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

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62A successful FRA is characterized by the iterative process of the assessmentof flood risk and impacts and then subsequent design of mitigation andcompensation measures is shown in Figure A2.Planning GuidelinesFig. A2: Approach to Flood Risk Assessment (SFRA and FRA)Flooding From Other Sources, Screening and AssessmentFlooding from other sources other than the coast and rivers, such as overlandflow are more difficult but essential to address and normally requireconsiderably more detailed approaches. The flooding of August 2008 includedmany instances of overland flow in areas not historically known to flood.There are a range of interactive mapping (GIS), topographical analysis andoverland routing techniques that can be used to assess and map flood riskfrom other sources to be harnessed in FRA. These methods provides anindication of overland flow routes and areas prone to surface water floodingthat are not identified by flood zone mapping. Initial screening may focus
on assessment of storm events that exceed the available capacity of surfacewater systems and of flash floods.63Model results generated from this screening process provides information onthe peak depth of flooding. An example map of rainfall data is included asFigure A3.Fig. A3: Example of rapid surface water run off mapping(Image provided courtesy of City of Wakefield MBC)Surface water flood risk mapping requires a 3 dimensional representation ofthe area of interest, in the form of a DTM, and a rainfall hyetograph for a stormof fixed magnitude and duration. The water depths are then applied and thestorm water is free to flow over the area. This provides a prediction of thoseareas where water will collect, or ‘pond’, and the location and magnitude offlow routes to leading to these areas. The output shown above is thenthematically mapped by depth, removing predicted flood depths below athreshold.1.6 Outputs from FRARegional Flood Risk AssessmentsAs a minimum, regional level appraisal should include the following:• Summary plans/figures (ideally with accompanying digital spatialdatasets) showing the broad spatial distribution of flood risk;Planning Guidelines
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At the site-specific level, develop
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Planning Guidelines
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2regard to the guidelines in the pe
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4Planning GuidelinesReport of the F
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6Chapter 2:Flooding - Key ConceptsP
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82.5 Increase in flooding due to de
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10Flood risk2.13 Understanding floo
Page 22 and 23: 122.21 In undertaking a flood risk
Page 24 and 25: 142.30 Increases in rainfall intens
Page 26 and 27: 16after periods of heavy rainfall.
Page 28 and 29: 18that also meet the objectives of
Page 30 and 31: 20more than 1 in 200). Development
Page 32 and 33: 22Government under Section 28 of th
Page 34 and 35: 24Planning GuidelinesDevelopment in
Page 36 and 37: 26Chapter 4:Flooding and Spatial Pl
Page 38 and 39: 28floodplain. Effective co-ordinati
Page 40 and 41: 30Planning GuidelinesFig. 4: Develo
Page 42 and 43: 32• Include zoning objectives to
Page 44 and 45: 34specific areas, ensuring that flo
Page 46 and 47: 36should use the flood risk informa
Page 48 and 49: 38planning authority to ensure that
Page 50 and 51: 40• these guidelines, and in part
Page 52 and 53: 425.22 Where development proposals
Page 54 and 55: 44Chapter 6:ConclusionPlanning Guid
Page 56 and 57: 46TermsDefinitionPlanning Guideline
Page 64 and 65: 54Appendix A - Screening for andCar
Page 66 and 67: 56Climate changeincreased intensity
Page 68 and 69: 58Strategic assessments provide the
Page 70 and 71: 60As part of a FRA, information on
Page 74 and 75: 64• Suggested policies for sustai
Page 76 and 77: 66Planning Guidelines• The impact
Page 78 and 79: 68An additional document on interpr
Page 80 and 81: 70Table A2: The Flood Risk Balance
Page 82 and 83: 72Appendix B - Addressing FloodRisk
Page 84 and 85: 74Figure B2 below illustrates how t
Page 86 and 87: 76drainage processes and removing p
Page 88 and 89: 78• Signing of floodplain areas s
Page 90 and 91: 80flood level. Care must be taken t
Page 92 and 93: 82Appendix C - Frequently AskedQues
Page 94 and 95: 84What does the SFRA not provide?Th
Page 96 and 97: 86pressure in the embankment and ge
Page 98: Printed on recycled paper containin
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