Planning and Flood Risk Patricia Calleary BE MEngSc MSc CEng MIEI - PowerPoint PPT Presentation

Planning and Flood Risk Patricia Calleary BE MEngSc MSc CEng MIEI

After the Beast from the East… Patricia Calleary

Flood Risk and Planning Flooding in Ireland » Floods are a natural and inevitable part of life in Ireland that pose a risk to human life and well-being, property and the environment. » It is likely that the effects of climate change will make flooding more frequent and severe in the future. » Past - structural or engineered flood protection measures in response to flood events » Current – Flood Management Approach - proactive

Flood Risk and Planning Flood Hazard Sources » Fluvial » Rivers, Streams , Drainage ditches » Coastal » Coastal Zones (harbours, quays, coastline areas, estuaries » Groundwater » Turloughs / Seasonal lakes, Springs / Karst Features, Groundwater Table » Pluvial » Ponding of overland flow from intense rainfall » Urban Drainage » Stormwater Drainage

Crossmolina, Co.Mayo – December 2015

Crossmolina, Co.Mayo – July 2016

Flood Risk and Planning Flood Protection Measures » Structural Measures » Flood level reduction » Conveyance measures widening, regrading removal of constrictions » Diversions » On line and off line storage, controlled storage - to attenuation the Flood Peak » Flood Defence » Permanent Structures – Walls and embankments » Demountable Structures » Tidal barrage

Flood Risk and Planning Flood Protection Measures » Non Structural Measures » Planning control – (Flood Risk Management Planning Guidelines) » Land use management - » Green Infrastructure - Slowing the flood through provision of increased catchment storage » Catchment wide policy integrated with the WFD » Difficult to measure success » Conflict with agricultural enterprise » Flood Response Planning

Flood protection measures Patricia Calleary

Flood Risk and Planning EU Floods Directive EU Directive on the assessment and management of flood risks [2007/60/EC] – the ‘Floods Directive’ required: » Undertake a Preliminary Flood Risk Assessment (PFRA) by 22 nd December 2011, to identify areas of existing or foreseeable future potentially significant flood risk (referred to as ‘Areas for Further Assessment’ or ‘AFA’s) Prepare flood hazard and risk maps for the AFAs by 22 nd December » 2013 Prepare flood risk management plans by 22 nd December 2015, setting » objectives for managing the flood risk within the AFAs and setting out a prioritised set of measures for achieving those objectives Transposed into Irish Law by European Communities (Assessment and Management of Flood risks) Regulations 2010. SI 122/2010

Flood Risk and Planning CFRAM Programme » NATIONAL ‘CFRAM’ PROGRAMME » 6 Contract Areas » Catchment-Based Flood Risk Assessment and Management (CFRAM) Studies » Key Outputs Flood Maps • Catchment Flood Risk Management Plan • » 300 Areas of Further Assessments (AFAs) » More information on cfram.ie

Flood Risk and Planning PFRA Mapping ‘PFRA’ Maps – Predictive maps of lands estimated to be flood prone in the 300 areas around Ireland. » Broadly Indicative of Flood Prone Areas » Acceptable Accuracy for PFRA (‘Available & Readily - Derivable’) » Not Precise Flood Extent Maps » Not Always Locally Accurate » Not Suitable for Local / Site-Level Decisions » Published for PFRA Consultation

OPW – CFRAM Study Interactive Mapping maps.opw.ie/floodplans/fhr_map/en

Flood Risk Management Plans

Flood Risk and Planning The Planning System and Flood Risk Management » Guidelines, published in Nov 2009 under S.28 PDA » Chapter 1 – Background » Chapter 2 - Key Concepts » Chapter 3 - Principles » Section 4 - Spatial Planning » Section 5 - Development Management Guidelines Appendices

The Guidelines Chapter 2 – Key Concepts Flood Risk = Likelihood (probability) of Flooding x Consequences of Flooding

The Guidelines Chapter 2 – Key Concepts Source-Pathway-Receptor Model

The Guidelines Chapter 2 – Key Concepts Staged Approach to Flood Risk Assessment » Stage 1 – Flood Risk identification - any flooding or surface water management issues » Stage 2 – Initial Flood Risk assessment (FRA) -scope the extent of the risk of flooding » Stage 3 – Detailed Flood Risk assessment – provide quantitative appraisal of potential flood risk as a result of a development including mitigation » Appendix A contains a checklist of content of each stage of FRA and sources of information as well as required outputs

