood Studies Report Flood Studies Update (Ireland) Greater Dublin Strategic Drainage Study Geographic Information Systems General Packet Radio Service Global System for Mobile Communications Impact Zones Light Detecting and Ranging Major Emergency Management An Interreg IIIB organization for research in to the rapid transfer of data with respect to flood prevention. National Roads Authority Office of Public Works Ordnance Survey Ireland Preliminary Flood Risk Review Principal Response Agency Public Switched Telephone Network Radio Detection and Ranging River Basin District Relational Database Management Systems Rapid Flood Spreading Model Strategies and Actions for Flood Emergency Risk management Street as Streams/Roads as Rivers Sustainable Urban Drainage Tipping Bucket Raingauge World Meteorological Organization Weighing Principle Gauge Final Report Dublin x

15 SECTION 1 SPATIAL PLANNING AND BUILDING REGULATIONS 1.1 Introduction Codes of Practice relating to Spatial Planning and Building Regulations and to Flood Resilience and Adaptation Measures have been developed to support pluvial flood risk management. Code of Practice 1: Spatial Planning and Building Regulations introduced in the following sub-sections, is presented in Appendix V3-A of this document. Code of Practice 2: Flood Resilience and Adaptation Measures is introduced in Section 2 and presented in Appendix V3-B of this document. Code of Practice 2 provides guidance on appropriate resistance / resilience measures to address pluvial flood risk relevant to both new and retrofit properties. Code of Practice 1: Spatial Planning and Building Regulations conveys how the appropriate consideration of pluvial flood hazard and risk within the spatial planning process can be achieved by extending the application of the principles of the Guidelines for Planning Authorities on Flood Risk Management, prepared by the Department of Environment, Heritage and Local Government 1 (DEHLG) and the Office of Public Works (OPW) (November 2009). It is intended that this Code of Practice is read in conjunction with these DEHLG/OPW Guidelines as the flood risk management principles and guidelines are not repeated in detail, and only those guidelines/recommendations which will require some diversion from these principles are outlined in Code of Practice 1. The following sections outline the background to the development of Code of Practice 1: Spatial Planning and Building Regulations as well as recommendations for its application Objectives Dublin City Council recognise that European experience in the early 2000 s and more recently the OPW in their flooding policies have identified inclusion of flood risk management in the spatial planning process as the single most effective first step in the flood resilience process. In this regard, the specification for the Dublin FloodResilienCity project set out the objectives for this element of the study: Review a number of existing national and local/regional policy documents and develop a formal DCC policy in regard to pluvial/surface water flooding and the spatial planning process. These will be developed into a code of practice related to pluvial flood risk management and will be complementary to that developed under the Greater Dublin Strategic Drainage Study Context The development of policy in this area is viewed as a potential early-win measure to address pluvial flood risk across Dublin assuming that changes in policy and guidance 1 This department is now the Department of Environment, Community and Local Government. References to this publication will use the acronym DEHLG/OPW, however all other references to this Department will use the new acronym, DECLG. Final Report Dublin 1

16 can be implemented relatively quickly and easily. In applying it across the Dublin administrative area it will mitigate pluvial flood risk in all areas including those for which site specific measures may not be justified. It aims to complement measures under Code of Practice 2: Flood Resilience and Adaptation Measures which is provided in Appendix V3-B of this report Volume. Code of Practice 1: Spatial Planning and Building Regulations will allow for the relevant pluvial flood-related policies to be integrated into the application of sustainable planning and building control activities in Dublin Approach This task has been largely based on a Literature Review where a number of existing national and local/regional policy documents have been reviewed (refer to Section 1.2). Various policy and guideline documents have been collated, and we have discussed issues and experience directly with Dublin City Council staff from various relevant departments. The Literature Review identified opportunities for the development of existing floodrelated policies to account more specifically for pluvial flood hazard. Section 1.4 outlines the policy recommendations for the future provision and management of pluvial flood hazard in Dublin City. In researching and developing the policy elements, we have endeavoured to assess how pluvial flooding is currently managed within the Greater Dublin area, whilst taking into account approaches taken by FRC partners and other authorities across Europe and in the United States. In developing the Code of Practice we have aimed to consider the following elements of the Dublin FRC Project: City-wide hazard and risk mapping (Volume Two); Inform spatial planning/zoning decisions (including public realm), providing opportunities to avoid areas with high-medium probability of pluvial flooding and to minimise flood risk; Facilitate specific/more stringent requests of planning applicants. Detailed pluvial flood hazard and risk mapping for pilot areas (Volume Four); In addition to the points noted above, this can inform more detailed spatial planning/zoning decisions e.g. at Local Area Plan level, and can facilitate future plans for flood resilience and adaptation; Recommendations for flood resilience and adaptation measures and how this can be established and maintained (Volume Three, Appendix V3-B); Rainfall characteristics and categorisation, and climate change influences (Volume One). Final Report Dublin 2

17 1.2 Review of Existing Policy Documents for Relevance to Pluvial Flooding National Spatial Strategy and National Guidance National planning policy supports the consideration of flood risk management as an important part of achieving proper planning and sustainable development. It recognises that spatial planning at regional and local levels is an essential part of the overall implementation mechanisms for the National Spatial Strategy (NSS), and planning at these levels is required to address the suitability of locations for development including considerations relating to flood risk. Ireland s future policy related to flood risk is summarised by the Office of Public Works (OPW) Report of the Flood Policy Review Group: to minimise the national level of risk of loss of life and/or damage to property and personal well-being that might arise from flooding in a sustainable and cost effective manner through the integrated, proactive and river basin based management of existing and potential future flood risk, and the mitigation of the impacts of flood events through non-structural, as well as structural, flood relief measures. This policy will be delivered through the OPW Catchment-based Flood Risk Assessment and Management (CFRAM) Studies currently underway across Ireland, and local authorities are required to assist the OPW in implementing this policy. However, the current scope of these studies concentrates primarily on fluvial and coastal flood risk, and it does not at present include for the assessment of pluvial (or groundwater) flood risk. Planning authorities are required to have regard to the DEHLG and the OPW Planning System and Flood Risk Management Guidelines (November 2009) in carrying out their functions under the Planning Acts to ensure that, where relevant, flood risk is a key consideration in preparing development plans and local area plans and in the assessment of planning applications. In addition to providing guidance for planning authorities, the DEHLG/OPW Guidelines also aim to assist developers and the wider public in addressing flood risk in preparing development proposals. Appendix B of the DEHLG/OPW Guidelines provides specific guidance on addressing flood risk management in the design of development in flood risk zones 2. The DEHLG/OPW Guidelines will revise and strengthen planning policy on development and flood risk across Ireland. Figure 1.1 below illustrates how the DEHLG/OPW Guidelines require flood risk assessment to be incorporated into spatial planning: 2 Defined as geographical areas within which the likelihood of flooding is in a particular range Final Report Dublin 3

18 Figure 1.1: Flood risk management and the planning system (extract from DEHLG / OPW, 2009) Planning can have a significant role to play with respect to flood risk management, in particular in avoiding or minimising future increases in flood risk. To achieve the aims and objectives of the DEHLG/OPW Guidelines, some key principles to be adopted by regional and local authorities, developers and their agents are outlined: Avoid development in areas at risk from flooding, unless there are proven wider sustainability grounds that justify development. Where this is the case, development must be appropriate and flood risks must be effectively managed to reduce the level of risk. Adopt a Sequential Approach to flood risk management when assessing the locations for new development based on avoidance, reduction, and mitigation of risk. Incorporate flood risk assessment into planning application decisions and appeals. To facilitate the achievement of these principles, the DEHLG/OPW Guidelines identify three types of flood zones relevant to river and coastal flooding to be established for use within the planning system. Flood Zone A where the probability of flooding from rivers and the sea is highest (greater than 1% or 1 in 100 AEP for river flooding or 0.5% or 1 in 200 for coastal flooding); Flood Zone B where the probability of flooding from rivers and the sea is moderate (between 0.1% or 1 in 1000 AEP and 1% or 1 in 100 AEP for river Final Report Dublin 4

