The Planning System and Flood Risk Management - Offaly County ...
The Planning System and Flood Risk Management - Offaly County ...
The Planning System and Flood Risk Management - Offaly County ...
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the flooding for the duration of the flood event, as well as causing damage tothe road or railway itself. <strong>Flood</strong>ing of water distribution infrastructure suchas pumping stations or of electricity sub-stations can result in loss of wateror power supply over large areas. This can magnify the impact of floodingwell beyond the immediate community <strong>and</strong> reinforces why decisions to locatedevelopment in floodplain should be taken very carefully (see paragraphs2.24 <strong>and</strong> 2.36 below). This was a key lesson learnt from recent floods in Irel<strong>and</strong>when national primary roads <strong>and</strong> railway lines were flooded, <strong>and</strong> also theSummer 2007 floods in the UK, during which water supply to large areas wascut off for a number of weeks.<strong>Flood</strong> risk assessment2.19 <strong>The</strong> assessment of flood risk requires an underst<strong>and</strong>ing of where the watercomes from (i.e. the source), how <strong>and</strong> where it flows (i.e. the pathways) <strong>and</strong>the people <strong>and</strong> assets affected by it (i.e. the receptors). <strong>The</strong> source – pathway– receptor model is described in greater detail in Appendix A.Overl<strong>and</strong> runoff<strong>and</strong> muddyflooding due tointensive rainfallClimate changeincreased intensityof summer stormsGroundwaterflooding due toraised water tableSurcharged sewercauses basementfloodingUrban creep:increased pavingSewerexceedancefloodingDirect overl<strong>and</strong>flow <strong>and</strong> pondingin low spots (sinks)<strong>Flood</strong>ingthrough thealluvialsBlockage or sewer collapseImpervious paved areaFig. 2: Sources, pathways <strong>and</strong> receptors of <strong>Flood</strong>ingReservoir orcanal breach2.20 <strong>The</strong> principal sources are rainfall or higher than normal sea levels , the principalpathways are rivers, drains, sewers, overl<strong>and</strong> flow <strong>and</strong> river <strong>and</strong> coastalfloodplains <strong>and</strong> their defence assets <strong>and</strong> the receptors can include people,their property <strong>and</strong> the environment. All three elements must be examinedas part of the flood risk assessment. Mitigation measures typically used indevelopment management can reduce the impact on people <strong>and</strong> communities,for example, by blocking or impeding pathways but they have little or noeffect on the sources of flooding. <strong>The</strong> planning process is primarily concernedwith the location of receptors, taking appropriate account of potential sources<strong>and</strong> pathways that might put those receptors at risk.11<strong>Planning</strong> Guidelines