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

with the Water Framework Directive (WFD) River Basin Management Plans(RBMPs), will establish a prioritised set of flood risk management measuresfor their relevant areas, including the use of structural and non-structuralresponses as outlined above.152.35 Planning can have a significant role to play with respect to flood riskmanagement, in particular in avoiding or minimising future increases in floodrisk. The planning process therefore constitutes a parallel, but related andinter-dependent, process to that of flood risk management. As such, the twoprocesses should each have regard to the objectives, direction and constraintsof the other to ensure alignment between planning instruments, such asDevelopment Plans and the Flood Risk Management Plans (FRMPs).2.36 A major function performed by the floodplain and wetlands is to hold excesswater until it can be released slowly back into a river system or seep into theground as a storm subsides. Floodplains have, therefore, a valuable functionboth in attenuating or storing floodwater and through their ability to conveyfloodwater in a relatively controlled and safe way. Areas of floodplain andwetlands should, therefore, be recognised and preserved to the extent possibleas natural defences against flood risk. It is important to identify and, wherepossible, safeguard areas of floodplain against development in both urbanand rural areas. By retaining open spaces for storage and conveyance offloodwater, flood risk to both upstream and downstream areas can be moreeffectively managed without reliance on flood defences. This is an importantelement of the now internationally accepted philosophy of “leaving space forwater”.Sustainable drainage systems2.37 Development of previously ‘green’, or permeable, land within an urban area(such as gardens) increases the impermeable area. Rain falling on impervioussurfaces is usually directed into receiving watercourse through surface waterdrainage systems. Although such drainage systems are effective at transferringsurface water quickly, they provide only limited attenuation causing thevolume of water in the receiving watercourse to increase more rapidly andincreasing flood risk. As a consequence sustainable drainage systems (SuDS)can play a role in reducing and managing run-off to surface water drainagesystems. In this context the Department is currently reviewing its document“Recommendations for Site development Works for Housing Areas” whichtraditionally was used to provide guidance on design standards for smallerdrainage systems. The aim of this review is to set out best practice in regardto the use of sustainable drainage systems in respect of surface water drainage.2.38 A small-scale yet practical example of a sustainable drainage system (SuDS)is the use of permeable pavements which can help to reduce run-off rates andflow volumes from parking areas as well as access roads. Permeable pavementsallow rain-water to infiltrate through the paved surface and into underlyinglayers and sometimes storage containers allowing gradual release of waterPlanning Guidelines