19 flooding and between 0.1% or 1 in 1000 AEP and 0.5% or 1 in 200 AEP for coastal flooding); and Flood Zone C where the probability of flooding from rivers and the sea is low (less than 0.1% or 1 in 1000 AEP for both river and coastal flooding). Flood Zone C covers all areas of the plan which are not in zones A or B. As part of the Dublin FRC Code of Practice 1 presented in Appendix V3-A of this Volume, it is proposed that a similar zoning system specific to pluvial flood hazard is used to assist Dublin City Council incorporate the above key principles into the planning system. The DEHLG/OPW Guidelines define pluvial flooding as follows: Usually associated with convective summer thunderstorms or high intensity rainfall cells within longer duration events, pluvial flooding is a result of rainfall-generated overland flows which arise before run-off enters any watercourse or sewer. The intensity of rainfall can be such that the run-off totally overwhelms surface water and underground drainage systems. OPW s National Pluvial Screening Project (2010) has screened pluvial flood hazard arising from overland flow and ponding based on a review of intense rainfall events and the associated flood risk across Ireland (excluding Northern Ireland). As a result the following data is available on a national scale: Flood depth data Maximum flood depth maps, 10m resolution, for 1 in 30, 1 in 100, 1 in 1000 AEP rainfall events. Flood risk data Expressed as the Expected Annual Damage (EAD) based on property damage, 100m resolution, for 1 in 5, 1 in 10, 1 in 30, 1 in 50, 1 in 100 and 1 in 1000 AEP rainfall events. As noted above, the CFRAM Studies currently underway across Ireland do not address pluvial flood risk, concentrating primarily on fluvial and coastal flood risk. However, the Dublin FRC Project has developed City-wide pluvial hazard (with hazard being a function of flood depth and flow velocity) and risk maps which can be used as spatial planning tools for Dublin City. To supplement the pro-active approach to flood risk management initiated by the National Flood Policy and DEHLG/OPW Guidelines, the Department of Environment, Communications and Local Government (DECLG) is reviewing its document Recommendations for Site development Works for Housing Areas with an aim to set out best practice in regard to the use of Sustainable Drainage Systems (SuDS). Also, the DECLG propose to review the provisions of the Exempted Development Regulations under existing planning legislation, such as paving over residential garden areas, to encourage greater use of SuDS, i.e. only those complying with sustainable drainage principles will be exempted. Prior to the completion of these reviews, the DEHLG/OPW Guidelines advise planning authorities to advocate such sustainable drainage principles in considering planning applications through discussions at consultation stage. The Planning and Development Acts, 2000 to 2011, provide that development plans may include objectives for regulating, restricting or controlling development in areas of risk of flooding (whether inland or coastal), erosion and natural hazards. Also, there are provisions for the refusal of planning permission without compensation for proposed development in an area which is at risk of flooding. It is to be assumed that flooding relates to all flood hazards, including pluvial. Policy Objective SIO772 of the Dublin City Development Plan acknowledges this provision (refer to Section ). Final Report Dublin 5

20 The Code of Practice 1: Spatial Planning and Building Regulations presented in Appendix V3-A of this document outlines how planning authorities can consider pluvial flood hazard and risk when developing and implementing City and Local Area Plans as well as when assessing planning applications for development in accordance with the provisions of the DEHLG/OPW (2009) guidelines Regional Planning Guidelines The Greater Dublin Area Regional Planning Guidelines for the period have been adopted by the Regional Authorities. Although the regional flood risk appraisal outlined in these Regional Planning Guidelines does not specifically examine pluvial flood risk, one strategic policy and a number of recommendations for regional flood risk management are considered relevant to pluvial flooding and these are outlined in Table 1.1 below. Table 1.1: Regional Planning Guidelines strategic policy and recommendations relevant to pluvial flooding / flood risk management Existing Strategic Policy and Recommendations FP1 That flood risk be managed pro-actively at all stages in the planning process avoiding development in flood risk areas where possible and by reducing the risks of flooding to and from existing and future development. It aims to be implemented through a number of Strategic Recommendations: FR1 FR2 FR3 New development should be avoided in areas at risk of flooding. Alongside this, the Regional Flood Risk Appraisal recognises the need for continuing investment and development within the urban centres of flood vulnerable designated growth towns and the City and for this to take place in tandem with the completion of CFRAM Studies and investment in comprehensive flood protection and management. Development and Local Area Plans should include a Strategic Flood Risk Assessment, and all future zoning of land for development in areas at risk of flooding should follow the sequential approach set out in the Departmental Guidance on Flood Risk Management. All Flood Risk Assessments and CFRAM studies should take place in coordination and consultation with adjoining local authorities and regions and in coordination with the relevant River Basin Management Plans. Local authorities should take the opportunities presented to optimise improvements in biodiversity and amenity when including policies and actions in development plans/local area plans (such as flood plain protection and SuDS) for existing and future developments. Relevance Is pluvial flooding / FRM represented? Yes - assumed to capture all flood hazards. Yes - assumed to capture all flood hazards. However, the CFRAM Studies do not as yet specifically address pluvial flooding. Yes - assumed to capture all flood hazards. Yes - assumed to capture all flood hazards. FR4 Plans and projects associated with flood risk management that have the potential to negatively impact on Natura 2000 sites will be subject to a Habitats Directive Assessment (HDA) according to Article 6 of the habitats directive and in accordance with best practice and guidance. Yes - assumed to capture all flood hazards. Final Report Dublin 6

21 Existing Strategic Policy and Recommendations PIR20 PIR21 PIR24 Full implementation of new development and environmental management policies developed in the GDSDS project, including Sustainable Drainage Systems (SuDS). Integration within urban areas of pluvial and drainage models to achieve an integrated response and mutually supportive actions to prevent pluvial flooding and pollution of receiving waters. All water management plans should take account of the possible impact of climate change in the future in relation to changes to volumes of rainfall, river flows, sea level rise, drought events and frequency of storm events. Relevance Is pluvial flooding / FRM represented? Yes, and this can now be supplemented with the findings of the Dublin FRC Project (particularly Code of Practice 2: Flood Resilience and Adaptation Measures (Appendix V3-B)) Yes, and this can now be supplemented with the findings of the Dublin FRC Project (particularly Volumes Two and Four which detail the hydraulic modelling undertaken for the City)) Yes. The findings of the Dublin FRC Project can inform any such plans (particularly Volumes One, Two and Four) In addition, to the tabulated policy and recommendations, Green Infrastructure is recognised by the Regional Guidelines as an important emerging concept in flood risk management and some strategic recommendations are made in relation to development of this concept. This is of particular relevance to pluvial flooding Greater Dublin Strategic Drainage Study (GDSDS) The deliverables of the Greater Dublin Strategic Drainage Study (GDSDS) included a Final Strategy Report and a set of Regional Drainage Policies. To produce the Policy documents, the GDSDS undertook a review of local authority drainage practices in five key areas and recommended policies for the future provision and management of drainage services in the Greater Dublin Area. The policies are summarised in an Overall Policy Document and five Technical Documents provide the background and details of the policies under the topics New Development; Environmental Management; Climate Change; Inflow, Infiltration and Exfiltration; and Basements. These policies were developed prior to the DEHLG/OPW Guidelines however the overall principles for proactive flood risk management are similar to those of the Guidelines. It is clear that many of the Objective and Policy recommendations outlined in these Regional Drainage documents can support the assessment and management of pluvial flood risk (refer to Table 1.2). The GDSDS Technical Documents identified (drainage-related) objectives to be encapsulated in the general policy statements of Development Plans, some of which identify inter alia, issues and areas of improvement relevant to pluvial flood risk management. For example the New Development Policy recognised the need for a register of basements to help identify properties currently at risk and potentially at future risk from new development and climate change effects. The Climate Change Final Report Dublin 7

22 Policy recognised the absence of a future stochastic rainfall time series to properly reflect the projected change in seasonal rainfall pattern across the Dublin region. These recommendations are echoed in Section 1.4 below in which policy recommendations for the future provision and management of pluvial flood hazard in Dublin City are outlined. As with the GDSDS policies, it is intended that the recommended policies / policy amendments developed for CoP 1 Spatial Planning and Building Control are incorporated into the Dublin City Development Plans, to be implemented through the planning process, for all new developments and extensions / modifications to existing developments. With further development and consultation, such policies can then be incorporated with other local authority policies to bring a standardised approach to future provision and management of pluvial risk. The GDSDS policies were used to develop the Greater Dublin Regional Code of Practice for Drainage Works. That Regional Code of Practice aims to promote a consistent approach to drainage infrastructure planning, design, construction and operation throughout the Greater Dublin Area. The guidelines include: Drainage Requirements; Guidelines for Planning and Construction; Post Construction Certification; Private Drainage; Pipelines; Culverts; Road Gullies and Pumping Stations; and various related topics and issues. A specific chapter is included on Stormwater Management Policy for Developers. The GDSDS Overall Policy report states that while these policies remain the overriding documents, the GDSDS Code of Practice sets out the requirements for the local authorities in a more concise format for day to day use. This was acknowledged in developing the Dublin FRC Codes of Practice relating to pluvial flooding and flood risk management. Table 1.2 below includes extracts from the GDSDS Code of Practice for Drainage Works which are considered relevant to flooding and flood risk management (FRM). The Relevance column briefly summarises if the scope of these requirements in their current form sufficiently include for pluvial flooding / flood risk management. Final Report Dublin 8

