The Planning System and Flood Risk Management - Offaly County ...

122.21 In undertaking a flood risk assessment, it is necessary to calculate the probabilityof flooding occurring, to assess the hazards that will arise (e.g. to identify areaswhere deep or fast-flowing water would be expected in the event of a flood)and to examine the vulnerability of the receptors and the potential consequencesof those hazards. Risks to people, property and the environment should beassessed over the full range of probabilities, including extreme events. Theflood risk assessment should cover all sources of flooding, including the effectsof run-off from a development on flood risk both locally and beyond thedevelopment site.Planning Guidelines2.22 A staged approach should be adopted, carrying out only such assessment asis needed for the purposes of decision-making. The stages of assessment are:• Screening assessment – to identify whether there may be any floodingor surface water management issues related to a plan area or proposeddevelopment site that may warrant further investigation;• Scoping assessment – to confirm sources of flooding that may affect aplan area or proposed development site, to appraise the adequacy ofexisting information and to scope the extent of the risk of flooding andpotential impact of a development on flooding elsewhere and of thescope of possible mitigation measures; and• Appropriate risk assessment – to assess flood risk issues in sufficientdetail and to provide a quantitative appraisal of potential flood risk toa proposed or existing development, of its potential impact on floodrisk elsewhere and of the effectiveness of any proposed mitigationmeasures.Further information on flood risk assessment and its application within theplanning system, along with sources of information to support the assessments,is contained in Appendix A.Flood zones2.23 Flood zones are geographical areas within which the likelihood of floodingis in a particular range and they are a key tool in flood risk management withinthe planning process as well as in flood warning and emergency planning.There are three types or levels of flood zones defined for the purposes of theseguidelines:• Flood zone A – where the probability of flooding is highest (greater than1% or 1 in 100 for river flooding or 0.5% or 1 in 200 for coastal flooding)and where a wide range of receptors would be vulnerable;• Flood zone B – where the probability of flooding is moderate (between0.1% or 1 in 1000 and 1% or 1 in 100 for river flooding and between0.1% or 1 in 1000 year and 0.5% or 1 in 200 for coastal flooding); and