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 ...
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
82Appendix C - Frequently AskedQuestions<strong>Planning</strong> GuidelinesWhat is flooding?<strong>Flood</strong>ing is when l<strong>and</strong> that is normally dry is covered by water. This can haveboth beneficial <strong>and</strong> adverse consequences. Deposition of sediments from riverfloods form the level floodplains alongside rivers <strong>and</strong> contribute to its agriculturalfertility <strong>and</strong> its biodiversity. When it affects human activities, it can threaten life,cause social <strong>and</strong> health impacts, damage buildings <strong>and</strong> their contents, interruptcommunications <strong>and</strong> lead to pollution that can cause environmental damage.What causes flooding?<strong>Flood</strong>ing at the coast is caused by higher sea levels than normal. Inl<strong>and</strong> floodingis due to intense <strong>and</strong> or prolonged rainfall which exceeds the capacity for it to sinkinto the ground. As a result, it runs off over l<strong>and</strong> <strong>and</strong> into rivers <strong>and</strong> artificialdrainage systems. When the capacity of these is exceeded, the result is river <strong>and</strong>sewer flooding. <strong>The</strong> roofs of buildings, roads <strong>and</strong> hard st<strong>and</strong>ings prevent watersoaking into the ground thus increasing run-off <strong>and</strong> exacerbating the problems.<strong>Flood</strong>ing can also occur when water that has soaked into the ground fills theunderground storage <strong>and</strong> overflows onto the surface.How will climate change influence flooding?Climate change could potentially have a very significant effect on flooding in thelonger term. Higher sea levels <strong>and</strong> wetter winters, with more intense rain storms,together with possible increases in storminess could significantly increase both thefrequency <strong>and</strong> intensity of flooding. For example, floods which currently have a1 in 100 chance (1% probability) of occurring in any one year could occur muchmore frequently.How is flood risk measured?<strong>Flood</strong> risk is a combination of the likelihood of occurrence <strong>and</strong> the consequencesof a flood occurring. This is normally expressed as:<strong>Flood</strong> risk = probability x consequencesProbability is difficult to estimate because it has to take account of the uncertaintyof hydrological predictions based on the analysis of many years of flow records.Consequences are also complex to measure in terms of the potential loss of life,damage to property etc., which depend on the vulnerability of the l<strong>and</strong>-use <strong>and</strong>property affected by the flood.What is a source-pathway-receptor model?A source-pathway-receptor model is a representation of the components of floodrisk. <strong>The</strong> three components are a source of floodwater (prolonged or intense rainfall,high sea levels), the receptors (l<strong>and</strong>, buildings <strong>and</strong> structures, people) that are