23 Table 1.2: GDSDS Code of Practice for Drainage Works requirements relevant to Pluvial Flooding / Flood Risk Management in Dublin City Existing Code of Practice Requirements Drainage Requirements 3.11 Flooding Relevance: Is pluvial flooding / FRM represented? It is a policy to control development in the natural flood plain of a river and to develop guidelines, in co-operation with the Local Sanitary Authority, for permitted development in the different flood risk category areas. The risk categories for future development are: Low Risk: No restrictions to development. Medium Risk: Development may be allowed following the recommendations of a flood impact assessment. High Risk: Limited development may be allowed subject to a flood impact assessment, flood defences and warning facilities been approved by the Local Sanitary Authority Known Areas of Flooding: As a rule development is not permitted in known a flood plain. Where flood risk maps are not available the Developer will be required to carry out a flood risk assessment in accordance with the above requirements. Where the development has the potential to reduce flood plain storage and/or the potential to increase the flood risk in the relevant catchments the Developer must satisfy the Local Sanitary Authority that the appropriate risk reduction measures can be put in place to offset any increased risk of flooding. Currently limited to fluvial zones. This could now be expanded to include areas subject to pluvial flooding using project findings documented in Volume Two and Volume Three, Appendix V3-A. Assumed to capture all flood hazards. However, it is recommended that these risk categories are supplemented with the use of pluvial 'flood zones' which are discussed in Section A2.2.1 of Code of Practice 1: Spatial Planning and Building Regulations (Appendix V3-A). A large area of Dublin City is at risk of pluvial flooding, and therefore the prevention of development in known areas of flooding may not be practical in many areas for pluvial flood hazards Climate Change 3.12 All new development must allow for climate change as set out in the GDSDS Technical Document, Volume 5, Climate Change. The key points documented are listed below: Climate Change Category Characteristics: River: flows 20% increase in flows for all return periods up to 100 years Sea level: 450+mm rise Rainfall: 10% increase in depth (factor all intensities by 1.1) The reference to rainfall characteristics could be expanded to take into account findings of the Dublin FRC Project (Volume Two City-wide (Type 1) and Volume Four Detailed (Type 2) pluvial flood depth and hazard mapping. Allowances should be subject to ongoing review as further data and research becomes available. Final Report Dublin 9

24 Existing Code of Practice Requirements Relevance: Is pluvial flooding / FRM represented? 3.18 Basement Drainage Planning Access to basement car parks should be designed such that surface water run-off from the surrounding paved areas cannot flow down the ramp. The Developer shall limit storm water discharge from the proposed development in accordance with the GDSDS Technical Documents, Volume 2, New Development Policy. (Linked to 16 - Stormwater Management Policy for Developers) All new developments must allow for Climate Change as set out in the GDSDS Technical Documents, Volume 5, Climate Change Stormwater Management Policy for Developers The Developer shall comply with the Greater Dublin Strategic Drainage Study, Volume 2, New Development Policy All new development must allow for climate change, see Key design criteria relevant to 30 and 100 year return periods (1 in 30 and 1 in 100 AEP) are outlined for Level of service (flooding) for the site, e.g. No internal property 16.3 flooding. Planned flood routing and temporary flood storage accommodated on site for short high intensity storms. Site critical duration events. SuDS are a mandatory requirement of each Local Sanitary Authority Attenuation Tanks/Enlarged Pipes: These are not true SuDS devices and should only be considered as a last resort where it can be shown that SuDS measures are not achievable. Yes, and planning control for this can now be supplemented with the findings of the Dublin FRC Project (particularly Volume Two and Volume Three, Appendix V3-B) Yes, and planning control for this can now be supplemented with the findings of the Dublin FRC Project (particularly Volume Two and Volume Three, Appendix V3-B) References to rainfall characteristics and information sources / tools could now be expanded to take into account the findings of the Dublin FRC Project (Volumes One, Two and Four). Allowances should be subject to ongoing review as further data and research becomes available. In compliance with these policies, SuDS features are already being established and integrated as part of the existing surface drainage system in Dublin. These policies are directly applicable to pluvial flood risk management and these can now be supplemented with the findings of the Dublin FRC Project (particularly Code of Practice 2: Flood Resilience and Adaptation Measures (Appendix V3-B)) to support these policy requirements. Final Report Dublin 10

25 1.2.4 Dublin City Development Plan The preparation of the current Dublin City Development Plan had regards to a Draft version of the DEHLG/OPW Guidelines. Also, in accordance with recent planning and development regulations, the development plan introduces a core strategy conveying that the development objectives in the Plan are consistent, as far as practicable, with national and regional development objectives set out in the National Spatial Strategy and regional planning guidelines. With regards flood risk management, the Development Plan states that through the application of the sequential approach and justification test as set out in the Planning System and Flood Risk Management Guidelines it is considered that the elements of the core strategy can be achieved while managing flood risk appropriately.' Flood Risk Management On identifying water-related challenges, the requirement of flood risk assessment and management in response to climate change and the impact of increased flood risk due to extremes of weather are noted as key issues to be addressed through the implementation of the DEHLG/OPW Guidelines. Of the main water-related strategic issues identified for the current Dublin City Council Development Plan period (relating to the achievement of the core strategy), the following are considered relevant to pluvial flooding: Using Flood Risk Assessment techniques, identification and management of these risks to be put in place through the identification and protection of existing and proposed flood defences and the need for flood resilient urban and building design and construction; and Improve the city s resilience and ability to adapt to climate change. The Development Plan flood risk management and SuDS policies and objectives considered relevant to pluvial flooding are outlined in Table 1.3 below. Green Infrastructure ( Greening the City ) This is identified as a strategic approach which DCC will actively promote to help achieve a green connected city and more sustainable neighbourhoods in line with the core strategy for the plan period ( ). By connecting green spaces and other natural features such as rivers and canals, Green Infrastructure can provide a sustainable approach to pluvial flood risk management in an urban area as well as providing a water quality improvement function. A range of assets are outlined in the development plan, with those of relevance to pluvial flooding identified as follows: Functional spaces such as flood storage areas and sustainable drainage schemes; and Buildings and hard surfaced areas incorporating greening initiatives such as green roofs, green walls, and planters. Relevant policies and objectives relating green infrastructure and pluvial flooding are outlined in Table 1.3 below as well as those guiding principles relating to sustainable site design, sustainable buildings and green corridors which are considered relevant to pluvial flooding. Final Report Dublin 11

26 Development Standards The qualitative and quantitative development standards used to assess development proposals (in the context of the core strategy) are specified in the Development Plan. A number of these standards could be supplemented / edited to help manage pluvial flood risk. Those identified as relevant to pluvial flooding are outlined in Table 1.3 below. Table 1.3: Spatial Planning Policies, Objectives Guiding Principles and Standards relevant to pluvial flooding / flood risk management in Dublin City Policies, Objectives, Guiding Principles and Standards Flood Risk Management Policies and Objective Relevance Is pluvial flooding / FRM represented? SI48 SI49 SIO772 To carry out flood risk assessment and introduce Flood Risk Management in all areas which have been flooded in recent years recognising that areas of the City are at risk of flooding. To have regard to the Guidelines for Planning Authorities on Flood Risk Management, November 2009, published by the Department of the Environment, Heritage and Local Government when assessing planning applications and in the preparation of plans both statutory and nonstatutory. To require all applicants, where appropriate, to carry out a Flood Risk Assessment in accordance with the Departmental Guidelines on Flood Risk Management. The flood risk assessment shall accompany the planning application and should be sufficiently detailed to quantify the risks and the effects of any necessary mitigation / adaptation, together with the measures needed to manage residual risks. Local Area Plans or other land use plans or policies drawn up by Dublin City Council under the Development Plan are also subject to a flood risk assessment as appropriate in accordance with the Guidelines. Assumed to capture all flood hazards, particularly now that the Dublin FRC Project is supplementing the Dublin Flood Initiative 3 by assessing pluvial flood hazard and risk. Pluvial flood risk assessment completed for Dublin City (refer to Volume Two: City-wide Pluvial Flood Risk Assessment) Assessment approaches in the Guidelines are directed at fluvial and coastal, but can be supplemented using the findings of the Dublin FRC Project to include for pluvial. The scope of this existing policy and its objective can be extended to include pluvial flood hazard or supplemented with a new policy specific to pluvial (refer to Code of Practice 1: Spatial Planning and Building Regulations in Appendix V3-A). 3 The Dublin Flood Initiative (DFI) is Dublin City Council s collective strategy for managing flood risks from all flood hazards drainage, dam break, coastal, riverine, and now pluvial. The DFI aims to proactively respond to the need to address flood risks and develop a unified and fully integrated flood risk management strategy. It also aims to raise the level of awareness and participation through policy makers, professionals and the general public. Final Report Dublin 12

