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…

Flood Risk and Planning

» 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

Flooding in Ireland

Flood Risk and Planning

» 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

Flood Hazard Sources

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 Directive on the assessment and management of flood risks [2007/60/EC] – the ‘Floods Directive’ required: » Undertake a Preliminary Flood Risk Assessment (PFRA) by 22nd 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 22nd December 2013 » Prepare flood risk management plans by 22nd December 2015, setting

• bjectives 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

EU Floods Directive

Flood Risk and Planning

» 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

CFRAM Programme

Flood Risk and Planning

‘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

PFRA Mapping

OPW – CFRAM Study Interactive Mapping

maps.opw.ie/floodplans/fhr_map/en

Flood Risk Management Plans

Flood Risk and Planning

» 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

The Planning System and Flood Risk 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

• f 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

» 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

Main Components of a FRA

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,

• peration 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

» Flood Hydrology is an inexact science and extremely dependent

• n 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

Uncertainty associated with flood risk

Flood Risk and Planning

Computerised Fluid Dynamic (CFD) Modelling

1-D Model 2-D Model 3-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