The Guidelines Chapter 2 – Key Concepts Sustainable Drainage » Consider Design Standards for Storm Water Drainage Capacity » Consider On-Site Storm Water Retention » SuDS » Permeable Paving » ‘Green Infrastructure’ Climate Change » Adopt a precautionary approach to allow for climate change e.g. raise building heights Green Schools – Climate Change Entry

The Guidelines Chapter 3 – Principles and Key Mechanisms » Avoid Development if in area at risk of flooding (Use lower hazard areas) » Substitute with land less vulnerable » Mitigate and Manage (Reduce Risk) » Exceptions require Justification test – Planning need and sustainable management of Flood risk » Proceed but only when proposal passes the test!

Flow Diagram – Fig. 3.2 Guidelines

The Guidelines Chapter 3 – Principles and Key Mechanisms Vulnerability and Flood Zones » Vulnerability classification (Table 3.1). Residential (dwelling houses and student residences) classified as ‘ highly vulnerable development ’ Retail – Less Vulnerable, Amenity Open Space – Water Compatible

The Guidelines Chapter 5 – Flooding and Development Management Flood Risk Assessment (FRA) – Site Specific » Plans showing the site and development proposal and its relationship with watercourses and structures which may influence local hydraulics » Surveys of site levels and cross-sections relating relevant development levels to sources of flooding and likely flood water levels » Potential sources of flooding, Flood alleviation measures, potential impact of flooding on the site; reduce risk (layout and form), surface water management proposals, mitigation, residual risk and management of risks

Flood Risk and Planning Main Components of a FRA » Flood Hazard Identification of Flood Hazards • • The probability, magnitude (e.g. Depth, velocity, discharge) and duration of flooding » Exposure Economic nature of the assets subjected to flood hazard • » Vulnerability The relationship of flood hazard properties to economic loss • » Performance The effectiveness and behaviour of flood protection measures that modify • the flood hazard, the exposure, or the vulnerability » Flood Impact The effect of mitigation measures on the flood hazard •

The Guidelines Chapter 5 – Flooding and Development Management » PA / Board may consider granting permission subject to conditions which ensure the Justification test is satisfied and residual risk dealt with. » Conditions should not normally require major drainage or flood related structural work. » E.g. of appropriate conditions: • Requiring inspection and maintenance of local flood defences (e.g. swales, earth bunds) • Requiring flood resilient street furniture • Arrangements to be put in place by developer/management company to ensure installation, operation and maintenance of adequate flood warning and emergency plan

The Guidelines Chapter 5 – Flooding and Development Management Minor Development Proposals » Minor Proposals e.g. ‘extensions’ (houses or commercial) and ‘change of use’ are unlikely to raise significant flood issue and the Justification test will not normally apply. » A commensurate assessment of the risks of flooding should accompany planning applications nonetheless.

Flood Risk and Planning Uncertainty associated with flood risk » Flood Hydrology is an inexact science and extremely dependent on past records » Flood Flow Estimation » Gauged and ungauged methods » Statistical methods » Rainfall Runoff methods » Hydraulic Modelling » Flood Level Estimation » Prediction error associated with flood estimation using a mathematical hydraulic model or extrapolation from a nearby gauge » Climate Change and Environmental Change

Flood Risk and Planning Computerised Fluid Dynamic (CFD) Modelling 2-D Model 3-D Model 1-D Model

OPW – National Flood Hazard Mapping website : www.floodmaps.ie

Flood Risk and Planning Positive steps achieved in flood-proofing Ireland » Implementation of the Floods Directive » The establishment of a sole agency (OPW) responsible For Flood Risk Management » The Flood Risk Management Planning Guidelines in Planning Control » Flood Study’s Update program » CFRAM Studies » Improved flood defence technologies National Planning Framework - Ensuring flood risk management informs place-making by avoiding inappropriate development in areas at risk of flooding in accordance with The Planning System and Flood Risk Management Guidelines for Planning Authorities.

Flood Risk and Planning Dublin – June 1963 – From RTÉ Archives