27 Policies, Objectives, Guiding Principles and Standards Relevance Is pluvial flooding / FRM represented? Sustainable Drainage Systems (SuDS) Policies SI51 SI52 To incorporate and promote the use of Sustainable Drainage Systems within City Council developments and other infrastructural projects as set out in the Greater Dublin Regional Code of Practice for Drainage Works (see also Policy GCO4 and section ) To require the use of Sustainable Drainage Systems in all new developments, where appropriate, as set out in the Greater Dublin Regional Code of Practice for Drainage Works. The following measures will apply: The infiltration into the ground through the development of porous pavement such as permeable paving, swales, detention basins. The holding of water in storage areas through the construction of green roofs, rainwater harvesting, detention basins, ponds, wetlands. The slow down of the movement of water Yes - captures pluvial flood hazard, and both the scope and application of these policies can now be supplemented with the findings of the Dublin FRC Project (particularly Code of Practice 2 (Appendix V3-B) and Volume Four) Yes - captures pluvial flood hazard, and both the scope and application of these policies can now be supplemented with the findings of the Dublin FRC Project (particularly Code of Practice 2 (Appendix V3-B) and Volume Four) Green Infrastructure Network/Strategy Policy and Objectives GC7 GCO1 GCO3 GCO4 To co-ordinate between open space, biodiversity and flood management, in progressing a green infrastructure network To progress the illustrated strategic green infrastructure network and to devise a programme of specific works to be implemented within the current development plan timeframe (see Strategic Green Network Map and also City Centre Routes Map, Figures 10 and 11) To establish an interdepartmental task force on green roofing within the City Council to examine the suitability of various technical designs of green roofs for new and existing developments in the city To review existing road construction standards and to prepare a design guide for new developments to ensure the integration of Sustainable Drainage Systems (SUDS) in relation to Taking in Charge Standards Yes - assumed to capture pluvial flood hazard, and both the scope and application of this policy can now be supplemented with the findings of the Dublin FRC Project Yes - assumed to capture pluvial flood hazard, and both the scope and application of these objectives can now be supplemented with the findings of the Dublin FRC Project. Final Report Dublin 13

28 Policies, Objectives, Guiding Principles and Standards Relevance Is pluvial flooding / FRM represented? 16.0 Green Infrastructure Guiding Principles Sustainable Site Design, Sustainable Drainage Systems, Sustainable Buildings, Green Roofs, Green Networks Flood Risk Areas 17.0 Development Standards Sustainable Site and Building Design Hard Landscaping Standards for Residential Accommodation: Basements Yes, and the application of these principles can now be supplemented with the findings of the Dublin FRC Project (particularly Code of Practice 2: Flood Resilience and Adaptation Measures (Appendix V3-B)) Currently focuses on fluvial and coastal only. Can be expanded to include pluvial. Yes, and both the scope and application of these standards can now be supplemented with the findings of the Dublin FRC Project (particularly Code of Practice 2: Flood Resilience and Adaptation Measures (Appendix V3-B)) The Strategic Environmental Assessment (SEA) for the Dublin City Development Plan includes the use of environmental protection objectives specific to flooding and flood risk management. Table 1.4 is an extract from the SEA s Environmental Report outlining how Dublin City Council proposes to monitor the implementation of these objectives. These are directly relevant to pluvial flooding. Table 1.4: Dublin City Council Development Plan SEA Objectives, Targets and Indicators relevant to flood risk Environmental Receptor Climatic Factors Environmental Protection Objective Reduce and manage the risk of flooding Target Compliance with the Floods Directive and with OPW / DEHLG Flood Risk Management in the Planning Process standards Flood Risk Assessment be carried out for all new developments Indicator Number of planning permissions compliant with the Floods Directive and OPW / DEHLG s Flood Risk Management in the Planning Process standards Number of planning permissions incorporating flood risk assessment and conditions requiring appropriate flood resilient measures for new developments Final Report Dublin 14

29 Environmental Receptor Environmental Protection Objective Target Indicator Avoid the development risk of destruction of flood defences, flood defence structures and features Number of flood defences, flood defence structures and features identified in the development plan Identify Sustainable Drainage Systems (and features which are identified as having a flood defence function) in all new developments. Number of Sustainable Drainage Systems and flood defence features required in new planning applications. Landscape and Soils Preserve or enhance area of natural rainfall infiltration to water table within the city landscape to minimise storm water flooding No storm water flooding and associated risks (e.g. water contamination) % Area of city landscape as pervious area The combined effect of many people paving over their front gardens can increase the amount of surface runoff which adds to the risk of flooding. Planning permission is required for new entrances/driveways or widening an existing entrance/driveway. However, paving over green areas for some off-street parking and hard landscaping is currently exempt from planning. The DECLG intends to review such exempted development provisions to ensure that only those complying with sustainable drainage principles will be exempted. Dublin City Council s Guidance titled Parking Cars in Front Gardens includes a requirement for SuDs, requesting that proposals should indicate how the design aims to control surface water runoff in a sustainable fashion through the use of permeable or porous surfaces such as gravel and green areas, etc rather than excessive hard surfacing. In the UK (since 1 October 2008) planning permission is required if more than five square metres of a new or replacement driveway is to be covered with traditional, impermeable materials that do not provide for the water to run to a permeable area Building Regulations Irish Building Regulations apply to the construction of new buildings and to extensions and material alterations to buildings. Their primary purpose is to provide for the health, safety and welfare of people in and around buildings. Some aspects of the Regulations also apply to a material change in the use of buildings. Current Building Regulations do not apply to buildings constructed prior to 1 June, Building Control Regulations are in place to assist the enforcement of, and compliance with, the Building Regulations. Final Report Dublin 15

30 Persons / Developers must issue a Commencement Notice to DCC for any works or material changes of use to which the Building Regulations apply (some exemptions apply). Existing technical guidance (see below) for Irish Building Regulations , for which the primary purpose is to provide for the health, safety and welfare of people in and around buildings, does not specifically provide information on preventing or reducing the impacts of pluvial flooding. However, the DECLG is continuously reviewing and updating the Building Regulations and associated Technical Guidance Documents, and in response to National Flood Policy and DEHLG/OPW Guidelines, the DECLG is reviewing its document Recommendations for Site Development Works for Housing Areas with an aim to set out best practice in regard to the use of Sustainable Drainage Systems (SuDS). Such reviews/revisions should enable the requirement for, and guidance on, pluvial flood resistance and resilience to be easily incorporated into the building control system. The DECLG have published a series of Technical Documents detailing how to construct a building so that it complies with the Regulations. A review of these Technical Guidance Documents was undertaken to identify any existing requirements relating to pluvial flood risk management and also where these Guidance Documents could be enhanced to include for such flood risk management. Those considered of potential relevance to pluvial flood risk management are highlighted in bold italics in the list below: Part A Structure Relevance: Currently outlines basic requirements for stability which can be extended to acknowledge specific requirements of developments in flood prone areas. Part B - Fire Safety Part C - Site Preparation and Resistance to Moisture Relevance: Currently includes requirements for site preparation and drainage, as well as outlining requirements for preventing moisture entering or damaging a building. This however does not specifically address moisture sourced from surface water (pluvial flow paths / ponding) as it assumes that the site of the building is not subject to flooding or, if it is, that appropriate steps are being taken. Part D - Materials and Workmanship Part E - Sound Part F - Ventilation Part G - Hygiene Part H - Drainage and Waste Water Disposal Relevance: This includes specific requirements for preventing/reducing basement flooding through drains. Part J - Heat Producing Appliances Part K - Stairways Ladders Ramps and Guards Part L - Conservation of Fuel and Energy - Dwellings and Buildings Other Than Dwellings Final Report Dublin 16

31 Part M - Access and Use Relevance: This guidance includes the requirements for adequate provisions for people to access and use a building, its facilities and its environs. To satisfy the requirements of Part M for dwellings, it is required that elements of the building do not constitute an undue hazard for people, especially for people with vision, hearing or mobility impairments. The Code of Practice 1: Spatial Planning and Building Regulations (Appendix V3-A) recommends how the Dublin FRC Project can help incorporate pluvial flood risk management into application and enforcement of the current Building Regulations and their associated Technical Documents. It is acknowledged that legislative changes may be required to alter the Technical Documents. However, recommendations are made to help Dublin City Council supplement the current building regulations and associated Technical Documents to help support the local building control authority monitor and enforce pluvial flood resilience / resistance in the building control system. These recommendations for procedural changes are closely supported by Code of Practice 2: Flood Resilience and Adaptation Measures in Appendix V3-B. 1.3 European and International Practice FRC Partner and European Guidance Recommendations for the Establishment of Flood Risk Management Plans, German Working Group on Water Issues of the Federal States and the Federal Government (2010): In reviewing possible flood management actions, this guidance includes advice on precautionary building including flood adapted planning, construction and renovation. Measures to Prevent Floodwater Entering Buildings, City of Bradford Council (2010) A an Interreg IVB FloodResilienCity partner Bradford City Council have been involved in preparation of an interactive leaflet for householders which provides a step by step guide on resistance and resilience measures in support of planning and building control policies to raise resilience to flooding including surface water flooding. Construction in Flood-Prone Areas, Diagnosing and Reducing the Impact of Flood Hazards Methodological Guide, Department of Loiret, CEPRI, France (2010): French technical guide for the investigation and diagnosis of the vulnerability of public or private buildings. It also provides a reference for communities wishing to engage in the process of reducing the vulnerability of residential and public buildings that have been built in flood zones. Although developed for fluvial flood hazards, this guide would prove very useful to inform pluvial flood risk assessments as well as building control. Final Report Dublin 17

32 1.3.2 UK Practice and Guidance Planning Policy Statement 25: Development and Flood Risk - Practice Guide, Department of Communities and Local Government (December 2009) 4 : In England the Government has revised and strengthened planning policy on development and flood risk. The key planning objectives of PPS25 are to deliver sustainable development by: ensuring that flood risk is taken into account at all stages of the planning process providing a more strategic approach to managing flood risk, ensuring that this is considered as early as possible in the planning process clarifying the types of development that can be built in areas with a range of flood risks, and avoiding inappropriate development strengthening guidance on the need to include Flood Risk Assessments at all levels of the planning process providing opportunities to reduce flood risk to communities by re-creating and safeguarding the flood plain promoting more green space and sustainable drainage systems within urban areas ensuring that new development takes climate change into account and does not increase flooding elsewhere. An important section of PPS25 is the production of a site specific Flood Risk Assessment (FRA), which must accompany all planning applications, except for sites less than 1ha and not known to be in an area of flood risk. In addition to identifying the flood risk at the site and ensuring that flood risk is not increased for others, the FRA will consider ways to reduce the residual flood risk which can include, amongst other elements, incorporating resilience measures in the building design. Through application of a sequential approach to avoidance, resistant and resilient techniques are considered in certain areas with residual or low risk of flooding or which cannot be protected by traditional defences. However there can be justification for departures from the sequential approach (the Exception Test ) where it is necessary to meet the wider aims of sustainable development. The DEHLG/OPW Guidelines have adopted a similar approach to the UK s PPS25 to revise and strengthen planning policy on development and flood risk across Ireland. 4 In March 2012, the National Planning Policy Framework (NPPF) replaced Planning Policy Statement 25 'Development and Flood Risk'. However, the policy principles remain unchanged, supporting Technical Guidance has been issued and the associated Practice Guide remains in place until Government chooses to replace it. rk/ Final Report Dublin 18

33 1.4 Proposed Policy Elements A review of the existing flood-related policy (refer to Section 1.2) has identified some opportunities for communicating and strengthening the requirements for pluvial flood risk assessment and management in both the planning and building control systems (Tables ). The following sections provide recommendations to facilitate / enhance the application of the policy documents discussed in Section 1.2 to pluvial flood risk assessment and management. It is important to note that although Code of Practice 1: Spatial Planning and Building Control (Appendix V3-A) focuses on the pluvial aspects, these opportunities are intended for in combination application with fluvial and coastal flood risk assessment and management Planning Relevance to National Policy (DEHLG/OPW Guidelines) Continue to advocate sustainable drainage principles in considering planning applications (including exempted development) through discussions at consultation stage. Initiate the use of pluvial (hazard) zones to inform spatial planning and to help incorporate the key principles of the DEHLG/OPW Guidelines into the planning system. Relevance to Regional Planning Policy (Greater Dublin Area) Incorporate pluvial flood hazard assessment into Strategic Flood Risk Assessments using the principles of the sequential approach set out in DEHLG/OPW Guidance so that future zoning of land for development in areas prone to pluvial flooding can be assessed for Development and Local Area Plans. Relevance to Regional Drainage Policy (GDSDS) New Development Policy: Initiate the use of pluvial flood risk and hazard mapping to categorise existing and future development areas respectively in terms of pluvial flooding hazard with appropriate planning controls, and incorporate into Development Plans. Create a register of basements (location, use, floor level, drainage infrastructure and flooding history) to help identify properties currently at risk and potentially at future risk from new development and climate change effects. All Planning Applications are to be vetted by the Drainage Department, irrespective of size of development or whether the drainage will be taken-incharge or not. Final Report Dublin 19

34 All new development shall incorporate SuDS facilities and identify taking in charge arrangements, unless the developer can demonstrate that SuDS are impractical due to site circumstances. Where SuDS cannot be provided, the developer shall provide alternative means of dealing with surface water flow. Expand policy to include restrictions on hard landscaping of green areas / gardens for which proposals exceed 5 square metres as in UK. Planning Regulations currently allow for this in areas at risk of flooding, but to help manage urban creep, pluvial hazard maps could be used to impose restrictions. Climate Change Policy: Utilise the findings of the Dublin FRC Technical Report, specifically Volume One: Pluvial Rainfall and Forecasting (which outlines Dublin s rainfall characteristics and recommendations for a pluvial flood forecasting and warning system), and Volume Two: City-wide Pluvial Flood Risk Assessment (for which climate change has been considered for the 1% (annual exceedance probability (AEP) event modelled for Dublin City), to help improve knowledge regarding the following outstanding policy recommendations: A new time series rainfall should be produced which represents future rainfall conditions; and A future stochastic rainfall time series should be produced to properly reflect the projected change in seasonal rainfall pattern across the Dublin region. Greater Dublin Regional Code of Practice for Drainage Works Extend the policy to control development in the natural flood plain of a river to include that in areas with a high or moderate probability of pluvial flooding. Utilise pluvial flood models and maps produced by the Dublin FRC Project (refer to Volumes Two and Four) to ensure all new development allows for climate change (climate change has been estimated as approximately equivalent to a 0.5% or 1 in 200 AEP event). To enhance the long-term effectiveness of SuDS, commitments for ongoing maintenance could be sought from developers at planning stage. Relevance to Dublin City Council Development Plan Policies Prepare a Communications and Engagement Plan in order to improve community and business awareness raising and education in pluvial flood risk and flood risk management. Means to raise awareness could include information provision through a dedicated website (possibly a section within the DCC website) supported by guidance leaflets, as well as individual support to businesses to assist their preparation of Business Continuity Plans. Raising Awareness of pluvial flood risk within the council, partner organisations and with the public should be a first step in encouraging community groups and property owners to consider property level resistance and resilience and other measures, and encouraging reporting and recording of flooding. The latter will facilitate the gathering of evidence of a problem, which could be used to target resourcing and funding in the future. Awareness raising would be an essential precursor to effective flood warning and response. Introduce new pluvial-related polices, or alternatively edit those in place to recognise pluvial flood hazard. Examples of a new pluvial-related policy and objective are proposed as follows: Final Report Dublin 20

35 Proposed new Pluvial Policy: To apply the principles of the sequential approach and justification test as set out in the Guidelines for Planning Authorities on Flood Risk Management, November 2009, published by the Department of the Environment, Heritage and Local Government for pluvial flood risk when assessing planning applications and in the preparation of plans both statutory and non-statutory. Proposed new Pluvial Objective: To require all applicants, where appropriate, to carry out an assessment of pluvial flood risk using the principles of the sequential approach and justification test as set out in the Departmental Guidelines on Flood Risk Management. The flood risk assessment shall accompany the planning application and should be sufficiently detailed to quantify the risks and the effects of any necessary mitigation/adaptation, together with the measures needed to manage residual risks. Local Area Plans or other land use plans or policies drawn up by Dublin City Council under the Development Plan are also subject to a flood risk assessment as appropriate applying the principles of the sequential approach and justification test set out in these Guidelines. To incorporate detailed pluvial flood risk assessments undertaken as part of the Dublin FRC Project for the Pilot Areas (Volume Four), and any future detailed pluvial flood risk assessments, to the relevant Local Area Plans, introducing Flood Risk Management in all areas which have been flooded in recent years, and areas where there may be a high risk of pluvial flooding. To require the use of Sustainable Drainage Systems in all new developments, where appropriate, as set out in the Greater Dublin Regional Code of Practice for Drainage Works supplemented by Code of Practice 2: Flood Resilience and Adaptation Measures. Utilise the pluvial flood depth, velocity and combined hazard mapping produced as part of the Dublin FRC Project (Volumes Two and Four) to help progress the green infrastructure network and inform the design guide for new developments to ensure the integration of Sustainable Drainage Systems (SUDS) in relation to Taking in Charge Standards. Green Infrastructure Utilise the Greater Dublin Regional Code of Practice for Drainage Works supplemented by Code of Practice 2: Flood Resilience and Adaptation Measures (Volume Three, Appendix V3-B) to investigate the potential for using parking and other open space areas for greening, incorporating SuDS infiltration where feasible, aggregated micro-storage potential etc Building Control As noted in Section 1.1.2, the development of policy in this area is viewed as a potential early-win measure to address pluvial flood risk across Dublin assuming that changes in policy and guidance can be implemented relatively quickly and easily (although the full benefit of this measure is incremental due to the incremental nature of development). The implementation of the planning policy elements noted in Section above will help empower Dublin City Council Planners to ensure pluvial flood resilience/resistance requirements are incorporated into proposed building designs by setting out the appropriate principles earlier in the spatial planning process. In the absence of flood-related amendments to Building Regulations and associated Technical Documents, this early-win can provide a template for the Building Control Final Report Dublin 21

36 Division when inspecting features of design / materials / construction in areas susceptible to pluvial flooding. The use of vulnerability classes when classifying proposed land use and development types for the purpose of the sequential approach will help specify some pluvial flood resilience / resistance characteristics required of a development prior to application of the building control process. For example, application of the Justification Test 5 for a proposed residential development (highly vulnerable) in an area with a high or moderate probability of pluvial flooding (i.e. pluvial zone pa or pb) would need to demonstrate appropriate access thresholds, SuDS and/or evacuation routes as part of its suite of mitigation measures. Incorporation of such features into the building control system will help ensure that these are developed, communicated and implemented appropriately. Amendments to the current Building Regulations and associated Technical Documents would help ensure all design and construction practices are cognisant of flood risk. This is specifically relevant to the incorporation of basement protection requirements, and as pluvial flood risk becomes more embedded in the spatial planning system, developers will become conditioned to provide protection against basement and underground car park (or other below-ground infrastructure) flooding in all new developments. In the absence of such amendments, Code of Practice 2: Flood Resilience and Adaptation Measures (Appendix V3-B; particularly Sections B6.1 and B6.2) can be used to supplement the Technical Guidance Documents when inspecting the flood resilience / resistance of buildings. Dublin City Council can also use this Code of Practice to extend the application of Part M Access and Use to include appropriate flood evacuation routes as well as access for emergency services. Increased public awareness of the causes of flooding and the methods of protection will help to ensure that even the small developments / building modifications are planned, designed and constructed with flood risk in mind. To highlight the importance of flood risk, Commencement Notices could be edited to include a check box to confirm the consideration of potential flood risk for any developments proposed in flood zones which are not considered appropriate and therefore should have undertaken some form of flood risk assessment (refer to Section 2 of Appendix V3-A for the definition of appropriate development in this context). Dublin City Council is active in their consultation with the Irish Insurers Federation (IIF). It is recommended that this cooperation is maintained to support the insurance industry's commitment to continue offering flood risk insurance to the vast majority of homes and businesses in flood risk areas including areas at risk from pluvial flooding. The findings of the Dublin FRC Project help to demonstrate that the routine implementation of resistance / resilience measures at planning, design, construction and/or modification stages are effective at reducing pluvial flood risk. Consultations with insurance companies in this instance should include discussions relating to discounts for properties using resilience / resistance measures. While local authorities should have no role in determining insurance cover itself, they should share a common goal with the Irish Insurers Federation to improve flood mapping and provide the best available information to the public. The scope for making properties more flood resistant/resilient as part of reinstatement following flooding should also be examined as this could be a cost effective means of raising the overall level of resilience especially in areas that may be at higher risk of pluvial flooding. 5 Refer to Appendix V3-A: Code of Practice 1 Spatial Planning and Building Control for further information on the Justification Test and pluvial zones Final Report Dublin 22

37 Disruption during implementation of measures would also be reduced if undertaken at the same time as reinstatement. The primary criteria which should be satisfied by the building control system is how is the proposed development designed to be safe during a flood and reduce risk to people and the emergency services? Key learning outcomes from Section 1 with regard to Spatial Planning and Building Regulations are as follows: The Spatial Planning and Building Regulations Code of Practice (Code of Practice 1) that has been developed under the Dublin FRC Project is introduced. The background to the development of Code of Practice 1: Spatial Planning and Building Regulations (included as Appendix V3-A) is outlined as well as recommendations for its application. The development of the Code of Practice 1: Spatial Planning and Building Regulations is based on a review of existing national and local policy and guidance documents, as well as other studies and plans relevant to pluvial flood risk management in Dublin. It also considers wider European guidance and practice. Details of this review are outlined. The findings from these reviews are used to inform recommendations for proposed policy to improve pluvial flood risk management. These recommendations are focused on planning and building control aspects. Final Report Dublin 23

38 SECTION 2 FLOOD RESILIENCE AND ADAPTATION MEASURES 2.1 Introduction Codes of Practice on Spatial Planning and Building Regulations and on Flood Resilience and Adaptation Measures have been developed to support pluvial flood risk management. Code of Practice 2: Flood Resilience and Adaptation Measures introduced in the following sub-sections, is presented in Appendix V3-B of this document. Code of Practice 2 provides guidance on appropriate resistance / resilience measures to address pluvial flood risk relevant to both new and retrofit properties. Code of Practice 1: Spatial Planning and Building Regulations, introduced in Section 1, is presented in Appendix V3-A of this document. Code of Practice 1 reviews existing policy and guidance and outlines how pluvial flood risk assessment and management can be integrated in the application of sustainable planning and building control activities relevant to new and modified/extended developments in Dublin. The following sections outline the background to the development of Code of Practice 2: Flood Resilience and Adaptation Measures as well as recommendations for its application Objectives The specification for the Dublin FloodResilienCity (FRC) project sets out the specific objectives for Code of Practice 2: Produce a Manual of corrective and adaptive measures which are to be suitable for: Managing surface and overland flows; and Creating resilience in existing buildings. This Manual will provide examples of measures outlined, their effectiveness and indicative costs Context Code of Practice 2: Flood Resilience and Adaptation Measures relates closely to Code of Practice 1 on Spatial Planning and Building Regulations and should be read in conjunction with it. The consideration of both codes is fundamental to addressing pluvial flood risk across Dublin City and development of an integrated pluvial flood risk management strategy which will be underpinned by a pluvial flood forecasting and warning system Approach Preparation of Code of Practice 2 has been largely based on a literature review. Discussions have also been held with Dublin City Council staff from relevant departments. Literature sources include: Current guidance and good practice across Europe; Final Report Dublin 24

39 Office of Public Works and other national agency publications; Work completed by European FRC project partners; DEFRA Surface Water Management Plan Technical Guidance (Appendix F); The Code of Practice provided in Appendix V3-B makes recommendations for providing information to at risk properties to enable effective resilience and resistance measures to be retro-fitted or included in a new property. Appendix V3-B also provides guidance on various barrier flood protection products and other suitable systems. Means to review and report on the level of consistency achieved in compliance with guidance and in application and operation are considered. For resistance and resilience measures relevant to existing buildings, Section B6.3 of the Code of Practice provides an assessment template which can be made available for properties in susceptible areas (where there is a need to determine risk factors and options to mitigate pluvial flood risk). A number of case studies documenting the implementation of successful measures in some of the EU FRC partner countries are also included here. In preparing Code of Practice 2: Flood Resilience and Adaptation Measures a number of innovative techniques and approaches are considered which provide an opportunity for added value for DCC (refer to Section for further details). It should be noted that justifying many of the resistance and resilience measures economically may be difficult at a householder level assuming that householders have insurance in place. However, with the increasing trend of flood insurance being limited, particularly in known flood risk areas, some householders, if sufficiently informed, may be more inclined to implement their own measures, whilst others will not have the financial means to implement the measures or may simply accept the risk of flooding. This has wider implications in terms of the strategic approach to encourage uptake of such measures through flood resistance and resilience grant funding although this is outside of the scope of the Dublin FRC study Adaptability With all measures, whether at household level or larger scale more capital intensive measures, there is need to consider adaptability in terms of resilience to climate change uncertainty and to allow for future development Categories of Measures Measures outlined in Code of Practice 2: Flood Resilience and Adaptation Measures have been grouped according to the following categories: Generic and Early Win Measures those which can be applied universally across the whole of the Dublin administrative area and aim to raise the overall level of resilience to pluvial flood risk. Community Flood Resilience Measures require engagement and participation at community or householder level. Site Specific Measures are normally applicable only in areas of identified high risk and likely to involve capital investment and ongoing maintenance commitment. Final Report Dublin 25

40 2.2 Review of Relevant Guidance Irish Guidance Greater Dublin Regional Code of Practice for Drainage Works (V6-0): As described in Section Further information is available at: egional_code_of_practice_v6-0.pdf Regional Drainage Policies - Overall Policy Document (March 2005): As described in Section Further information is available at: gicdrainagestudy/documents/vol%201%20-%20overall%20policy%20document.pdf The Planning System and Flood Risk Management, DEHLG & OPW (November 2009): As described in Section Appendix B of these guidelines provide specific guidance on addressing flood risk management in the design of development in flood risk zones. Office of Public Works flooding.ie website Aims to provide practical help to all those homes or businesses which may be at risk, and includes a library downloadable guidance leaflets such as Making a home flood resistant and In the event of a flood. A tool for the Initial Assessment of the Surface Water Storage Volume Requirements for a Site: This tool is available on the Irish SuDS website ( which was developed to facilitate the implementation of the Greater Dublin Strategic Drainage System policies and particularly the use of SuDS. The tool enables stormwater storage requirements to be assessed for any specific location within the Greater Dublin area. Green Roofs Over Dublin, A Green Roof Policy Guidance Paper for Dublin, Dublin City Council (2008): Draft guidelines for Dublin City Council to develop planning directives for the incorporation of green roofs in new development. Alive and Well, Bringing Nature Back into Building Design, Construct Ireland, (2008): Article on green roofs and other emerging technologies and designs that use nature to improve performance of buildings Irish / UK Guidance Improving the flood performance of new buildings, Department for Communities and Local Government (UK) (2007): This document provides guidance to developers and designers (whilst also useful to useful to planners, building control officers and loss adjusters) on how to improve the resilience of new properties in low or residual flood risk areas by the use of suitable materials and construction details. These approaches are appropriate for areas where the probability of flooding is low or areas where flood risk management or mitigation measures have been put in place. Specifically this guidance document provides: practical and easy-to-use guidance on the design and specification of new buildings (primarily housing) in low or residual flood risk areas in order to reduce the impacts of flooding; and Final Report Dublin 26

41 recommendations for the construction of flood resistant and resilient buildings. Benefits of Green Infrastructure, Report by Forest Research (October 2010): This report discusses green infrastructure benefits in the context of climate change and reducing flood risk, health and wellbeing, economic growth and investments, land regeneration, wildlife and habitats, stronger communities. Guidance on the permeable surfacing of front gardens, Department for Communities and Local Government (UK), 2008: Provides advice to householders regarding the options for achieving permeability for proposed hard surfaces. This is in response to legislation that makes hard surfacing of more than fiver square metres of domestic front gardens permitted development. Retrofitting Green Infrastructure for rainwater- what s stopping us? Report by foundation for Water Research, Wastewater research & Industry Support Forum (2011): Series of papers discussing the following: example of Portland as a pioneer of sustainable storm water management, Urban greening in London, Opportunities for Green Infrastructure in UK, SWMP for London Greater Area - Drain London project, retrofitting surface water management measures, green roofs. Guidance for Household-level Flood Protection Schemes, Environment Agency (February 2011): Outlines the Environment Agency Flood Defence Grant scheme for property-level flood protection. Discusses Eligibility and selection of communities, process overview, quality standards of applied measures, process elements funding allocation, community engagement, house surveys, planning, building control and heritage issues, product selection and procurement, agreement with beneficiaries, reporting, post event performance, financial audit and liability. Surface Water Management Plan Technical Guidance, Defra, (March 2010): This SWMP guidance seeks to provide a simplified overarching framework which allows different organisations to work together and develop a shared understanding of the most suitable solutions to surface water flooding problems. Information is provided on various measures and practices to mitigate surface water flood risk. Design for Exceedance in Urban Drainage, Good Practice, CIRIA C635, (2006) This guidance provides technical advice on the design and management of urban sewerage and drainage systems to reduce the impacts from drainage exceedance. It includes information on the effective design of both underground systems and overland flood conveyance. Provides advice on risk assessment procedures and planning to reduce the impact that extreme events may have on people and property within the surrounding area. The SUDS Manual, CIRIA C697 (2007): Technical Guidance on urban drainage, environmental good practice, pollution prevention, sustainable construction, water quality, urban hydrogeology, rivers and waterways. Developing the Evidence Base for Flood Resistance and Resilience, Summary Report, Defra / Environment Agency (2008): A key element of the project was the examination of the effectiveness of property based resilience and resistance measures in reducing flood risk. Primary focus of the research was on the application of flood resistance and resilience to existing properties rather than new development. Feasibility Study for Retrofitting Green Roofs, University of Sheffield (2005): Design issues are looked at with a view to building onto existing roofs (retrofitting), Final Report Dublin 27

42 supported by calculations of typical and specific roof structures. A review is provided of retrofit projects around the world, and U.K. cases are considered in more detail. Preparing for Flooding A guide for Small and Medium Sized Businesses in Scotland, Scottish Flood Forum: Advice to business for Business Continuity Management in the extreme weather events. Further information available on Forming a Flood Group, Scottish Flood Forum: Outlines good practice steps in establishing community based flood action group to work on behalf of the local residents and businesses in finding ways of minimising the effects of flooding. Further information available on Local Community Flood Wardens, Scottish Flood Forum: Discusses the role of community Flood wardens, flood watch, flood warning etc. Further information available on Flood Resistance and Resilience Solutions: R&D Scoping Study, DEFRA, (2007): This document reports the findings of a short research study commissioned by Defra to broadly determine the suitability and cost effectiveness of a variety of flood resistance and resilience measures at property level, in particular, those that could be supported through a potential future pilot grant scheme. Retrofit SUDS, Cost Estimates and Decision-support Tools, Institution of Civil Engineers, Sheffield (2007): This paper focuses on the construction costs associated with a range of SuDS devices likely to be implemented in a retrofit context. Green Infrastructure Valuation Toolkit, Natural Economy Northwest & Partners (2010): This consists of a set of individual spreadsheet-based tools to assess the value of green assets or projects across a wide range of potential areas of benefit such as climate change, health, or property values. Where possible, results are provided in monetary terms FRC Partner and European Guidance Project Developer s Guide (PDG) for the Zollhafen Mainz development, Stadtwerke Mainz AG, Heinrich Webler, IAHR European Congress Edinburgh (2010): This framework enables developers to create a truly flood-resilient development for the Zollhafen development area which is located within the Rhine floodplain. It explains the obligations that have to be fulfilled in order to build and the potential for innovative construction in a flood-prone area. For each site, the PDG gives relevant excerpts from the development plan, a detailed description of requirements and specifications relevant to its position in the Zollhafen development area. The guidance includes reference examples of various approaches that have been applied elsewhere including: Development on stilts; similar to the Bohte, Richter, Teherani project in Hamburg; Temporary flooding of basement car parks; and Various examples of defensive systems (and their operational requirements). A glossary is provided which indicates the suitability of materials, and their required qualitative properties, for flood-adaptive building. Final Report Dublin 28

43 Flood Risk Management Guide (FRMG) for the Zollhafen Mainz development, Stadtwerke Mainz AG, Heinrich Webler, IAHR European Congress Edinburgh (2010): This takes the form of a brochure for people who will live or work in the new Zollhafen development area. It answers 10 central questions about the flood risk and its management. Topics covered by the questions include: Explanation of current and future flood risk; Advice on how to protect or adapt domestic power and water supplies, communication systems and sewerage systems; How to protect moveable equipment; Insurance advice; Where to obtain further information on a predicted flood and on the warning system which would be implemented; The role of the local authority; How to prepare for an approaching flood; and Actions to take during a flood and the functions of the relevant emergency services. Skills Integration and New Technologies (SKINT), Cases Studies: This Interreg IVB project provides details of case studies such as: Solar City (Stad van de Zon), Heerhugowaard, Netherlands - sustainable designed city; Wauchope Square Redevelopment, Edinburgh, Scotland example use of SuDS permeable pavement; Polderweijde, Obdam, Netherlands - example of design with excess water storage facilities waterbank ; Dunfermline Eastern Expansion. Dunfermline, Scotland - example of sustainable urban water management of a large scale multi-purpose development site; Almere Poort, Netherlands, example of integrated water management where the plan is linked to the specific circumstances of a deep polder 5m below sea level. Further information is available at: Construction in Flood-Prone Areas, Diagnosing and Reducing the Impact of Flood Hazards Methodological Guide, Department of Loiret, CEPRI, France (2010): French technical guide for the investigation and diagnosis of the vulnerability of public or private buildings. It also provides a reference for communities wishing to engage in the process of reducing the vulnerability of residential and public buildings that have been built in flood zones. Recommendations for the Establishment of Flood Risk Management Plans, German Working Group on Water Issues of the Federal States and the Federal Government (2010): As described in Section Other International Guidance Sustainable Stormwater Best Management Practices, Environmental Services City of Portland: Guidance on green stormwater management best management practice developed as part of an ongoing program since the early 1990s. Green street projects have been installed throughout Portland, and more are being planned Retrofitting to form green streets has included landscaped curb extensions, swales, Final Report Dublin 29

44 planter strips, pervious pavement, and street trees to intercept and infiltrate stormwater. Guidance includes specific advice for residents on at source stormwater management and storage including rainwater barrels. Further information is available on: City of Dallas Flood Roadway Warning System: The City of Dallas has implemented a road signage system to provide real time information on actual and predicted road closures due to watercourse and surface water flooding together with associated guidance on this system. Information is provided for public access through the following website: Flood Risk Management on Urban Surfaces (based on the Yucatan Peninsula, Mexico), John Blanksby (2011): Presentation illustrating urban measures that support the thesis that in regions where there are more frequent and extreme events, the more exposure the general public have to them and the higher the awareness, solutions become more obvious, people get to see them in action and benefits are more apparent. Measures are easier to implement and technical solutions become common sense. City of Philadelphia Stormwater Management Guidance Manual The manual was created to assist developers in meeting the requirements of the Philadelphia Stormwater Regulations. It provides guidance for the entire site design process, beginning with initial site design considerations, through the post-construction stormwater management plan submittal elements, and ultimately the acquisition of stormwater plan approval. Tools are provided to assist in completion and submittal of a stormwater management plan. Further information is available on: Technical Guidance on Implementing the Stormwater Runoff Requirements for Federal Projects US Environment Protection Agency (2009) The guidance focuses generally on retaining rainfall on-site through infiltration, evaporation / transpiration, and re-use to the same extent as occurred prior to development. The guidance provides background information, key definitions, case studies, and advice on meeting specific federal requirements. Guidance is provided on rain gardens, infiltration planters, vegetated swales, green roofs, pocket wetlands and rainwater harvesting. Introduction to Urban Stormwater Management in Australia, Department of the Environment and Heritage (2002). As part of the Living Cities Urban Stormwater Initiative this guidance provides advice on water sensitive urban design with various examples of Australian practice in stormwater management. Further information is available on: Stormwater Management Manual, Government of Western Australia, Department of Water (2007) Chapters include best planning practice for stormwater management, issues associated with retrofitting to improve stormwater management in an urban environment, and advice on education and awareness raising. Further information is available on ment+manual/default.aspx Final Report Dublin 30

45 2.3 Scope and Application of Code of Practice 2: Flood Resilience and Adaptation Measures The Source-Pathway-Receptor (SPR) Model Water that could flood properties and infrastructure in the Dublin urban area can arise from multiple sources: from rainfall running off the urban area (pluvial flooding); exceedance of the capacity of the sewers; from rivers and local watercourses; tidal flooding from the sea; and flooding from dam or canal breaches though very unlikely. Flooding in urban areas may be more complex than in rural areas, due to the inadvertent modification of natural processes and flow paths. Streams may have been culverted many years ago and their presence forgotten. Culverts, like storm sewers, are unlikely to be sized for extreme events and once their capacity is exceeded the roads, properties and other infrastructure built close to them may be damaged by floodwater. Drainage system capacities cannot easily be increased without increasing the flood risk downstream. The challenge is to find ways in urban areas of replicating natural processes that reduce flooding. Buildings cannot easily be moved out of the path of water, but longer term planning can provide opportunities to replicate the natural processes which reduce runoff and make space for water. With pluvial/surface water flooding, the source of flooding, the impact and who should be responsible for flood risk management are not always clear. Therefore, the challenge is to create a framework in which all stakeholders can operate together to reduce flood risk. A common approach to assessing flood risk is to look at the Source, the Pathway (route taken and mechanism of flooding) and the Receptor (what is flooded). Runoff is best controlled close to the source where it is easier to manage rather than further along the pathway where volumes are much greater. Where surface water sewers are separate from the foul sewer system, there are greater opportunities for storm water to be managed on the surface. There are many areas of Dublin served by combined sewers. It is therefore important that new developments use separate systems and do not increase the load in the existing combined system. Flood modelling and mapping identifies where flood water for different rainfall events is likely to go. The opportunity exists now to develop measures to hold water up as close to the source as possible, even on the roofs of buildings, or modify the routes where surface water flows. The streets and open spaces could be reshaped to direct flood water to safe places and hold it there until the peak flows in the drains and rivers have subsided. This is referred to as the Streets-as-Streams / Roads-as-Rivers concept. This can reduce flood risk to others further downstream. Final Report Dublin 31

46 2.3.2 Integrated Delivery and Long-term View In many cases, the options to better manage pluvial/surface water flooding may not be quick fixes, though some may be possible. The options need to be sustainable and holistic addressing all sources of flooding and considering social and environmental aspects. Such schemes are likely to be implemented: incrementally over time; taking advantage of opportunities as they arise with other development work or maintenance; and through planning policy and control. Options should aim to provide multiple and mutual benefits to all parties likely to be impacted and all stakeholders that may benefit in order to share costs of implementation of measures and/or gain support for implementation. As a principle, options should seek to keep water on the ground surface rather than underground wherever possible. Surface options are generally less expensive, easier to maintain and provide more opportunities for social and environmental enhancement. This can only be done by planners, engineers and political leaders working in an integrated way. The relevance of shared space to integrate drainage is that planners should arrive at the understanding that the space can be designed for a wider range of uses: not only cars, wheelchairs, bikes and pedestrians but also for managing surface water and flood risk by creating spaces for water to flow and to be stored safely. Conceptually, this issue is common in social planning and also relevant to infrastructure related issues where a large number of stakeholders need to take an integrated approach to solving common problems. Solutions primarily require organisation, but also the implementation of sustainable measures. Best practice examples are most evident in cities where the organisational role is largely with a single authority that has the power and leadership to implement policy, incentives and measures necessary for change. It is evident that changes to infrastructure and its management need to be planned for and implemented over the medium to long term and that all stakeholders need to be involved throughout. There are a range of measures available related to controlling surface water runoff at its source, along its pathway or ultimately at the location of the receptor (refer to Appendix V3-B Code of Practice 2). However, the choice of and delivery of a flood management option may depend on incentives, funding and coordinating implementation. It is important to note that flood risk can be reduced but never totally eliminated. It may be more appropriate, at least in the short term, to ensure people are risk aware and to issue flood warnings rather than implement engineered solutions. However, over time, with effective planning and implementation of sustainable measures, flood risk can be significantly reduced in a sustainable way Evaluation of Measures Once individual measures to manage pluvial/surface water flooding are identified they can be scored as an initial screening according to the following four criteria: technical, economic, social and environmental benefits. Using this multi-criteria matrix approach, a wide range of measures can be considered which will provide differing levels of protection. These measures will have a range of benefits and costs associated with them. The measures can be grouped according to the Source-Pathway-Receptor model or under the broad category headings adopted in Code of Practice 2: Flood Resilience and Adaptation Measures. An extract of a scoring matrix is shown in Figure Final Report Dublin 32

47 2.1 as an example of standard practice which can be applied. This type of matrix has been applied for the Dublin FRC Project and is documented in Volume Four - Detailed Pluvial Flood Risk Assessment of Pilot Areas. Individual measures which pass this initial screening process can then be brought together to form options. The evaluation of potential management options should consider: previous studies; initial multi-criteria scoring analysis of measures; site inspection information; detailed modelling showing likely flow routes; consultation with stakeholders. These options are then assessed using the same technical, economic, social and environmental criteria to score and then prioritise them but in more detail than under the initial screening phase. Final Report Dublin 33

48 Volume 3: Pluvial Flood Risk Management Figure 2.1: Example Evaluation Matrix for Initial Screening of Measures Final Report Dublin 34

49 Volume Three: Pluvial Flood Risk Management Responsibilities for Implementation Code of Practice 2: Flood Resilience and Adaptation Measures (Appendix V3-B) conveys how the responsibility for the implementation of measures is shared between Government agencies / Municipality, developers and the community. Community Flood Resilience Measures require individual or collective community action to implement. Successful application of these measures will require: Raising the level of awareness of pluvial flood risk and providing readily available and understandable information on the level of risk and likely consequences of not taking action to mitigate this risk. Engagement by the community and householders such that they are motivated to take ownership and responsibility for flood mitigation actions. This is likely to require the preparation and dissemination of simple and clear self-help guidance underpinned by a Community Engagement and Participation Plan (CEPP). A robust Flood Alerting System to initiate actions. The preparation of the CEPP and appropriate guidance would be the responsibility of Dublin City Council. Incentivisation, financial or otherwise, may be required to achieve the necessary level of motivation for community groups and householders to initiate actions. Ensuring consistency in the implementation of actions set out in an Action Plan to address pluvial flooding issues is likely to be a challenge and the evaluation of Community Resilience Measures should consider the extent to which lack of action by any one individual or group might compromise the overall effectiveness of risk mitigation e.g. if a householder did not take action to protect their property could this pose a risk to the adjacent property where the householder has taken the appropriate actions. For further information relating to community measures, refer to Sections B3, B5 and B6 of Code of Practice 2: Flood Resilience and Adaptation Measures (Appendix V3-B). Dublin City Council will generally have lead responsibility (with other stakeholders) or sole responsibility for implementation of many of the Generic/Early Win Actions and also for Site Specific Measures which may require the development and implementation of a capital works scheme. Responsibilities for implementation may be spread across several departments within the Council and internal integration will be an important aspect. Once a programme of appropriate and cost effective measures/options has been identified, implementation and delivery should be effected through a Pluvial Flood Risk Mitigation Action Plan. The evaluation of specific measures/options and their relative performance, cost and resourcing requirements will enable priority actions to be established and thus, an overall programme for the implementation of actions to be prepared according to those which should be short, medium and long term. It should be note that some high priority SPR actions, though cost effective, may entail significant capital cost and may need to be phased. The Action Plan also needs to clearly establish responsibility not only for implementation but also for ongoing maintenance associated with any action. The Action Plan will not be sustainable unless funding mechanisms to meet both capital and maintenance costs of measures/options during each phase are identified and put in place. Where a measure/option requires further investigation in order to complete evaluation this in itself can be identified as a specific measure in the Action Plan. Final Report Dublin 35

50 Volume Three: Pluvial Flood Risk Management An example layout for a similar type of Action Plan prepared for a UK lead local flood authority Surface Water Management Plan is shown in Figure 2.2. Note that responsibilities for food risk management in the UK are different from those in Ireland. However in the example Action Plan extract in Figure 2.2, the UK Met Office has similar responsibilities to Met Eireann and the UK Environment Agency has some similar responsibilities at a national level to the OPW in Ireland. Local Authority responsibilities in the UK for local flood risk management relate to those of Dublin City Council. Final Report Dublin 36

51 Volume Three: Pluvial Flood Risk Management Figure 2.2: Example Extract of an Action Plan for a Pluvial Flood Risk Mitigation SWMP prepared for a UK lead local flood authority. Final Report Dublin 37